AD620_04 AD [Analog Devices], AD620_04 Datasheet - Page 14

• Manufacturer Part Number: AD620_04
• Description: Low Cost Low Power Instrumentation Amplifier
• Manufacturer: AD [Analog Devices]

AD620
Regardless of the system in which it is being used, the AD620
provides greater accuracy at low power and price. In simple
systems, absolute accuracy and drift errors are by far the most
significant contributors to error. In more complex systems
with an intelligent processor, an autogain/autozero cycle will
remove all absolute accuracy and drift errors, leaving only the
resolution errors of gain, nonlinearity, and noise, thus allowing
full 14-bit accuracy.
Table 3. Make vs. Buy Error Budget
Error Source
ABSOLUTE ACCURACY at T
Input Offset Voltage, µV
Output Offset Voltage, µV
Input Offset Current, nA
CMR, dB
DRIFT TO 85°C
Gain Drift, ppm/°C
Input Offset Voltage Drift, µV/°C
Output Offset Voltage Drift, µV/°C
RESOLUTION
Gain Nonlinearity, ppm of Full Scale
Typ 0.1 Hz to 10 Hz Voltage Noise, µV p-p
G = 100, V
(All errors are min/max and referred to input.)
PRECISION BRIDGE TRANSDUCER
R = 350 Ω
R = 350 Ω
S
= ±15 V
.
10V
R = 350 Ω
R = 350 Ω
A
= 25°C
AD620 Circuit Calculation
125 µV/20 mV
1000 µV/100 mV/20 mV
2 nA ×350 Ω/20 mV
110 dB(3.16 ppm) ×5 V/20 mV
(50 ppm + 10 ppm) ×60°C
1 µV/°C × 60°C/20 mV
15 µV/°C × 60°C/100 mV/20 mV
40 ppm
0.28 µV p-p/20 mV
SUPPLY CURRENT = 1.3mA MAX
499 Ω
R
G
Figure 39. Make vs. Buy
AD620A MONOLITHIC
INSTRUMENTATION
AMPLIFIER, G = 100
Rev. G | Page 14 of 20
AD620A
REFERENCE
Note that for the homebrew circuit, the OP07 specifications for
input voltage offset and noise have been multiplied by √2. This
is because a three op amp type in-amp has two op amps at its
inputs, both contributing to the overall input error.
“Homebrew” Circuit Calculation
Total Absolute Error
100 ppm/°C Track × 60°C
Total Drift Error
(0.38 µV p-p × √2)/20 mV
Total Resolution Error
Grand Total Error
(150 µV × √2)/20 mV
((150 µV × 2)/100)/20 mV
(6 nA ×350 Ω)/20 mV
(0.02% Match × 5 V)/20 mV/100
(2.5 µV/°C × √2 × 60°C)/20 mV
(2.5 µV/°C × 2 × 60°C)/100 mV/20 mV
40 ppm
100 Ω **
**DISCRETE 1% RESISTOR, 100ppm/ ° C TRACKING
*0.02% RESISTOR MATCH, 3ppm/ ° C TRACKING
"HOMEBREW" IN-AMP, G = 100
SUPPLY CURRENT = 15mA MAX
OP07D
OP07D
10k Ω **
10k Ω **
AD620
Error, ppm of Full Scale
14,663
10k Ω *
10k Ω *
6,250
7,559
3,600
3,000
7,050
500
791
450
18
40
14
54
OP07D
10k Ω *
Homebrew
10k Ω *
10,607
11,310
10,607
16,757
28,134
6,000
150
500
150
53
40
27
67