AD622AR [ADI]

Low Cost Instrumentation Amplifier; 低成本仪表放大器
AD622AR
型号: AD622AR
厂家: ADI    ADI
描述:

Low Cost Instrumentation Amplifier
低成本仪表放大器

仪表放大器 放大器电路 光电二极管
文件: 总11页 (文件大小:154K)
中文:  中文翻译
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Low Cost  
Instrumentation Amplifier  
a
AD622  
CONNECTION DIAGRAM  
FEATURES  
Easy to Use  
Low Cost Solution  
Higher Performance than Two or Three Op Amp Design  
Unity Gain with No External Resistor  
Optional Gains with One External Resistor  
(Gain Range 2 to 1000)  
Wide Power Supply Range (؎2.6 V to ؎15 V)  
Available in 8-Lead PDIP and SOIC  
Low Power, 1.5 mA max Supply Current  
1
2
3
4
8
7
6
5
R
G
R
G
+V  
–IN  
+IN  
S
OUTPUT  
REF  
–V  
S
AD622  
GOOD DC PERFORMANCE  
0.15% Gain Accuracy (G = 1)  
125 V max Input Offset Voltage  
1.0 V/؇C max Input Offset Drift  
5 nA max Input Bias Current  
66 dB min Common-Mode Rejection Ratio (G = 1)  
NOISE  
PRODUCT DESCRIPTION  
12 nV/Hz @ 1 kHz Input Voltage Noise  
0.60 V p-p Noise (0.1 Hz to 10 Hz, G = 10)  
The AD622 is a low cost, moderately accurate instrumentation  
amplifier that requires only one external resistor to set any gain  
between 2 and 1,000. Or for a gain of 1, no external resistor  
is required. The AD622 is a complete difference or subtracter  
amplifier “system” while providing superior linearity and common-  
mode rejection by incorporating precision laser trimmed resistors.  
EXCELLENT AC CHARACTERISTICS  
800 kHz Bandwidth (G = 10)  
10 s Settling Time to 0.1% @ G = 1–100  
1.2 V/s Slew Rate  
The AD622 replaces low cost, discrete, two or three op amp  
instrumentation amplifier designs and offers good common-  
mode rejection, superior linearity, temperature stability, reliabil-  
ity, and board area consumption. The low cost of the AD622  
eliminates the need to design discrete instrumentation amplifi-  
ers to meet stringent cost targets. While providing a lower cost  
solution, it also provides performance and space improvements.  
APPLICATIONS  
Transducer Interface  
Low Cost Thermocouple Amplifier  
Industrial Process Controls  
Difference Amplifier  
Low Cost Data Acquisition  
REV. C  
Information furnished by Analog Devices is believed to be accurate and  
reliable. However, no responsibility is assumed by Analog Devices for its  
use, nor for any infringements of patents or other rights of third parties  
which may result from its use. No license is granted by implication or  
otherwise under any patent or patent rights of Analog Devices.  
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.  
Tel: 781/329-4700  
Fax: 781/326-8703  
World Wide Web Site: http://www.analog.com  
© Analog Devices, Inc., 1999  
(typical @ +25؇C, V = ؎15 V, and R = 2 kunless otherwise noted)  
AD622–SPECIFICATIONS  
S
L
AD622  
Typ  
Model  
Conditions  
Min  
Max  
Units  
GAIN  
G = 1 + (50.5 k/RG)  
Gain Range  
1
1000  
Gain Error1  
G = 1  
VOUT = ±10 V  
0.05  
0.2  
0.2  
0.2  
0.15  
0.50  
0.50  
0.50  
%
%
%
%
G = 10  
G = 100  
G = 1000  
Nonlinearity,  
G = 1–1000  
G = 1–100  
Gain vs. Temperature  
VOUT = ±10 V  
RL = 10 kΩ  
RL = 2 kΩ  
Gain = 1  
10  
10  
ppm  
ppm  
ppm/°C  
ppm/°C  
10  
–50  
Gain >11  
VOLTAGE OFFSET  
Input Offset, VOSI  
Average TC  
Output Offset, VOSO  
Average TC  
(Total RTI Error = VOSI + VOSO/G)  
VS = ±5 V to ±15 V  
VS = ±5 V to ±15 V  
VS = ±5 V to ±15 V  
VS = ±5 V to ±15 V  
60  
125  
1.0  
1500  
15  
µV  
µV/°C  
µV  
600  
µV/°C  
Offset Referred to the  
Input vs.  
Supply (PSR)  
G = 1  
G = 10  
G = 100  
G = 1000  
VS = ±5 V to ±15 V  
80  
95  
110  
110  
100  
120  
140  
140  
dB  
dB  
dB  
dB  
INPUT CURRENT  
Input Bias Current  
Average TC  
Input Offset Current  
Average TC  
2.0  
3.0  
0.7  
2.0  
5.0  
2.5  
nA  
pA/°C  
nA  
pA/°C  
INPUT  
Input Impedance  
Differential  
Common-Mode  
Input Voltage Range2  
Over Temperature  
10ʈ2  
10ʈ2  
GʈpF  
GʈpF  
V
V
V
V
VS = ±2.6 V to ±5 V  
VS = ±5 V to ±18 V  
–VS + 1.9  
–VS + 2.1  
–VS + 1.9  
–VS + 2.1  
+VS – 1.2  
+VS – 1.3  
+VS – 1.4  
+VS – 1.4  
Over Temperature  
Common-Mode Rejection  
Ratio DC to 60 Hz with  
1 kSource Imbalance  
G = 1  
VCM = 0 V to ±10 V  
66  
86  
103  
103  
78  
98  
118  
118  
dB  
dB  
dB  
dB  
G = 10  
G = 100  
G = 1000  
OUTPUT  
Output Swing  
RL = 10 k,  
VS = ±2.6 V to ±5 V  
–VS + 1.1  
–VS + 1.4  
–VS + 1.2  
–VS + 1.6  
+VS – 1.2  
+VS – 1.3  
+VS – 1.4  
+VS – 1.5  
V
V
V
V
Over Temperature  
VS = ±5 V to ±18 V  
Over Temperature  
Short Current Circuit  
±18  
mA  
–2–  
REV. C  
AD622  
AD622  
Typ  
Model  
Conditions  
Min  
Max  
Units  
DYNAMIC RESPONSE  
Small Signal –3 dB Bandwidth  
G = 1  
G = 10  
G = 100  
G = 1000  
Slew Rate  
1000  
800  
120  
12  
kHz  
kHz  
kHz  
kHz  
V/µs  
1.2  
Settling Time to 0.1%  
G = 1–100  
10 V Step  
10  
µs  
NOISE  
Total RTI Noise = (e2 )+(eno / G)2  
Voltage Noise, 1 kHz  
Input, Voltage Noise, eni  
Output, Voltage Noise, eno  
RTI, 0.1 Hz to 10 Hz  
G = 1  
ni  
12  
72  
nV/Hz  
nV/Hz  
4.0  
0.6  
0.3  
100  
10  
µV p-p  
µV p-p  
µV p-p  
fA/Hz  
pA p-p  
G = 10  
G = 100–1000  
Current Noise  
f = 1 kHz  
0.1 Hz to 10 Hz  
REFERENCE INPUT  
RIN  
IIN  
20  
+50  
kΩ  
µA  
V
VIN+, VREF = 0  
+60  
+VS – 1.6  
Voltage Range  
Gain to Output  
–VS + 1.6  
1 ± 0.0015  
POWER SUPPLY  
Operating Range3  
Quiescent Current  
Over Temperature  
±2.6  
±18  
1.3  
1.5  
V
mA  
mA  
VS = ±2.6 V to ±18 V  
0.9  
1.1  
TEMPERATURE RANGE  
For Specified Performance  
–40 to +85  
°C  
NOTES  
1Does not include effects of external resistor RG.  
2One input grounded. G = 1.  
3This is defined as the same supply range that is used to specify PSR.  
Specifications subject to change without notice.  
REV. C  
–3–  
AD622  
ABSOLUTE MAXIMUM RATINGS1  
ORDERING GUIDE  
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±18 V  
Internal Power Dissipation2 . . . . . . . . . . . . . . . . . . . . 650 mW  
Input Voltage (Common Mode) . . . . . . . . . . . . . . . . . . . ±VS  
Differential Input Voltage . . . . . . . . . . . . . . . . . . . . . . . ±25 V  
Output Short Circuit Duration . . . . . . . . . . . . . . . . Indefinite  
Storage Temperature Range (N, R) . . . . . . . –65°C to +125°C  
Operating Temperature Range  
Temperature  
Range  
Package  
Option*  
Model  
AD622AN  
AD622AR  
AD622AR-REEL  
AD622AR-REEL7  
–40°C to +85°C  
–40°C to +85°C  
–40°C to +85°C  
–40°C to +85°C  
N-8  
SO-8  
13" Reel  
7" Reel  
AD622A . . . . . . . . . . . . . . . . . . . . . . . . . . . 40°C to +85°C  
Lead Temperature Range  
*N = Plastic DIP, SO = Small Outline.  
(Soldering 10 seconds) . . . . . . . . . . . . . . . . . . . . . . . +300°C  
NOTES  
1Stresses above those listed under Absolute Maximum Ratings may cause perma-  
nent damage to the device. This is a stress rating only; functional operation of the  
device at these or any other conditions above those indicated in the operational  
section of this specification is not implied. Exposure to absolute maximum rating  
conditions for extended periods may affect device reliability.  
2Specification is for device in free air:  
8-Lead Plastic Package: θJA = 95°C/Watt  
8-Lead SOIC Package: θJA = 155°C/Watt  
CAUTION  
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily  
accumulate on the human body and test equipment and can discharge without detection.  
Although the AD622 features proprietary ESD protection circuitry, permanent damage may  
occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD  
precautions are recommended to avoid performance degradation or loss of functionality.  
WARNING!  
ESD SENSITIVE DEVICE  
(@ +25؇C, V = ؎15 V, R = 2 k, unless otherwise noted)  
Typical Characteristics  
S
L
50  
40  
50  
SAMPLE SIZE = 191  
SAMPLE SIZE = 383  
40  
30  
20  
10  
0
30  
20  
10  
0
60  
80  
100  
120  
140  
0
0.40  
–1.00  
–0.80  
–0.40  
0.80  
1.00  
COMMON-MODE REJECTION RATIO – dB  
OUTPUT OFFSET VOLTAGE – mV  
Figure 1. Typical Distribution of Output Offset Voltage  
Figure 2. Typical Distribution of Common-Mode Rejection  
REV. C  
–4–  
AD622  
(@ +25؇C, V = ؎15 V, R = 2 k, unless otherwise noted)  
Typical Characteristics  
S
L
2
140  
120  
G = 1000  
1.5  
G = 100  
G = 10  
100  
80  
60  
40  
20  
0
1
0.5  
0
G = 1  
0
1
2
3
4
5
0.1  
1
10  
100  
1k  
10k  
100k  
1M  
WARM-UP TIME – Minutes  
FREQUENCY – Hz  
Figure 3. Change in Input Offset Voltage vs. Warm-Up  
Time  
Figure 6. CMR vs. Frequency, RTI, Zero to 1 kSource  
Imbalance  
1000  
180  
160  
140  
GAIN = 1  
G = 1000  
100  
120  
GAIN = 10  
100  
G = 100  
80  
10  
G = 10  
GAIN = 100, 1,000  
60  
40  
GAIN = 1000  
BW LIMIT  
G = 1  
1
0
0.1  
1
10  
100  
1k  
10k  
100k  
1
10  
100  
1k  
10k  
100k  
1M  
FREQUENCY – Hz  
FREQUENCY – Hz  
Figure 7a. Positive PSR vs. Frequency, RTI (G = 1–1000)  
Figure 4. Voltage Noise Spectral Density vs. Frequency,  
(G = 1–1000)  
1000  
180  
160  
140  
120  
100  
100  
G = 1000  
80  
G = 100  
60  
G = 10  
40  
G = 1  
10  
0
0.1  
0
10  
100  
FREQUENCY – Hz  
1000  
1
10  
100  
1k  
10k  
100k  
1M  
FREQUENCY – Hz  
Figure 5. Current Noise Spectral Density vs. Frequency  
Figure 7b. Negative PSR vs. Frequency, RTI (G = 1–1000)  
–5–  
REV. C  
(@ +25؇C, VS = ؎15 V, RL = 2 k, unless otherwise noted)  
AD622–Typical Characteristics  
1000  
1000  
100  
100  
10  
1
10  
0
100  
1
1
10  
100  
1000  
1k  
10k  
100k  
1M  
10M  
GAIN  
FREQUENCY – Hz  
Figure 8. Gain vs. Frequency  
Figure 11. Settling Time to 0.1% vs. Gain, for a 10 V Step  
30  
V
= ؎15V  
S
10µV  
2V  
G = 10  
100  
90  
20  
ø
10  
10  
0%  
0
10  
100  
1k  
10k  
LOAD RESISTANCE – ⍀  
Figure 9. Output Voltage Swing vs. Load Resistance  
Figure 12. Gain Nonlinearity, G = 1, RL = 10 kΩ  
(20 µV = 2 ppm)  
20  
15  
10k⍀  
0.01%  
1k⍀  
10T  
10k⍀  
0.1%  
INPUT  
20V p-p  
100k⍀  
0.1%  
V
OUT  
TO 0.1%  
+V  
S
11k1k⍀  
100⍀  
0.1%  
10  
0.1%  
0.1%  
G=1  
G=1000  
5
0
AD622  
G=10  
G=100  
51.15115.62k⍀  
0
5
10  
15  
20  
–V  
S
OUTPUT STEP SIZE – Volts  
Figure 10. Settling Time vs. Step Size (G = 1)  
Figure 13. Settling Time Test Circuit  
REV. C  
–6–  
AD622  
THEORY OF OPERATION  
Make vs. Buy: A Typical Application Error Budget  
The AD622 is a monolithic instrumentation amplifier based on  
a modification of the classic three op-amp approach. Absolute  
value trimming allows the user to program gain accurately (to  
0.5% at G = 100) with only one resistor. Monolithic construc-  
tion and laser wafer trimming allow the tight matching and  
tracking of circuit components, thus insuring its performance.  
The AD622 offers a cost and performance advantages over  
discrete “two op-amp” instrumentation amplifier designs along  
with smaller size and less components. In a typical application  
shown in Figure 14, a gain of 10 is required to receive and am-  
plify a 0–20 mA signal from the AD694 current transmitter.  
The current is converted to a voltage in a 50 shunt. In appli-  
cations where transmission is over long distances, line imped-  
ance can be significant so that differential voltage measurement  
is essential. Where there is no connection between the ground  
returns of transmitter and receiver, there must be a dc path from  
each input to ground, implemented in this case using two 1 kΩ  
resistors. The error budget detailed in Table I shows how to  
calculate the effect various error sources have on circuit accuracy.  
The input transistors Q1 and Q2 provide a single differential-  
pair bipolar input for high precision. Feedback through the  
Q1-A1-R1 loop and the Q2-A2-R2 loop maintains constant  
collector current of the input devices Q1, Q2 thereby impressing  
the input voltage across the external gain-setting resistor RG.  
This creates a differential gain from the inputs to the A1/A2  
outputs given by G = (R1 + R2)/RG + 1. The unity-gain sub-  
tracter A3 removes any common-mode signal, yielding a  
single-ended output referred to the REF pin potential.  
The AD622 provides greater accuracy at lower cost. The higher  
cost of the “homebrew” circuit is dominated in this case by the  
matched resistor network. One could also realize a “homebrew”  
design using cheaper discrete resistors which would be either  
trimmed or hand selected to give high common-mode rejection.  
This level of common-mode rejection would however degrade  
significantly over temperature due to the drift mismatch of the  
discrete resistors.  
The value of RG also determines the transconductance of the  
preamp stage. As RG is reduced for larger gains, the transcon-  
ductance increases asymptotically to that of the input transistors.  
This has three important advantages: (a) Open-loop gain is  
boosted for increasing programmed gain, thus reducing gain-  
related errors. (b) The gain-bandwidth product (determined by  
C1, C2 and the preamp transconductance) increases with pro-  
grammed gain, thus optimizing frequency response. (c) The  
input voltage noise is reduced to a value of 12 nV/Hz, deter-  
mined mainly by the collector current and base resistance of the  
input devices.  
Note that for the homebrew circuit, the LT1013 specification  
for noise has been multiplied by 2. This is because a “two op-  
amp” type instrumentation amplifier has two op amps at its  
inputs, both contributing to the overall noise.  
The internal gain resistors, R1 and R2, are trimmed to an abso-  
lute value of 25.25 k, allowing the gain to be programmed  
accurately with a single external resistor.  
1/2  
LT1013  
R
L2  
10  
1k⍀  
V
IN  
1/2  
AD694  
0–20mA  
TRANSMITTER  
1k⍀  
1k⍀  
LT1013  
R
G
0–20mA  
AD622  
50⍀  
5.62k⍀  
1k⍀  
9k*  
REFERENCE  
R
L2  
1k*  
1k*  
9k*  
10⍀  
*0.1% RESISTOR MATCH, 50ppm/ C TRACKING  
0–20 mA Current Loop  
AD622 Monolithic  
“Homebrew” In Amp, G = 10  
with 50 Shunt Impedance  
Instrumentation Amplifier,  
G = 9.986  
Figure 14. Make vs. Buy  
–7–  
REV. C  
AD622  
Table I. Make vs. Buy Error Budget  
Total Error  
in ppm  
Total Error  
in ppm  
AD622 Circuit  
Calculation  
“Homebrew” Circuit  
Calculation  
Relative to 1 V FS Relative to 1 V FS  
AD622 Homebrew  
Error Source  
ABSOLUTE ACCURACY at TA = +25°C  
Total RTI Offset Voltage, µV  
Input Offset Current, nA  
CMR, dB  
250 µV + 1500 µV/10  
2.5 nA × 1 kΩ  
86 dB50 ppm × 0.5 V  
800 µV × 2  
15 nA × 1 kΩ  
(0.1% Match × 0.5 V)/10 V  
400  
2.5  
25  
1600  
15  
50  
Total Absolute Error  
427.5  
1665  
DRIFT TO +85°C  
Gain Drift, ppm/°C  
Total RTI Offset Voltage, µV/°C  
Input Offset Current, pA/°C  
(50 ppm + 5 ppm) × 60°C  
(2 µV/°C + 15 µV/°C/10) × 60°C 9 µV/°C × 2 × 60°C  
2 pA/°C × 1 kΩ × 60°C  
(50 ppm)/°C × 60°C  
3300  
210  
0.12  
3000  
1080  
9.3  
155 pA/°C × 1 kΩ × 60°C  
Total Drift Error  
3510.12  
4089.3  
RESOLUTION  
Gain Nonlinearity, ppm of Full Scale  
10 ppm  
20 ppm  
10  
20  
Typ 0.1 Hz–10 Hz Voltage Noise, µV p-p 0.6 µV p-p  
0.55 µV p-p × √2  
0.6  
0.778  
Total Resolution Error  
Grand Total Error  
10.6  
20.778  
5575  
3948  
GAIN SELECTION  
Table II. Required Values of Gain Resistors  
The AD622’s gain is resistor programmed by RG, or more pre-  
cisely, by whatever impedance appears between Pins 1 and 8.  
The AD622 is designed to offer gains as close as possible to  
popular integer values using standard 1% resistors. Table II  
shows required values of RG for various gains. Note that for  
G = 1, the RG pins are unconnected (RG = ). For any arbitrary  
gain RG can be calculated by using the formula  
Desired  
Gain  
1% Std Table  
Value of RG,  
Calculated  
Gain  
2
5
10  
20  
51.1 k  
12.7 k  
5.62 k  
2.67 k  
1.988  
4.976  
9.986  
19.91  
33  
40  
50  
1.58 k  
1.3 k  
1.02 k  
32.96  
39.85  
50.50  
50.5 kΩ  
G 1  
RG  
=
To minimize gain error avoid high parasitic resistance in series  
with RG, and to minimize gain drift, RG should have a low  
TC—less than 10 ppm/°C for the best performance.  
65  
100  
200  
787  
511  
255  
65.17  
99.83  
199.0  
500  
1000  
102  
51.1  
496.1  
989.3  
REV. C  
–8–  
AD622  
INPUT AND OUTPUT OFFSET VOLTAGE  
RF INTERFERENCE  
The low errors of the AD622 are attributed to two sources,  
input and output errors. The output error is divided by G when  
referred to the input. In practice, the input errors dominate at  
high gains and the output errors dominate at low gains. The  
total VOS for a given gain is calculated as:  
The circuit of Figure 15 is recommended for AD622 series in-  
amps and provides good RFI suppression at the expense of  
reducing the (differential) bandwidth. In addition, this RC input  
network also provides additional input overload protection (see  
input protection section). Resistors R1 and R2 were selected to  
be high enough in value to isolate the circuit’s input from ca-  
pacitors C1–C3, but without significantly increasing the circuit’s  
noise.  
Total Error RTI = input error + (output error/G)  
Total Error RTO = (input error × G) + output error  
REFERENCE TERMINAL  
+V  
C1  
S
1000pF 5%  
The reference terminal potential defines the zero output voltage  
and is especially useful when the load does not share a precise  
ground with the rest of the system. It provides a direct means of  
injecting a precise offset to the output, with an allowable range  
of 2 V within the supply voltages. Parasitic resistance should be  
kept to a minimum for optimum CMR.  
0.33F  
0.01F  
R1  
4.02k1%  
3
1
–IN  
+IN  
7
C3  
AD622  
R
G
6
V
0.047F  
OUT  
5
8
2
INPUT PROTECTION  
4
R2  
4.02k1%  
C2  
The AD622 features 400 of series thin film resistance at its  
inputs, and will safely withstand input overloads of up to ±25 V  
or ±60 mA for up to an hour. This is true for all gains and  
power on and off, which is particularly important since the  
signal source and amplifier may be powered separately. For  
continuous input overload, the current should not exceed 6 mA  
(IIN VIN/400 ). For input overloads beyond the supplies,  
clamping the inputs to the supplies (using a diode such as an  
IN4148) will reduce the required resistance, yielding lower  
noise.  
1000pF 5%  
0.33F  
0.01F  
LOCATE C1–C3 AS CLOSE TO  
THE INPUT PINS AS POSSIBLE  
–V  
S
Figure 15. RFI Suppression Circuit for AD622 Series In-Amps  
R1/R2 and C1/C2 form a bridge circuit whose output appears  
across the in-amp’s input pins. Any mismatch between the C1/  
R1 and C2/R2 time constant will unbalance the bridge and  
reduce common-mode rejection. C3 insures that any RF signals  
are common mode (the same on both in-amp inputs) and are  
not applied differentially.  
This low pass network has a –3 dB BW equal to: 1/(2π (R1 +  
R2) (C3 + C1 + C2)). Using a C3 value of 0.047 µF as shown,  
the –3 dB signal BW of this circuit is approximately 400 Hz.  
When operating at a gain of 1000, the typical dc offset shift over  
a frequency range of 1 Hz to 20 MHz will be less than 1.5 µV  
RTI and the circuit’s RF signal rejection will be better than  
71 dB. At a gain of 100, the dc offset shift is well below 1 mV  
RTI and RF rejection better than 70 dB.  
The 3 dB signal bandwidth of this circuit may be increased to  
900 Hz by reducing resistors R1 and R2 to 2.2 k. The perfor-  
mance is similar to that using 4 kresistors, except that the  
circuitry preceding the in-amp must drive a lower impedance  
load.  
This circuit should be built using a PC board with a ground  
plane on both sides. All component leads should be made as  
short as possible. Resistors R1 and R2 can be common 1%  
metal film units but capacitors C1 and C2 need to be ±5%  
tolerance devices to avoid degrading the circuit’s common-mode  
rejection. Either the traditional 5% silver micas, miniature size  
micas, or the new Panasonic ±2% PPS film capacitors are  
recommended.  
–9–  
REV. C  
AD622  
GROUNDING  
GROUND RETURNS FOR INPUT BIAS CURRENTS  
Input bias currents are those currents necessary to bias the input  
transistors of an amplifier. There must be a direct return path  
for these currents; therefore when amplifying “floating” input  
sources such as transformers, or ac-coupled sources, there must  
be a dc path from each input to ground as shown in Figure 17.  
Refer to the Instrumentation Amplifier Application Guide (free  
from Analog Devices) for more information regarding in amp  
applications.  
Since the AD622 output voltage is developed with respect to the  
potential on the reference terminal, it can solve many grounding  
problems by simply tying the REF pin to the appropriate “local  
ground.” The REF pin should however be tied to a low imped-  
ance point for optimal CMR.  
The use of ground planes is recommended to minimize the  
impedance of ground returns (and hence the size of dc errors).  
In order to isolate low level analog signals from a noisy digital  
environment, many data-acquisition components have separate  
analog and digital ground returns (Figure 16). All ground pins  
from mixed signal components such as analog to digital converters  
should be returned through the “high quality” analog ground  
plane. Maximum isolation between analog and digital is  
achieved by connecting the ground planes back at the supplies.  
The digital return currents from the ADC which flow in the  
analog ground plane will in general have a negligible effect on  
noise performance.  
+V  
S
–INPUT  
2
1
7
R
6
G
V
AD622  
OUT  
5
8
3
LOAD  
4
+INPUT  
REFERENCE  
–V  
S
TO POWER  
SUPPLY  
GROUND  
Figure 17a. Ground Returns for Bias Currents with  
Transformer Coupled Inputs  
ANALOG P.S.  
–5V  
DIGITAL P.S.  
+5V  
+5V  
C
C
+V  
S
0.1F  
0.1F  
–INPUT  
2
1
7
0.1F  
R
6
AD622  
G
V
OUT  
5
8
3
LOAD  
V
AGND  
DGND  
V
GND  
DD  
DD  
4
12  
+INPUT  
AD622  
V
1
REFERENCE  
IN  
PROCESSOR  
AD7892-2  
–V  
S
V
2
IN  
TO POWER  
SUPPLY  
GROUND  
Figure 16. Basic Grounding Practice  
Figure 17b. Ground Returns for Bias Currents with  
Thermocouple Inputs  
+V  
S
–INPUT  
R
G
V
OUT  
AD622  
LOAD  
+INPUT  
REFERENCE  
100k⍀  
100k⍀  
–V  
S
TO POWER  
SUPPLY  
GROUND  
Figure 17c. Ground Returns for Bias Currents with  
AC Coupled Inputs  
REV. C  
–10–  
AD622  
OUTLINE DIMENSIONS  
Dimensions shown in inches and (mm).  
Plastic DIP (N-8) Package  
0.430 (10.92)  
0.348 (8.84)  
8
5
4
0.280 (7.11)  
0.240 (6.10)  
1
0.325 (8.25)  
0.300 (7.62)  
0.060 (1.52)  
0.015 (0.38)  
PIN 1  
0.195 (4.95)  
0.115 (2.93)  
0.210 (5.33)  
MAX  
0.130  
(3.30)  
MIN  
0.160 (4.06)  
0.115 (2.93)  
0.015 (0.381)  
0.008 (0.204)  
SEATING  
PLANE  
0.100  
(2.54)  
BSC  
0.022 (0.558)  
0.014 (0.356)  
0.070 (1.77)  
0.045 (1.15)  
SOIC (SO-8) Package  
0.1968 (5.00)  
0.1890 (4.80)  
8
1
5
4
0.1574 (4.00)  
0.1497 (3.80)  
0.2440 (6.20)  
0.2284 (5.80)  
PIN 1  
0.0688 (1.75)  
0.0532 (1.35)  
0.0196 (0.50)  
x 45°  
0.0098 (0.25)  
0.0040 (0.10)  
0.0099 (0.25)  
8°  
0°  
0.0500  
(1.27)  
BSC  
0.0192 (0.49)  
0.0138 (0.35)  
SEATING  
PLANE  
0.0098 (0.25)  
0.0075 (0.19)  
0.0500 (1.27)  
0.0160 (0.41)  
–11–  
REV. C  

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