MITEL PDSP16510AMAAC1R

PDSP16510A MA
PDSP16510A MA
Stand Alone FFT Processor
Supersedes January 1997 version, DS3762 - 2.0
DS3762 - 3.0 October 1998
The PDSP16510 performs Forward or Inverse Fast
Fourier Transforms on complex or real data sets containing up
to 1024 points. Data and coefficients are each represented by
16 bits, with block floating point arithmetic for increased
dynamic range.
An internal RAM is provided which can hold up to 1024
complex data points. This removes the memory transfer
bottleneck, inherent in building block solutions. Its organisation allows the PDSP16510 to simultaneously input new data,
transform data stored in the RAM, and to output previous
results. No external buffering is needed for transforms containing up to 256 points, and the PDSP16510 can be directly
connected to an A/D converter to perform continuous transforms. The user can choose to overlap data blocks by either
0%, 50%, or 75%. Inputs and outputs are asynchronous to the
40MHz system clock used for internal operations.
A 1024 point complex transform can be completed in
some 98µs, which is equivalent to throughput rates of 450
million operations per second. Multiple devices can be connected in parallel in order to increase the sampling rate up to
the 40MHz system clock. Six devices are needed to give the
maximum performance with 1024 point transforms.
Either a Hamming or a Blackman-Harris window operator
can be internally applied to the incoming real or complex data.
The latter gives 67dB side lobe attenuation. The operator
values are calculated internally and do not require an external
ROM nor do they incur any time penalty.
The device outputs the real and imaginary components of
the frequency bins. These can be directly connected to the
PDSP16330 in order to produce magnitude and phase values
from the complex data.
Fig. 1. Block Diagram
FEATURES
Completely self contained FFT Processor
Internal RAM supports up to1024 complex points
16 bit data and coefficients plus block floating point for
increased dynamic range
450 MIP operation gives 98 microsecond transformation times for 1024 points
Rev
Date
A
B
C
D
MAR 1993 JAN 1997 OCT 1998
Up to 40MHz sampling rates with A grade multiple
devices.
NOTE
Internal window operator gives 67dB side lobe
attenuation and needs no external ROM.
Polyimide is used as an inter-layer dielectric and as
glassivation.
132 pin surface mount package
Polymeric material is also used for die attach which according
to the requirement in paragraph 1.2.1.b. (2) precludes
catagorising this device as fully compliant. In every other
respect this device has been manufactured and screened in
full accordance with the requirements of Mil-Std 883 (latest
revision).
CHANGE NOTIFICATION
The change notification requirements of MIL-PRF-38535 will
be implemented on this device type. Known customers will be
notified of any changes since the last buy when ordering
further parts if significant changes have been made.
ORDERING INFORMATION
PDSP16510A MA GCPR
(Power Ceramic QFP Package
- HIREL LEVEL A Screening)
PDSP16510A MA AC1R
(Power Ceramic PGA Package
- HIREL LEVEL A Screening)
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PDSP16510A MA
Fig. 2. Typical 256 Point Real Only System Performing Continuous Transforms
Pin Out for 84 PGA Package (AC84) - bottom view
2
PDSP16510A MA
Pin Out for 132 Leaded Chip Carrier (GC132)
3
PDSP16510A MA
SIGNAL
TYPE
DESCRIPTION
D15:0
I
Data input during real only mode, The real component in complex data mode.
AUX15:0
I
When DEF is active AUX15:0 are used to define the operating mode as defined in Table 3.
When DEF is in-active AUX15:0 either provide the 16 bit imaginary component of complex
input data, or a second set of real only inputs.
R15:0
O
These pins output the real component of the transformed data when DAV and DEN are active.
Otherwise they are high impedance.
I15:0
O
These pins output the imaginary component of the transformed data when DAV and DEN are
active. Otherwise they are high impedance.
DEF
I
The high going edge of DEF is used to internally latch the contents of AUX15:0, which then
define the operating mode. In the simplest system DEF is a power on reset. When DEF is low
the internal control logic is reset.
SCLK
I
System clock used for internal computations.
S3:0
O
These pins indicate the number of shifts towards the binary point which have occurred as the
result of the conditional scaling logic. When the data path right shift is restricted to 2 places
per pass, state 15 is used to indicate an overflow and only a total of 14 shifts is possible.
LFLG
O
This flag indicates that data is being loaded into the device. It goes active in response to an
INEN input, and may be programmed to go in-active after the complete, one quarter, or one
half a data block has been loaded.
INEN
I
The use of this input is mode dependent. It is either used as an active low, load enabling,
signal for the DIS strobe, or it is used to initiate a new block load operation.
DIS
I
The rising edge of this asynchronous input is used to load data into the device.
DOS
I
The rising edge of this asynchronous input is used to dump data from the device. In most
applications it may be tied to the DIS input, even if the output rate must be higher than the input
rate because of overlapped data blocks. The DIS input is then internally divided down.
DAV
O
An active low signal that indicates that a transform is complete. Transformed data will then
be outputed in normal sequential order using DOS. It may be optionally programmed to be
delayed by 24 DOS strobes to match the delay through a PDSP16330.
DEN
I
This input is used to enable the data dump operation when DAV has gone active. If it is tied
low the device will automatically dump data when DAV goes active. Otherwise the device will
wait for the enabling signal to go low before the dump operation commences.
DISAB
I
Only available in the 132 pin GC package. When high the block floating logic is disabled.
VDD
P
+5V pins
GND
P
Ground pins
NOTE. All references to DEF, INEN, DAV, and DEN within the text do not contain the bar designator, signifying an active low
signal. This is considered to be implied by the signal name and is not meant to imply a change in the signal function.
FUNCTIONAL OPERATION
The PDSP16510 performs decimation in time, radix 4,
forward or inverse Fast Fourier Transforms. Data is loaded
into an internal workspace RAM in normal sequential order,
processed, and then dumped in the correct order. With real
only input data the processing time can approximately be
4
halved for a given transform size. Two real inputs then replace a
single complex input, and are processed in parallel.
Either a Blackman Harris or a Hamming window can be
generated internally, and applied to the incoming real or complex
data with no time penalty. No external ROM is needed to support
these windows. The Blackman Harris window gives improved
dynamic range over the Hamming window when two closely
PDSP16510A MA
spaced frequencies are to be detected, and one is of smaller
magnitude than the other. It does, however, reduce the actual
frequency resolution, and the Hamming window may then be
preferable.
Data in and out of the device is represented by 16 bit real
and imaginary components, with 16 bit sine and cosine values
contained in an internal ROM. Conditional scaling, coupled
with word growth through the butterfly data path, gives increased dynamic range. Transforms can be computed with
sample sizes of either 256 or 1024 data points. The 256 point
option can alternatively be used to simultaneously execute
either four 64 point transforms, or sixteen 16 point transforms.
The 16 point mode can only be used with a rectangular
window, and no overlapping of data blocks is possible.
The device can be configured, either, to perform continuous transforms in a real time application, or as slave processor
to a more general purpose signal processing system. In the
continuous mode, with transform sizes of 256 points or less,
it contains three internal control units which simultaneously
allow new data to be loaded, present data to be transformed,
and previous results to be dumped. Additional, external, input/
output buffering is not needed. The internal input buffer also
allows data blocks to be overlapped by either 50% or 75%,
apart from the mode with no overlaps.
When 1024 point transforms are to be calculated, without loss
of incoming data during the transform time, it is necessary to
use an input buffer. This requirement is satisfied by a single
PDSP16540 support device.
In any of the real or complex modes it is possible to obtain
higher performance by connecting devices in parallel. It is then
possible to increase the sampling rate to that of the system
clock used for internal operations.
The mode of operation of the device is controlled by 16
bits in a control register. These are loaded through the
AUX15:0 port when a control signal DEF is active low. This
port is also used to provide the imaginary component of
complex input data, and, if complex transforms are to be
performed, an external tristate buffer will be needed to isolate
the control information. This should only be enabled when
DEF is active. DEF is also used to initiliase the internal
circuitry, and can be a simple power on reset if control
parameters need not be subsequently changed.
DATA PRECISION
During each pass of a radix-4 fast Fourier transform it is
possible for either component of a particular result to grow by
a factor of up to four in the first pass, and 5.242 in subsequent
passes. This is between two and three bits in each pass and
the data path must allow for this word growth to avoid any
possibility of overflow. At the end of the data path the word is
again reduced to 16 bits by discarding least significant bits..
Any un-necessary word growth to prevent overflow thus
results in loss of arithmetic precision, and has a detrimental
effect on the dynamic range achievable.
In practice these large word growths only occur when
bipolar complex square waves are transformed, and even
then will not occur on every pass. The PDSP16510 compromises by allowing a 2 bit word growth during the butterfly
calculation in the first pass. This is equivalent to ignoring the
most significant bit of the 19 bit final result ,which is assumed
to be an extra sign bit, and then selecting the next 16 bits for
Fig. 3 One of Four Data Paths
storage. In subsequent passes a Control Register Bit allows
the user to continue to select these 16 bits, or instead to use
the 16 most significant bits. The latter option is equivalent to
a 3 bit word growth. The 2 or 3 bit word growth option applies
to ALL subsequent passes and is not a per pass option.
If the 2 bit option is selected there is a possibility of
overflow occurring in one of the passes. The prediction of
overflow is mathematically difficult, and only occurs with
specific complex square waves. Scaling down the inputs
cannot be guaranteed to prevent overflow because of the
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PDSP16510A MA
block floating point shifting scheme, which is discussed later.
Overflow can NEVER occur if the 3 bit option is chosen, but at
the expense of worse dynamic range.
When overflow does occur a flag is raised which can be
read by the user ( see later discussion on scale tag bits ), and
the results ignored. In addition all frequency bins are forced
to zero to prevent any erroneous system response.
Even with only 2 bit word growth poor dynamic range will
be obtained if the data is simply reduced to 16 bits, and
becomes worse when the incoming data does not fully occupy
all the bits in the word. These problems are overcome in the
PDSP16510, however, by a block floating point scheme which
compensates for any unnecessary word growth.
During each pass the number of sign bits in the largest
result is recorded. Before the next pass, data is shifted left
[multiplied by 2], once for every extra sign bit in this recorded
sample. At least one component in the block then fully occupies the 16 bit word, and maximum data accuracy is preserved
Up to four shifts are possible before every pass after the
first, with a total of fifteen for the complete transform. At the end
of the transform the number of left shifts that have occurred is
indicated on S3:0. Lack of pins prevents a separate output
being available to indicate that overflow has occurred in the 2
bit word growth option. For this reason the maximum number
of compensating left shifts in this mode is restricted to 14.
State 15 is then used to indicate that overflow has occurred.
The first step in the butterfly calculation multiplies 16 bit
data values with 16 bit sine/cosine values, to give 18 bit
results. This increased word length preserves accuracy
through the following adder network, and has been shown
through simulations to be an optimum size for transform sizes
up to 1024 points. This is particularly true when the input data
is restricted to below 16 bits, as is necessary with practical A/
D converters with very high sampling rates. The bottom bit of
this 18 bit word is forced to logical one and as such is a
compromise between truncation and true rounding. It gives a
lower noise floor in the outputs compared to simple truncation.
To prevent any possibility of overflow during the butterfly
calculation the word length is allowed to grow by one bit
through each of the three adders. The least significant bit is
always discarded in the first two adders . Sixteen bits are then
chosen from the final adder in the manner discussed earlier,
and the number of sign bits in the largest result is recorded for
use in the following pass.
Fig. 3 shows one of the four internal data paths which can
compute a radix-4 butterfly in twelve system clock cycles. This
equates to completing the butterfly in 3 cycles for the complete
device.
Fig. 5. RAM Organization with 1024 Point Transforms
RAM has been designed for use in a wide variety of applications. The provision of an asynchronous input strobe (DIS),
allows data to be loaded without the need for additional
external buffering. An asynchronous output strobe (DOS) also
allows transformed data to be dumped with the sampling
clock, this being particularly useful when the device is performing the inverse transform back to the time domain. Inputs
and outputs are both supported by flag and enabling signals
which allow transfers to be properly co-ordinated with the
internal transform operation.
In many applications the DIS and DOS inputs can be tied
together and fed by the sampling clock. If the output rate must
be higher than the input rate, as with multiple devices supporting overlapped data samples, both strobes can still be connected together. The clock supplied should then be twice or
four times the sampling clock, and an internal divider can be
used to provide the correctly reduced input rate. The provision
of a separate DOS pin does, however, allow the output rate to
be asynchronous to the input rate, and therefore faster than
strictly needed. Further output processing at higher rates is
then possible if this is advantageous to system requirements.
The internal workspace is double buffered when 256
point transforms are to be performed. A separate output buffer
is also provided. These resources, together with separate
input and output buses, allow new data to be loaded and old
results to be dumped, whilst the present transform is being
computed. Additional, external, input buffering is not needed
to prevent loss of incoming data whilst a transform is being
performed.
When block overlapping is required, internally stored
data will be re-used, and a proportionally smaller number of
new samples need be loaded. Note that the internal window
operator still functions correctly since it is actually applied
during the first pass, and not whilst data is being loaded. The
internal RAM organisation is shown in Fig. 4. It should be
noted that the amount of overlap between I/O transfers and
transforms is completely under the control of the system, since
an input enable signal (INEN) and an output enable (DEN) can
be used to initiate transfers.
In the 1024 point mode there is insufficient workspace for
DATA TRANSFERS
The data transfer mechanism to and from the internal
Fig. 4. RAM Organization with 256 Data Points
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Fig. 6. 1024 Point Transforms with I/P Buffer
PDSP16510A MA
input and output buffering in addition to working memory. The
device is then configured in a mode with separate load,
transform and dump operations. The internal arrangement is
shown in Fig. 5. The support of an external input buffer is
needed if incoming samples are not to be lost whilst a
transform is in progress. This is loaded at the sample clock
rate and transferred to the FFT processor as quickly as
possible. In this mode the PDSP16510 always expects to
receive 1024 words, regardless of the amount of block overlapping. Data stored internally cannot be re-used when block
overlapping is required, and data from the external buffer must
be re-read as necessary.
Fig. 6 illustrates a typical 1024 point system with an input
buffer which supports complex input data. The input buffer
can be provided by a PDSP16540 Bucket Buffer without the
need for any external control logic. It supplies RAM for 1024
x 32 complex words, and allows transfers to the FFT Processor at the full system clock rate. The PDSP16540 also supports the standard 50% and 75% data block overlapping, but
in addition allows the user to define the amount of overlap to
within 32 words.
If no incoming data is to remain un-processed, the user
must ensure that the time taken to acquire sufficient data to
instigate a new transform is greater than or equal to the
transformation time itself. The latter can be calculated from
Table 4, once the system clock rate has been defined. When
1024 point transforms are performed, both the time to read
data from the input buffer, and also the time to dump data,
must be included in the calculation to determine the minimum
time in which data can be loaded into the external buffer.
The peak transfer rate is limited by the characteristics of
the I/O circuits, but can be greater than the sampling rate
which is determined by the transform time. When load and
dump operations are not concurrent with transform operations
( as in the 1024 point modes ), then the maximum I/O rate is
equal to the system clock rate, Ø. When other transform sizes
are specified, the sampling rate, S, is reduced by a factor F.
This is defined below where Ø is in MHz and L is the system
clock low time in nanoseconds;
S = FØ,
4
6 + 0.001ØL
F is typically 0.66 and applies to all transforms except for those
of 1024 points, even if INEN is driven such that concurrent
operations do not actually occur. If this causes a system
limitation in a single device application, then the device can be
configured for pseudo, Mode 2, multiple device operation.
Separate load, transform, and then dump operations will then
always occur, but DEN must be low when a transform is
Symbol
Characteristic
where F =
16510A
Min
Max
Units
†
Data In set up Time
TSD
10
ns
†
Data In Hold Time
THD
0
ns
†
INEN active going set up
TSA
8
ns
†
INEN active Hold Time
THA
0
ns
†
INEN in-active Hold Time to ensure no load
THI
2
ns
†
INEN in-active going set up for no load operation
TSI
8
ns
†
Delay to LFLG going active ( 30 pf load )
TFH
10
ns
†
Delay to LFLG going in-active ( 30 pf load )
TFL
10
ns
†
Min time to INEN low in edge mode
TED
15
ns
Table 1. Advanced Timing Information with Continuous Inputs.
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PDSP16510A MA
complete or DAV will never go active. See the section on
multiple device operation.
LOADING DATA
Data loading is controlled by three signals; DIS an input
strobe, INEN a load enable, and LFLG an output flag. Detailed
timing information is given in Table 1. Once sufficient data has
been acquired, a transform will automatically commence. This
is normally after a complete block has been loaded, except
when a single device is performing overlapped transforms of
256 points or less. With 75% overlapping, transforms will
commence after 25% of a new block has been loaded, and
with 50% overlapping transforms commence after 50% of the
data has been loaded. The remainder of the block is provided
by data already stored in the internal RAM.
The data strobe is used to load data into the internal
workspace RAM, and data must meet the specified set up and
hold times with respect to its rising edge. This strobe can be
asynchronous to the system clock used internally, and the
device will perform the necessary internal synchronisation.
DIS can be a continuous input since the device only loads data
when an input enabling signal is active.
An internal synchronisation interval is necessary between the last sample being loaded with the DIS strobe and
transforms being started with the system clock. This can be up
to twelve system clock periods when data transfers and
transforms are overlapped. The transform times given later in
Table 4 are maximum values, and include these twelve
periods.
The way in which the INEN signal controls data loading
is dependent on whether a single or multiple device is to be
implemented, and the status of Control Register Bit 12.
When Bit12 is set in a SINGLE device system the INEN
signal is simply used as an enable for the DIS strobes. When
INEN is low, and provided the relevant set up and hold times
have been satisfied, data will be loaded with the rising edge of
the DIS strobe. If no gaps occur within the incoming data,
INEN can be tied permanently low, provided that the sampling
rate has been chosen such that transforms are completed
before a new block of data is loaded. For transforms of less
than 1024 points, data will then be continually processed
without any loss of information. In the 1024 point modes the
device will cease loading data when 1024 samples have been
loaded, and even if INEN remains low no more data will be
accepted until the previous results have been dumped.
In a multiple device system an edge is ALWAYS needed
to commence a load operation, and Bit 12 has a different
purpose. The edge is provided by INEN going low. Loading
will cease when a complete block (or group of blocks with
multiple concurrent transforms) of data has been loaded, even
if INEN remains low. INEN must go high at some point after the
minimum hold time has been satisfied, and then return low
AFTER ALL DATA HAS BEEN LOADED, before a new load
operation can commence. Low going edges which occur
before all data has been loaded will be ignored.
The INEN edge mode is actually provided for the correct
operation of multiple device systems, but if Bit 12 in the Control
Register is reset in the SINGLE device mode, the edge
activated operation will still be possible. With all but 256 point
complex transforms, the single device edge mode of operation
is identical to that of a multiple device system. With 256 point
8
transforms, and their concurrent derivatives, the location of
the low going edge in the data steam is dependent on the
amount of block overlapping. The low going edge transition
must be provided after 64 samples have been loaded with
75% overlapping, and after 128 samples have been loaded
with 50% overlapping. With no overlapping the edge must be
provided after 256 samples have been loaded.
In a single device system with Bit 12 set, INEN can be
taken high to inhibit the load operation when gaps occur in the
data stream. In the INEN edge activated mode gaps in the
data stream can only be accommodated if the DIS clock is
externally inhibited. Taking INEN high will not inhibit the
loading of data in this mode.
With gaps in the data stream the peak sampling rates can
be higher than continuous sampling rates. When data loading
is not coincident with transform operations the peak rate can
equal that of the system clock, otherwise it is reduced by the
factor, F, given on the opposite page.
When Control Register Bit 12 is set in any multiple device
mode, the DEF high going edge will also initiate a load
operation after it has been internally synchronised to the rising
DIS edge. If the first device in a multiple device system is
programmed in this manner, the transform sequence will
automatically start when DEF goes in-active. The other devices need the INEN edge as usual, and must have Bit 12
reset. A fuller explanation of the use of Bit 12 in a multiple
device mode is given in the section on I/O In Multiple Device
Systems. Note that the use of Bit 12 in a single device system
( Control Register Bits 10:9 = 00) is completely different to its
use in a multiple device mode.
The LFLG output goes active in response to the DIS rising
edge used to load the first data sample, and indicates that a
load operation is occurring. In an edge activated system the
LFLG output will go high as the result of the first high going DIS
edge after INEN has gone low. In the simple INEN enabling
mode, internal logic counts the number of valid inputs and
detects when the programmed block length has been
reached. LFLG then goes low and will go high again in
response to the next valid DIS strobe. LFLG will go low when
DEF is active and will go high in response to the first INEN
enabled DIS edge after DEF has gone in- active.
The active going LFLG edge does not normally have any
system significance, but in the block overlapping modes the
in-active going edge will occur when 50% or 75% of the data
has been loaded. By driving the INEN input on one device with
the LFLG output from a previous device, this edge can be used
to partition data between several devices in a multiple device
system. It can also be used to provide an address marker for
a user defined input buffer, when executing 1024 point transforms with a single device. It is not needed, however, when the
input buffer is provided by the PDSP16540.
DUMPING DATA
Data output is controlled by an asynchronous output
strobe [DOS], a dump enable signal [DEN], and a Data
Available signal [DAV]. The DAV signal is used to indicate that
the internal output buffer contains transformed data, and the
DEN input is used to control the outputing of that data. The
output buffer within the device is clocked by the DOS input,
and must be primed with four DOS strobes once a transform
is complete in order to transfer data to the output pins. DAV will
PDSP16510A MA
not go active until this priming has occurred. The DOS priming
strobes must be enabled by the DEN input, unless the device
has been configured in one of the multiple device modes ( See
section on Multiple Device Systems ).
The state of the DEN input at the end of a transform is
used to control the transition of the active going edge of the
DAV output with respect to the DOS strobes. The latter are
then used to transfer data from the device to the next system
component. If the DEN input is tied low in a single device
system, the active going DAV transition will be internally
synchronised to the rising edge of a DOS clock. If DEN is not
tied low it must be guaranteed to be low at the end of the
internal transform operation for this synchronization to occur.
Since there is no external indication of this event, the user
must take care to only allow DEN to go high whilst DAV is
active, if this DAV synchronous mode is needed.
SYNCHRONIZED DAV OPERATION
In the DAV synchronised mode the first rising edge of the
DOS clock, after DAV has gone active, must be used to
transfer the first transformed sample from the output pins to
the next system component. It should be noted that the output
buffer will have been primed before the active DAV transition,
since DOS must be a continuous clock, and there is then no
delay before the first output becomes valid. The DAV output
can be used as a clock enable for this next device, and
transfers will continue in normal sequential order until the
required data has been dumped. DAV will then go inactive in
response to the last DOS edge which was used to transfer
data to the next device.
This mode of automatically dumping data when it is ready
finds applications in real time data flow systems, and detailed
timing is given in Table 2. It should be noted that the DOS input
MUST be continually present before DAV goes active. If this
is not the case the DAV output will not go active at the correct
time, and the internal output circuitry will not be primed. Once
DAV is active, however, it is possible for DOS to be irregular,
and DEN can be used to inhibit the action of the output strobe
as discussed previously. For the correct operation of the
device the user must ensure that DOS becomes continuous
and DEN remains low once DAV goes in-active.
When continuously transforming data such that new
outputs are internally available before the previous block has
been completely dumped, then DAV would normally stay
active and give no indication that one block dump had been
finished and another block started. Additional internal circuitry
is, however, provided to ensure that DAV goes inactive for one
DOS high time, thus supplying an inter block marker.
ASYNCHRONOUS DAV MODE
If DEN is not active in a single device when the transform
is complete, then the device will wait for DEN to go active
before any data is dumped. This mode is suitable for applications in which output processing is under the control of a
remote host, such as a general purpose digital signal processor. The DAV output will then go active as soon as the output
buffer is full, and will not be synchronised to the DOS edge. In
such systems the DOS strobe may not necessarily be present
at this time. Table 3 gives the relevant timing information.
In this host controlled dump mode the PDSP16510 waits
for the host to activate the DEN input after DAV has gone
active. DEN then functions as an enable for the host produced
data strobes on the DOS pin. DEN may either stay active for
the complete transfer, or may be used to enable each DOS
16510A
Symbol
Characteristic
Min
Max
Units
TLZ
15
ns
Output Disable Time
THZ
15
ns
†
Data Delay Time ( 30 pf load )
TDD
15
ns
†
Data Hold Time
TDH
2
†
DAV active Delay Time ( 30 pf load )
TVD
1
10
ns
†
DAV in active Delay Time ( 30 pf load )
TVI
1
10
ns
†
Output Enable Time
†
Table 2. Output Timing with DEN tied low. ( Advanced Data )
ns
9
PDSP16510A MA
input. When DEN and DOS are both active an internal read
operation occurs, and an address generator is incremented.
DAV goes in-active in response to the DOS edge needed to
read the last output, unless Bit 15 in the Control Register is set.
In this case DAV goes in-active when the next INEN edge is
received for reasons given later.
In host controlled systems the time to dump data could be
longer than the transform time. The dump time in such a
system will dictate the maximum sampling rate that can be
used without the loss of incoming data. In the 1024 point
mode, when the loss of data is not important, the PDSP16510
is designed to not accept new data until the previous results
have been dumped. Such a system needs no input buffer, and
INEN can be permanently tied low if the edge activated mode
is not in use. If the loss of data is to be avoided an input buffer
is needed and the host must have received all the results
before a new block of data has been loaded into the buffer.
For 256 point transforms, with host controlled dumping,
it is still possible to overlap load and dump operations. The
maximum dump times , however, must be less than the load
times to avoid data corruption. Previously converted outputs
will be actually corrupted , rather than inputs simply not being
used.
If the loss of incoming data is not important, the device
can be forced to do separate load, transform, and then dump
operations. The corruption of results will then never occur, no
matter what dump time is taken. This can be achieved by
ensuring that INEN is not active between loading a block of
data and completing the dump of the results from that data.
The same ends can be achieved if the INEN edge activated
mode ( Bit 12 reset ) is used, and the inverted DAV edge is
used to drive the INEN input. This then initializes a new load
operation only when the previous dump has been completed.
In such a system the INEN edge will be asynchronous to the
DIS strobe, and the set up time given in Table 1 may not be
obeyed. This will simply cause an extra input sample to be
possibly ignored, but will not cause data corruption.
Results are transferred from the device with the rising
edge of the DOS strobe when DEN is active. This is consistent
with using the device in a data flow architecture, as is commonly employed in data processing systems. In a typical
microprocessor based system, however, data is normally
expected to become valid before the end of the data strobe
produced by the processor. It is thus necessary for the user
to provide a ‘dummy’ data strobe in order to transfer data to
the outputs which can then be read by the host during the next
data strobe. In addition a further three ' dummy ' strobes are
needed each time DAV goes active in order to prime the output
circuitry. The actual output sequence is given in Table 3, and
illustrates that four DEN enabled DOS strobes are needed
before the first frequency bin appears on the output pins. This
is then read by the host with the fifth DOS strobe. DAV does
not go inactive until the DOS edge after the last bin appeared
on the output pins.
In addition to the above requirements it is necessary to
provide at least four DOS strobes after DEF has gone inactive, but before DAV goes active. These initialize the
internal address counters and do not rely on DEN also being
active. They are needed every time DEF has been used to
change the operating mode.
16510A
Symbol
Charactreristic
Min
Max
Units
†
DEN Set Up Time
TPS
10
ns
†
Host Strobe Width
TPW
10
ns
†
DEN Hold Time
TPH
5
†
DAV in-active going Delay ( 30 pf load )
TVI
10
ns
†
Output Enable Time ( see Fig 13 )
TLZ
10
ns
†
Output Data Delay Time ( 30 pf load )
TDD
15
ns
†
Output Disable Time ( see Fig 13 )
THZ
10
ns
†
Read Cycle Times
TRC
25
ns
†
Old Data Hold Time
TOH
2
ns
Table 3. Host Controlled Output Timing. ( Advanced Data )
10
ns
PDSP16510A MA
Fig. 7. Host Controlled System
Figure 8. 1024 Point Real Transforms
GENERAL DUMP CONSIDERATIONS
The tri-state drivers on the output buses are only enabled
when both DAV and DEN are active. When DEN is tied
permanently, low the output bus will start to become valid from
the DOS edge which also generates the DAV output. The next
DOS edge can then be used to transfer the first output to the
next device. When DEN is driven low in response to the DAV
output, the outputs start to become valid when DEN goes low.
The Scale Tag outputs become valid at the same time as data,
and when enabled will continue to indicate the correct value
until all frequency bins have been dumped. If at any time
during the dump operation DEN goes in- active, then both the
data and scale tag outputs will go high impedance after the
delay shown in Table 3.
Valid transformed data is actually available within the
device from DAV going active until INEN again goes active,
and a new set of data is loaded. The output tristate drivers,
however, normally go high impedance when DAV goes inactive once a dump operation has been completed. In order to
support systems in which it may be necessary to read the
transformed data more than once, a Control Register Bit is
provided which keeps the DAV output active until a further
INEN edge is received. The user must then keep track of how
many outputs have been dumped before INEN is generated to
start a new load operation.
The DAV output can be delayed by an amount equivalent
to the pipeline delay through the PDSP16330. This option is
invoked by setting a control bit, and allows DAV to indicate that
polar data is available at the output of the PDSP16330. When
the option is used the tri-state outputs will be enabled when
data is actually available and DEN is active, and not when DAV
eventually goes active.
Two Control Register Bits allow a range of dump size
options to be supported. In some applications the results of
interest may only lie in the lower 25 or 50% of the frequency
bins, the sampling rate having been chosen to prevent
aliasing, and the transform size having been selected to give
the required frequency resolution. In other systems it is only
necessary to output the second half of a given sized transform.
This is useful when filtering is to be performed in the frequency
domain using Overlap /Discard Fast Convolutions. With this
method FIR filters with N taps can be implemented in the
frequency domain using 50% overlapped transforms on 2N
samples. After multiplication in the frequency domain with the
required frequency response, the inverse transform is performed and the first half of each output is discarded. Since only
half the results are dumped, the dump clock need not be twice
the rate of the clock used to load data.
FULL CO - PROCESSOR OPERATION
A single device can be configured as a co-processor to a
host system in which both the loading and dumping of data is
under the control of the host. Such a system is shown in Figure
7, in which DEN is a host provided enable for host read
operations, and INEN is an enable for host write operations.
DIS and DOS are host data strobes.
The host loads a block of data into the PDSP16510, using
DIS enabled by INEN, which is then automatically transformed. The DAV output provides a flag indicating that the
transform is complete, and results are then read by the host
using DOS enabled by DEN. A new set of inputs is not
normally loaded until the previous results are complete. If,
however, 1024 point transforms are not to be performed,
loading new data could coincide with dumping previous results. This, however, would require a host system with separate input and output buses, and which also allowed coincident transfers. As discussed previously, transferring results
must take no longer than loading new data to prevent corruption of the outputs.
In the system illustrated by Figure 7, the host also controls
the mode of operation of the FFT processor. The DEF signal
is produced from an address decode, and the control parameters are loaded from the host bus by connecting the AUX
inputs to the data outputs.
REAL ONLY TRANSFORMS WITH A SINGLE DEVICE
In the simplest case real transforms can, of course, be
computed by forcing zero levels on the imaginary input pins.
The device can, however, be configured to internally perform
two simultaneous real transforms instead of a single complex
transform. The block floating point logic will then use data from
both blocks when it determines the number of shifts to be
applied. This dual transform technique is used to increase the
maximum permissible sampling rates, but since an additional
data pass is required in order to un-scramble the transformed
data, the actual performance is not quite double that possible
11
PDSP16510A MA
with a complex transform of the same size. The 4 x 64 point
complex mode becomes an 8 x 64 real mode, but the change
from 16 x 16 complex transforms to 32 x 16 real transforms is
not supported.
When a real transform is performed the algorithm produces complex results for each of the incoming data blocks,
but each result only represents the first half of the frequency
domain data. This does not cause any loss of information
since the two halves are mirror images of each other. As with
complex transforms, it is necessary for a different system
configuration to be used when 1024 point transforms are
required. These are considered later, and the following only
applies to 256 or 64 point transforms.
In a single device system, performing non overlapped
transforms on data from a SINGLE source, only the Real input
pins are used, and the Imaginary inputs are redundant except
when configuring the device. By setting Control Register Bits
8:6 to 101, however, it is possible for a single device to accept
data from two independent sources using the real and imaginary inputs. Maximum sampling rates will then only be half
those possible when a single source is used, if no incoming
data is to remain un-processed. With two sources a transform
must be completed in the time to load parallel blocks, otherwise incoming data will be lost. With one source a transform
need not be finished until two data blocks have been acquired.
In this dual input mode results from data on the real inputs
always precede those from the imaginary inputs.
If block overlapping is needed, it is always necessary to load
pairs of data blocks simultaneously, using both the real and
imaginary inputs. With dual sources of data this presents no
problem, and Control Bits 8:6 should be set to 110 or 111 for
the relevant amount of overlapping. If data is from a single
source an external FIFO is needed to provide a simple delay
for a block of data. Decodes 001 through 100 from Control Bits
8:6 must be used to select the required overlap.
The output of the FIFO must provide data for the real inputs.
Continuous inputs can still be accepted, and each block will
initially occur on the imaginary inputs, and then occur again on
the real inputs as an output from the FIFO. The data output
sequence will consist of the results from a pair of inputs,
followed by the results obtained after the required overlap.
Thus with 50% overlapping the sequence is 1 & 2 followed by
1.5 & 2.5 followed by 3 & 4 followed by 3.5 & 4.5 etc., where
1 2 3 4 are the sequential inputs to the external FIFO, 1.5 is the
overlap between 1 and 2, and 2.5 is the overlap between 2 and
3.
When eight simultaneous 64 point transforms are performed, the sampling rates given in Table 5 assume that data
is from a common source. The data outputs will be in the
correct sequence from 1 to 8, corresponding to inputs 1
through 8 in normal order from a single source. When data is
from two sources the sampling rates will be halved, and the
output sequence will be 1A 1B 2A 2B 3A 3B 4A 4B, where A
and B are the dual simultaneous sources on the real and
imaginary inputs respectively. If data block overlapping is
Configuration
Clock Periods
16 X 16PT
COMP
420
4 X 64PT
COMP
624
256PT
COMP
816
1024PT
COMP
3907
8 X 64PT
REAL
816
2 X 256PT
REAL
1032
2 X 1024PT
REAL
4699
Table 4. Computation Times in Clock Periods
used in either of the above cases, the eight outputs will be
followed by results from the same basic eight blocks but time
displaced to give the required overlap. If more than two
sources are to be handled the user must provide appropriate
buffering and multiplexing, and the sampling rates must be
proportionally reduced.
When two 1024 point transforms are performed with a
single device, on data from a single source, the input buffer
must be arranged to acquire two blocks before initialising a
transfer to the device. In order to improve the maximum
sampling rates possible, data should be read simultaneously
from each half of the buffer, and loaded into the real and
imaginary inputs. This halves the transfer time from the buffer
to the device, but requires the device to expect dual inputs.
Thus if block overlapping is not needed Control Register Bits
8:6 should be set to 101.
This fast transfer mode is supported by a special option
on the PDSP16540 Bucket Buffer. It will acquire two 1024
point non overlapping blocks using the sampling clock, and
then transfer the results to the FFT processor at the full system
clock rate. Figure 8 shows the system arrangement. It does
not support block overlapping.
With 1024 point transforms all block overlaps are handled
by the buffer logic, and not by the internal RAM, but the device
must still be programmed to expect the required overlap if the
external buffer makes use of the in-active LFLG edge to mark
the overlap point. To achieve the performance given in Table
5 with 50% overlaps, the buffer must provide sufficient storage
for at least 2.5 data blocks. With 75% overlaps it must provide
storage for 2.75 blocks. This extra storage allows transfers
between devices to be only needed when a complete new
block has been acquired for 50% overlaps, and when half a
new block has been acquired for 75% overlaps.If storage is
restricted to two data blocks, only half the sampling rates given
will be possible. Transfers between devices must then occur
when a half or a quarter of a new block has been acquired.
Since the minimum time between transfers must be no less
than the transform time itself, the sampling rates must be
proportionally reduced to prevent loss of data.
Table 5 Sampliing Rates in MHz Obtained with a Single Device and various overlaps.
12
PDSP16510A MA
SINGLE DEVICE SAMPLING RATES
In a single device system the maximum sampling rate is
dependent on the transform size, the data overlap, and
whether real or complex data is applied. Table 4 gives the
times taken to complete the transforms for the various block
sizes, which include an allowance for synchronisation between the DIS strobe and the system clock. If continuous data
is to be transformed, the time to acquire a new block of data
(or partial block with overlapping) must be at least equal to
these transform times. Load and dump times must also be
added in the 1024 modes. For non continuous transforms the
peak rate is limited by the system clock rate and the factor , F,
given previously.
The time taken to dump the transformed data must be no
more than the load time, if continuous inputs are to be
supported and I/O operations are concurrent with transforms.
With block overlapping the dump time must be reduced to the
time taken to load the partial block. This dump time must
include four extra DOS strobes needed to prime the output
circuitry when a transform is complete. These, in effect, can be
added to the transform time such that with concurrent I/O and
0%, 50%, or 75% overlapping;
nS or nS or nS must be greater than or equal to PK + 4W
2
4
where n is the transform size, S is the input DIS period, P is
the number of clock periods given in Table 4, K is the system
clock period, and W is the DOS period which can be less than
S if necessary.
When DIS and DOS are produced from a common source
the minimum allowable sampling period must be increased to
allow for the extra dumping time. Thus when DIS and DOS
have equal periods and, for example, there is no overlapping;
(n - 4)S must be greater than or equal to PK
The maximum sampling rates given in Table 5 allow for the
extra dumping time.
The load and dump operations are not concurrent with
transforms in the 1024 point modes, and an external input
buffer will be needed if loss of incoming data is to be avoided.
This is loaded at the sampling rate and then data is transferred
to the PDSP16510 at a user defined rate. The time taken to
load this external buffer must be at least equal to the sum of
the time to transfer data in and out of the FFT processor and
the transform time itself. When data blocks are overlapped by
50% or 75%, no more than one half or one quarter of the block,
respectively, must have been loaded in the same time. In the
1024 point modes the dump time can be any user defined
value, and need not be increased to allow for block overlapping. The dump time, however , does directly effect the
maximum sampling rates which can be accommodated without loss of incoming data.
The maximum sampling rates for 1024 point transforms
at any load and dump rate can be calculated from the following
relationship:
1024S or 512S or 256S > 1024B + PK + D
for 0%, 50%, or 75% overlapping respectively. S, P, and K
were defined opposite. B is the clock period in which data is
read from the input buffer and loaded into the device, D is the
total dump time allowing for the four extra DOS periods. The
periods of the load and dump clocks cannot be less than the
system clock period. The maximum sampling rates given in
Table 5 assume that a 40 MHz I/O rate is used, and that all
results are dumped.
MULTIPLE DEVICE SYSTEMS
Figure 9. Multiple Device Configuration
In real time applications several devices may be used in
parallel in order to increase the sampling rate, but not to
increase the transform size. When all outputs are commoned
together, and feed a single output processor, then the data
dump time must always be less than or equal to the time taken
to load the data block ( or 50% or 25% of the time with block
overlapping ). In most configurations with block overlapping
the dump rate requirements will limit the maximum input rate,
if only one output processor is provided. This can be avoided
if the system provides separate output processors for every
device. The system clock used for internal calculations then
ultimately imposes a limit on the maximum sampling rate
possible.
A multiple device system performing complex transforms
with a single output processor is shown in Figure 9. The INEN/
LFLG signals are used to co-ordinate the segmentation of
data between devices. The in-active going edge of LFLG
instigates the load procedure in the next device, and, since
this edge can be programmed to occur either 25%, 50%, or
100% through the load operation, it can cause the next device
to commence loading before the previous one has finished. In
this manner data block overlapping is achieved. When mul-
13
PDSP16510A MA
tiple concurrent transforms are performed ( for example 4 x 64
or 8 x 64 ) two LFLG transitions are sometimes needed to
support block overlapping. This is fully explained in the section
on Mode 1 sampling rates.
In any of the multiple device modes an INEN edge
transition is needed to start a new load procedure when the
previous one has finished. When the LFLG output from the last
device is fed back to the INEN input of the first device,
continuous transforms will be executed. This continuous sequence can be started by the rising edge of DEF if Control
Register Bit 12 is set in the first device (see section on Loading
Data). This bit must not be set in the other devices. Since all
devices are supplied from a common input bus and have a
common source of control parameters, this Bit 12 inversion is
best mechanized with an Exclusive OR gate in the AUX12
input line of the first device. The input can then be inverted
when DEF is active but otherwise not be effected. Once the
first device has been started with the DEF edge, the sequence
will continue automatically using the LFLG /INEN connection
between devices.
In many applications data is transformed continuously
after power on, and the concept of a first data sample does not
exist. If, however , the opposite is true, the first data sample
must be present on the input pins such that it can be loaded
with the second rising DIS edge after DEF has gone in-active.
The data must meet the set up and hold times given in Table
1, and DEF itself must meet the parameters normally met by
the INEN rising edge. The latter requirement is necessary to
avoid a possible one DIS cycle variance, due the internal DEF
synchronization logic. If the position of the first data sample is
not important, it is not necessary for DEF to have any set up
specification.
Without the feedback from the last device, the first device
would wait for another externally supplied initialising pulse. In
such a system with N devices in parallel, then N continuous
transforms must be executed before the first device can wait
for a new INEN input.
When only one output processor is provided the data
outputs from all devices are connected together, and internal
logic will enable the tri-state outputs when a device is ready to
output data i.e. DAV goes active. When data blocks are
overlapped it is possible that the output rate requirements will
limit the input sampling rate (see section on Multiple Device
Sampling Rates). Additional output processors will remove
this restriction, and the correct choice of multiple device
operating mode will optimise the sampling rates that can be
achieved with a given number of devices.
The synchronisation intervals, necessary to co-ordinate
input and output operations with the transform operation, lead,
in effect, to some uncertainty in the time needed to complete
a transform. Thus a particular device in a multiple device
system can effectively complete a transform in less system
clock periods than another device in the same system. To
prevent one device turning on its output bus before the
previous one has finished, it is either necessary to use a faster
output rate than would otherwise be required, or to use the
inverted DAV output from one device to drive the DEN input of
the next. The latter option allows DIS and DOS to be connected together, and ensures that the second device will not
output data until the first device has finished.
This method of driving the DEN input from the inverted
DAV output from a previous device requires a change to the
single device DAV and DEN operation. If DEN is active at the
end of a transform in a multiple device system, the DAV output
will go active when the output circuit has been primed by the
DOS strobes. This operation is identical to that provided for a
single device system, and is transparent to the user as long as
DEN and DOS are active . If DEN is not active, however, the
Figure 10. Three Device System with Separate Load, Transform, and Dump Operations
14
PDSP16510A MA
DAV output will not asynchronously go active as happens in a
single device system. Instead DAV will only go active when
DEN eventually goes active. Since DEN is the inverted DAV
output from a previous device, it is thus never possible for two
devices to be actively outputing data. The DAV active going
edge remains synchronised to the DOS strobe since the DEN
input will only go active when a previous DAV goes in-active.
A further change to the output circuitry ensures that the output
buffer is primed even though DEN is not active. The first word,
however, only progresses as far as the final output latch. The
output bus is not enabled, and address increments do not
occur, until DEN is finally received. This modification to the
internal control logic ensures that the output buffer does not
impose unnecessary gaps between consecutive transforms.
These gaps would, in turn, force the required DOS frequency
to be greater than the DIS frequency ( or greater than twice or
four times the frequency with 50% and 75% overlaps ).
The system illustrated by Figure 9 produces a common
DAV output by OR'ing together all the individual, active low,
DAV outputs. This is not guaranteed to give an indication when
one transform has finished, and the next one has started,
since it may simply glitch as one DAV goes in-active and the
next one goes active after some delay. This glitch will not
cause system problems since it occurs at a point clear of the
high going edge of the DOS strobe. To provide a marker for
the end of a transform each in-active going DAV edge should
set its own latch, which is then reset by a subsequent DOS
edge. The output of the latches can then be OR'd together if
necessary.
Three multiple device operating modes are actually provided, and are selected with Control Register Bits 10:9. The
choice of a particular mode is application dependent, and will
effect the maximum sampling rate achievable with a given
number of devices.
MULTIPLE DEVICE SAMPLING RATES
MODE 1. (BITS 10:9 = 01)
In this mode transfers in and out of the device are concurrent
with transform operations. This mode must not be used for
1024 point transforms due to internal memory size restrictions. When real transforms are performed in this mode, only
the real data input is used, regardless of the amount of block
overlapping.
The increase in performance is directly related to the
number of devices provided, but the input and output rates are
limited to FØ where F and Ø are as defined previously. Within
this restriction the theoretical performance is given by;
NnS > PK+4W, or 0.5NnS > PK+4W, or 0.25NnS > PK+4W
for 0%, 50%, or 75% overlapping. N is the number of devices,
n is the transform size, S is the DIS strobe period, P is the
number of system clock periods given in Table 4, K is the
system clock period, and W is the DOS strobe period.
If an output processor is provided for every device, two
devices with 50% block overlapping or four devices with 75%
block overlapping will give the same sampling rates as a single
device with no overlapping. If only one output processor is
provided, the two or four times increase needed in the output
rate over the input rate, usually imposes a limit on the input
rate, since the output rate is limited to a factor, F, of the system
clock.
In this operating mode the DIS and DOS strobes can
often be tied together, since a faster DOS strobe gives no
improvement in the sampling rates possible. This remains true
even when the output rate must be twice or four times the input
rate due to block overlapping. Options can then be used which
internally divide the DIS strobe by two or four, and thus allow
the input to be driven by the faster DOS strobe.
In this mode the LFLG goes in-active after 25%, 50%, or
100% of the block has been loaded. When multiple transforms
are performed concurrently (for example 4 x 64) a LFLG
transition occurs at the relevant point whilst the first block in
the group is being loaded. LFLG then goes high again and
returns low at the overlap point in the last block. This double
LFLG transition allows two devices to support 50% block
overlapping, since the first transition from the first device can
be used to initiate the load procedure in the second device.
The second transition from the second device then initiates a
new load procedure in the first device. The additional edges
from each device have no effect since they occur when the
device they are driving is already doing a load operation.
In such a two device system supporting 50% overlaps the
inverted DAV from the first device must drive the DEN input of
the second device. The data dumping time is then shared
equally between both devices. The second device only outputs data when the first has finished, but both dumps must be
finished in the time taken to load the group of blocks if only one
output processor is provided. Without the DAV/DEN connection one device would only have had the time needed to load
half of one sub block in which to dump its data.
In a similar manner four devices will handle 75% overlaps
when concurrent multiple transforms are to be computed. The
second, third, and fourth devices make use of the first transition, and ignore the second. The first device uses the second
transition from the last device, and ignores the first. With the
DAV/DEN connection each device will have one quarter of the
load time to dump its data when a single output processor is
provided .
More than two devices will provide increased performance for multiple transforms with 50% overlapping, and more
than four devices will increase the performance with 75%
overlapping. External logic is then needed to ensure that each
device only uses the correct LFLG transition. Any device
should only use the negative LFLG transition from a previous
device if its own LFLG is low, and the LFLG output from the
previous device plus one is low.
MODE 2 (BITS 10:9 = 10)
This mode is suitable for all transform sizes, since separate
load, transform, and then dump operations occur. More devices than required by Mode 1 are necessary to achieve a
given sampling rate, but the input and output rates can be any
value up to the full system clock rate with the A grade part. As
with Mode 1, additional output processors are needed to
avoid the sampling rate restriction imposed by block overlapping.
The number of devices, N, needed to achieve a given
sample rate can be derived from the following formula:
NnS > nS + PK + D for no overlapping
15
PDSP16510A MA
NnS > 2 X [nS + PK + D] for 50% overlapping
NnS > 4 X [nS + PK + D] for 75% overlapping
N is the number of devices, n is the transform size, S is the DIS
strobe period, P is the number of system clock periods given
in Table 4, K is the system clock period, and D is the total dump
time including 4 extra DOS periods as discussed previously.
The DIS and DOS periods are any value defined by the user,
down to the system clock period with the A grade part.
In this mode increasing the output clock frequency will
allow a greater continuous input rate. The provision of
separate DIS and DOS pins allows this to be mechanized, and
the DOS frequency can be increased to that of the system
clock used internally. When the sum of the dump time (
including four extra DOS periods for output priming ) plus 12
system clock periods (the transform time variation caused by
input synchronization) is less than the load time, one device
will be guaranteed to have finished dumping before the next
one starts. The inverted DAV to DEN connection between
devices is then not needed, and all DEN inputs can be
grounded.
The LFLG transitions occur at the same times as Mode 1,
except that the double transition does not occur with multiple
concurrent transforms. Fig. 10 illustrates a timing sequence
with three devices. Real transforms still only use the real
inputs regardless of the amount of block overlapping.
MODE 3 (BITS 10:9 = 11)
Multiple device Mode 3 is provided in order to improve the
performance when block overlapping is needed, and separate
output processors are provided. In this mode transfers in and
out of the device are never concurrent with transform operations. The device will actually load extra data such that the
required data to perform two overlapped transforms is stored
internally. The amount of internal RAM prohibits the use of this
mode when performing overlapped 1024 point transforms.
LFLG will go in-active after a normal data block have been
loaded, regardless of the overlap selected. The device, however, continues to load more data. Thus, for example, in the 4
x 64 mode, five 64 point blocks will be loaded. This technique
allows each device in the system to complete two or four
overlapped transforms (depending on the amount of overlap)
before any new data is needed. When doing a straightforward
256 point transform the device will load 256 + 128 data points.
The full benefits are only obtained if more than one output
processor is provided, but an extra processor is not always
necessary for every device. Sampling rates up to the system
clock rate are possible. The equations defining the sampling
rates become:
(N - 1)L > 2PK + 2D for 50% overlaps
(N - 1)L > 4PK + 4D for 75% overlaps
where L is the time needed to load a normal block of data but
not including the extra data, P is the number of system clock
periods given in Table 4, K is the system clock period, and D
is the total dump time including 4 extra DOS periods.
When real transforms are to be performed on single
sourced data, an external FIFO is needed to provide pairs of
data blocks. These are loaded simultaneously into the real
and imaginary inputs. See the section on real transforms.
16
OPERATING MODES
The operating mode of the PDSP16510 is determined by
the condition of 16 bits in an internal Control Register. The
status of these bits is defined by the inputs present on the
AUX15:0 pins when the DEF input is active. The DEF input can
be a simple power on reset if the operating mode is fixed once
power is supplied. The AUX pins are also used to provide the
imaginary component of the complex input data. Thus, if
complex inputs are needed, the mode definition must be
implemented through a tri-state buffer which is only enabled
when DEF is active. The imaginary input data must be
disabled during this time.
Table 6 lists the functionality of each of the bits in the
mode control register, and further explanations are as follows:BITS 2:0
These bits define one of 7 options for the sample size and
type of data. In the 1024 point options the device will assume
the non concurrent operating mode, regardless of whether a
single or multiple device system is specified. The internal
control logic will then ensure that data is loaded, transformed,
and dumped in sequential operations.
For other data set sizes, loading, transforming, and
dumping, can all occur simultaneously with a single device;
the actual overlap will be dependent on the relative occurrences of the INEN input. Only in Mode 1 can concurrent
operations be done with multiple devices.
BIT 3
This bit determines the number of right shifts built into the
data path. In either condition only two right shifts occur during
the first pass. If the bit is reset, three shifts occur in subsequent
passes and the block floating point scheme allows up to fifteen
compensating left shifts. If it is set, two shifts occur in every
pass and overflow is possible. This is indicated by reducing
the number of compensating left shifts to fourteen, and using
scale tag value fifteen to indicate that overflow has occurred.
BITS 5:4
These bits define the choice of window operator. If other
windows are needed they must be applied externally. The
fourth option is used to specify the inverse transform, which
does not require the use of a window operator. When 16 x 16
complex transforms are specified by Bits 2:0, only the rectangular window can be used. The use of any of the other options
will cause the device to enter an internal test mode.
BITS 8:6
These bits define 0%, 50%, or 75% data block overlapping, and the division factor on the DIS input. Overlapping
must not be specified with 16 x 16 complex transforms.
Two decodes allow the DIS input to be divided by two or four,
when 50% and 75% overlapping is respectively needed.
These options allow the DOS and DIS input pins to be still
supplied from a common source, even though the output rate
must be faster than the input rate. The frequency of this source
would be dictated by the output rate requirement, with the
input rate internally reduced by the correct amount.
Special decodes are provided to support real only transforms from dual sources, using both the real and auxiliary
PDSP16510A MA
inputs. When data is from a single source, and no overlaps are
needed, only the real input should be used. If 50% or 75%
overlaps are needed from a single source of real data, the
device always expects blocks to be simultaneously loaded. An
external FIFO is then needed to supply data to the real inputs
after a delay of one block. Each block is thus loaded twice,
firstly through the Auxiliary inputs and then through the Real
inputs.
BIT 10:9
These bits define a single device system, or one of three
multiple device possibilities. The choice between the first and
second multiple device mode is dependent on the transform
size and the sampling rate needed. The third mode should
only be used when overlapped multiple transforms with less
BITS
Dec'
OPTION
2:0
000
001
010
011
100
101
110
111
16 x 16 COMPLEX
4 x 64 COMPLEX
256 COMPLEX
1024 COMPLEX
8 X 64 REAL
2 X 256 REAL
2 X 1024 REAL
NOT USED
3
0
1
SHIFT 3 PLACES AFTER PASS1
ALWAYS SHIFT 2 PLACES
5:4
00
01
10
11
RECTANGULAR
HAMMING WINDOW
BLACKMAN-HARRIS
INVERSE TRANSFORM
8:6
000
001
010
011
100
101
110
111
NO OVERLAP
50% OVERLAP
50% OVERLAP AND DIS ÷ 2
75% OVERLAP
75% OVERLAP AND DIS ÷ 4
DUAL SOURCE, NO OVERLAP
DUAL SOURCE, 50% OVERLAP
DUAL SOURCE, 75% OVERLAP
10:9
00
01
10
11
SINGLE DEVICE
N DEVICES, CONCURRENT I/O
N DEVICES, LOAD-TRANS-DUMP
SPECIAL MULTIPLE TRANSFORM
11
00
01
DAV NOT DELAYED
24 CLK DAV DELAY
12
0
1
INEN EDGE ACTIVATED
INEN IS SIMPLE ENABLE
14:13
00
01
10
11
O/P FIRST QUARTER
O/P FIRST HALF
O/P LAST HALF
O/P ALL RESULTS
15
0
1
NORMAL DAV
KEEP DAV ACTIVE TILL INEN
Table 6. Mode Control Bit Allocations
than 1024 points are to be performed simultaneously. It
changes the LFLG logic and allows sampling rates up to the
system clock rate to be achieved with multiple output processors.
BIT 11
When this bit is set the PDSP16510 will not generate DAV
until 24 DOS clocks after data was actually valid. In this case
the output tri-state drivers will be enabled at the correct time,
even though the DAV signal was not externally valid. Host
controlled dumping should not be used.
BIT 12
When this bit is set in the single device mode, the INEN
input is a simple load enable signal. When it is reset an INEN
edge is needed at the end of a load sequence before a new
one can commence.
When it is reset in a multiple device mode it has no
action, but when it is set it will cause the DEF high going edge
to also initiate a load operation.
BIT 14:13
These bits allow four dump size options to be provided.
Individual frequency bins are not accessible.
BIT 15
Under normal circumstances DAV would be expected to
go invalid when a transform has been dumped. In some
applications, however, it may be necessary to read the outputs
more than once. When this bit is set, DAV will remain valid until
the next INEN input, and will indicate that the transformed data
still remains in the internal buffer. As soon as the next INEN is
received the transformed data will be overwritten. Whilst DAV
remains active the output tri-states will be enabled.
WINDOW OPERATORS
Since only a finite segment of a signal can be observed and
processed at any one time, it is impossible to obtain pure
spectral lines. Discontinuities are introduced at the boundaries of the observation interval which lead to spectral leakage.
Windows are weighting functions applied to the data in order
to reduce these discontinuities at the boundaries.
In the time domain the signal has to be observed through
a finite window as a matter of accord. This is in fact equivalent
to multiplying the signal with a set of uniform weights i.e. a
rectangular window operator. In the frequency domain the
spectrum of the data will be the spectrum of this weighting
function shifted to the sinusoidal frequencies of the components in the data.
The rectangular window has a Fourier Transform which is
a SINC(X) function. This has sidelobes which are only 13dB
down from the main lobe. This severely limits the dynamic
range of the system since a second sinusoid in close proximity
would have its main lobe swamped by this side lobe. This
would occur if its amplitude was a mere 13dB down from the
first sinusoid.
Window operators are thus mathematically constructed
to cancel these sidelobes as far as possible. Unfortunately this
is normally done at the expense of making the main lobe
spread over more frequency bins. This reduces the ability of
the system to resolve two frequencies, and can only be
17
PDSP16510A MA
mode.
If other operators are required these must be applied
externally. This can be conveniently achieved with either a
PDSP16112 or a PDSP16116, both of which are complex
multipliers but with different accuracies. Fig. 11 shows how
either one can be configured to perform two separate multiplications with one input common to both. This arrangement is
necessary to perform the window function on complex inputs.
Important features of the windows generated by
PDSP16510, and other commonly used windows, are illustrated in Table 7. The results are obtained from the reference
quoted, which should be consulted for a full mathematical
treatment. The significance of each parameter is outlined
below;
Fig. 11. External Window Generator
overcome by using more data samples. This may not always
be possible because of other system constraints.
A common rule of thumb defines the resolution of an FFT
system as half the full width of the mainlobe. The width of the
mainlobe for a rectangular window is two frequency bins; for
the Hamming window it is four bins; for the Blackman-Harris
window it is six bins.
The latter two windows are actually supported by the
PDSP16510. These are constructed on the fly as needed, and
take the general form;
A - Bcosx + Ccos2x where x = 2πn
N
n = 0 to N-1
For the Hamming window A = 0.54, B = 0.46, C = 0
For the Blackman-Harris window, A = 0.42323, B = 0.49755,
C = 0.07922
These windows can be applied to any of the transform
size options, except the 16 x 16 complex variant. When the
latter is specified the rectangular window option MUST be
selected, or the device will be configured in an internal test
Window
Operator
Highest
Side Lobe
Mid-Point
Loss dB
Highest Side Lobe Level
The inherent rectangular window has sidelobes which
are only 13dB down from the mainlobe. These severely limit
the dynamic range. The object of the window is to improve this
situation with better side load attenuation.
Mid-Point Loss
In line with the filter concept it is possible to conceive of
an additional processing loss for a tone of frequency mid-way
between two bins. This is defined as the ratio of the coherent
gains of two tones, one at the mid-point and one at the sample
point. It is expressed in dB in Table 8.
Overall loss
An overall figure for the reduction in signal to noise ratio
can be obtained by adding the mid-point loss to the reciprocal
of the equivalent noise power bandwidth in dB. It is a measure
of the ability of the window to detect single tones in broadband
noise. The variance between windows is less than 1dB.
6.0dB Bandwidth
This figure, expressed in bin widths, represents the ability
of the window to resolve two tones and should be as close to
unity as possible. As the highest sidelobe level is reduced, this
parameter tends to get worse, and a compromise must be
used when choosing a window.
Overall
Loss dB
6dB
Bandwidth
Overlap Correlation
75%
50%
Rectangular
-13
3.92
3.92
1.21
75
50
Hamming
-43
1.78
3.1
1.81
70.7
23.5
Dolph-Chebyshev
[C = 3.5]
Kaiser-Bessel
[C = 3]
Blackman
-70
1.25
3.35
2.17
60.2
11.9
-69
1.02
3.55
2.39
53.9
7.4
-58
1.1
3.47
2.35
56.7
9
Blackman-Harris
[3 term]
-67
1.13
3.45
1.81
57.2
9.6
Table 7. Window Performance ( from The use of Windows for Harmonic Analysis. F J Harris. Proc IEEE Vol 66. Jan 1978 )
18
PDSP16510A MA
Arithmetic Accuracy
16 bit,unconditional
scaling
24 bit arithmetic with
unconditional scaling,
16 bit inputs
16 bit inputs with
PDSP16510 block FP
Full 32 bit Floating point
with 16 bit inputs
Max Tone
WRT Noise
Slot Noise
Test
2 Tones
with
Freq Spread
60
44
45
88
67
65
74
61
63
93
82
67
Table 8. Comparative Dynamic Range Measurements
Overlap Correlation
In many practical systems the squared magnitudes of
successive transforms are averaged to reduce the variance of
the measurements. If, however, a windowed FFT is applied to
non overlapping partitions of the sequence, data near the
boundaries will be ignored since the window exhibits small
values at those points. To avoid this loss partitions are usually
overlapped by 50% or 75%, which might, at first sight, remove
the need to average successive transforms. If non-windowed
transforms are overlapped by 75% or 50%, then 75% or 50%
of the data will be correlated. When windows are applied,
however, the data common to both transforms will be operated
upon by different portions of the window waveform. The
difference in these portions will dictate the amount of correlation between overlapped data. At 50% overlap Table 7 shows
that with all windows the data is virtually independent, and
successive averaging would still be needed. At 75% overlap
figures are obtained which are closer to the 75% correlation
obtained with no window.
Examination of Table 7 shows that the Blackman-Harris
window gives performance very similar to that of the KaiserBessel and Dolph-Chebyshev windows. The latter two windows can not be computed as they are needed since they are
mathematically too complicated. The values are normally precomputed and stored in a ROM; this would need to contain 1M
bits to match the accuracy of the rest of the system.
Use of the Hamming window gives worse dynamic range
than the more complex windows, but it has less effect on the
overlap correlation and it has a smaller main lobe width.
SPECTRAL PERFORMANCE
There are two important parameters in the measurement
of spectral response: resolution and dynamic range. Resolution defines how closely two sinusoids can be spaced in
frequency and still be identified; dynamic range defines how
great the difference in the amplitudes of the sinusoids may be
and yet the smaller one still identified. Resolution is determined by the observation time [i.e. the width of the frequency
bin] and the window operator that is used. Dynamic range is
also determined by the window operator, but in a hardware
implementation it is also influenced by the number of bits used
to represent the data throughout the calculation.
The hardware effects include the accuracy of the A/D
converter, the number of bits representing the window operator and the twiddle factors, and the way the growth in word
length is handled as the FFT calculation proceeds. The
obvious way to overcome these limitations is to use floating
point arithmetic; but in real life the accuracy of the A/D
converter is fixed and the sample size is limited. Floating point
arithmetic is thus an overkill solution for the majority of
applications. This is especially true for transform sizes up to
1024 points, which is the intended application area.
Figures given for the dynamic range of a system must be
carefully interpreted, since there is no exact definition of the
measurement. Three different ways of measuring dynamic
range have been investigated using 1024 point transforms.
The ‘best’ dynamic range figures will be obtained with
single tone measurements, and these results are often quoted
to indicate the need for greater bit accuracies. The measure
is the ratio of a full scale sinusoid to the average noise level
and the results will be essentially independent of the window
operator. The results given by the PDSP16510 are compared
to various other configurations in the first column of Table 8.
With this method the dynamic range is bound to improve as
more bits are used to represent the data. Theoretically 6 dB of
dynamic range will be obtained for every bit representing the
input data, if the internal arithmetic accuracy gives no degradation in performance. In practice this improvement has no
significance since the incoming waveforms will be much more
complex than a single sinusoid.
An alternative method of determining dynamic range is
with a slot noise test. White noise is passed through a narrowband notch filter, several frequency bins wide, and the FFT
computed. There is no noise in the filtered slot at the input to
the FFT, but there is noise in the frequency bins corresponding
to the width of the notch. Dynamic range is measured as the
difference in dB of the average signal power and the average
noise power and can be considered to give more useful
results. Comparative results from various configurations are
also given in the second column of Table 8. The performance
with 24 bit data is seen to be little better than that obtained with
the PDSP16510. This can be attributed to the scaling scheme,
word growth, and rounding method used within the device.
When two nearby tones are to be capable of detection,
the window operator will dictate the performance of the
system. The final column in Table 8 illustrates the results
obtained using two sinusoids of different amplitudes, with the
larger one residing mid-way between two frequency bins, and
the smaller 5.5 bins away. The two frequencies are five bins
apart to avoid the effects of the mainlobe widths. The dB
figures given are the difference in amplitude between the two
signals when the smaller one is still just detectable as a
separate peak from the larger one.
This technique illustrates the performance of the window,
since the amount by which sidelobe structure of the larger
signal swamps the mainlobe of the smaller signal will effect
whether the smaller signal is detected. The theoretical attenuation of the highest sidelobe levels, with respect to the
mainlobe, for the window options provided by the PDSP16510
have been given in Table 7, and represent the dynamic range
that can be obtained if arithmetic effects are ignored. The
results in the final column in Table 8 are the practical results
given by the device, and as with the slot noise test indicate that
the arithmetic scheme used by the PDSP16510 is equivalent
to using 24 bit data. The Blackman Harris window was used
in all cases.
19
PDSP16510A MA
ABSOLUTE MAXIMUM RATINGS [See Notes]
Supply voltage Vcc
-0.5V to 7.0V
Input voltage VIN
-0.5V to Vcc + 0.5V
Output voltage VOUT
-0.5V to Vcc + 0.5V
Clamp diode current per pin IK (see note 2)
18mA
Static discharge voltage (HMB)
500V
Storage temperature TS
-65°C to 150°C
Junction Temperature, Military
155°C
Package power dissipation
5000mW
NOTES ON MAXIMUM RATINGS
1. Exceeding these ratings may cause permanent damage.
Functional operation under these conditions is not implied.
2. Maximum dissipation or 1 second should not be exceeded,
only one output to be tested at any one time.
3. Exposure to absolute maximum ratings for extended
periods may affect device reliablity.
4. Current is defined as positive into the device.
ELECTRICAL CHARACTERISTICS
Operating Conditions (unless otherwise state)
PDSP16510A MA
Tamb = -55 C to +125°C.
Vcc = 5.0v ± 10%
Characteristic
Symbol
Min.
*
*
*
*
*
†
*
†
Output high voltage
Output low voltage
Input high voltage
Input low voltage
Input leakage current
Input capacitance
Output leakage current
Output S/C current
VOH
VOL
VIH
VIL
IIN
CIN
IOZ
ISC
Units Sub group Notes
Value
Typ.
Max.
2.4
2.0
-10
V
V
V
V
µA
pF
µA
mA
0.4
0.8
+10
10
-50
10
+50
300
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
1, 2, 3
IOH = 4mA
IOL = -4mA
SCLK, DIS, DOS, DEN need 3V
DEN needs 0.7V max
GND < VIN < VCC
1, 2, 3
GND < VOUT < VCC
VCC = Max
SWITCHING CHARACTERISTICS
Characteristic
Symbol
Min
Max
Sub group
Conditions
16510A
MA
40
Max Ø high time is
*
Clock Frequency ( MHz )
Ø
DC
†
Clock High Period ( ns )
TCH
13
†
Clock Low Period ( ns )
TCL
10
*
ØD
FØ
9, 10, 11
*
Max DOS, DIS Frequency
Note F =
4
6 + 0.001ØTCL
Less than 1024 points
or Multiple Devices
Mode 1.
*
*
Max DIS Frequency
Max DOS Frequency
ØD
ØD
Ø
Ø
9, 10, 11
9, 10, 11
1024 points
or Multiple Devices
Modes 2 and 3.
9, 10, 11
1msec
All parameters marked * are tested during production
Parameters marked † are guaranteed by design and characterisation
20
PDSP16510A MA
Part No:
PDSP16510A MA Stand Alone FFT Processor
Package Type:
GC132
Pin No.
GC
Con.
Pin No.
GC
Con.
Pin No.
GC
Con.
Pin No.
GC
Con.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
V1
0V
N/C
N/C
N/C
N/C
V1
N/C
0V
N/C
V1
N/C
0V
N/C
V1
N/C
0V
V1
0V
0V
0V
0V
0V
V1
0V
0V
0V
V1
0V
0V
0V
0V
0V
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
V1
0V
V1
0V
0V
0V
0V
0V
V1
0V
0V
0V
V1
V1
0V
0V
N/C
0V
V1
V1
0V
0V
V1
V1
V1
V1
0V
V1
V1
V1
V1
V1
V1
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
V1
V1
V1
V1
0V
V1
V1
0V
V1
V1
V1
0V
V1
V1
V1
N/C
0V
N/C
0V
N/C
V1
N/C
0V
N/C
V1
N/C
0V
N/C
N/C
N/C
N/C
0V
V1
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
N/C
V1
N/C
N/C
N/C
N/C
0V
N/C
N/C
0V
N/C
0V
N/C
0V
V1
V1
V1
N/C
0V
N/C
0V
V1
N/C
N/C
0V
N/C
N/C
N/C
0V
V1
N/C
N/C
V1
VDD max = +5.5V = V1
N/C = not connected
Fig.12(a) Life Test/Burn-in connections for GC132 package
NOTE: PDA is 5% and based on groups 1 and 7
21
PDSP16510A MA
Part No:
PDSP16510A MA Stand Alone FFT Processor
Package Type:
AC84
Pin No.
AC
Con.
Pin No.
AC
Con.
Pin No.
AC
Con.
Pin No.
AC
Con.
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
A11
A12
A13
A14
A15
B1
B2
B3
B4
B5
B6
B7
B8
B9
B10
B11
B12
B13
B14
B15
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
C15
D1
D2
D3
D4
D5
D6
N/C
N/C
N/C
N/C
N/C
V1
N/C
0V
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
V1
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
D7
D8
D9
D10
D11
D12
D13
D14
D15
E1
E2
E3
E4
E5
E6
E7
E8
E9
E10
E11
E12
E13
E14
E15
F1
F2
F3
F4
F5
F6
F7
F8
F9
F10
F11
F12
F13
F14
F15
G1
G2
G3
G4
G5
G6
G7
G8
G9
G10
G11
G12
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
V1
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
V1
N/C
N/C
V1
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
V1
G13
G14
G15
H1
H2
H3
H4
H5
H6
H7
H8
H9
H10
H11
H12
H13
H14
H15
J1
J2
J3
J4
J5
J6
J7
J8
J9
J10
J11
J12
J13
J14
J15
K1
K2
K3
K4
K5
K6
K7
K8
K9
K10
K11
K12
K13
K14
K15
L1
L2
L3
N/C
N/C
N/C
0V
V1
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
0V
0V
N/C
N/C
V1
V1
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
0V
0V
N/C
N/C
V1
V1
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
0V
0V
N/C
N/C
V1
V1
N/C
L4
L5
L6
L7
L8
L9
L10
L11
L12
L13
L14
L15
M1
M2
M3
M4
M5
M6
M7
M8
M9
M10
M11
M12
M13
M14
M15
N1
N2
N3
N4
N5
N6
N7
N8
N9
N10
N11
N12
N13
N14
N15
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
0V
0V
N/C
N/C
V1
N/C
V1
V1
V1
0V
V1
V1
0V
0V
0V
N/C
0V
N/C
N/C
V1
V1
V1
V1
V1
V1
N/C
0V
0V
0V
0V
0V
0V
N/C
N/C
VDD max = +5.5V = V1
N/C = not connected
Fig.12(b) Life Test/Burn-in connections for AC84 package
NOTE: PDA is 5% and based on groups 1 and 7
22
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