7.2.1 Setting The Gain

Gain of the INA2128 is set by connecting a single external resistor, RG, connected as shown:

(1)

Commonly-used gains and resistor values are shown in Figure 7-1.

The 50 kΩ term in Equation 1 comes from the sum of the two internal feedback resistors, A1 and A2. These

on-chip metal film resistors are laser-trimmed to accurate absolute values. The accuracy and temperature

coefficient of these resistors are included in the gain accuracy and drift specifications of the INA2128.

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

gain accuracy and drift can be directly inferred from the gain equation (1). Low resistor values required for high

gain can make wiring resistance important. Sockets add to the wiring resistance which will contribute additional

gain error in gains of approximately 100 or greater.

7.2.2 Dynamic Performance

The typical performance curve Figure 6-1 shows that despite its low quiescent current, the INA2128 achieves

wide bandwidth, even at high gain. This is due to its current feedback topology. Settling time also remains

excellent at high gain—see Figure 6-9.

7.2.3 Noise Performance

The INA2128 provides very low noise in most applications. Low frequency noise is approximately 0.2 µVpp

measured from 0.1 Hz to 10 Hz (G ≥ 100). This provides dramatically improved noise when compared to

state-of-the-art chopper-stabilized amplifiers.

7.2.4 Offset Trimming

The INA2128 is laser-trimmed for low offset voltage and offset voltage drift. Most applications require no external

offset adjustment. Figure 7-2 shows an optional circuit for trimming the output offset voltage. The voltage applied

to Ref terminal is summed with the output. The op amp buffer provides low impedance at the Ref terminal to

preserve good common-mode rejection.

Figure 7-2. Optional Trimming of Output Offset Voltage

INA2128

SBOS035B – DECEMBER 1995 – REVISED MAY 2023

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