Figure 1. CDS-1401 Functional Block Diagram
S/
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S
ET
A
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TV
1
1
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INPUT 1
3
S/
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S
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9
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S
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2
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ANAL
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INPUT 2
4
S/
H1
CO
MMAND 11
S/
H2
CO
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5, 14, 21, 2
3
ANAL
OG
G
R
O
UND
2
4
+
15V
S
UPPLY
1
6
+
5V DI
G
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S
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1
5
D
I
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ITA
L
G
R
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7
S/
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8
S/
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S
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G
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2
2 V
OU
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18 A
/
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C
L
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K 1
6
S/
H1
OUT
O
PTI
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A
L
17 A
/
D
C
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K
1
19 A
/
D
C
L
OC
K
2
20 A
/
D
C
L
OC
K
2
C
H
= 100pF
1k
7
100
7
1
00
k7
1k
7
C
H
= 100p
F
100
k
7
1k
7
900
7
1
k
7
13
–1
5
V
SU
PPLY
–
+
–
+
BLOCK DIAGRAM
The CDS-1401 is an application-specifi c, cor-
related double sampling (CDS) circuit designed for
electronic-imaging applications that employ CCD’s
(charge coupled devices) as their photodetec-
tor. The CDS-1401 has been optimized for use in
digital video applications that employ 10 to 14-bit
A/D converters. The low-noise CDS-1401 can
accurately determine each pixel’s true video signal
level by sequentially sampling the pixel’s offset
signal and its video signal and subtracting the two.
The result is that the consequences of residual
charge, charge injection and low-frequency “kTC”
noise on the CCD’s output fl oating capacitor are
effectively eliminated. The CDS-1401 can also be
used as a dual sample-hold amplifi er in a data
acquisition system.
The CDS-1401 contains two sample-hold
amplifi ers and appropriate support/control circuitry.
Features include independent offset-adjust capabil-
ity for each S/H, adjustment for matching gain
between the two S/H’s, and four control lines for
triggering the A/D converter used in conjunction
with the CDS-1401. The CDS circuit’s “ping-pong”
timing approach (the offset signal of the “n+1”
pixel can be acquired while the video output of
the “nth” pixel is being converted) guarantees a
minimum throughput, in a 14-bit application, of
1.25MHz. In other words, the true video signal
(minus offset) will be available at the output of the
CDS-1401 every 800ns. This correlates with the
fact that an acquisition time of 400ns is required
for each internal S/H amplifi er (10V step setting to
±0.003%). The input and output of the CDS-1401
can swing up to ±10 Volts.
The functionally complete CDS-1401 is pack-
aged in a single, 24-pin, ceramic DDIP. It oper-
ates from ±15V and +5V supplies and consumes
700mW. Though the CDS-1401’s approach to
CDS appears straightforward (see Description of
Operation), the circuit actually exploits an elegant
architecture whose tradeoffs enable it to offer
wide-bandwidth, low-noise and highthrough-
put combinations unachievable until now. The
CDS- 1401 is a generic type of circuit that can be
used with almost any 10 to 14-bit A/D converter.
However, DATEL does offer A/D converters that are
optimized for use with the CDS-1401.
PRODUCT OVERVIEW
FEATURES
■ Use with 10 to 14-bit A/D converters
■ 1.25 Megapixels/second minimum throughput
(14 bits)
■ ±10V input/output ranges, Gain = –1
■ Low noise, 200μVrms
■ Two independent S/H amplifi ers
■ Gain matching between S/H's
■ Offset adjustments for each S/H
■ Four external A/D control lines
■ Small package, 24-pin ceramic DDIP
■ Low power, 700mW
■ Low cost
CDS-1401
14-Bit, Fast-Settling Correlated Double Sampling Circuit
®®
DATEL • 11 Cabot Boulevard, Mansfi eld, MA 02048-1151 USA • Tel: (508) 339-3000 • www.datel.com • e-mail: help@datel.com
01 Apr 2011 MDA_CDS-1401.B02 Page 1 of 8
PHYSICAL/ENVIRONMENTAL
PARAMETERS MIN. TYP. MAX. UNITS
Operating Temp. Range, Case
CDS-1401MC 0 — +70 °C
CDS-1401MM –55 — +125 °C
Thermal Impedance
Tjc — 5 — °C/Watt
Tca — 22 — °C/Watt
Storage Temperature Range –65 — +150 °C
Package Type 24-pin, metal-sealed ceramic DDIP
Weight 0.42 ounces (12 grams)
ABSOLUTE MAXIMUM RATINGS
PARAMETERS LIMITS UNITS
+15V Supply (Pin 24) 0 to +16 Volts
–15V Supply (Pin 13) 0 to –16 Volts
+5V Supply (Pin 16) 0 to +6 Volts
Digital Inputs (Pins 11, 12) –0.3 to +VDD +0.3 Volts
Analog Inputs (Pins 3, 4) ±12 Volts
Lead Temp. (10 seconds) 300 °C
+25°C 0 TO +70°C –55 TO +125°C
ANALOG INPUTS ➀MIN. TYP. MAX. MIN. TYP. MAX. MIN. TYP. MAX. UNITS
Input Voltage Range ±10 — — ±10 — — ±10 — — Volts
Input Resistance — 1000 — — 1000 — — 1000 — Ohms
Input Capacitance — 7 15 — 7 15 — 7 15 pF
DIGITAL INPUT
Logic Levels
Logic "1" +2 — — +2 — — +2 — — Volts
Logic "0" — — +0.8 — — +0.8 — — +0.8 Volts
Logic Loading "1" — — +10 — — +10 — — +10 μA
Logic Loading "0" — — –10 — — –10 — — –10 μA
PERFORMANCE
Sample Mode Offset Error - S/H1 — ±1 ±10 — ±2 ±10 — ±4 ±10 mV
Gain Error - S/H1 — ±0.2 ±1 — ±0.25 ±1 — ±0.3 ±1.5 %
Pedestal - S/H1 — ±15 ±35 — ±15 ±35 — ±15 ±35 mV
Sample Mode Offset Error - S/H2 — ±1 ±10 — ±2 ±10 — ±4 ±10 mV
Gain Error - S/H2 — ±0.2 ±1 — ±0.25 ±1 — ±0.3 ±1.5 %
Pedestal - S/H2 — ±15 ±35 — ±15 ±35 — ±15 ±35 mV
Sample Mode Offset Error - CDS — ±1 ±10 — ±2 ±10 — ±4 ±10 mV
Differential Gain Error - CDS — ±0.25 ±1 — ±0.3 ±1 — ±0.35 ±1.5 %
Pedestal - CDS — ±15 ±35 — ±15 ±35 — ±15 ±35 mV
Pixel Rate (14-bit settling) ➁ 1.25 — — 1.25 — — 1.25 — — MHz
Input Bandwidth, ±5V
Small Signal (–20dB input) — 7 — — 7 — — 7 — MHz
Large Signal (–0.5dB input) — 5 — — 5 — — 5 — MHz
Slew Rate — ±80 — — ±80 — — ±80 — V/μs
Aperture Delay Time — 10 — — 10 — — 10 — ns
Aperture Uncertainty — 5 — — 5 — — 5 — ps rms
S/H Acquisition Time ➁
(to ±0.003%, 10V step) — 340 400 — 350 400 — 350 400 ns
Hold Mode Settling Time
(to ±0.15mV) — TBD — — TBD — — TBD — ns
Noise — 200 — — 200 — — 200 — μVr ms
Feedthrough Rejection — 72 — — 72 — — 72 — dB
Overvoltage Recovery Time — 400 — — 400 — — 400 — ns
S/H Saturation Voltage — ±12.5 — — ±12.5 — — ±12.5 — Volts
Droop Rate — ±0.004 ±0.02 — ±0.4 ±2 — ±0.8 ±4 mV/μs
ANALOG OUTPUTS ➂
Output Voltage Range ±10 — — ±10 — — ±10 — — Volts
Output Impedance — 0.5 — — 0.5 — — 0.5 — Ohms
Output Current — — ±20 — — ±20 — — ±20 mA
DIGITAL OUTPUTS
Output Voltage Range ±10 — — ±10 — — ±10 — — Volts
Output Impedance — 0.5 — — 0.5 — — 0.5 — Ohms
Output Current — — ±20 — — ±20 — — ±20 mA
Voltage +9.95 +10.0 +10.05 +9.95 +10.0 +10.05 +9.95 +10.0 +10.05 Volts
Drift — ±5 — — ±5 — — ±5 — ppm/ºC
FUNCTIONAL SPECIFICATIONS
(TA = +25°C, ±Vcc = ±15V, +VDD = +5V, pixel rate = 1.25MHz, and a minimum warmup time of two minutes unless otherwise noted.)
CDS-1401
14-Bit, Fast-Settling Correlated Double Sampling Circuit
®®
DATEL • 11 Cabot Boulevard, Mansfi eld, MA 02048-1151 USA • Tel: (508) 339-3000 • www.datel.com • e-mail: help@datel.com
01 Apr 2011 MDA_CDS-1401.B02 Page 2 of 8
TECHNICAL NOTES
Footnotes:
➀ Pins 3 and 4.
➁ See Figure 4 for relationship between input voltage, accuracy, and acquisition time.
➂ Pins 6 and 22.
1. 1. To achieve specifi ed performance, all power supply pins should be
bypassed with 2.2μF tantalum capacitors in parallel with 0.1μF ceramic ca-
pacitors. All ANALOG GROUND (pins 5, 14, 21 and 23) and DIGITAL GROUND
(pin 15) pins should be tied to a large analog ground plane beneath the
package.
2. In the CDS confi guration, to avoid saturation of the S/H amplifi ers, the
maximum analog inputs and conditions are as follows:
ANALOG INPUT 1 < ±12V
(ANALOG INPUT 1 – ANALOG INPUT 2) < ±12V
3. The combined video and reference/offset signal from the CCD array must
be applied to S/H2, while the reference/offset signal is applied to S/H1.
4. To use as a CDS circuit, tie pin 8 (S/H2 SUMMING NODE) to either pin 6
(S/H1 OUT), through a 200 Ohm potentiometer, or directly to pin 7 (S/H1
ROUT). In both cases, the CCD's output is tied to pins 3 (ANALOG INPUT 1)
and 4 (ANALOG INPUT 2). As shown in Figure 5, the 200W potentiometer is
for gain matching.
5. To use as a dual S/H, leave pin 7 (S/H1 ROUT) and pin 8 (S/H2 SUMMING
NODE) fl oating. Pin 6 (S/H1 OUT) will be the output of S/H1 and pin 22 (V
OUT) will be the output of S/H2.
6. See Figure 4 for acquisition time versus accuracy and input voltage step
amplitude.
INPUT/OUTPUT CONNECTIONS
PIN FUNCTION PIN FUNCTION
1 OFFSET ADJUST V1 24 +15V ANALOG SUPPLY
2 OFFSET ADJUST I1 23 ANALOG GROUND
3 ANALOG INPUT 1 22 V OUT
4 ANALOG INPUT 2 21 ANALOG GROUND
5 ANALOG GROUND 20 A/D CLOCK2
6 S/H1 OUT 19 A/D CLOCK2
7 S/H1 ROUT 18 A/D CLOCK1
8 S/H2 SUMMING NODE 17 A/D CLOCK1
9 OFFSET ADJUST V2 16 +5V DIGITAL SUPPLY
10 OFFSET ADJUST I2 15 DIGITAL GROUND
11 S/H1 COMMAND 14 ANALOG GROUND
12 S/H2 COMMAND 13 –15V ANALOG SUPPLY
+25°C 0 TO +70°C –55 TO +125°C
POWER REQUIREMENTS MIN. TYP. MAX. MIN. TYP. MAX. MIN. TYP. MAX. UNITS
Power Supply Ranges
+15V Supply +14.75 +15.0 +15.25 +14.75 +15.0 +15.25 +14.75 +15.0 +15.25 Volts
–15V Supply –14.75 –15.0 –15.25 –14.75 –15.0 –15.25 –14.75 –15.0 –15.25 Volts
+5V Supply +4.75 +5.0 +5.25 +4.75 +5.0 +5.25 +4.75 +5.0 +5.25 Volts
Power Supply Currents
+15V Supply — +23 +27 — +23 +27 — +23 +27 mA
–15V Supply — –23 –27 — –23 –27 — –23 –27 mA
+5V Supply — +1 +2 — +1 +2 — +1 +2 mA
Power Dissipation — 700 850 — 700 850 — 700 850 mW
Power Supply Rejection — 100 — — 100 — — 100 — dB
CDS-1401
14-Bit, Fast-Settling Correlated Double Sampling Circuit
®®
DATEL • 11 Cabot Boulevard, Mansfi eld, MA 02048-1151 USA • Tel: (508) 339-3000 • www.datel.com • e-mail: help@datel.com
01 Apr 2011 MDA_CDS-1401.B02 Page 3 of 8
FUNCTIONAL DESCRIPTION
CORRELATED DOUBLE SAMPLING
All photodetector elements (photodiodes, photomultiplier tubes, focal
plane arrays, charge coupled devices, etc.) have unique output character-
istics that call for specifi c analog-signalprocessing (ASP) functions at their
outputs. Charge coupled devices (CCD’s), in particular, display a number
of unique characteristics. Among them is the fact that the “offset error”
associated with each individual pixel (i.e., the apparent photonic content
of that pixel after having had no light incident upon it) changes each and
every time that particular pixel is accessed.
Most of us think of an offset as a constant parameter that either can
be compensated for (by performing an offset adjustment) or can be
measured, recorded, and subtracted from subsequent readings to yield
more accurate data. Contending with an offset that varies from reading to
reading requires measuring and recording (or capturing and storing) the
offset each and every time, so it can be subtracted from each subsequent
data reading.
The “double sampling” aspect of CDS refers to the operation of sampling
and storing/recording a given pixel’s offset and then sampling the same
pixel’s output an instant later (with both the offset and the video signal
present) and subsequently subtracting the two values to yield what is
referred to as the “valid video” output for that pixel.
The “correlated” in CDS refers to the fact that the two samples must be
taken close together in time because the offset is constantly varying.
Reasons for this phenomena are discussed below.
At the output of all CCD’s, transported pixel charge (electrons) is converted
to a voltage by depositing the charge onto a capacitor (usually called
the output or “fl oating” capacitor). The voltage that develops across this
capacitor is obviously proportional to the amount of deposited charge
(i.e., the number of electrons) according to ΔV = ΔQ/C. Once settled, the
resulting capacitor voltage is buffered and brought to the CCD’s output pin
as a signal whose amplitude is proportional to the total number of photons
incident upon the relevant pixel.
After the output signal has been recorded, the fl oating capacitor is
discharged (“reset”, “clamped”, “dumped”) and made ready to accept
charge from the next pixel. This is when the problems begin. (This is a
somewhat oversimplifi ed explanation in that the fl oating capacitor is not
usually “discharged” but, in fact, “recharged” to some predetermined dc
voltage, usually called the “reference level”. The pixel offset appears as an
output deviation from that reference level.)
The fl oating capacitor is normally discharged (charged) via a shunt switch
(typically a FET structure) that has a non-zero “on” resistance. When the
switch is on, its effective series resistance exhibits thermal noise (Johnson
noise) due to the random motion of thermally energized charge. Because
the shunt switch is in parallel with the fl oating capacitor, the instanta-
neous value of the thermal noise (expressed in either Volts or electrons)
appears across the cap. When the shunt switch is opened, charge/voltage
is left on the fl oating cap.
The magnitude of this “captured noise voltage” is a function of absolute
temperature (T), the value of the fl oating capacitor (C) and Boltzman’s
constant (k). It is commonly referred to as “kTC” noise.
The second contributor to the constantly varying pixel offsets is the fact
that, at high pixel rates, the fl oating capacitor never has time to fully
discharge (charge) during the period in which its shunt switch is closed.
There is always some “residual” charge left on the cap, and the amount of
this charge varies as a function of what was the total charge held during
the previous pixel. This amount of residual charge is, in fact, deterministic
(if you know the previous charge and the number of time constants in the
discharge period), however, it is less of a contributor than kTC noise.
The third major contributor to pixel offset is the fact that as the shunt FET
is turned off, the voltage across (and the charge stored on) its parasitic
junction capacitances changes. The result is an “injection” of excess
charge onto the fl oating cap causing a voltage step normally called a
“pedestal.”
The fourth major contributor to pixel offset is a low-frequency noise com-
ponent (usually called 1/f noise or pink noise) associated with the CCD’s
output buffer amplifi er. Due to all of these contributing factors, "pixel
offsets" vary from sample to sample in an inconsistent, unpredictable
manner.
TRADITIONAL APPROACH TO CDS
There are a number of techniques for dealing with the varyingoffset
idiosyncrasy of CCD’s. The most prevalent has been what can be called
the “sample-sample-subtract” technique. This approach requires the use
of two high-speed sample-hold (S/H) amplifi ers and a difference amplifi er.
The fi rst S/H is used to acquire and hold a given pixel’s offset. Imme-
diately after that, the second S/H acquires and holds the same pixel’s
offset+video signal. After both the S/H outputs have fully settled, the
difference amplifi er subtracts the offset from the offset+video yielding the
valid video signal.
CDS-1401 APPROACH (SEE FIGURE 1)
The DATEL CDS-1401 takes a slightly different, though clearly superior,
approach to CDS. It can be called the “samplesubtract- sample” approach.
Note that the CDS-1401 has been confi gured to offer the greatest amount
of user fl exibility. Its two S/H circuits function independently. They have
separate input and output pins. Each has its own independent control
lines. The control-line signals are delayed, buffered, and brought back out
of the package so they can be used to control other circuit functions. Each
S/H has two pins for offset adjusting (if required), one for current and one
for voltage.
In normal operation, the output signal of the CCD is applied simultane-
ously to the inputs (pins 3 and 4) of both S/H amplifi ers. S/H1 will normally
be used to capture and hold each pixel’s offset signal. Therefore, S/H1
is initially in its signal-acquisition mode (logic “1” applied to pin 11, S/
H1 COMMAND). This is also called the sample or track mode. Following a
brief interval during which the output of the CCD and the output of S/H1
are allowed to settle, S/H1 is driven into its hold mode by applying a logic
“0” to pin 11. S/H1 is now holding the pixel’s offset value.
In most straightforward confi gurations, the output of S/H1 is connected to
the summing node of S/H2 by connecting pin 7 (S/H1 ROUT) to pin 8 (S/H2
SUMMING NODE).
When the offset+video signal appears at the output of the CCD, S/H2
is driven into its signal acquisition mode by applying a logic “1” to pin
12 (S/H2 COMMAND). S/H2 employs a current-summing architecture
that subtracts the output of S/H1 (the offset) from the output of the CCD
(offset+video) while acquiring only the difference signal (i.e., the valid
video). A logic “0” subsequently applied to pin 12 drives S/H2 into its hold
mode, and after a brief transient settling time, the valid video signal ap-
pears at pin 22 (V OUT).
CDS-1401
14-Bit, Fast-Settling Correlated Double Sampling Circuit
®®
DATEL • 11 Cabot Boulevard, Mansfi eld, MA 02048-1151 USA • Tel: (508) 339-3000 • www.datel.com • e-mail: help@datel.com
01 Apr 2011 MDA_CDS-1401.B02 Page 4 of 8
TIMING NOTES
See Figure 2, Typical Timing Diagram. It is advisable that neither of the
CDS-1401's S/H amplifi ers be in their sample/ track mode when large,
high-speed transients (normally associated with clock edges) are occurring
throughout the system. This could result in the S/H amplifi ers being driven
into saturation, and they may not recover in time to accurately acquire their
next signal.
For example, S/H1 should not be commanded into the sample mode until
all transients associated with the opening of the shunt switch have begun
to decay. Similarly, S/H2 should not be driven into the sample mode until
all transients associated with the clocking of pixel charge onto the output
capacitor have begun to decay. Therefore, it is generally not a good practice
to use the same clock edge to drive S/H1 into hold (holding the offset) and
S/H2 into sample (to acquire the offset + video signal).
S/H's that are in their signal-acquisition modes should be left there as long
as possible (so all signals can settle) and be driven into their hold modes
before any system transients occur. In Figure 2, S/H1 is driven into the
sample mode shortly after the transient from the shunt switch has begun
to decay. S/H1 is then kept in the sample mode while the offset signal and
the S/H output settle. S/H1 is driven into hold just prior to the system clock
pulse(s) that transfers the next pixel charge onto the output capacitor.
As soon as the transients/noise associated with the charge transport begins
to decay, S/H2 can be driven into the sample mode. S/H2 can then be left in
the sample mode until just before the reset pulse for the output capacitor.
In Figure 2, S/H's 1 and 2 both have the same acquisition time. If the pixel-
to-pixel amplitude variation of offset signals is much less than that of video
signals, it may not be necessary for the allocated acquisition time of S/H1
to be as long as that of S/H2.
As shown in the plot (Figure 4) of acquisition times vs. input signal step
size, the S/H's internal to the CDS-1401 acquire smaller-amplitude signals
quicker than they acquire largeramplitude signals. In "maximum-through-
put" applications, assuming "asymmetric" timing can be accommodated,
each S/H should only be given the time it requires, and no more, to acquire
its input signal. Leaving a S/H amp in the sample mode for a longer period
of time has little added benefi t.
As an example, the graph shows that it takes 160ns to acquire a 500mV
step to within 10mV of accuracy and 260ns to acquire a 500mV step to
within 0.5mV of accuracy. The fi gures in this graph are typical values at
room temperature.
The CDS-1401 brings out 4 control lines that can be used to trigger an A/D
converter connected to its output. If the A/D is a sampling type, system tim-
ing should be such that the A/D's input S/H amplifi er is acquiring the output
of the CDS-1401 at the same time the output is settling to its fi nal value.
For most sampling A/D's, the rising edge of the start-convert pulse drives
the internal S/H into the hold mode under the assumption the S/H has al-
ready fully acquired and is tracking the input signal. In this case, the same
edge can not be used to drive S/H2 into the hold mode and simultaneously
initiate the A/D conversion. The output of S/H2 needs time to settle its
sample-to-hold switching transient, and the input S/H of the A/D needs time
to fully acquire its new input signal.
As shown in Figure 1, output line A/D CLOCK1 (pin 18) is a slightly delayed
version of the signal applied to pin 11 (S/H1 COMMAND), and A/D CLOCK1
(pin 17) is its complement. A/D CLOCK2 (pin 19) is a delayed version of the
signal applied to pin 12 (S/H2 COMMAND), and A/D CLOCK2 (pin 20) is its
complement. Any one of these signals, as appropriate, may be used to trig-
ger the A/D conversion.
Figure 3 is a typical timing diagram for a CDS-1401 in front of DATEL's 12-
bit, 1.2MHz sampling A/D, the ADS-CCD1201.
Figure 2. CDS-1401 Typical Timing Diagram
ANALOG INPUT
FOR CDS (Pins 3 and
4 are tied)
S/H 1 (Pin 11)
A/D CLOCK 1 (Pin 17)
S/H 2 (Pin 12)
A/D CLOCK 1 (Pin 18)
A/D CLOCK 2 (Pin 19)
A/D CLOCK 2 (Pin 20)
VOLTAGE OUTPUT
VIDEO SIGNAL N-1 VIDEO SIGNAL N
(CCD OUTPUT)
100ns typ.
30ns typ.
30ns typ.
NOTE: Not Drawn to Scale
RESET N
OFFSET N
OFFSET +
VIDEO N
RESET N+1
OFFSET N+1 OFFSET +
VIDEO N+1
100ns typ.
HOLD
HOLD
CDS-1401
14-Bit, Fast-Settling Correlated Double Sampling Circuit
®®
DATEL • 11 Cabot Boulevard, Mansfi eld, MA 02048-1151 USA • Tel: (508) 339-3000 • www.datel.com • e-mail: help@datel.com
01 Apr 2011 MDA_CDS-1401.B02 Page 5 of 8
Figure 4. Acquisition Time versus Accuracy and Step Size
Figure 3. CDS-1401 in Front of ADS-CCD1201 at fCLK = 1MHz
S/H1
S/H2
START CONVERT
EOC
OUTPUT
DATA DATA N-1 VALID DATA N VALID
30ns typ.
90ns typ.
73ns max.
35ns max.
ANALOG INPUT
FOR CDS
(Pins 3 and 4 are tied)
(CCD OUTPUT)
DATA N+1 VALID
400ns
400ns
OFFSET (N+1) OFFSET +
VIDEO (N+1)
OFFSET (N+2) OFFSET +
VIDEO (N+2)
420ns
RESETRESET
±0.5mV accuracy
±1mV accuracy
±2mV accuracy
±5mV accuracy
±10mV accuracy
CDS-1401
14-Bit, Fast-Settling Correlated Double Sampling Circuit
®®
DATEL • 11 Cabot Boulevard, Mansfi eld, MA 02048-1151 USA • Tel: (508) 339-3000 • www.datel.com • e-mail: help@datel.com
01 Apr 2011 MDA_CDS-1401.B02 Page 6 of 8
CALIBRATION PROCEDURE
OFFSET ADJUST (FIGURE 5)
Offset and pedestal errors may be compensated for by applying external
voltages to pin 1 (OFFSET ADJUST V1) and/ or pin 9 (OFFSET ADJUST V2)
using either voltage-output DAC’s or potentiometers confi gured to appear
as voltage sources.
Offset and pedestal errors may also be compensated for by applying exter-
nal currents to pin 2 (OFFSET ADJUST I1) and/ or pin 10 (OFFSET ADJUST
I2) by using either current-output DAC’s or potentiometers confi gured to
appear as current sources.
1. Connect pin 8 (S/H2 SUMMING NODE) either directly to pin 7 (S/H1 ROUT)
or through a 200 Ohm potentiometer to pin 6 (S/H1 OUT).
2. Tie pins 3 (ANALOG INPUT 1) and 4 (ANALOG INPUT 2) to pin 5 (ANALOG
GROUND).
3. Adjust OFFSET ADJUST V1 or OFFSET ADJUST I1 (while S/H1 is in the
hold mode) until pin 6 (S/H1 OUT) equals 0V.
4. Adjust OFFSET ADJUST V2 or OFFSET ADJUST I2 (while S/H2 is in the
hold mode) until pin 22 (VOUT) equals 0V.
5. To negate the effect of output droop on the offset-adjust process, each
S/H must be continually switched between its sample and hold modes and
adjusted so its output equals zero immediately after going into the hold
mode.
The sensitivity of the voltage offset adjustments is 100mV per Volt. The
sensitivity of the current offset adjustments is 1V per mA. Pins 1, 2, 9 and
10 should be left open (fl oating) when not being used for offset adjustment.
GROSS OFFSET ADJUSTMENT
For gross offset adjustments use pin 2 (OFFSET ADJUST I1) and/or pin 10
(OFFSET ADJUST I2). All connections made to pin 2 and pin 10 should be
very short because these are very sensitive points.
Sourcing 1mA into OFFSET ADJUST I1 will cause a –1V offset change at pin
6 (S/H1 OUT). It will also cause a +1V offset change at pin 22 (V OUT) if pin
7 (S/H1 ROUT) is connected to pin 8 (S/H2 SUMMING NODE).
Sourcing 1mA into OFFSET ADJUST I2 will cause a –1V offset change at pin
22 (V OUT).
GAIN MATCHING ADJUSTMENT (DIFFERENTIAL GAIN)
BETWEEN S/H1 AND S/H2
The user can adjust the gain matching (differential gain) between S/H1 and S/
H2 by leaving pin 7 (S/H1 ROUT) fl oating (open) and connecting a 200 Ohm
potentiometer between pin 6 (S/H1 OUT) and pin 8 (S/H2 SUMMING NODE).
Note, offset adjustment should take place before gain matching adjustment.
Apply a full-scale input to both pins 3 (ANALOG INPUT 1) and 4 (ANALOG
INPUT 2). Adjust the 200 Ohm potentiometer (with both S/H's in the sample
mode) until pin 22 (V OUT) is 0V.
If gain matching adjustment is not required, leave pin 6 (S/H1 OUT) fl oating
(open) and tie pin 7 (S/H1 ROUT) to pin 8 (S/H2 SUMMING NODE).
Figure 5. CDS-1401 Typical Connection Diagram
OFFSET ADJUST V1
1
+15V
–15V
OFFSET ADJUST I1
2
ANALOG INPUT 1
3
ANALOG INPUT 2
4
ANALOG GROUND
5
S/H1 OUT
6
S/H1 ROUT
7
S/H2 SUMMING NODE
8
OFFSET ADJUST V2
9
+15V
–15V
OFFSET ADJUST I2
10
S/H1 COMMAND
11
S/H2 COMMAND
12
200 7
0.1F 2.2F
+15V
+
0.1F 2.2F
+
–15V
0.1F 2.2F
+5V
+
24
23
22
21
20
19
18
17
16
15
14
13
ANALOG GROUND
V OUT
ANALOG GROUND
A/D CLOCK 2
A/D CLOCK 2
A/D CLOCK 1
A/D CLOCK 1
+5V DIGITAL SUPPLY
DIGITAL GROUND
ANALOG GROUND
–15V ANALOG SUPPLY
+15V ANALOG SUPPLY
CDS-1401
CDS-1401
14-Bit, Fast-Settling Correlated Double Sampling Circuit
®®
DATEL • 11 Cabot Boulevard, Mansfi eld, MA 02048-1151 USA • Tel: (508) 339-3000 • www.datel.com • e-mail: help@datel.com
01 Apr 2011 MDA_CDS-1401.B02 Page 7 of 8
MECHANICAL DIMENSIONS INCHES (mm)
ORDERING INFORMATION
MODEL NUMBER OPERATING TEMP. RANGE ANALOG INPUT PACKAGE TYPE ACCESSORIES
CDS-1401MC 0 to +70°C ±10V DDIP HS-24 Heat Sink for all
CDS-1401 models
CDS-1401MM –55 to +125°C ±10V DDIP
Receptacles for pc board mounting can be ordered through Amp Inc., part number 3-331272-8 (component lead socket), 24 required.
For MIL-STD-883 products, or availability of surface mount packaging, contact DATEL.
24-PIN DDIP
24-PIN SURFACE MOUNT
0.200 MAX.
(5.080)
0.235 MAX.
(5.969)
0.600 ±0.010
(15.240)
0.80 MAX.
(20.32)
0.100 TYP.
(2.540)
0.100
(2.540)
0.018 ±0.002
(0.457)
0.100
(2.540)
0.040
(1.016)
1.31 MAX.
(33.27)
112
13
24
1.100
(27.940)
0.190 MAX.
(4.826)
0.010
(0.254)
+0.002
–0.001
SEATING
PLANE
0.025
(
0.635
)
(unless otherwise indicated):
2 place decimal (.XX) ±0.010 (±0.254)
3 place decimal (.XXX) ±0.005 (±0.127)
Kovar alloy
50 microinches (minimum) gold plating
over 100 microinches (nominal) nickel plating
0.80 MAX.
(20.32)
0.015
(0.381)
MAX. radius
for any pin
1.31 MAX.
(33.02)
0.100 TYP.
(2.540)
0.100
(2.540)
0.210 MAX.
(5.334)
0.040
(1.016)
0.020 TYP.
(0.508)
0.020
(0.508)
24 13
121
PIN 1
INDEX
0.130 TYP.
(3.302)
(unless otherwise indicated):
2 place decimal (.XX) ±0.010 (±0.254)
3 place decimal (.XXX) ±0.005 (±0.127)
Kovar alloy
50 microinches (minimum) gold plating
over 100 microinches (nominal) nickel plating
0.060 TYP.
(1.524)
0.010 TYP.
(0.254)
CDS-1401
14-Bit, Fast-Settling Correlated Double Sampling Circuit
. makes no representation that the use of its products in the circuits described herein, or the use of other
technical information contained herein, will not infringe upon existing or future patent rights. The descriptions contained herein do not
imply the granting of licenses to make, use, or sell equipment constructed in accordance therewith. Specifi cations are subject to change
without notice.
www.datel.com • e-mail: help@datel.com
®®
DATEL
11 Cabot Boulevard, Mansfi eld, MA 02048-1151 USA
ITAR and ISO 9001/14001 REGISTERED
01 Apr 2011 MDA_CDS-1401.B02 Page 8 of 8