CADEKA SPT7760BIK

SPT7760
8-BIT, 1 GSPS, FLASH A/D CONVERTER
OCTOBER 2002
FEATURES
APPLICATIONS
•
•
•
•
•
•
•
•
•
•
1:2 Demuxed ECL compatible outputs
Wide input bandwidth – 900 MHz
Low input capacitance – 15 pF
Metastable errors reduced to 1 LSB
Monolithic for low cost
Gray code output
GENERAL DESCRIPTION
The SPT7760 is a full parallel (flash) analog-to-digital converter capable of digitizing full scale (0 to –2 V) inputs into
eight-bit digital words at an update rate of 1 GSPS. The
ECL-compatible outputs are demultiplexed into two separate output banks, each with differential data ready outputs
to ease the task of data capture. The SPT7760’s wide input
bandwidth and low capacitance eliminate the need for ex-
BLOCK DIAGRAM
ternal track-and-hold amplifiers for most applications. A
proprietary decoding scheme reduces metastable errors
to the 1 LSB level. The SPT7760 operates from a single
–5.2 V supply, with a nominal power dissipation of 5.5 W.
The SPT7760 is available in an 80-lead surface-mount
MQuad package over the industrial temperature range
(–25 °C to +85 °C).
CLK CLK
CLOCK
BUFFER
Analog
VRT Input
Preamp
Digital oscilloscopes
Transient capture
Radar, EW, ECM
Direct RF down-conversion
DEMUX
CLOCK
BUFFER
Comparator
256
127
64
63
2
1
VRB
D7B
D8B (OVR)
D6B
D7B (MSB)
D5B
D6B
D4B
D5B
D3B
D2B
D5
D4
D3
D2
D1
D0
(LSB)
D1B
D0B
D8A
D7A
D6A
D5A
D4B
BANK B
D6
D8B
DRB (DATA READY)
D3B
D2B
D1B
D0B (LSB)
DRA (DATA READY)
DRA (DATA READY)
D8A (OVR)
D7A (MSB)
D6A
D4A
D5A
D3A
D4A
D2A
D3A
D1A
D2A
D0A
D1A
D0A (LSB)
BANK A
VRM
D7
(MSB)
1:2 DEMULTIPLEXER
128
256 TO 8 Bit Decoder
With Metastable Error Correction
152
151
DRB (DATA READY)
D8
(OVR)
ECL Output Buffers And Latches
255
ABSOLUTE MAXIMUM RATINGS (Beyond which damage may occur)1 25 °C
Supply Voltages
Negative Supply Voltage (VEE TO GND) –7.0 to +0.5 V
Ground Voltage Differential .................... –0.5 to +0.5 V
Output
Digital Output Current ............................... 0 to –28 mA
Temperature
Operating Temperature, ambient ............ –25 to +85 °C
case .......................... +125 °C
junction ...................... +150 °C
Lead Temperature, (soldering 10 seconds) ...... +300 °C
Storage Temperature ............................ –65 to +150 °C
Input Voltage
Analog Input Voltage ............................... +0.5 V to VEE
Reference Input Voltage .......................... +0.5 V to VEE
Digital Input Voltage ................................ +0.5 V to VEE
Reference Current VRT to VRB ........................... 35 mA
Note: 1. Operation at any Absolute Maximum Rating is not implied. See
Electrical Specifications for proper nominal applied conditions
in typical applications.
ELECTRICAL SPECIFICATIONS
TJ = TC = TA = +25 °C , VEE=–5.2 V, VRB=–2.0 V, VRM=–1.0 V, VRT=0.00 V, ƒCLK=1 GHz, Duty Cycle=50%, unless otherwise specified.
PARAMETERS
TEST
CONDITIONS
TEST
LEVEL
MIN
Resolution
DC Accuracy
Integral Linearity Error (ILE)
Differential Linearity Error
(DLE)
No Missing Codes
Analog Input
Input Voltage Range
Input Bias Current
Input Resistance
Input Capacitance
Input Bandwidth
Small Signal
Large Signal
Offset Error VRT
Offset Error VRB
Input Slew Rate
Clock Synchronous
Input Currents
SPT7760A
TYP
MAX
MIN
8
ƒCLK = 100 kHz
I
–1.0
ƒCLK = 100 kHz
I
–0.85
8
+1.0
–1.5
+0.95
–0.95
Guaranteed
VIN=0 V
Over Full Input Range
I
I
V
V
VRB
.75
15
15
V
V
IV
IV
V
Bits
+1.5
LSB
+1.5
LSB
VRT
2.0
V
mA
kΩ
pF
Guaranteed
VRT
2.0
VRB
.75
15
15
900
500
5
5
MHz
MHz
mV
mV
V/ns
2
2
µA
80
30
Ω
MHz
2
250
1.4
1.75
GHz
ps
ps
ns
ns
–30
–30
V
SPT7760B
TYP
MAX UNITS
900
500
+30
+30
–30
–30
+30
+30
Reference Input
Ladder Resistance
Reference Bandwidth
I
V
60
Timing Characteristics
Maximum Sample Rate
Aperture Jitter
Acquisition Time
Clock to Data Delay
CLK to Data Ready Delay
I
V
V
IV
IV
1
0.9
1.25
I
I
45
43
43
41
dB
dB
I
I
–44
–36
–42
–34
dBc
dBc
I
I
42
35
40
33
dB
dB
Dynamic Performance
Signal-To-Noise Ratio
(without Harmonics)
ƒIN = 50 MHz
ƒIN = 250 MHz
Total Harmonic Distortion
ƒIN = 50 MHz
ƒIN = 250 MHz
Signal-to-Noise and Distortion
ƒIN = 50 MHz
ƒIN = 250 MHz
2
80
30
60
1
2
250
1.4
1.75
1.9
2.25
0.9
1.25
1.9
2.25
SPT7760
October 2002
ELECTRICAL SPECIFICATIONS
TJ = TC = TA = +25 °C , VEE=–5.2 V, VRB=–2.0 V, VRM=–1.0 V, VRT=0.00 V, ƒCLK=1 GHz, Duty Cycle=50%, unless otherwise specified.
PARAMETERS
TEST
CONDITIONS
Dynamic Performance
Spurious Free Dynamic Range
ƒIN = 50 MHz
ƒIN = 250 MHz
Digital Inputs
Input High Voltage
(CLK, CLK)
Input Low Voltage
(CLK, CLK)
Clock Pulse Width High (tPWH)
Clock Pulse Width Low (tPWL)
Digital Outputs
Logic 1 Voltage
Logic 0 Voltage
Rise Time
Fall Time
20% to 80%
20% to 80%
Power Supply Requirements
Voltage VEE
Current IEE
Power Dissipation
TEST
LEVEL
MIN
I
I
47
39
I
–1.1
–0.7
I
I
I
0.5
0.5
–1.8
0.4
0.4
I
I
V
V
–1.1
IV
I
I
–4.95
SPT7760A
TYP
MAX
MIN
SPT7760B
TYP
MAX UNITS
43
35
–0.9
–1.8
450
450
–5.2
1.05
5.5
–1.1
–0.7
0.5
0.5
–1.8
0.4
0.4
–1.5
–1.1
–1.5
–5.45
1.2
6.25
dB
dB
–4.95
–0.9
–1.8
450
450
–5.2
1.05
5.5
V
–1.5
–1.5
V
ns
ns
V
V
ps
ps
–5.45 V
1.2 A
6.25 W
Typical Thermal Impedance: θJC = +4 °C/W.
TEST LEVEL CODES
All electrical characteristics are subject to the
following conditions:
All parameters having min/max specifications
are guaranteed. The Test Level column indicates the specific device testing actually performed during production and Quality Assurance inspection. Any blank section in the data
column indicates that the specification is not
tested at the specified condition.
LEVEL
I
II
III
IV
V
VI
TEST PROCEDURE
100% production tested at the specified temperature.
100% production tested at TA = +25 °C, and sample tested at the
specified temperatures.
QA sample tested only at the specified temperatures.
Parameter is guaranteed (but not tested) by design and characterization data.
Parameter is a typical value for information purposes only.
100% production tested at TA = +25 °C. Parameter is guaranteed
over specified temperature range.
Unless otherwise noted, all test are pulsed
tests; therefore, TJ = TC = TA.
3
SPT7760
October 2002
GENERAL DESCRIPTION
makes the part easier to drive than previous flash converters. The preamplifiers also add a gain of two to the input
signal so that each comparator has a wider overdrive or
threshold range to “trip” into or out of the active state. This
gain reduces metastable states that can cause errors at
the output.
The SPT7760 is one of the fastest monolithic 8-bit parallel
flash A/D converters available today. The nominal conversion rate is 1 GSPS and the analog bandwidth is in
excess of 900 MHz. A major advance over previous flash
converters is the inclusion of 256 input preamplifiers
between the reference ladder and input comparators (see
block diagram). This not only reduces clock transient kickback to the input and reference ladder due to a low AC
beta, but also reduces the effect of the dynamic state of
the input signal on the latching characteristics of the input
comparators. The preamplifiers act as buffers and stabilize the input capacitance so that it remains constant over
different input voltage and frequency ranges and therefore
The SPT7760 has true differential analog and digital data
paths from the preamplifiers to the output buffers (Current
Mode Logic) for reducing potential missing codes while
rejecting common mode noise.
Signature errors are also reduced by careful layout of the
analog circuitry. The output drive capability of the device
can provide full ECL swings into 50 Ω loads.
Figure 1 – SPT7760 Typical Interface Circuit
DRB
50 W
DRA
VIN
DRA
DRB (DATA READY)
DRA (DATA READY)
U3
DRA (DATA READY)
50 W
VIN
50 W
VIN**
DRB (DATA READY)
U3
DRB
–2.0 V Pulldown (Digital)
VRTF
D8B (OVR)
D7B (MSB)
D6B
D5B
D4B
D3B
D2B
D1B
D0B (LSB)
VRTS
R
22 W
+
U1
–
*
VRM
R
*
CLK
U2
50 W
–5.2 V
CLK
50 W
–2 V
Pulldown
(Analog)
.1 µF
*
DGND
50 W
AGND
Convert
VRBF
50 W
–5.2 V
VRBS
VEE
–2.0 V
Reference
22 W 2N2907
–
+U1
D8A (OVR)
D7A (MSB)
D6A
D5A
D4A
D3A
D2A
D1A
D0A (LSB)
–2.0 V
Pulldown
(Digital)
FB = Ferrite bead
U1 = OP291 or equivalent with low offset/noise.
R = 1 kW; 0.1% matched.
FB
= AGND
–5.2 V
= DGND
U2 = ON Semiconductor ECLinPS LITE, MC10EL16,
differential receiver with 250 ps (typ) propagation delay.
U3 = MC10EL16 or MC100EL16.
*
= 10 µF Tantalum Capacitor and 0.1 µF Chip Capacitor
** = Care must be taken to avoid exceeding the maximum rating
for the input, especially during power up sequencing of the
analog input driver.
4
SPT7760
October 2002
TYPICAL INTERFACE CIRCUIT
VRBF, VRBS, VRTF, VRTS, VRM (REFERENCE INPUTS)
The circuit in figure 1 is intended to show the most elaborate method of achieving the least error by correcting for
integral linearity, input induced distortion, and power supply/ground noise. This is achieved by the use of external
reference ladder tap connections, input buffer, and supply
decoupling. Please contact the factory for the SPT7760
evaluation board application note that contains more
details on interfacing the SPT7760. The function of each
pin and external connections to other components is as
follows:
There are two reference inputs and one external reference
voltage tap. These are –2 V (VRB force and sense), midtap (VRM) and AGND (VRT force and sense). The reference pins and tap can be driven by op amps as shown in
figure 1 or VRM may be bypassed for limited temperature
operation. These voltage inputs can be bypassed to
AGND for further noise suppression if so desired.
Table I – Output Coding
VIN
>–0.5 LSB
–0.5 LSB
VEE, AGND, DGND
VEE is the supply pin with AGND as ground for the device.
The power supply pins should be bypassed as close to the
device as possible with at least a .01 µF ceramic capacitor. A 10 µF tantalum can also be used for low frequency
suppression. DGND is the ground for the ECL outputs and
is to be referenced to the output pulldown voltage and appropriately bypassed as shown in figure 1.
–1.5 LSB
•
•
•
–1.0 V
•
•
•
–2.0 V +0.5 LSB
VIN (ANALOG INPUT)
There are two analog input pins that are tied to the same
point internally. Either one may be used as an analog input
sense and the other for input force. This is convenient for
testing the source signal to see if there is sufficient drive
capability. The pins can also be tied together and driven by
the same source. The SPT7760 is superior to similar devices due to a preamplifier stage before the comparators.
This makes the device easier to drive because it has constant capacitance and induces less slew rate distortion.
<(–2.0 V +0.5 LSB)
D8
1
1
0
0
0
•
•
•
0
0
•
•
•
0
0
0
D7
10
10
10
10
10
.
0
0
0
0
0
110
010
000
000
000
. .
000
000
000
000
000
•
•
•
000
000
•
•
•
000
000
000
D8
00
00
00
00
01
00
00
01
00
00
Indicates the transition between the two codes
THERMAL MANAGEMENT
The typical thermal impedance is as follows:
ΘCA = +17 °C/W in still air with no heat sink
CLK, CLK (CLOCK INPUTS)
The clock inputs are designed to be driven differentially
with ECL levels. The duty cycle of the clock should be kept
at 50% to avoid causing larger second harmonics. If this is
not important to the intended application, then duty cycles
other than 50% may be used.
D0 TO D8, DR, DR, (A AND B)
The digital outputs can drive 50 Ω to ECL levels when
pulled down to –2 V. When pulled down to –5.2 V, the outputs can drive 130 Ω to 1 kΩ loads. All digital outputs are
grey code with the coding as shown in table I. CADEKA recommends using differential receivers on the outputs of the
data ready lines to ensure the proper output rise and fall
times.
5
We highly recommend that a heat sink be used for this
device with adequate air flow to ensure rated performance
of the device. We have found that a Thermalloy 17846
heat sink with a minimum air flow of 1 meter/second (200
linear feet per minute) provides adequate thermal performance under laboratory tests. Application specific conditions should be taken into account to ensure that the
device is properly heat sinked.
SPT7760
October 2002
OPERATION
prior to the clock transition and output logic codes in sequence from the top comparators, closest to VRT (0 V),
down to the point where the magnitude of the input signal
changes sign (thermometer code). The output of each
comparator is then registered into four 64-to-6 bit decoders when the CLK is changed from high to low. At the output of the decoders is a set of four 7-bit latches which are
enabled (“track”) when the clock changes from high to low.
From here, the output of the latches are coded into 6 LSBs
from 4 columns and 4 columns are coded into 2 MSBs.
Finally, 8 ECL output latches and buffers are used to drive
the external loads. The conversion takes one clock cycle
from the input to the data outputs.
The SPT7760 has 256 preamp/comparator pairs which
are each supplied with the voltage from VRT to VRB divided
equally by the resistive ladder as shown in the block diagram. This voltage is applied to the positive input of each
preamplifier/comparator pair. An analog input voltage applied at VIN is connected to the negative inputs of each
preamplifier/comparator pair. The comparators are then
clocked through each one’s individual clock buffer. When
the CLK pin is in the low state, the master or input stage of
the comparators compare the analog input voltage to the
respective reference voltage. When the CLK pin changes
from low to high the comparators are latched to the state
Figure 2 – Timing Diagram
N
VIN
N+5
N+1
N+2
N+6
N+4
2.0 ns
N+3
CLK
CLK
DRA
1.75 ns
typ
DRA
Data Bank A
N-2
N
N+2
N+4
1.4 ns
typ
1.75 ns
typ
DRB
DRB
Data Bank B
N-1
N+1
N+3
1.4 ns
typ
6
SPT7760
October 2002
Figure 3 – Subcircuit Schematics
Input Circuit
Output Circuit
DGND
AGND
AGND
VIN
Clock Input
AGND
VR
CLK
CLK
Data Out
VEE
VEE
PACKAGE OUTLINE
80-Lead MQuad
G
F
H
I
A B
Symbol
A
B
C
D
E
F
G
H
I
J
K
L
M
J
C
D
E
K
Inches
Min
Max
0.904
0.923
0.777
0.781
0.472 typ
0.541
0.545
0.667
0.687
0.031 typ
0.012
0.018
0.109
0.134
0.010
0.024
0.724 typ
0.099
0.110
0°
7°
0.029
0.041
Millimeters
Min
Max
22.95
23.45
19.74
19.84
12.00 typ
13.74
13.84
16.95
17.45
0.80 typ
0.30
0.45
2.76
3.40
0.25
0.60
18.40 typ
2.51
2.80
0°
7°
0.73
1.03
M
L
7
SPT7760
October 2002
PIN FUNCTIONS
D1B
VEE
D0B
DGND
DRB
DGND
DRB
DGND
D8A
DGND
D7A
DGND
D6A
VEE
D5A
D4A
AGND
Analog Ground
VRTF
Reference Voltage Force Top, Nominally 0 V
VRTS
Reference Voltage Sense Top
VRM
Reference Voltage Middle, Nominally –1 V
VRBF
Reference Voltage Force Bottom, Nominally –2 V
VRBS
Reference Voltage Sense Bottom
VIN
Analog Input Voltage, Can Be Either Voltage or
Sense
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
MQUAD
64
63
62
61
60
59
58
57
56
55
54
53
52
51
50
49
48
47
46
45
44
43
42
41
N/C
N/C
D3A
D2A
VEE
D1A
DGND
D0A
DGND
DRA
DGND
DRA
AGND
AGND
CLK
VEE
CLK
VEE
VEE
AGND
AGND
VRTS
VRTF
N/C
FUNCTION
VEE
Negative Supply Nominally –5.2 V
DGND
Digital Ground
D0–D7A
Data Output Bank A
D0–D7B
Data Output Bank B
DRA
Data Ready Bank A
DRA
Not Data Ready Bank A
DRB
Data Ready Bank B
DRB
Not Data Ready Bank B
D8A
Overrange Output Bank A
D8B
Overrange Output Bank B
CLK
Clock Input
CLK
Clock Input
AGND
AGND
VEE
VEE
AGND
AGND
N/C
VIN
VIN
N/C
VRM
AGND
AGND
VEE
VEE
VEE
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
D2B
D3B
D4B
VEE
VEE
D5B
DGND
D6B
DGND
D7B
DGND
D8B
N/C
N/C
AGND
AGND
AGND
AGND
VEE
VEE
VRBF
VEE
VEE
VRBS
NAME
80
79
78
77
76
75
74
73
72
71
70
69
68
67
66
65
PIN ASSIGNMENTS
ORDERING INFORMATION
PART NUMBER
DESCRIPTION
TEMPERATURE RANGE
PACKAGE
SPT7760AIK
ILE = 1.0 LSB
–25 to +85 °C
80L MQuad
SPT7760BIK
ILE = 1.5 LSB
–25 to +85 °C
80L MQuad
8
SPT7760
October 2002