INA848 datasheet(13/33 Pages) TI

13 / 33 page

8 Detailed Description

8.1 Overview

The INA848 is a monolithic precision instrumentation amplifier incorporating a current-feedback input stage and

a four-resistor difference amplifier output stage. The differential input voltage is buffered by Q1 and Q2 and is

forced across RG, which causes a signal current to flow through RG, R1, and R2. The output difference amplifier

(A3) removes the common-mode component of the input signal and refers the output signal to the REF pin. The

VBE and voltage drop across R1 and R2 produce output voltages on A1 and A2 that are approximately 0.8 V

lower than the input voltages.

In common instrumentation amplifiers, an external gain resistor is used to set the gain. However, this external

gain resistor affects the gain drift due to the mismatch in tempertature coefficient between the external and

internal resistors. The INA848 integrates the gain setting resistor with a fixed gain of 2000, thus matching the

temperature drifts of the resistor network. This integration results in an total gain accuracy of 5 ppm/°C

(maximum).

8.2 Functional Block Diagram

3 k

+VS

íVS

+VS

íVS

+VS

íVS

+VS

íVS

+VS

Super-

NPN

Super-

NPN

+VS

í IN

+IN

REF

OUT

+VS

IB Cancellation

3 k

120 k

6 k

30.15

6 k

+VS

í VS

+VS

í VS

+ FIL

í FIL

íVS

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INA848

SBOS946 – SEPTEMBER 2020

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