The SPT7920 A/D converter is the industry's first 12-bit
monolithic analog-to-digital converter capable of sample
rates greater than 10 MSPS. On board input buffer and
track/hold function assures excellent dynamic performance without the need for external components. Drive
requirement problems are minimized with an input capacitance of only 5 pF.
Logic inputs and outputs are TTL. An overrange output
signal is provided to indicate overflow conditions. Output
APPLICATIONS
• Radar Receivers
• Professional Video
• Instrumentation
• Medical Imaging
• Electronic Warfare
• Digital Communications
• Digital Spectrum Analyzers
• Electro-Optics
data format is straight binary. Power dissipation is very low
at only 1.1 watts with power supply voltages of +5.0 and
-5.2 volts. The SPT7920 also provides a wide input voltage
range of ±2.0 volts.
The SPT7920 is available in 32-lead ceramic sidebrazed
DIP and 44-lead cerquad packages over the commercial
temperature range. Consult the factory for availability of die,
military temperature and /883 versions.
BLOCK DIAGRAM
V
Input
IN
Buffer
Analog Gain
Compression
Processor
Signal Processing Technologies, Inc.
4-Bit Flash
Converter
Track-and-Hold
Amplifiers
Asynchronous
SAR
4
Correction,
Output TTL
8
4755 Forge Road, Colorado Springs, Colorado 80907, USA
Phone: (719) 528-2300 FAX: (719) 528-2370
Error
Decoding
and
Drivers
Digital
Output
12
Page 2
ABSOLUTE MAXIMUM RATINGS (Beyond which damage may occur)1 25 °C
Supply Voltages
VCC...........................................................................+6 V
Output
Digital Outputs .............................................. 0 to -30 mA
VEE........................................................................... -6 V
Temperature
Input Voltages
Analog Input............................................... VFB≤VIN≤V
VFT, VFB. ................................................... +3.0 V, -3.0 V
Reference Ladder Current .....................................12 mA
CLK IN ...................................................................... V
FT
CC
Operating Temperature ................................. 0 to +70 °C
Junction Temperature .........................................+175 °C
Lead Temperature, (soldering 10 seconds)........ +300 °C
Storage Temperature................................ -65 to +150 °C
Note:1. Operation at any Absolute Maximum Rating is not implied. See Electrical Specifications for proper nominal
applied conditions in typical applications.
ELECTRICAL SPECIFICATIONS
TA=T
unless otherwise specified.
PARAMETERSCONDITIONSLEVELMINTYPMAXUNITS
Resolution12Bits
DC AccuracyT
Analog Input
Reference Inputf
Timing Characteristics
Dynamic Performance
to T
MIN
Integral Nonlinearity± Full ScaleV±2.0LSB
Differential Nonlinearity100 kHz Sample RateV±0.8LSB
No Missing CodesVIGuaranteed
Input Voltage Rangef
Input Bias CurrentT
Input ResistanceV
Input CapacitanceV5pF
Input Bandwidth3 dB Small SignalV120MHz
+FS ErrorV±5.0LSB
Spurious Free Dynamic Range
Differential Phase
Differential Gain
2
2
Digital Inputsf
Logic 1 VoltageT
Logic 0 VoltageT
Maximum Input Current LowT
Maximum Input Current HighT
T
T
T
1
TA=+25 °CV74dB
A=TMIN
A=TMIN
A=TMIN
to T
to T
to T
MAX
MAX
MAX
IV5558dB
IV5557dB
IV5456dB
TA=+25 °CV0.2Degree
TA=+25 °CV0.7%
=1 MHz
CLK
=+25 °CI2.44.5V
A
=+25 °CI0.8V
A
=+25 °CI0+5+20µA
A
=+25 °CI0+5+20µA
A
Pulse Width Low (CLK)IV30ns
Pulse Width High (CLK)IV30300ns
Digital Outputsf
Logic 1 VoltageT
=1 MHz
CLK
=+25 °CI2.4V
A
Logic 0 VoltageTA=+25 °CI0.6V
Power Supply Requirements
Voltages V
DV
-V
CurrentsI
DI
-I
CC
EE
CC
CC
EE
TA=+25 °CI135150mA
CC
TA=+25 °CI4570mA
IV4.755.05.25V
IV4.755.05.25V
IV-4.95-5.2-5.45V
I4055mA
Power DissipationVI1.11.3W
Power Supply Rejection +5 V ±0.25 V, -5.2 ±0.25 VV1.0LSB
Typical thermal impedances (unsoldered, in free air):
32L sidebrazed DIP:
θ
= +50 °C/W
ja
44L cerquad:
θ
= +78 °C/W
ja
at 1 M/s airflow = +58 °C/W
θ
ja
= +3.3 °C/W
θ
jc
1
fIN = 1 MHz.
2
fIN = 3.58 and 4.35 MHz.
SPT
SPT7920
33/10/97
Page 4
TEST LEVEL CODES
TEST LEVEL
TEST PROCEDURE
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.
Figure 1A: Timing Diagram
N
tt
pwHpwL
II
III
IV
V
VI
I
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.
N+1
N+2
CLK
t
d
OUTPUT
DATA
N-2N-1
DATA VALID
N
DATA VALID
N+1
Figure 1B: Single Event Clock
CLK
t
d
OUTPUT
DATA
DATA VALID
Table I - Timing Parameters
PARAMETERSDESCRIPTIONMINTYPMAXUNITS
t
d
t
pwH
CLK to Data Valid Prop Delay-1418ns
CLK High Pulse Width30-300ns
t
pwL
SPT
CLK Low Pulse Width30--ns
SPT7920
43/10/97
Page 5
SPECIFICATION DEFINITIONS
APERTURE DELAY
Aperture delay represents the point in time, relative to the
rising edge of the CLOCK input, that the analog input is
sampled.
APERTURE JITTER
The variations in aperture delay for successive samples.
DIFFERENTIAL GAIN (DG)
A signal consisting of a sine wave superimposed on various
DC levels is applied to the input. Differential gain is the
maximum variation in the sampled sine wave amplitudes at
these DC levels.
DIFFERENTIAL PHASE (DP)
A signal consisting of a sine wave superimposed on various
DC levels that is applied to the input. Differential phase is the
maximum variation in the sampled sine wave phases at these
DC levels.
EFFECTIVE NUMBER OF BITS (ENOB)
SINAD = 6.02N + 1.76, where N is equal to the effective
number of bits.
DIFFERENTIAL NONLINEARITY (DNL)
Error in the width of each code from its theoretical value.
(Theoretical = VFS/2N)
INTEGRAL NONLINEARITY (INL)
Linearity error refers to the deviation of each individual code
(normalized) from a straight line drawn from -Fs through +Fs.
The deviation is measured from the edge of each particular
code to the true straight line.
OUTPUT DELAY
Time between the clock's triggering edge and output data
valid.
OVERVOLTAGE RECOVERY TIME
The time required for the ADC to recover to full accuracy after
an analog input signal 125% of full scale is reduced to 50%
of the full-scale value.
SIGNAL-TO-NOISE RATIO (SNR)
The ratio of the fundamental sinusoid power to the total noise
power. Harmonics are excluded.
SINAD - 1.76
N =
+/- FULL-SCALE ERROR (GAIN ERROR)
Difference between measured full scale response
[(+Fs) - (-Fs)] and the theoretical response (+4 V -2 LSBs)
where the +FS (full scale) input voltage is defined as the
output transition between 1-10 and 1-11 and the -FS input
voltage is defined as the output transition between 0-00 and
0-01.
INPUT BANDWIDTH
Small signal (50 mV) bandwidth (3 dB) of analog input stage.
6.02
SIGNAL-TO-NOISE AND DISTORTION (SINAD)
The ratio of the fundamental sinusoid power to the total noise
and distortion power.
TOTAL HARMONIC DISTORTION (THD)
The ratio of the total power of the first 64 harmonics to the
power of the measured sinusoidal signal.
SPURIOUS FREE DYNAMIC RANGE (SFDR)
The ratio of the fundamental sinusoidal amplitude to the
single largest harmonic or spurious signal.
SPT
SPT7920
53/10/97
Page 6
PERFORMANCE CHARACTERISTICS
50
20
30
40
60
70
80
10
-1
10
0
10
1
THD vs Input Frequency
Input Frequency (MHz)
Total Harmonic Distortion (dB)
fs = 10 MSPS
Signal-to-Noise and Distortion (dB)
20
30
40
50
60
70
80
10
-1
10
0
10
1
SINAD vs Input Frequency
Input Frequency (MHz)
fs =10 MSPS
SNR, THD, SINAD vs Temperature
Temperature (°C)
SNR, THD, SINAD (dB)
55
60
65
70
75
50
f
S
= 10 MSPS
f
IN
= 1 MHz
SINAD
THD
SNR
-250+25+50+75
SNR vs Input Frequency
80
70
60
50
40
Signal-to-Noise Ratio (dB)
30
20
-1
10
SNR, THD, SINAD vs Sample Rate
80
70
60
50
= 1 MHz
f
IN
40
SNR, THD, SINAD (dB)
30
fs = 10 MSPS
0
10
Input Frequency (MHz)
SNR,
THD
SINAD
1
10
20
10
0
0
-30
-60
Amplitude (dB)
SPT
-90
-120
012345
10
1
Sample Rate (MSPS)
SPT7920
Spectral Response
Frequency (MHz)
f
= 10 MSPS
S
= 1 MHz
f
IN
10
2
SPT7920
63/10/97
Page 7
TYPICAL INTERFACE CIRCUIT
The SPT7920 requires few external components to achieve
the stated operation and performance. Figure 2 shows the
typical interface requirements when using the SPT7920 in
normal circuit operation. The following section provides a
description of the pin functions and outlines critical performance criteria to consider for achieving the optimal device
performance.
POWER SUPPLIES AND GROUNDING
The SPT7920 requires -5.2 V and +5 V analog supply
voltages. The +5 V supply is common to analog VCC and
digital DVCC. A ferrite bead in series with each supply line is
intended to reduce the transient noise injected into the
analog VCC. These beads should be connected as closely as
possible to the device. The connection between the beads
and the SPT7920 should not be shared with any other
device. Each power supply pin should be bypassed as
closely as possible to the device. Use 0.1 µF for VEE and
VCC, and 0.01 µF for DVCC (chip caps are preferred).
AGND and DGND are the two grounds available on the
SPT7920. These two internal grounds are isolated on the
device. The use of ground planes is recommended to achieve
optimum device performance. DGND is needed for the DV
CC
return path (40 mA typical) and for the return path for all digital
output logic interfaces. AGND and DGND should be separated from each other and connected together only at the
device through a ferrite bead.
Figure 2 - Typical Interface Circuit
A Schottky or hot carrier diode connected between AGND
and VEE is required. The use of separate power supplies
between VCC and DVCC is not recommended due to potential
power supply sequencing latch-up conditions. Using the
recommended interface circuit shown in figure 2 will provide
optimum device performance for the SPT7920.
VOLTAGE REFERENCE
The SPT7920 requires the use of two voltage references: V
FT
and VFB. VFT is the force for the top of the voltage reference
ladder (+2.5 V typ), VFB (-2.5 V typ) is the force for the bottom
of the voltage reference ladder. Both voltages are applied
across an internal reference ladder resistance of 800 ohms.
The +2.5 V voltage source for reference VFT must be current
limited to 20 mA maximum if a different driving circuit is used
in place of the recommended reference circuit shown in figures
2 and 3. In addition, there are five reference ladder taps (VST,
V
RT1, VRT2, VRT3,
the reference ladder (+2.0 V), V
and VSB). VST is the sense for the top of
is the midpoint of the
RT2
ladder (0.0 V typ) and VSB is the sense for the bottom of the
reference ladder (-2.0 V). V
RT1
and V
are quarter point
RT3
ladder taps (+1.0 and -1.0 V typical, respectively). The
voltages seen at VST and VSB are the true full scale input
voltages of the device when VFT and VFB are driven to the
recommended voltages (+2.5 V and -2.5 V typical respectively). V
scale input voltage of the device. V
and VSB should be used to monitor the actual full
ST
RT1, VRT2
and V
RT3
should not be driven to the expected ideal values as is
commonly done with standard flash converters. When not
being used, a decoupling capacitor of .01 µF connected to
AGND from each tap is recommended to minimize high
frequency noise injection.
V
OUT
Tri m
32
+
IC2
OP-07
7
6
-
R1
100 Ω
± 2.5 V Max
6
5
- 5.2 V
4
.01 µF
+
10 kΩ
1 µF
30 kΩ
30 kΩ
C17
C16
1 µF
+
CLK
(TTL)
V
IN
(±2 V)
2
V
+ 5 V
C19
1 µF
+5 V
Notes to prevent latch-up due to power sequencing:
1) D1 = Schottky or hot carrier diode, P/N IN5817.
2) FB = Ferrite bead, Fair Rite P/N 2743001111
to be mounted as close to the device as possible. The ferrite bead to the ADC
connection should not be shared with any other device.
3) C1-C13 = Chip cap (recommended) mounted as close to the device's pin as
possible.
4) Use of a separate supply for VCC and DVCC is not recommended.
5) R1 provides current limiting to 45 mA.
6) C8, C9, C10 and C11 should be ten times larger than C12 and C13.
7) C10 = C11 = 0.1 µF cap in parallel with a 4.7 µF cap.
IC1
IN
+
(REF-03)
4
GND
1
10 kΩ
8
C18
.01 µF
C1
.01 µF
+2.5 V
C7
.01 µF
-2.5 V
CLK
17
V
IN
24
V
FT
21
.01 µF
.01 µF
.01 µF
.01 µF
.01 µF
C2
C3
C4
C5
C6
R
V
ST
22
2R
V
RT3
23
2R
V
RT2
25
2R
V
26
RT1
2R
V
27
SB
R
V
28
FB
EE
EE
V
V
18 3119 3020 2916 321 15
C8
.1 µF
C9
.1 µF
D1
C15
10 µF
COARSE
ANALOG
PRESCALER
SUCCESSIVE
INTERPOLATION
STAGE # 1
SUCCESSIVE
INTERPOLATION
STAGE # N
AGND
AGND
C10
C11
C14
10 µF
+
-5.2 V
AGND
(Analog)
14
D12
(OVERRANGE)
D11
13
A/D
CC
V
FB
4
D E C O D I N G N E T W O R K
CC
CC
CC
V
DGND
DV
DV
C12
.01 µF
C13
.01 µF
FB
D10
DGND
(MSB)
12
D9
11
10
D8
D7
9
8
D6
D5
7
D4
6
5
D3
D2
4
D1
3
2
D0
(LSB)
FB
D I G I T A L O U T P U T S
+
+5 V
(Analog)
DGND
SPT
SPT7920
73/10/97
Page 8
Figure 3 - Analog Equivalent Input CircuitThe drive requirements for the analog inputs are minimal
VCC
when compared to conventional Flash converters due to the
SPT7920’s extremely low input capacitance of only 5 pF and
very high input impedance of 300 kΩ. For example, for an
input signal of ± 2 V p-p with an input frequency of 10 MHz,
the peak output current required for the driving circuit is only
VIN
V
FT
628 µA.
CLOCK INPUT
ANALOG PRESCALER
VEE
The analog input range will scale proportionally with respect
to the reference voltage if a different input range is required.
The maximum scaling factor for device operation is ± 20% of
the recommended reference voltages of VFT and VFB. However, because the device is laser trimmed to optimize performance with ± 2.5 V references, the accuracy of the device will
degrade if operated beyond a ± 2% range.
An example of a recommended reference driver circuit is
shown in figure 2. IC1 is REF-03, the +2.5 V reference with a
tolerance of 0.6% or +/- 0.015 V. The potentiometer R1 is
10 kΩ and supports a minimum adjustable range of up to
150 mV. IC2 is recommended to be an OP-07 or equivalent
device. R2 and R3 must be matched to within 0.1% with good
TC tracking to maintain a 0.3 LSB matching between VFT and
VFB. If 0.1% matching is not met, then potentiometer R4 can
be used to adjust the VFB voltage to the desired level. R1 and
R4 should be adjusted such that VST and VSB are exactly
+2.0 V and -2.0 V respectively.
The following errors are defined:
+FS error = top of ladder offset voltage = ∆(+FS -VST)
-FS error = bottom of ladder offset voltage = ∆(-FS -VSB)
Where the +FS (full scale) input voltage is defined as the
output 1 LSB above the transition of 1—10 and 1—11 and the
-FS input voltage is defined as the output 1 LSB below the
transition of 0—00 and 0—01.
ANALOG INPUT
The SPT7920 is driven from a single-ended TTL input (CLK).
For optimal noise performance, the clock input slew rate
should be a minimum of 6 ns. Because of this, the use of
fast
logic is recommended. The clock input duty cycle should be
50% where possible, but performance will not be degraded if
kept within the range of 40-60%. However, in any case the
clock pulse width (tpwH) must be kept at 300 ns maximum to
ensure proper operation of the internal track and hold amplifier (see timing diagram). The analog input signal is latched on
the rising edge of the CLK.
The clock input must be driven from fast TTL logic (V
≤4.5 V, T
<6 ns). In the event the clock is driven from a
RISE
IH
high current source, use a 100 Ω resistor in series to current
limit to approximately 45 mA.
DIGITAL OUTPUTS
The format of the output data (D0-D11) is straight binary.
(See table II.) The outputs are latched on the rising edge of
CLK with a propagation delay of 14 ns (typ). There is a one
clock cycle latency between CLK and the valid output data.
(See timing diagram.)
Table II - Output Data Information
ANALOG INPUTOVERRANGEOUTPUT CODE
D12D11-DO
>+2.0 V + 1/2 LSB11111 1111 1111
+2.0 V -1 LSBO1111 1111 111Ø
0.0 VOØØØØ ØØØØ ØØØØ
-2.0 V +1 LSBOOOOO OOOO OOOØ
<-2.0 VOOOOO OOOO OOOO
(Ø indicates the flickering bit between logic 0 and 1).
VIN is the analog input. The full scale input range will be 80%
of the reference voltage or ±2 volts with VFB=-2.5 V and
VFT=+2.5 V.
SPT
The rise times and fall times of the digital outputs are not
symmetrical. The propagation delay of the rise time is typically 14 ns and the fall time is typically 6 ns. (See figure 4.)
The nonsymmetrical rise and fall times create approximately
8 ns of invalid data.
SPT7920
83/10/97
Page 9
Figure 4 - Digital Output Characteristics
N
N+1
CLK IN
DATA OUT
(Actual)
DATA OUT
(Equivalent)
2.4 V
3.5 V
2.4 V
0.8 V
0.5 V
6 ns
typ.
(N-2)
(N-2)
tpd1
(14 ns typ.)
Invalid
Data
Invalid
Data
OVERRANGE OUTPUT
The OVERRANGE OUTPUT (D12) is an indication that the
analog input signal has exceeded the full scale input voltage
by 1 LSB. When this condition occurs, the outputs will switch
to logic 1s. All other data outputs are unaffected by this
operation. This feature makes it possible to include the
SPT7920 into higher resolution systems.
Rise Time
≤ 6 ns
Invalid
(N-1)
(N-1)
Data
Invalid
Data
(N)
(N-1)
EVALUATION BOARD
The EB7920 evaluation board is available to aid designers in
demonstrating the full performance of the SPT7920. This
board includes a reference circuit, clock driver circuit, output
data latches and an on-board reconstruction of the digital
data. An application note (AN7920) describing the operation
of this board as well as information on the testing of the
SPT7920 is also available. Contact the factory for price and
availability.
-5.2 V Supply
+5.0 V Supply
Voltage Reference Taps
Analog Input
Digital +5.0 V Supply (TTL Outputs)
Force for Top of Reference Ladder
Sense for Top of Reference Ladder
Force for Bottom of Reference Ladder
Sense for Bottom of Reference Ladder
N/C
36
CC
DV
32
CC
V
31
EE
AGND
30
29
V
CC
28
V
FB
V
27
SB
26
V
RT1
25
V
RT2
24
V
IN
V
23
RT3
22
V
ST
21
V
FT
20
V
CC
19
AGND
18
V
EE
17
CLK
V
N/C
35
34
33
N/C
V
32
FB
V
31
SB
V
30
RT1
V
29
RT2
V
28
IN
V
27
RT3
V
26
ST
V
25
FT
N/C
24
V
23
CC
1
D0
2
3
D1
4
D2
5
D3
D4
6
7
D5
8
D6
D7
D8
D9
CC
32L Sidebrazed
9
10
11
12
13
14
15
16
N/C
DØ
D1
42
44
43
DGND
CC
41
DV
40
EE
AGND
V
N/C
39
38
37
44L Cerquad
12
N/C
13
D12
14
DGND
15
CC
DV
16
N/C
17
CLK
18
N/C
19
EE
21
22
V
AGND
N/C
N/C
20
ORDERING INFORMATION
PART NUMBERTEMPERATURE RANGEPACKAGE
SPT7920SCJ0 to +70 °C32L Sidebrazed Dip
SPT7920SCQ0 to +70 °C44L Cerquad
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.
SPT7920
SPT
113/10/97
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