Datasheet SPT7755AIK, SPT7755BIK Datasheet (SPT)

SPT7755

8-BIT, 750 MSPS FLASH A/D CONVERTER

FEATURES

• 1:2 Demuxed ECL Compatible Outputs

• Wide Input Bandwidth - 900 MHz

• Low Input Capacitance - 15 pF (MQUAD)

• Metastable Errors Reduced to 1 LSB

• Monolithic for Low Cost

• Gray Code Output

GENERAL DESCRIPTION

The SPT7755 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 750 MSPS. 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 SPT7755's wide input
bandwidth and low capacitance eliminate the need for exter­nal track-and-hold amplifiers for most applications. A propri-

CLK CLK

BLOCK DIAGRAM

CLOCK

Analog

V

RT

Input

Preamp Comparator

256

BUFFER

APPLICATIONS

• Digital Oscilloscopes

• Transient Capture

• Radar, EW, ECM

• Direct RF Down-Conversion

etary decoding scheme reduces metastable errors to the
1 LSB level. The SPT7755 operates from a single -5.2 V
supply, with a nominal power dissipation of 5.5 W.

The SPT7755 is available in an 80L surface-mount MQUAD
package over the industrial temperature range of -25 to
+85 °C. Contact the factory for availability of die and /883
versions.

DEMUX
CLOCK

BUFFER

255

152

151

128

V

RM

V

RB

127

64

63

2

1

D8

(OVR)

D7

(MSB)

D6

D5

D4

256 TO 8 BIT DECODER

D3

WITH METASTABLE ERROR CORRECTION

D2

D1

DO

(LSB)

D8B
D7B

•

•

D5B

•

•

D2B
D1B
D0B
D8A
D7A

•

•

•

1:2 DEMULTIPLEXER

D5A

•

•

•

D2A
D1A
D0A

DRB (DATA READY)
DRB (DATA READY)
D8B (OVR)
D7B (MSB)
D6B
D5B
D4B
D3B
D2B
D1B
D0B (LSB)
DRA (DATA READY)
DRA (DATA READY)
D8A (OVR)
D7A (MSB)
D6A
D5A

ECL OUTPUT BUFFERS AND LATCHES

D4A
D3A
D2A
D1A
D0A (LSB)

BANK B

BANK A

Signal Processing Technologies, Inc.

4755 Forge Road, Colorado Springs, Colorado 80907, USA

Phone: [phone] FAX: [phone]

ABSOLUTE MAXIMUM RATINGS (Beyond which damage may occur)1 25 °C

Supply Voltages
Negative Supply Voltage (V

TO GND)........ .-7.0 to +0.5 V

EE

Output

Digital Output Current ........................................ 0 to -28 mA

Ground Voltage Differential............................. .-0.5 to +0.5 V

Temperature

Input Voltage

Analog Input Voltage....................................... +0.5 V to V

Reference Input Voltage ................................. +0.5 V to V

Digital Input Voltage ........................................ +0.5 V to V

EE
EE
EE

Reference Current VRT to VRB................................. 35 mA

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

Notes: 1. Operation at any Absolute Maximum Rating is not implied. See Electrical Specifications for proper nominal applied condi-

tions in typical applications.

ELECTRICAL SPECIFICATIONS

TJ = TC = TA = +25 °C , VEE=-5.2 V, VRB=-2.00 V, VRM=-1.0 V, VRT=0.00 V, f

TEST TEST SPT7755A SPT7755B

PARAMETERS CONDITIONS LEVEL MIN TYP MAX MIN TYP MAX UNITS

Resolution 8 8 Bits
DC Accuracy (+25 °C)

Integral Nonlinearity f
Differential Nonlinearity f

= 100 kHz I -1.0 +1.0 -1.5 +1.5 LSB

CLK

= 100 kHz I -0.85 +0.95 -0.95 +1.5 LSB

CLK

No Missing Codes Guaranteed Guaranteed

Analog Input

Input Voltage Range I V
Input Bias Current V

=0 V I .75 2.0 .75 2.0 mA

IN

Input Resistance V 15 15 kΩ
Input Capacitance Over Full Input Range V 15 15 pF
Input Bandwidth

Small Signal V 900 900 MHz

Large Signal V 500 500 MHz
Offset Error V
Offset Error V

RT
RB

Input Slew Rate V 5 5 V/ns
Clock Synchronous

Input Current V 2 2 µA

Reference Input

Ladder Resistance I 60 80 60 80 Ω
Reference Bandwidth V 30 30 MHz

Timing Characteristics

Maximum Sample Rate I 750 750 MHz
Aperture Jitter V 2 2 ps
Acquisition Time V 250 250 ps
CLK to Data Ready Delay IV 0.9 1.4 1.9 0.9 1.4 1.9 ns
Clock to Data Delay IV 1.25 1.75 2.25 1.25 1.75 2.25 ns

Dynamic Performance

Signal-To-Noise Ratio
(without Harmonics)

= 50 MHz I 46 44 dB

f

IN

= 250 MHz I 44 42 dB

f

IN

Total Harmonic Distortion

f

= 50 MHz I -45 -43 dBc

IN

f

= 250 MHz I -37 -35 dBc

IN

=750 MHz, Duty Cycle=50%, unless otherwise specified.

clk

RB

V

RT

V

RB

VRTV

IV -30 +30 -30 +30 mV
IV -30 +30 -30 +30 mV

SPT

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SPT7755

3/5/97

ELECTRICAL SPECIFICATIONS

TJ = TC = TA = +25 °C , VEE=-5.2 V, VRB=-2.00 V, VRM=-1.0 V, VRT=0.00 V, f

TEST TEST SPT7755A SPT7755B

PARAMETERS CONDITIONS LEVEL MIN TYP MAX MIN TYP MAX UNITS

Dynamic Performance

Signal-to-Noise and Distortion

= 50 MHz I 43 41 dB

f

IN

= 250 MHz I 36 34 dB

f

IN

Spurious Free Dynamic Range

f

= 50 MHz I 48 44 dB

IN

f

= 250 MHz I 40 36 dB

IN

Digital Inputs

Input High Voltage

(CLK, NCLK) I -1.1 -0.7 -1.1 -0.7 V
Input Low Voltage

(CLK, NCLK) I -1.8 -1.5 -1.8 -1.5 V
Clock Pulse Width High (t
Clock Pulse Width Low (t

Digital Outputs

Logic "1" Voltage I -1.1 -0.9 -1.1 -0.9 V
Logic "0" Voltage I -1.8 -1.5 -1.8 -1.5 V
Rise Time 20 to 80% V 450 450 ps
Fall Time 20 to 80% V 450 450 ps

Power Supply Requirements

Voltage V
Current I
Power Dissipation I 5.5 6.25 5.5 6.25 W

EE

EE

) I 0.67 0.5 0.67 0.5 ns

PWH

) I 0.67 0.5 0.67 0.5 ns

PWL

=750 MHz, Duty Cycle=50%, unless otherwise specified.

clk

IV -4.95 -5.2 -5.45 -4.95 -5.2 -5.45 V

I 1.05 1.2 1.05 1.2 A

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.

Unless otherwise noted, all tests are pulsed
tests; therefore, TJ = TC = TA.

TEST 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.

SPT

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SPT7755

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GENERAL DESCRIPTION

The SPT7755 is one of the fastest monolithic 8-bit parallel
flash A/D converters available today. The nominal conver­sion rate is 750 MSPS 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

Figure 1 - SPT7755 Typical Interface Circuit

**

V

IN

50 Ω

V

IN

V

IN

and frequency ranges and therefore 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 SPT7755 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.

-2.0 V

Reference

Convert

V

RTF

V

*

*

50 Ω

RTS

V

RM

V

RBS

V

RBF

CLK
NCLK

-5.2 V

50 Ω

.1 µF

EE

V

AGND

DGND

FB

*

FB=  Ferrite bead
U1= OP291 or equivalent with low offset/noise.
R = 1 k Ω; 0.1% matched.
 = AGND
 = DGND
U2= Motorola ECLinPS Lite, MC10EL16, differential receiver

  with 250 ps (typ) propagation delay.
*  = 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.

R

22 Ω

+

U1

-

R

2N2907

22 Ω

-

U1

+

50 Ω

-5.2 V

-2 V

Pulldown

(Analog)

-5.2 V

U2

DRB (DATA READY)
DRB (DATA READY)
D8B (OVR)
D7B (MSB)
D6B
D5B
D4B
D3B
D2B
D1B
D0B (LSB)
DRA (DATA READY)
DRA (DATA READY)
D8A (OVR)
D7A (MSB)
D6A
D5A
D4A
D3A
D2A
D1A
D0A (LSB)

50 Ω

-2.0 V

Pulldown

(Digital)

BANK B

A

BANK

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SPT7755

3/5/97

TYPICAL INTERFACE CIRCUIT

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 SPT7755 evaluation board
applications note that contains more details on interfacing the
SPT7755. The function of each pin and external connections
to other components is as follows:

(VRM) and AGND (VRT force and sense). The reference pins
and tap can be driven by op amps as shown in figure 1 or V
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

V

IN

> -0.5 LSB

D8

D7 • • • D0

1

1 0 0 0 0 0 0 0

RM

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 1 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 5.

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 SPT7755 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.

CLK

CLK,

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.

(CLOCK INPUTS)

-0.5 LSB

-1.5 LSB

•

•

•

-1.0 V

•

•

•

-2.0 V+

< (-2.0 V +1/2 LSB)

THERMAL MANAGEMENT

The typical thermal impedance is as follows:

1/2 LSB

Indicates the transition between the two codes

1

1 0 0 0 0 0 0 0

0

1 0 0 0 0 0 0 0

0

1 0 0 0 0 0 0 0

0

1 0 0 0 0 0 0 1

•

•

•

•

•

•

0

1 1 0 0 0 0 0 0

0

0 1 0 0 0 0 0 0

•

•

•

•

•

•

0

0 0 0 0 0 0 0 1

0

0 0 0 0 0 0 0 0

0

0 0 0 0 0 0 0 0

D0 TO D8, DR, NDR (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 1.

V

, V

RBF

(REFERENCE INPUTS)

There are two reference inputs and one external reference
voltage tap. These are -2 V (VRB force and sense), mid-tap

RBS

, V

RTF

, V

RTS

, V

RM

SPT

ΘCA = +17 °C/W in still air with no heat sink

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.

5

SPT7755

3/5/97

OPERATION

The SPT7755 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 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.

Figure 2 - Timing Diagram

V

IN

CLK

NCLK

DRA

NDRA

Data Bank A

DRB

NDRB

Data Bank B

Figure 3 - Subcircuit Schematics

N

N+1

1.3 ns

1.4 ns typ

N+5

N+2

N+3

N-2 N N+2 N+4

1.75 ns typ

1.4 ns typ

N-1 N+1 N+3

1.75 ns typ

N+4

N+6

N+7

V

IN

SPT

INPUT CIRCUIT OUTPUT CIRCUIT

AGND

AGND

V

R

V

EE

6

DGND

Data Out

CLOCK INPUT

CLK

AGND

V

CLK

EE

SPT7755

3/5/97

A

B

F

G

PACKAGE OUTLINE

80-PIN MQUAD

H

I

SYMBOL MI N MA X MIN MAX

J

INCHES MILLIMETERS

A 0.937 0.945 23.80 24.00
B 0.777 0.785 19.72 19.93
C 0.472 TYP 12.0 TYP
D 0.541 0.549 13.73 13.94
E 0.701 0.709 17.80 18.00
F 0.032 TYP 0.80 TYP
G 0.014 TYP 0.36 TYP
H 0.114 0.122 2.90 3.10

I .006 TYP 0.15 TYP

J 0.724 TYP 18.4 TYP
K 0.099 0.109 2.51 2.77
L7° 7°
M 0.026 0.036 0.66 0.91

C
D

E

K

M

L

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SPT7755

3/5/97

PIN ASSIGNMENTS

PIN FUNCTIONS

D2B
D3B
D4B
V

EE

V

EE

D5B
DGND
D6B
DGND
D7B
DGND
D8B
N/C
N/C
AGND
AGND
AGND
AGND
V

EE

V

EE

V

RBF

V

EE

V

EE

V

RBS

10

12
13
14
15
16
17
18
19
20
21
22
23
24

D1B

80

EE

V

79

DØB

78

DRB

DGND

76

77

NDRB

DGND

74

75

D8A

DGND

72

73

D7A

DGND

70

71

D6A

DGND

68

69

V

EE

67

D5A

66

D4A

65

NAME FUNCTION

V

EE

Negative Supply Nominally -5.2 V

AGND Analog Ground

1
2
3
4
5
6
7
8
9

1
1

MQUAD

25

27

29

31

33

35

37

26

28

30

32

34

V

AGND

AGND

V

EE

EE

AGND

V

N/C

V

AGND

IN

V

N/C

IN

RM

36
AGND

39

38
V

AGND

V

EE

EE

EE

40
V

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
V

EE

D1A
DGND
DØA
DGND
NDRA

DGND
DRA
AGND
AGND
CLK
V

EE

NCLK
V

EE

V

EE

AGND
AGND
V

RTS

V

RTF

N/C

V

RTF

V

RTS

V

RM

V

RBF

V

RBS

V

IN

DGND Digital Ground
D0-D7A Data Output Bank A
D0-D7B Data Output Bank B
DRA Data Ready Bank A
NDRA Not Data Ready Bank A
DRB Data Ready Bank B
NDRB Not Data Ready Bank B
D8A Overrange Output Bank A
D8B Overrange Output Bank B
CLK Clock Input

Reference Voltage Force Top,
Nominally 0 V
Reference Voltage Sense Top
Reference Voltage Middle, Nominally -1 V
Reference Voltage Force Bottom,
Nominally -2 V
Reference Voltage Sense Bottom
Analog Input Voltage, Can Be Either
Voltage or Sense

NCLK Clock Input

ORDERING INFORMATION

PART NUMBER DESCRIPTION TEMPERATURE RANGE PACKAGE TYPE

SPT7755AIK INL = 1.0 LSB -25 to +85 °C 80L MQUAD
SPT7755BIK INL = 1.5 LSB -25 to +85 °C 80L MQUAD

Signal Processing Technologies, Inc. reserves the right to change products and specifications without notice. Permission is hereby expressly
granted to copy this literature for informational purposes only. Copying this material for any other use is strictly prohibited.

WARNING - LIFE SUPPORT APPLICATIONS POLICY - SPT products should not be used within Life Support Systems without the specific
written consent of SPT. A Life Support System is a product or system intended to support or sustain life which, if it fails, can be reasonably
expected to result in significant personal injury or death.

Signal Processing Technologies believes that ultrasonic cleaning of its products may damage the wire bonding, leading to device
failure. It is therefore not recommended, and exposure of a device to such a process will void the product warranty.

SPT7755

3/5/97

SPT

8