Data Sheet

ADA4522-1/ADA4522-

2/ADA4522-4

analog.com

Rev I 37 of 48

APPLICATIONS INFORMATION

Single-Supply Instrumentation Amplifier

The extremely low offset voltage and drift, high open-loop gain, high common-mode rejection, and high power

supply rejection of the ADA4522-1/ADA4522-2/ADA4522-4 make them excellent op amp choices as discrete, single-

supply instrumentation amplifiers.

Figure 82

shows the classic 3-op-amp instrumentation amplifier using the ADA4522-1/ADA4522-2/ADA4522-4. The

key to high CMRR for the instrumentation amplifier are resistors that are well matched for both the resistive ratio

and relative drift. For true difference amplification, matching of the resistor ratio is very important, where R5/R2 =

R6/R4. The resistors are important in determining the performance over manufacturing tolerances, time, and

temperature. Assuming a perfect unity-gain difference amplifier with infinite common-mode rejection, a 1%

tolerance resistor matching results in only 34 dB of common-mode rejection. Therefore, at least 0.01% or

better resistors are recommended.

Figure 82.Discrete 3-Op-Amp Instrumentation Amplifier

To build a discrete instrumentation amplifier with external resistors without compromising on noise, pay close

attention to the resistor values chosen. RG1 and RG2each have thermal noise that is amplified by the total noise gain

of the instrumentation amplifier and, therefore, a sufficiently low value must be chosen to reduce thermal noise

contribution at the output while still providing an accurate measurement. Table 10 shows the external resistorsʼ

noise contribution referred to the output (RTO).

Table 10.Thermal Noise Contribution Example

RESISTOR

VALUE (kΩ)

RESISTOR THERMAL

NOISE (nV/√Hz)

THERMAL NOISE RTO

(nV/√Hz)

RG1

0.4

2.57

128.30

RG2

0.4

2.57

128.30

R1

10

12.83

25.66

R2

10

12.83

25.66

R3

10

12.83

25.66

R4

10

12.83

25.66

R5

20

18.14

18.14

R6

20

18.14

18.14

VIN1

VIN2

A1

A3

A2

RG1

RG2

R1

R3

R2

R4

R5

VOUT

R6

RG1 = RG2, R1 = R3, R2 = R4, R5 = R6

VOUT = (VIN2 – VIN1) (1 + R1/RG1) (R5/R2)