NSC ADC08B200CIVS

ADC08B200
8-Bit, 200 MSPS A/D Converter with Capture Buffer
General Description
Features
The ADC08B200 is a high speed analog-to-digital converter
(ADC) with an integrated capture buffer. The 8-bit, 200 MSPS
A/D core is based upon the proven ADC08200 with integrated
track-and-hold and is optimized for low power consumption.
This device contains a selectable size capture buffer of up to
1,024 bytes that allows fast capture of an input signal with a
slower readout rate. An on-chip clock PLL circuit provides the
option of on-chip clock rate multiplication to provide the high
speed sampling clock.
The ADC08B200 is resistant to latch-up and the outputs are
short-circuit proof. The top and bottom of the ADC08B200's
reference ladder are available for connections, enabling a
wide range of input possibilities. The digital outputs are TTL/
CMOS compatible with a separate output power supply pin to
support interfacing with 2.7V to 3.3V logic. The digital inputs
and outputs are low voltage TTL/CMOS compatible and the
output data format is straight binary.
The ADC08B200 is offered in a 48-pin plastic package
(TQFP) and is specified over the extended industrial temperature range of −40°C to +105°C. An evaluation board is
available to assist in the easy evaluation of the ADC08B200.
■
■
■
■
■
■
■
Single-ended input
Selectable capture buffer size
PLL for clock multiplication
Reference Ladder Top and Bottom accessible
Linear power scaling with sample rate
FPGA training pattern
Power-down feature
Key Specifications
■
■
■
■
■
■
(PLL Bypassed)
Resolution
Maximum sampling frequency
DNL
ENOB (fIN= 49 MHz)
THD (fIN= 49 MHz)
Power Consumption
— Operating, 50 MHz Input
— Power Down
8 Bits
200 MSPS (min)
±0.4 LSB (typ)
7.2 bits (typ)
−53 dBc (typ)
2 mW / Msps (typ)
2.15 mW (typ)
Applications
■ Laser Ranging
■ RADAR
■ Pulse Capturings
Pin Configuration
20214701
© 2007 National Semiconductor Corporation
202147
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ADC08B200 8-Bit, 200 MSPS A/D Converter with Capture Buffer
June 2008
ADC08B200
Ordering Information
Order Number
Temperature Range
ADC08B200CIVS
−40°C ≤ TA ≤ +105°C
ADC08B200EB
Package
TQFP
Evaluation Board
Block Diagram
20214702
Pin Descriptions and Equivalent Circuits
Pin No.
Symbol
6
VIN
Analog signal input. Conversion range is VRB to VRT.
3
VRT
Analog Input that is the high (top) side of the reference ladder
of the ADC. Voltage on VRT and VRB inputs define the VIN
conversion range. VRT should be more positive than VRB.
Bypass well.
9
VRM
Analog input that is the mid-point of the reference ladder.
This pin should be bypassed to a quiet point in the ground
plane with a 0.1 µF capacitor. DO NOT LOAD this pin.
10
VRB
Analog Input that is the low side (bottom) of the reference
ladder of the ADC. The voltages on VRT and VRB inputs
define the VIN conversion range. Bypass well.
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Equivalent Circuit
Description
2
Symbol
13
PD
Chip Power Down input. When this pin is high, the entire chip
is in the Power Down mode. Any data in the capture buffer
is lost and the output pins hold the last byte that was output.
41
PDADC
ADC Power Down Input. When this pin is high, the ADC is
powered down. The capture buffer is active and the data
within it may be clocked out.
CLK
CMOS/TTL compatible digital clock Input. When the PLL is
bypassed, the clock signal at this pin is the ADC sampling
clock and VIN is sampled on the rising edge of this clock input.
When the PLL is enabled, the signal at this input is the
reference clock, which is multiplied to provide a higher
frequency sample clock.
19
RCLK
Buffer Read Clock input. When the capture buffer is enabled,
this input signal is used to read the data from the internal
buffer. The data output and the buffer empty flag (EF)
transition with the rise of this clock.
17
WEN
Write Enable input. A high level at this input causes a byte
of data to be written into the capture buffer with the rise of
each sample clock.
20
REN
Read Enable input. A high level at this input causes a byte
of data to be read from the capture buffer with the rise of each
RCLK input. This rise of the REN input should be
synchronous with the RCLK input and should not be high
while the WEN input is high.
22
RESET
Device Reset Input. A high level at this input resets all control
logic on the chip.
37
OE
Output Enable input. A high level at this input enables the
output buffers. A low level at this input puts the digital data
output pins into a high impedance state.
14
OEDGE/TEN
Output Edge Select or Test Mode Enable input. If this input
is high, the data outputs transition with the rising edge of the
DRDY output. If this input is low, the data outputs transition
with the falling edge of the DRDY output. Forcing a potential
of VA/2 at this input enables the Test Mode.
18
WENSYNC
Synchronized WEN output. The WEN control input is
synchronized on-chip with the internal sample clock and is
provided at this output.
31
DRDY
Data Ready output. This signal transitions with the transition
of the digital data outputs and indicates that the output data
is ready.
26 thru 29
and
33 thru 36
D0–D7
Digital data digital Outputs. D0 is the LSB, D7 is the MSB.
16
FF
Buffer Full Flag. This output is high when the capture buffer
is full.
15
EF
Buffer Empty Flag. This output is high when the capture
buffer is empty.
46
Equivalent Circuit
Description
3
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ADC08B200
Pin No.
ADC08B200
Pin No.
Symbol
Equivalent Circuit
Description
Auto-Stop Write input. This pin has a dual function. With the
buffer enabled, this pin acts as the ASW input. When this
input is high, writing to the buffer is halted when the capture
buffer is full (FF high). When the buffer is disabled, this pin
is ignored. When the device is in Test Mode, this pin acts as
the Output Edge Select signal, functioning in accordance
with the description of the OEDGE/TEN pin.
25
ASW
23,24
BSIZE(1:0)
Buffer Size input. These inputs determine the size of the
buffer, as described in the Functional Description.
38, 39
MULT(1:0)
Clock Multiply Factor input. These inputs determine the
internal clock PLL's multiplication factor.
1, 4, 12
VA
Positive analog supply pin. Connect to a voltage source of
+3.3V.
43, 44, 48
VP
PLL supply pin. Connect to a voltage source of +3.3V.
40
VD
Digital core supply pin. Connect to a voltage source of +3.3V.
32
VDR
Power supply for the output drivers. Connect to a voltage
source of 2.7V to VD.
2, 5, 8, 11, 21,
42, 45, 47
GND
The ground return for the chip core.
7
SIG GND
Analog input signal ground.
30
DR GND
The ground return for the output drivers.
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4
Operating Ratings
(Notes 1, 2)
−40°C ≤ TA ≤ +105°C
(Notes 1, 2)
Operating Temperature Range
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage (VA)
Driver Supply Voltage (VDR)
Maximum Supply Voltage
VD, VP
CLK Frequency
PLL Bypassed
PLL used
RCLK Frequency (Note 12)
RCLK Duty Cycle
Ground Difference |GND - DR GND|
Upper Reference Voltage (VRT)
Lower Reference Voltage (VRB)
Reference Delta (VRT − VRB)
VIN Voltage Range
Supply Voltage (VA, VP, VD, VDR)
Driver Supply Voltage (VDR)
Voltage on Any Input or Output Pin
Reference Voltage (VRT, VRB)
Input Current, Data Outputs
Input Current all other pins (Note 3)
Package Input Current (Note 3)
Power Dissipation at TA = 25°C
ESD Susceptibility (Note 5)
Human Body Model
Machine Model
Charged Device Model
Soldering Temperature, Infrared,
10 seconds (Note 6)
Storage Temperature
-0.3V to 3.8V
-0.3V to VA +0.3V
−0.3V to VA
GND to VA
±1 mA
±25 mA
±50 mA
See (Note 4)
2500V
200V
1000V
+3.0V to +3.6V
+2.7V to (VA + 0.3V)
VA + 0.3V
1 to 210 MHz
15 to 105 MHz
2 - 210 MHz
35% to 65%
0V to 300 mV
0.5V to (VA − 0.3V)
0V to (VRT − 0.5V)
0.5V to 2.3V
VRB to VRT
Package Thermal Resistance
235°C
−65°C to +150°C
Package
θJA
48-Lead TQFP
76 °C/W
Converter Electrical Characteristics
The following specifications apply for VA = VD = VP = VDR = +3.3VDC, VRT = +1.9V, VRB = 0.3V, CL = 10 pF, fCLK = 200 MHz at 50%
duty cycle, OEDGE/TEN = 1, Buffer and PLL bypassed. Boldface limits apply for TJ = TMIN to TMAX: all other limits TJ = 25°C
(Notes 7, 8)
Symbol
Parameter
Conditions
Typical
(Note 9)
Limits
(Note 9)
Units
(Limits)
DC ACCURACY
INL
Integral Non-Linearity
±0.55
±1.3
LSB (max)
DNL
Differential Non-Linearity
±0.40
±0.9
LSB (max)
0
(max)
Missing Codes
FSE
Full Scale Error
−39
−80
0
mV (min)
mV (max)
VOFF
Zero Scale Offset Error
55
70
mV (max)
ANALOG INPUT AND REFERENCE CHARACTERISTICS
VRB
V (min)
VRT
V (max)
VIN
Input Voltage
CIN
VIN Input Capacitance
4
pF
RIN
Analog Input Resistance
>1
MΩ
FPBW
Full Power Bandwidth
500
1.6
VIN = 0.75V +0.5 Vrms
(CLK LOW)
(CLK HIGH)
3
VRT
Top Reference Voltage
1.9
VRB
Bottom Reference Voltage
0.3
VRT - VRB Reference Voltage Delta
RREF
Reference Ladder Resistance
1.6
VRT to VRB
160
5
pF
MHz
VA
V (max)
0.5
V (min)
VRT − 0.5
V (max)
0
V (min)
0.5
V (min)
2.3
V (max)
145
Ω (min)
200
Ω (max)
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ADC08B200
Absolute Maximum Ratings
ADC08B200
Symbol
Parameter
Typical
(Note 9)
Limits
(Note 9)
Units
(Limits)
OEDGE/TEN
2.2
2.7
V (min)
Others
1.6
2.1
V (min)
OEDGE/TEN
0.9
0.5
V (max)
Others
1.3
0.7
V (max)
OEDGE/TEN
Operational
Test Mode
10
70
µA
µA
Others
10
nA
−10
−600
µA
µA
−50
nA
3
pF
Conditions
DIGITAL INPUT CHARACTERISTICS
VIH
VIL
IIH
Logic High Input Voltage
Logic Low Input Voltage
Logic High Input Current
IIL
Logic Low Input Current
CIN
Logic Input Capacitance
VIH = VDR = VA = 3.6V
OEDGE/TEN
Operational
VIL = 0V, VDR = VA = 3.0V
Test Mode
Others
DIGITAL OUTPUT CHARACTERISTICS
VOH
High Level Output Voltage
VA = VDR = 3.0V, IOH = −5 mA
3.0
2.4
V (min)
VOL
Low Level Output Voltage
VA = VDR = 3.0V, IOL = 5 mA
0.25
0.5
V (max)
COUT
Digital Output Capacitance
2
pF
fIN = 10 MHz, VIN = FS − 0.25 dB
7.4
Bits
fIN = 49 MHz, VIN = FS − 0.25 dB
7.2
fIN = 49 MHz, VIN = FS − 0.25 dB, PLL x8
7.2
Bits
fIN = 100 MHz, VIN = FS − 0.25 dB
7.0
Bits
fIN = 100 MHz, VIN = FS − 0.25 dB, PLL x4
6.9
Bits
fIN = 10 MHz, VIN = FS − 0.25 dB
46
fIN = 49 MHz, VIN = FS − 0.25 dB
45
fIN = 49 MHz, VIN = FS − 0.25 dB, PLL x8
45
dBc
fIN = 100 MHz, VIN = FS − 0.25 dB
44
dBc
DYNAMIC PERFORMANCE
ENOB
SINAD
Effective Number of Bits
Signal-to-Noise & Distortion
fIN = 100 MHz, VIN = FS − 0.25 dB, PLL x4
SNR
SFDR
THD
Signal-to-Noise Ratio
Spurious Free Dynamic Range
Total Harmonic Distortion
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6.8
Bits (min)
dBc
42.7
dBc (min)
43.4
dBc
fIN = 10 MHz, VIN = FS − 0.25 dB
47
dBc
fIN = 49 MHz, VIN = FS − 0.25 dB
46.3
fIN = 49 MHz, VIN = FS − 0.25 dB, PLL x8
45.8
fIN = 100 MHz, VIN = FS − 0.25 dB
45.6
dBc
fIN = 100 MHz, VIN = FS − 0.25 dB, PLL x4
45.6
\dBc
fIN = 10 MHz, VIN = FS − 0.25 dB
56
dBc
fIN = 49 MHz, VIN = FS − 0.25 dB
56
dBc
fIN = 49 MHz, VIN = FS − 0.25 dB, PLL x8
56
dBc
fIN = 100 MHz, VIN = FS − 0.25 dB
50
dBc
fIN = 100 MHz, VIN = FS − 0.25 dB, PLL x4
49.7
dBc
fIN = 10 MHz, VIN = FS − 0.25 dB
−55
dBc
fIN = 49 MHz, VIN = FS − 0.25 dB
−53
dBc
fIN = 49 MHz, VIN = FS − 0.25 dB, PLL x8
−53
dBc
fIN = 100 MHz, VIN = FS − 0.25 dB
−49
dBc
fIN = 100 MHz, VIN = FS − 0.25 dB, PLL x4
-47.5
dBc
6
43.7
dBc (min)
dBc
HD2
Parameter
2nd Harmonic Distortion
Conditions
3rd Harmonic Distortion
−57
dBc
−55
dBc
fIN = 49 MHz, VIN = FS − 0.25 dB, PLL x8
−55
dBc
fIN = 100 MHz, VIN = FS − 0.25 dB
−50
dBc
−49.9
dBc
fIN = 10 MHz, VIN = FS − 0.25 dB
−62
dBc
fIN = 49 MHz, VIN = FS − 0.25 dB
−63
dBc
fIN = 49 MHz, VIN = FS − 0.25 dB, PLL x8
−62
dBc
−56
dBc
−54.6
dBc
f1 = 11 MHz, VIN = FS − 6.25 dB
f2 = 12 MHz, VIN = FS − 6.25 dB
-50
dBc
DC Input
72.5
mA
fIN = 50 MHz
76.8
PD High
0.3
mA
DC Input, Buffer bypassed
1.2
mA
fIN = 50 MHz, Buffer bypassed
1.6
2.1
mA (max)
fIN = 50 MHz, 1k writing to Buffer (Note 10)
38
42.4
mA
PDADC High, reading Buffer (Note 10)
1.1
PD High
0.3
PLL x2
8.8
10.1
mA (max)
PLL disabled
3.6
4.3
mA (max)
PD High
20
mA
DC Input
7
mA
fIN = 50 MHz
41
PD High
25
µA
DC Input, Buffer bypassed, PLL x2
(Note 10)
97.5
mA
50 MHz Input, writing to Buffer, PLL X2
(Note 10)
164.6
fIN = 100 MHz, VIN = FS − 0.25 dB, PLL x4
Intermodulation Distortion
Units
(Limits)
fIN = 49 MHz, VIN = FS − 0.25 dB
fIN = 100 MHz, VIN = FS − 0.25 dB
IMD
Limits
(Note 9)
fIN = 10 MHz, VIN = FS − 0.25 dB
fIN = 100 MHz, VIN = FS − 0.25 dB, PLL x4
HD3
Typical
(Note 9)
POWER SUPPLY CHARACTERISTICS
IA
ID
IP
IDR
IA + ID +
IP + IDR
PC
Analog Supply Current
Digital Core Supply Current
PLL Supply Current
Output Driver Supply Current
Total Operating Current
PDADC = Hi, reading Buffer,
RCLK = 200 MHz, D.C. input
Power Consumption
88.3
mA (max)
mA
mA
57
198
20
mA (max)
mA (max)
mA
PD High
0.65
mA
DC Input, Buffer & PLL bypassed
306
mW
50 MHz Input, writing to Buffer, PLL X2
(Note 10)
543
PDADC High, reading Buffer, PLL disabled
(Note 10)
66
mW
653
mW (max)
PD High
2.15
mW
PSRR1
D.C. Power Supply Rejection Ratio FSE change with 3.0V to 3.6V change in VA
48
dB
PSRR2
A.C. Power Supply Rejection Ratio
TBD
dB
SNR reduction with 200 mV at 10MHz on
supply
7
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ADC08B200
Symbol
ADC08B200
Converter Timing Characteristics
The following specifications apply for VA = VDR = +3.3VDC, VRT = +1.9V, VRB = 0.3V, CL = 50 pF, fCLK = 200 MHz at 50% duty cycle,
OEDGE/TEN = 1, Buffer and PLL bypassed. Boldface limits apply for TJ = TMIN to TMAX: all other limits TJ = 25°C (Notes 7, 8)
Symbol
Typical
(Note 9)
Limits
(Note 9)
Units
(Limits)
PLL Disabled
210
200
MHz (min)
Using PLL
15
105
MHz (min)
Parameter
Conditions
fC1
Maximum Input Clock Rate
fC2
Minimum Input Clock Rate
tCL
Minimum CLK Low Time
(Note 11)
tCH
Minimum CLK High Time
(Note 11)
fRC1
Maximum RCLK Rate
(Note 12)
210
fRC2
Minimum RCLK Rate
(Note 12)
2
tRCL
Minimum RCLK Low Time
(Note 11)
tRCH
Minimum RCLK High Time
(Note 11)
ΔDC
DRDY to RCLK Duty Cycle Delta
0.3
tSU
REN to RCLK Set-Up Time
tRR
PLL Disabled
1
Using PLL
15
MHz
MHz
1.7
ns (min)
1.7
ns (min)
200
MHz (min)
2.0
ns (min)
2.0
ns (min)
±3
%
−0.4
−0.8
4.0
ns (min)
ns (max)
RCLK Rising to DRDY Rising
3.8
2.4
5.9
ns (min)
ns (max)
tRF
RCLK Falling to DRDY Falling
3.5
tSKDR
DRDY Rising to DATA Skew
160
MHz
ns
ps
1.8
7.4
ns (min)
ns (max)
tSKR
RCLK Falling to DATA Skew
2.3
tSKEF
DRDY Rising to EF Skew
36
ps
tCFF
CLK rise to FF Delay
4.2
ns
tFFW
FF to WENSYNC Delay
ASW pin high
4.2
ns
tCW
CLK to WENSYNC Delay
PLL Disabled
3.5
tRST
RESET Pulse Width
(Note 11)
tr
Output Data Rise Time
(0.4V to 2.5V)
CL = 10 pF
tf
Output Data Fall Time
(2.4V to 0.4V)
tODF
RCLK Rise to Output Fall to 0.4V
Output
2.4
5.5
ns (min)
ns (max)
4
Write Clock
Cycles (min)
0.9
ns
CL = 20 pF
2
ns
CL = 10 pF
1.4
ns
CL = 20 pF
3.2
Reading Buffer
7.0
Buffer bypassed, PLL disabled
5.5
Reading Buffer
6.5
Buffer bypassed, PLL disabled
5.5
ns
4.0
11.7
ns (min)
ns (max)
2.3
13.1
ns (min)
ns (max)
ns (min)
ns (max)
ns (min)
ns (max)
ns
tODR
RCLK Rise to Output Rise to 2.5V
Output
tOHF
Data High to Fall Hold to 2.5V
Output
Reading Buffer
3.8
2.4
5.5
tOHR
Data Low to Rise Hold to 0.4V
Output
Reading Buffer
4.5
2.6
6.9
tSLEW
Output Slew Rate
Output Falling (2.4V to 0.4V)
1.5
V / ns
Output Rising (0.4V to 2.5V)
2.3
V / ns
PLL Enabled
20
µs
PLL Bypassed
2
µs
ns
tDRDY1
PD Low to Device Active
tDRDY2
PDADC Low to Device Active
2
µs
Pipeline Delay (Latency)
6
Clock Cycles
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8
tAD
tAJ
Parameter
Sampling (Aperture) Delay
Aperture Jitter
Typical
(Note 9)
Conditions
Limits
(Note 9)
Units
(Limits)
PLL on
3.4
PLL off
3.9
ns
PLL Bypassed
2
ps rms
PLL Enabled in x8 mode (Note 13)
7
ps rms
CLK Rise to
Acquisition of Data
ns
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed
specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test
conditions.
Note 2: All voltages are measured with respect to GND = DR GND = 0V, unless otherwise specified.
Note 3: When the input voltage at any pin exceeds the power supplies (that is, less than GND or DR GND, or greater than VA, VP, VD or VDR), the current at that
pin should be limited to 25 mA. The 50 mA maximum package input current rating limits the number of pins that can safely exceed the power supplies with an
input current of 25 mA to two.
Note 4: The absolute maximum junction temperature (TJmax) for this device is 150°C. The maximum allowable power dissipation is dictated by TJmax, the
junction-to-ambient thermal resistance (θJA), and the ambient temperature (TA), and can be calculated using the formula PDMAX = (TJmax − TA) / θJA.
Note 5: Human body model is 100 pF capacitor discharged through a 1.5 kΩ resistor. Machine model is 220 pF discharged through ZERO Ohms.
Note 6: See AN-450, “Surface Mounting Methods and Their Effect on Product Reliability”.
Note 7: The analog inputs are protected as shown below. Input voltage magnitudes up to VA + 300 mV or to 300 mV below GND will not damage this device.
However, errors in the A/D conversion can occur if the input goes above VA or below GND by more than 100 mV. For example, if VA is 3.3VDC the input voltage
must be ≤3.4VDC to ensure accurate conversions.
20214707
Note 8: To guarantee accuracy, it is required that VA, VD, VP and VDR be well bypassed. Each supply pin should be decoupled with separate bypass capacitors.
Note 9: Typical figures are at TJ = 25°C, and represent most likely parametric norms. Test limits are guaranteed to National's AOQL (Average Outgoing Quality
Level).
Note 10: This current or power is used only during the short time that the buffer is being written to or read from, depending upon the specification.
Note 11: This parameter is guaranteed by design and/or characterization and is not production tested.
Note 12: RCLK should be stopped with the buffer is not being read.
Note 13: Jitter with the PLL enabled is measured with 32k samples and the PLL in the x8 multiplication mode.
9
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ADC08B200
Symbol
ADC08B200
VOFF = VZT − 1/2 LSB = VZT - (VRT − VRB) / 512
Specification Definitions
where VZT is the first code transition input voltage.
OUTPUT DELAY is the time delay after the rising edge of the
RCLK input before the data update is present at the output
pins.
OUTPUT HOLD TIME is the length of time that the output data
is valid after the rise of CLK or RCLK output.
PIPELINE DELAY (LATENCY) is the number of clock cycles
between initiation of conversion and when that data is presented to the output driver stage. New data is available at
every clock cycle, but the data lags the conversion by the
Pipeline Delay plus the Output Delay.
POWER SUPPLY REJECTION RATIO (PSRR) is a measure
of how well the ADC rejects a change in the power supply
voltage. For the ADC08B200, PSRR1 is the ratio of the
change in Full-Scale Error that results from a change in the
DC power supply voltage, expressed in dB. PSRR2 is a measure of how well an a.c. signal riding upon the power supply
is rejected at the output.
SIGNAL TO NOISE RATIO (SNR) is the ratio, expressed in
dB, of the rms value of the input signal at the output to the rms
value of the sum of all other spectral components below onehalf the sampling frequency, not including harmonics or d.c.
SIGNAL TO NOISE PLUS DISTORTION (S/(N+D) or
SINAD) is the ratio, expressed in dB, of the rms value of the
input signal at the output to the rms value of all of the other
spectral components below half the clock frequency, including harmonics but excluding d.c.
SPURIOUS FREE DYNAMIC RANGE (SFDR) is the difference, expressed in dB, between the rms values of the input
signal at the output and the peak spurious signal, where a
spurious signal is any signal present in the output spectrum
that is not present at the input.
TOTAL HARMONIC DISTORTION (THD) is the ratio expressed in dB, of the rms total of the first nine harmonic levels
at the output to the level of the fundamental at the output. THD
is calculated as
APERTURE (SAMPLING) DELAY is that time delay after the
rise of the sample clock until the input signal is sampled within
the ADC.
APERTURE JITTER is the variation in aperture delay from
sample to sample. Aperture jitter shows up as input noise.
CLOCK DUTY CYCLE is the ratio of the time that the clock
waveform is at a logic high to the total time of one clock period.
DIFFERENTIAL NON-LINEARITY (DNL) is the measure of
the maximum deviation from the ideal step size of 1 LSB.
Measured at 200 MSPS with a ramp input.
EFFECTIVE NUMBER OF BITS (ENOB, or EFFECTIVE
BITS) is another method of specifying Signal-to-Noise and
Distortion Ratio, or SINAD. ENOB is defined as (SINAD –
1.76) / 6.02 and says that the converter is equivalent to a perfect ADC of this (ENOB) number of bits.
FULL POWER BANDWIDTH is a measure of the frequency
at which the reconstructed output fundamental drops 3 dB
below its low frequency value for a full scale input.
FULL-SCALE ERROR is a measure of how far the last code
transition is from the ideal 1½ LSB below VRT and is defined
as:
FSE = Vmax + 1.5 LSB – VRT
where Vmax is the voltage at which the transition to the maximum (full scale) code occurs.
INTEGRAL NON-LINEARITY (INL) is a measure of the deviation of each individual code from a line drawn from zero
scale (½ LSB below the first code transition) through positive
full scale (½ LSB above the last code transition). The deviation of any given code from this straight line is measured from
the center of that code value. The end point test method is
used. Measured at 200 MSPS with a ramp input.
INTERMODULATION DISTORTION (IMD) is the creation of
additional spectral components as a result of two sinusoidal
frequencies being applied to the ADC input at the same time.
it is defined as the ratio of the power in the second and third
order intermodulation products to the power in one of the
original frequencies. IMD is usually expressed in dBFS.
MISSING CODES are those output codes that are skipped
and will never appear at the ADC outputs. These codes cannot be reached with any input value.
OFFSET ERROR is the error in the input voltage required to
cause the first code transition. It is defined as the difference
between the voltage required to cause the first code transition
and the ideal voltage (1/2 LSB) to cause that transition.
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where Af1 is the RMS power of the fundamental (output) frequency and Af2 through Af10 are the RMS power of the first 9
harmonic frequencies in the output spectrum
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ADC08B200
Timing Diagrams (PLL Bypassed)
20214757
ADC08B200 Data Capture and Read Operation
20214731
ADC08B200 Capture and Write Enable Timing
20214754
ADC08B200 Buffer Write Timing
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ADC08B200
20214755
ADC08B200 Buffer Read Timing (OEDGE/TEN = 1)
20214758
ADC08B200 Buffer Read Timing (OEDGE/TEN = 0)
20214756
ADC08B200 Buffer Bypassed Timing
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VA = VD = VP = VDR = 3.3V, fCLK = 200 MHz, fIN = 50 MHz, PLL & Buffer bypassed, TA = 25°C, unless otherwise stated
INL
INL vs. Supply Voltage
20214708
20214715
INL vs. Temperature
INL vs. Sample Rate
20214714
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DNL
DNL vs. Supply Voltage
20214709
20214718
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ADC08B200
Typical Performance Characteristics
ADC08B200
DNL vs. Temperature
DNL vs. Sample Rate
20214717
20214711
Offset Error vs. Temperature
Full Scale Error vs. Temperature
20214761
20214762
SNR vs. Supply Voltage
SNR vs. Input Frequency
20214721
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20214723
14
ADC08B200
SNR vs. Temperature
SNR vs. Sample Rate
20214720
20214712
SNR vs. Clock Duty Cycle
Distortion vs. Supply Voltage
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20214726
Distortion vs. Input Frequency
Distortion vs. Temperature
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20214725
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ADC08B200
Distortion vs. Sample Rate
Distortion vs. Clock Duty Cycle
20214713
20214729
SINAD vs. Supply Voltage
SINAD vs. Input Frequency
20214738
20214739
SINAD vs. Temperature
SINAD vs. Sample Rate
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20214716
16
ADC08B200
SINAD vs. CLK Duty Cycle
SFDR vs. Supply Voltage
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20214727
SFDR vs. Input Frequency
SFDR vs. Temperature
20214741
20214742
SFDR vs. Sample Rate
SFDR vs. Clock Duty Cycle
20214744
20214745
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ADC08B200
Power Consumption vs. Sample Rate
Power Consumption vs. Temperature
20214760
20214719
Spectral Response @ fIN = 49 MHz
Spectral Response @ fIN = 76 MHz
20214746
20214747
Spectral Response @ fIN = 99 MHz
Intermodulation Distortion
20214743
20214748
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The ADC08B200 integrates an 8-bit, high speed ADC and a
configurable capture buffer of up to 1 kilobyte, allowing the
sampling and processing tasks to be independent of each
other. This functionality is intended for those applications that
need to sample an input signal at a high rate and then read
the collected samples at a slower rate. The Timing Diagrams
illustrate the operation of the ADC08B200.
The analog input signal that is within the voltage range set by
VRT and VRB is digitized to eight bits. Input voltages below
VRB will cause the output word to consist of all zeroes. Input
voltages above VRT will cause the output word to consist of
all ones.
The ADC08B200 exhibits a power consumption that is proportional to frequency, limiting power consumption to what is
needed at the clock rate that is used. This, its excellent performance over a wide range of clock frequencies and the
incorporation of a capture buffer make ADC08B200 an ideal
choice for many 8-bit ADC applications.
Data is acquired at the rising edge of the sample clock and,
in the buffer bypass mode, the digital equivalent of that data
is available at the digital outputs 6 clock cycles plus tOD later.
When the Buffer is enabled, the converted data is written to
the buffer with each internal conversion clock cycle and can
be read out with the RCLK signal. The ADC08B200 will convert as long as a CLK signal is present, but when using the
buffer no writing to the buffer will occur when that buffer is full.
The output coding is straight binary.
The entire device is in the active state when the Power Down
pin (PD) is low. When the PD pin is high, the entire device is
in the power down mode, consuming very little power. Holding
the clock input low after raising the Power Down pin will further
reduce the power consumption in the power down mode.
When the PDADC pin is high, only the A/D converter itself is
in the power down mode. The rest of the chip is left powered
up so that the capture buffer may be read. If both the PD and
PDADC pins are high, the PD pin dominates and the entire
device is powered down.
The A/D converter sample clock can be either the clock signal
at the CLK input pin or a multiplied version of that clock. The
clock multiplier can be 2, 4 or 8. In any case, the sample clock
is also used to write the converter data into the capture buffer
when that buffer is used.
As long as the chip is not in a power down state and there is
a clock signal present, the A/D converter is converting the input signal. However, the data is stored into the capture buffer,
when the buffer is used, only while the Write Enable (WEN)
input is high. The data is read from the capture buffer with the
RCLK signal, which can be a free running clock, while the
Read Enable (REN) signal is high.
Note that the capture buffer on this chip must be entirely filled
to its configured size before reading its contents can begin. It
is not possible to write to and read from the buffer at the same
time and the WEN and REN inputs should not be high at the
same time. If they are high at the same time, the REN input
is ignored. This is true even if the REN input is high first and
a read operation is progressing normally when the WEN input
goes high. Asserting the WEN input while REN is high will
Applications Information
1.0 REFERENCE INPUTS
The reference inputs VRT and VRB are the top and bottom of
the reference ladder, respectively. Input signals between
these two voltages will be digitized to 8 bits. External voltages
applied to the reference input pins should be within the range
specified in the Operating Ratings and the Electrical Characteristics table. Any device used to drive the reference pins
should be able to source sufficient current into the VRT pin and
sink sufficient current from the VRB pin to maintain the desired
voltages.
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ADC08B200
cause the read operation to be aborted and the capture operation to begin. Although this device is intended for fast
capture and slower read out applications, it is possible for the
RCLK to operate at the same rate or faster than the sample
clock.
Two status flags are provided to manage the capture buffer.
As the name suggests, the Full Flag (FF) goes high when the
buffer is full. The next sample clock rise after the assertion of
FF will begin writing over the oldest data because the write
pointer will "wrap around". This is called an "over run" condition. Similarly, the Empty Flag (EF) indicates that the last of
the data has been read and the buffer is empty. When EF
goes high, the DRDY and Data outputs stop switching and
both DRDY and the Data lines remain low if OEDGE=1. Both
remain high if OEDGE=0.
The user has the option to stop writing to the buffer automatically upon a buffer full condition with the use of the ASW
(Auto Stop Write) input. If the ASW input is low, the buffer will
be continually written to, resulting in the possibility of the write
pointer "wrapping around" and the data continually being
overwritten as long as there is a clock and the WEN input is
high. If the ASW input is high, the write operation stops upon
reaching the "full" condition.
FF goes low upon device reset and when the "full" condition
is removed by starting a transfer operation with the assertion
of REN. The EF output goes low when the "empty" condition
is removed by starting a capture operation with the raising of
WEN. The EF output goes high upon device reset because
resetting empties the buffer.
The RESET signal resets the read and write pointers and the
EF and FF flags. The RESET signal also stops the read operation early (before the EF flag goes high). Consequently,
only a partial read is performed if the RESET input goes high
while a buffer read out is under way. This allows the buffer
pointers to be reset so a new capture operation can begin.
The RESET signal has no effect upon the A/D converter,
which has its own internal Power-On Reset circuit.
Note that the RCLK input does not need to be as noise (jitter)
free as does the CLK signal. The reason for this is that RCLK
is only used to read the Capture Buffer, while the CLK signal
is either the ADC sample clock or is the reference for the internal PLL that generates the sample clock for the ADC.
Consequently, CLK jitter directly affects the ADC's SNR performance. There is no requirement for the RCLK to have any
fixed relationship with CLK in terms of phase or frequency.
Functional Description
ADC08B200
20214732
FIGURE 1. Simple, low component count reference biasing. Because of the ladder and external resistor tolerances, the
reference voltage of this circuit can vary too much for some applications.
The reference bias circuit of Figure 1 is very simple and the
performance is adequate for many applications. However,
circuit tolerances will lead to a wide reference voltage range.
Better reference tolerance can be achieved by driving the reference pins with low impedance sources.
The circuit of Figure 2 will allow a more accurate setting of the
reference voltages, with upper and lower reference accuracies of about 16 mV, or about 2 1/2 LSB. The upper amplifier
must be able to source the reference current as determined
by the value of the reference resistor and the value of (VRT −
VRB). The lower amplifier must be able to sink this reference
current. Both amplifiers should be stable with a capacitive
load.
The LM8272 was chosen because of its rail-to-rail input and
output capability, its high output current capability and its ability to drive large capacitive loads.
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The divider resistors at the inputs to the amplifiers could be
changed to suit the application reference voltage needs, or
the divider can be replaced with potentiometers or DACs for
precise settings. The bottom of the ladder (VRB) may be returned to ground if the minimum input signal excursion is 0V.
VRT should always be at least 0.5V more positive than VRB.
While VRT may be as high as the VA supply voltage and VRB
may be as low as ground, the difference between these two
voltages (VRT − VRB should not exceed 2.3V to prevent a slight
waveform distortion.
The VRM pin is the center of the reference ladder and should
be bypassed to a quiet point in the ground plane with a 0.1 µF
capacitor. DO NOT leave this pin open and DO NOT load this
pin with more than 10µA.
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ADC08B200
20214733
FIGURE 2. Driving the reference to force desired values requires driving with a low impedance source.
for this circuit depends not only upon the amplifier and ADC,
but also upon the circuit layout and board material. The
LMH6702 and the LMH6628 have been found to be good
amplifiers to drive the ADC08B200.
Figure 3 shows an example of an input circuit using the
LMH6702 at the ADC08B200 input. The input amplifier should
incorporate some gain as most operational amplifiers exhibit
better phase margin and transient response with gains above
2 or 3 than with unity gain. If an overall gain of less than 3 is
required, attenuate the input and operate the amplifier at a
higher gain, as indicated in Figure 3.
This will provide optimum SNR performance for Nyquist applications. Best THD performance is realized when the capacitor and resistor values are both zero, but this would
compromise SNR and SINAD performance. Generally, the
capacitor should not be added for undersampling applications.
The circuit of Figure 3 has both gain and offset adjustments.
If you eliminate these adjustments normal circuit tolerances
may result in signal clipping unless care is exercised in the
worst case analysis of component tolerances and the input
signal excursion is appropriately limited to account for the
worst case conditions.
Full scale and offset adjustments may also be made by adjusting VRT and VRB, perhaps with the aid of a pair of a DACs
or a dual DAC.
2.0 THE ANALOG INPUT
The analog input of the ADC08B200 is a switch followed by
an integrator. The input capacitance changes with the clock
level, appearing as 3 pF when the clock is low, and 4 pF when
the clock is high. The sampling nature of the analog input
causes current spikes at the input that result in voltage spikes
there. These spikes are normal and need not be eliminated.
However, any amplifier used to drive the analog input must
be able to settle within the clock high time. Using a single pole
RC filter between the amplifier and the ADC input will minimize the effects of these transients on the driving amplifier.
The cutoff frequency of this filter should be approximately the
same as the ADC sample rate for Nyquist applications.
Choose a capacitor value of 33 pF to 51 pF and a resistor
value according to the formula
where fS is the converter sample rate. The added 6 pF in the
formula above allows for the ADC input capacitance and a
small board capacitance. For undersampling applications,
eliminate the capacitor and chose a pole frequency of about
2 to 3 times the maximum input frequency, using the ADC
input capacitance when the the clock is high, plus trace capacitance, for the filter capacitor. The optimum time constant
21
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ADC08B200
20214734
FIGURE 3. The input amplifier should incorporate some gain for best performance (see text).
even on a transient basis. This can be a problem upon application of power and power shut-down. Be sure that the supplies to circuits driving any of the input pins, analog or digital,
do not come up any faster than does the voltage at the
ADC08B200 power pins.
3.0 POWER SUPPLY CONSIDERATIONS
A/D converters draw sufficient transient current to corrupt
their own power supplies if not adequately bypassed. Generally, a 10 µF tantalum or aluminum electrolytic capacitor
should be provided for each of the four supplies and a 0.1 µF
ceramic chip capacitor placed within one centimeter of each
converter power supply pin.
To further lower the inductance in series with the capacitors,
mount the 0.1 µF capacitors on the same side of the board as
the ADC and use 2 to 4 closely spaced through holes to connect the ground side of the capacitors to the ground plane.
The through holes used to ground one side of these capacitors should not be used to connect anything else to ground.
Leadless chip capacitors are preferred because they have
low lead inductance.
While a single voltage source is recommended for the VA,
VD and VP supplies of the ADC08B200, the VA supply pins
should be well isolated from the other supply pins to prevent
any digital noise from being coupled into the analog portions
of the ADC. A choke is recommended between the VDR supply
pin and the other supply pins with adequate bypass capacitors close to each supply pin, as shown in Figure 1, Figure 2
and Figure 3.
As is the case with all high speed converters, the ADC08B200
should be assumed to have little power supply rejection. None
of the supplies for the converter should be the supply that is
used for other digital circuitry in any system with a lot of digital
power being consumed. The ADC supplies should be the
same supply used for other analog circuitry.
No pin should ever have a voltage on it that is in excess of the
supply voltage or below ground by more than 300 mV, not
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4.0 THE DIGITAL INPUT PINS
The ADC08B200 has 14 digital input pins, 6 of which are used
for buffer control and 2 of which are used for PLL control.
4.1 The PD Pin
The Power Down (PD) pin, when high, puts the ADC08B200
into a low power mode where power consumption is significantly reduced below its operating power. Stopping the clock
after raising the PD input will reduce power consumption even
more. The ADC is active and will perform normally about 2
microseconds after the PD pin is brought low. However, the
PLL, if used, requires 20 microseconds to stabilize after the
PD pin is brought low.
The digital output pins retain the last conversion output code
when either the clock is stopped or the PD pin is high. The
buffer contents are lost when PD is brought high.
4.2 The PDADC Pin
When the PDADC pin is high the ADC is powered down. The
capture buffer is active and the data within it may be clocked
out.
This is helpful for reduction of average power consumption as
the ADC can be powered down while data is being read from
the buffer. As with the PD pin, the ADC is active and will perform normally about 2 microseconds after the PDADC pin is
22
4.5 The OEDGE/TEN Pin
If this Output Edge Select input is high, the data outputs transition with the rising edge of the DRDY output. If this input is
low, the data outputs transition with the falling edge of the
DRDY. Forcing a potential of VA/2 at this input enables the
Test Mode. There is an on-chip pull-up resistor at this pin, so
the device interprets a floating input at this pin to be a logic
high. See Section 10.0 TEST PATTERN OUTPUT for the
output test pattern.
4.3 The Master CLK Pin
Although the ADC08B200 is tested and its performance is
guaranteed with a 200 MHz clock, it typically will function well
with clock frequencies as indicated in the Electrical Characteristics table.
The low and high times of the clock signal can affect the performance of any A/D Converter. Because achieving a precise
duty cycle is difficult, the ADC08B200 is designed to maintain
performance over a range of duty cycles. While it is specified
and performance is guaranteed with a 50% clock duty cycle
and 200 Msps, ADC08B200 performance is typically maintained with clock high and low times and a clock frequency
range as indicated in the electrical table. Note that clock minimum low and high times may not be simultaneously imposed.
The ADC Clock input line should be series terminated at the
clock source in the characteristic impedance of that line if the
clock line is longer than
4.6 The OE Pin
A high level at this Output Enable input enables the output
buffers. A low level at this input puts the digital data output
pins, including the DRDY output, into a high impedance state.
Caution: Although this device has a TRI-STATE output, maintaining optimum noise performance requires keeping the capacitance on the data output pins as low as possible.
Therefore, it is never a good idea to connect the output pins
to a bus. Each output pin should be connected to a single
input with lines as short as possible.
4.7 Buffer-Associated Pins
The on-chip buffer is 1 kilobyte (1,024 bytes) in size and is
controlled through six (6) TTL-CMOS compatible digital input
pins.
where tr is the clock rise time and tprop is the propagation rate
of the signal along the trace. Typical tprop is about 150 ps/inch
(59 ps/cm) on FR-4 board material.
It is always best and advisable that one clock source pin drive
a single destination pin for best signal integrity. However, if
the clock source is used to drive more than just one destination, the CLK pin should be a.c. terminated with a series RC
to ground such that the resistor value is equal to the characteristic impedance of the clock line and the capacitor value is
4.7.1 THE RCLK PIN
When the capture buffer is enabled, the RCLK input is used
to read the data from the buffer. The data output and the EF
flag transition with the rise of RCLK.
It is best to halt the RCLK when not reading the buffer to minimize its impact upon noise performance. RCLK may be
stopped in either the high or the low state.
4.7.2 THE WEN PIN
A high level at this Write Enable input causes data to be written into the capture buffer. One byte is written with the rise of
each sample clock. This input may go high asynchronously.
4.7.3 THE REN PIN
A high level at this Read Enable input causes data to be read
from the capture buffer. One byte is read with the rise of each
RCLK input. This signal should go high synchronous with the
RCLK input and should not be high while the WEN input is
high. If this input is high while the WEN input is high, the WEN
input has priority and the REN input is ignored, regardless of
which of these two inputs is high first. It is not possible to read
from the buffer while a write to the buffer is in progress.
where tPROP is the signal propagation rate down the clock line,
"L" is the line length and ZO is the characteristic impedance
of the clock line. The units of "L" must be compatible with the
units of tPROP. This termination should be located as close as
possible to, but within one centimeter of, the ADC08B200
clock pin. Furthermore, this termination should be beyond the
receiving pin as seen from the clock source. For FR-4 board
material, the value of C becomes
4.7.4 THE ASW PIN
This Auto-Stop Write input has a dual function. With writing to
the buffer enabled and this ASW high, this pin acts as the
ASW (Auto-Stop Write) input, which causes writing to the
buffer to halt once the buffer is full (FF high). This prevents
write "wrap around" and the over-writing of older data. When
writing to the buffer is disabled, this pin is ignored. When the
device is in Test Mode, this pin acts as the Output Edge Select
input and functions as described for the OEDGE/TEN input.
Where L is the length of the clock line in inches.
4.4 The RESET Pin
A high level at this Reset input resets all control logic on the
chip, including the buffer's read and write counters. The FF
output is reset low and the EF flag is reset high upon a device
reset. Invoking a reset during the WRITE phase can cause
buffer data to be corrupted. A reset during the READ phase
will stop the READ phase before it is completed.
4.7.5 THE BSIZE PINS
The two Buffer Size input pins (BSIZE0 and BSIZE1) are used
to select the required buffer size for the application or to by-
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ADC08B200
The RESET signal is asynchronous and should be at least 4
sample clock cycles wide. If no RESET is provided, the chip
generates its own internal reset signal at the beginning of the
buffer write phase.
brought low. Again the PLL, if used, requires 20 microseconds
to stabilize after the PD pin is brought low.
The PLL remains active when the PDADC input is high to allow for faster initiation of data capture after PDADC is lowered. Stopping the input clock when PDADC is invoked can
result in a loss of PLL lock and a longer than normal recovery
time from PDADC.
ADC08B200
pass the buffer altogether. Refer to Section 8.0 USING THE
DATA BUFFER for use of these pins
6.4 The EF Pin
This Empty Flag goes high, synchronous with the internal
sample clock, when the Capture Buffer is empty, either by the
buffer having been completely read or upon RESET of the
device. This output goes low when one or more bytes is written to the buffer. When EF goes high, the DRDY and Data
outputs stop switching and both DRDY and the Data lines remain low if OEDGE=1, or high if OEDGE=0.
5.0 PLL CONTROL: THE MULT PINS
The two MULT input pins (MULT0 and MULT1) are used to
select the CLK Multiplier for the internal PLL, or to bypass the
PLL. Refer to Section 7.0 CLOCK OPTIONS for more information.
6.0 DIGITAL OUTPUT PINS
The ADC08B200 has 12 digital output pins: 8 Digital Data
Output pins, DRDY, WENSYNC, EF and FF
6.5 The FF Pin
The Full Flag output indicates that the buffer is full and goes
high, synchronous with the internal sample clock, when the
capture buffer is full. If the WEN input remains high, the rise
of the next sample clock after the FF output goes high will
cause the buffer pointer to "wrap around" and start writing
over the previous data unless the ASW input is high. The FF
signal goes low when the REN signal goes high and the full
condition no longer exists. This signal also goes low upon a
RESET of the device.
6.1 Digital Data Outputs
This 8-bit bus is LVTTL/LVCMOS compatible, with a Straight
Binary output format. Data is clocked out on this bus in one
of two ways. When the internal buffer is bypassed, data is
clocked out at the sample clock rate. When the internal buffer
is used, data is clocked out at the RCLK rate. In either case,
data is clocked out on the rising edge of the appropriate clock.
Refer to Section 7.0 CLOCK OPTIONS for information on
sample rate determination.
When the Capture Buffer is bypassed, data is read directly
from the converter at the sample clock rate.
When the capture buffer is used, data is read from the capture
buffer and presented at these pins when the REN input is
high. If OEDGE/TEN is high, the digital data output and DRDY
are held low when no valid data is being sent out. If OEDGE/
TEN is low, the digital data and DRDY are held high when no
valid data is being sent out. These pins source data at the
converter sample rate when the buffer is disabled.
Whether the buffer is enabled or not, the output data is provided synchronous with DRDY. That is, the data transition
occurs with the edge of DRDY defined by OEDGE/TEN such
that the data transitions on the rise of DRDY if OEDGE/TEN
is high or on the fall of DRDY if OEDGE/TEN is low.
The data output drivers are capable of sourcing and sinking
a relatively high current to enable rapid charging and discharging of the output capacitance, thereby allowing fast
output rise and fall times. The data outputs should be as lightly
loaded as possible to minimize on-chip noise and the resulting
loss of SNR performance. Note the specified load capacitance at the heading of the Electrical Characteristics Table.
7.0 CLOCK OPTIONS
The ADC08B200 incorporates a PLL to facilitate clocking.
The PLL, like any PLL or DLL, can add phase noise to the
clock signal and so to the conversion process. The effect of
this phase noise increases with higher analog signal input
frequencies. If a stable clock source at the desired sample
rate is available, it is preferable to use that clock as the sample
clock for the ADC08B200, bypassing the PLL. If such a source
is not available, the internal PLL may be used to multiply the
input clock frequency by 2, 4 or 8 to obtain the desired sample
rate from a lower frequency clock source.
Bypassing the PLL or setting the CLK frequency multiplier is
accomplished through the use of the two MULT pins as indicated in Table 1. Expected noise performance with and without the use of the PLL is indicated in the Typical Performance
Characteristics of this data sheet.
TABLE 1. MULT Pin Function
6.2 The DRDY Pin
This output is intended for use to latch output data into a receiving device and transitions with the transition of the digital
data outputs. The synchronizing edge of the DRDY signal can
be selected with the OEDGE input. When the buffer is not
used, DRDY is active as long as the ADC is functioning. When
the buffer is enabled, DRDY is active only while data is being
sent out. When no valid data is being sent out, the DRDY
output sense is the opposite of the OEDGE input. As long as
PD is low, this signal is always active (not high impedance)
whether or not the buffer is enabled.
The DRDY output should be have a load that is identical to
the load of the digital data outputs to ensure that one DRDY
output edge transitions at the same time as does the data.
MULT0
CLK
Frequency
Multiplier
CLK Freq.
Range (MHz)
0
0
1
1 - 210
0
1
2
15 - 105
1
0
4
15 - 50
1
1
8
15 - 25
The internal sampling clock frequency is the input clock frequency at the CLK pin multiplied by the multiplier in Table 1.
When the PLL is bypassed, the input clock at the CLK pin is
used as the sample clock and the PLL is disabled.
8.0 USING THE DATA BUFFER
The Data Buffer has read and write pointers and the first word
written to it is the first word read from it. The Data Buffer is
configurable to 256-, 512-, or 1024- bytes, and must be completely filled to the configured number of bytes before it can
be read. The "FF" flag goes high once the configured number
of bytes is in the buffer are read. Once the data buffer contents
are completely read, indicated by the "EF" flag going high, the
same data cannot be read again. It is possible to read back
only part of the contents, after which a RESET must be issued, clearing the remaining data stored in the data buffer,
before the buffer may be written to again.
The WEN (Write Enable) input is used to enable writing to the
buffer, while the REN (Read Enable) input is used to enable
reading from the buffer. If both of these are high, the WEN
6.3 The WENSYNC Pin
This output is synchronous with the internal sample clock and
is provided as an indication as to when sampling takes place.
The actual point in time when sampling takes place is as indicated in the "Capture and Write Enable" Timing Diagram.
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MULT1
24
control inputs (WEN, REN, ASW and RCLK) are ignored and
the EF and FF outputs are held low. The DRDY output may
be used to capture the data at the output port.
TABLE 2. BSIZE Pin Function
BSIZE1
BSIZE0
Buffer Size
0
0
Buffer is bypassed
0
1
256 bytes
1
0
512 bytes
1
1
1024 bytes
9.0 MODES OF OPERATION
The ADC08B200 has several modes of operation. These
modes are detailed in Table 3.
The buffer function is controlled by the BSIZE pins, BSIZE0
and BSIZE1, as indicated in Table 4. The buffer can be bypassed and data read directly from the ADC by setting both
of the BSIZE pins low.
TABLE 3. Modes of Operation
PD
PDADC
1
x
WEN REN
x
x
Power State
0
1
0
0
0
x
0
1
Active
Data is being read from buffer with RCLK
0
0
0
0
Active
If buffer is bypassed, data is present at output bus. If buffer is used,
the chip is ready to capture data to the buffer.
0
0
1
x
Active
The ADC's digital output is being captured to the buffer. The REN input
is ignored.
0
1
1
x
Shutdown
Operational State
Shutdown, non-operational
Buffer Active, ADC
ADC powered down, no data can be captured. Buffer may be read.
Shutdown
Buffer Active, ADC
PROHIBITED. WEN input is ignored.
Shutdown
and Figure 3, except the input amplifier is shown without any
gain and offset adjustments. The overall nominal gain of the
input amplifier circuit is 1.98 and the nominal −3 dB input
bandwidth is about 195 MHz. Note that this circuit does not
show an anti-aliasing filter.
A 50 MHz clock oscillator is used for the input clock source.
The MULT0 input grounded and the MULT1 input high means
(from Table 1) that this 50 MHz input clock is multiplied by the
internal PLL by 4 to provide a 200 Msps capture rate.
Since the BSIZE0 and BSIZE1 pins are both high, the internal
capture buffer size is set to 1,024 bytes (see Table 2). Data
writing to the internal buffer will automatically stop when the
buffer is full because the ASW input is high. The FF (Full Flag)
will go high when the buffer is full and data is ready to be read.
The OEDGE pin is high, meaning the output data will transition at the rise of the DRDY output. Since the PD pin is
grounded and the OE pin is high, the device will never be
completely powered down and the outputs are always enabled. Since the PDADC pin is driven from the controlling
device, the ADC may be powered down, leaving the output
buffer active, when the device buffer is being read, or when
the device is not in use.
The digital lines between the ADC08B200 and the receiving
device have 33 Ohms at the signal source end as source terminators, assuming output impedances of about 20 Ohms
and 50-Ohm lines. The RESET and PDADC lines are not terminated because these are basically d.c. lines and it is assumed that they do not toggle frequently.
TABLE 4. Buffer Write/Read
BSIZE1 BSIZE0 WEN REN
Buffer Function
0
0
x
x
Buffer bypassed
0
1
1
x
Write to 256 byte buffer
1
0
1
x
Write to 512 byte buffer
1
1
1
x
Write to 1k byte buffer
0
1
0
1
Read from 256 byte buffer
1
0
0
1
Read from 512 byte buffer
1
1
0
1
Read from 1k byte buffer
10.0 TEST PATTERN OUTPUT
The ADC08B200 has a test mode whereby the data outputs
have a test pattern which may be used to "train" a receiving
device, such as a PLD. The Test Mode is invoked by forcing
a potential of VA/2 at the OEDGE/TEN input. There is an onchip pull-up resistor at this pin, so the device interprets a
floating input at this pin to be a logic high. This pattern is used
to test the integrity of the buffer, so the RCLK (Read Clock)
input must be used to get the output pattern.
The test pattern that is put out is a continuously repeated pattern of output codes 00h - FFh - 00h - FFh - 00h. Note that
this pattern repeats as long as the test mode is invoked and
RCLK is running, so that every second time a logic low appears it will be present for two bit times.
11.0 APPLICATION EXAMPLE
Figure 4 shows an example of a typical application. The analog input and reference circuits are as described in Figure 2
25
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ADC08B200
input dominates and the REN input is ineffective until WEN
goes low. If the WEN pin remains high after the buffer is full,
the previous contents are over-written. The ASW (Auto-Stop
Write) pin may be used to automatically stop writing to the
buffer when it is full to the configured number of bytes. See
Sections 4.7.2 THE WEN PIN, 4.7.3 THE REN PIN and 4.7.4
THE ASW PIN for information on these inputs.
The BSIZE inputs are used to configure the Data Buffer size
(described in Table 2). The user has a choice of using the
buffer or bypassing it.
When the buffer is used and its contents have been read, the
DRDY and the Data Outputs maintain the opposite sense of
the OEDGE input. When the buffer is bypassed, it is not used
and the data is presented at the ADC data output pins at the
same rate as the sample clock. Table 2 indicates the choices
available and the BSIZE pin settings to achieve each.
When the buffer is bypassed (both BSIZE pins low), the ADC
output is sent directly to the output port at the sample clock
rate without going through the buffer. In this mode all buffer
ADC08B200
20214736
FIGURE 4. Example of a Typical Application.
The average power consumption of the ADC08B200 (assuming a new capture is taken as soon as the buffer contents is
read) may be calculated by taking power consumed while
capturing and writing to the buffer and multiplying it by the
capture time divided by the throughput time (interval between
the successive rises of the WEN signal), added to the power
while reading the buffer with PDADC high (assuming the
PDADC input is taken high whenever data is not being captured) multiplied by the time that PDADC is high (Buffer read
time plus any idle time) divided by the throughput rate.
Assuming a Capture Power of 543 mW, a 200 Msps capture
rate and a 66mW Read Power with PDADC high, a 50 MHz
data read rate and no completely idle time, the average power
consumption would be 161.4 mW.
high impedance, which could further result in excessive noise
on the power supply. The frequency beyond which adequate
bypassing may be effective depends primarily upon the
chemistry of the capacitor dielectric, but can also vary a little
from one manufacturer to another. Even so, this frequency is
in the hundreds of Megahertz. Note, however, that a 200 MHz
clock will have significant harmonic energy far beyond this.
The result could be high frequency noise on the supply lines
that could effect the SNR performance of the converter.
The use of adjacent power and ground planes will go a long
way toward reducing the impedance of the power distribution
system and is encouraged. Furthermore, we suggest placing
the lowest value of bypass capacitor close to the supply pin
on the same side of the board as the ADC and connect the
ground end of the bypass capacitor to the ground plane with
at least two through holes. The through holes have an inductance associated with them and using two or more such holes
puts these inductances in parallel, lowering the effective inductance to ground.
12.0 POWER SUPPLY CONSIDERATIONS
It is important to note that capacitors have an equivalent series inductance associated with them such that, beyond a
certain frequency, the capacitor behaves more like an inductance than a capacitance and adequate bypassing may be
infective, resulting in the power distribution system having a
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26
ADC08B200
12.1 Supply Voltages
The ADC8D200 will perform well with power supply voltages
in the range specified in the Operating Ratings, just before the
Electrical Table. Many individual devices may perform well
down to supply voltages of 2.7V, but this should not be relied
upon because part of the product distribution, depending upon normal fabrication process tolerances, could result in the
majority of some production runs not functioning well below
3.0V.
While all supplies may be of the same voltage, the digital
supply (VD), the PLL supply (VP) and the output driver supply
(VDR) ADC08B200 should never be higher than 300 mV
above the analog supply (VA). Furthermore, the output driver
supply, VDR may be as low as 2.7V only when using the buffer
and when the buffer read clock (RCLK) frequency is no higher
than 50 MHz because the output slew rate decreases at low
VDR voltages and the output eye may not be open enough to
allow reliable data capture.
20214737
FIGURE 5. Isolating the ADC Clock from Digital Circuitry
It is good practice to keep the ADC clock line as short as possible and to keep it well away from other signals, which can
introduce jitter into the clock signal. The clock signal can also
introduce noise into a nearby signal path.
15.0 COMMON APPLICATION PITFALLS
Driving the inputs (analog or digital) beyond the power
supply rails. For proper operation, all inputs should not go
more than 300 mV below the ground pins or 300 mV above
the supply pins. Exceeding these limits on even a transient
basis may cause faulty or erratic operation. It is not uncommon for high speed digital circuits (e.g., 74F and 74AC devices) to exhibit undershoot that goes more than a volt below
ground. A 47Ω resistor in series with the offending digital input, close to the driving source, will usually eliminate the
problem.
Care should be taken not to overdrive the inputs of the
ADC08B200. Such practice may lead to conversion inaccuracies and even to device damage.
Attempting to drive a high capacitance digital data bus.
The more capacitance the output drivers must charge for
each conversion, the more instantaneous digital current is required from VDR and DR GND. These large charging current
spikes can couple into the analog section, degrading dynamic
performance. Buffering the digital data outputs may be necessary if the data bus capacitance exceeds 10 pF. Dynamic
performance can also be improved by adding 12Ω to 27Ω series resistors at each digital output, reducing the energy coupled back into the converter input pins.
Using an inadequate amplifier to drive the analog input.
As explained in Section 2.0 THE ANALOG INPUT, there are
voltage spikes at the ADC analog input. These voltage spikes
can cause instability in a feedback type amplifier used to drive
the analog input. These spikes need not be filtered out, but
should settle quickly. The amplifier should be fast enough to
handle the frequencies presented to it, but not so fast that it
would readily oscillate. A single-pole RC filter, as explained
in Section 2.0 THE ANALOG INPUT will help ensure amplifier
stability and accurate data capture.
Driving the VRT pin or the VRB pin with devices that can
not source or sink the current required by the ladder. As
mentioned in Section 1.0 REFERENCE INPUTS, care should
be taken to see that any driving devices can source sufficient
current into the VRT pin and sink sufficient current from the
VRB pin. If these pins are not driven with devices than can
handle the required current, these reference pins will not be
stable, resulting in a reduction of dynamic performance.
Using a clock source with excessive jitter, using an excessively long clock signal trace, or having other signals
coupled to the clock signal trace. This will cause the sampling interval to vary, causing excessive output noise and a
13.0 LAYOUT AND GROUNDING
Proper grounding and proper routing of all signals are essential to ensure accurate conversion. A single, unified ground
plane should be used. Do not split the ground plane.
Coupling between the typically noisy digital circuitry and the
sensitive analog circuitry can lead to poor performance that
may seem impossible to isolate and remedy. The solution is
to keep all lines separated from each other by at least six
times the height above the reference plane, and to keep the
analog circuitry well separated from the digital circuitry.
The DR GND connection to the ground plane should not use
the same through holes used by other ground connections.
High power digital components should not be located near
any analog components.
Generally, analog and digital lines should cross each other at
90° to avoid getting digital noise into the analog path. In high
frequency systems, however, avoid crossing analog and digital lines altogether. Clock lines should be isolated from ALL
other lines, analog AND digital. Even the generally accepted
90° crossing should be avoided as even a little coupling can
cause problems at high frequencies. Best performance at
high frequencies is obtained with a straight signal path.
The reference and analog inputs should be isolated from
noisy signal traces to avoid coupling of spurious signals into
the input. Any external component (e.g., a filter capacitor)
connected between the converter's input and ground should
be connected to a very clean point in the ground plane and
preferably with 2 to 4 closely spaced through holes.
14.0 DYNAMIC PERFORMANCE
The ADC08B200 is a.c. tested and its dynamic performance
is guaranteed. To meet the published specifications, the clock
source driving the CLK input must exhibit as little jitter as possible. For best a.c. performance, each clock destination
should be driven by a separate source, such as with a clock
distribution chip or with a clock tree such as seen
in Figure 5.
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ADC08B200
reduction in SNR performance. The use of simple gates with
RC timing is generally inadequate as a clock source.
Busing the data outputs. SNR performance of all ADCs,
especially high speed ADCs, is sensitive to the amount of capacitance at the data outputs because the currents required
of the ADC data outputs to charge and discharge these ca-
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pacitances cause voltage spikes (noise) on the die. Minimizing the output capacitance will help maintain noise performance of the converter. Busing the outputs adds undesired
capacitive loading to the ADC. Similarly, it is important to keep
trace capacitance to a minimum by using short traces at the
ADC outputs.
28
ADC08B200
Physical Dimensions inches (millimeters) unless otherwise noted
NOTES: UNLESS OTHERWISE SPECIFIED
REFERENCE JEDEC REGISTRATION mo-153, VARIATION AD, DATED 7/93.
48-Lead Package BC
Order Number ADC08B200CIVS
NS Package Number VBC48A
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ADC08B200 8-Bit, 200 MSPS A/D Converter with Capture Buffer
Notes
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