8.2.1 Design Requirements

For the traces shown in Figure 8-2 and Figure 8-3:

• Common-mode rejection of at least 80 dB

• Gain of 250

8.2.2 Detailed Design Procedure

8.2.2.1 Setting the Gain

Gain is set by connecting an external resistor, RG:

g = 5 + 80 kΩ / RG

(1)

Commonly used gains and RG resistor values are shown in Figure 8-1.

The 80-kΩ term in Equation 1 comes from the internal metal-film resistors, which are laser-trimmed to accurate

absolute values. The accuracy and temperature coefficient of these resistors are included in the gain accuracy

and drift specifications.

The stability and temperature drift of the external gain setting resistor, RG, also affects gain. The RG contribution

to gain accuracy and drift can be directly inferred from Equation 1. Low resistor values required for high gain can

make wiring resistance important. Sockets add to the wiring resistance, which contributes additional gain error in

gains of approximately 100 or greater.

8.2.2.2 Offset Trimming

The INAx126 family features low offset voltage and offset voltage drift. Most applications require no external

offset adjustment. Figure 8-2 shows an optional circuit for trimming the output offset voltage. The voltage applied

to the Ref pin is added to the output signal. An operational amplifier buffer provides low impedance at the Ref pin

to preserve good common-mode rejection.

10kΩ

OPA237

±10mV

Adjustment Range

100Ω

100Ω

100µA

1/2 REF200

100µA

1/2 REF200

V+

V–

R

G

INA126

Ref

V

O

V

IN

–

V

IN

+

Dual version has

external sense connection.

Figure 8-2. Optional Trimming of Output Offset Voltage

INA126, INA2126

SBOS062C – SEPTEMBER 2000 – REVISED JANUARY 2022

www.ti.com

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