V

V

V

CM

10µA

V

B

10µA

A

2

A

1

C

1

C

2

60k

60k

60k

60k

A

3

V

O

Ref

R

2

25k

R

1

25k

R

G

(External)

Q

2

Q

1

V

IN

V

IN

A

A

) + V

Output Swing Range A

Amplifier Linear Input Range: (V+) – 0.65V to (V–) + 0.98V

–

V

+

–

+

–

+

Input Bias Current

Compensation

Output Swing Range:

(V+) – 0.8V to (V–) + 0.35V

INA118

www.ti.com

SBOS027A – SEPTEMBER 2000 – REVISED JANUARY 2016

7 Detailed Description

7.1 Overview

Figure 25 shows a simplified representation of the INA118 and provides insight into its operation. Each input is

protected by two FET transistors that provide a low series resistance under normal signal conditions, preserving

excellent noise performance. When excessive voltage is applied, these transistors limit input current to

approximately 1.5 to 5 mA.

signal and refers the output signal to the Ref terminal.

7.2 Functional Block Diagram

Figure 25. INA118 Simplified Circuit Diagram

7.3 Feature Description

The INA118 input sections use junction field effect transistors (JFET) connected to provide protection up to

±40 V. The current-feedback architecture provides maximum bandwidth over the full range of gain settings.

7.4 Device Functional Modes

7.4.1 Noise Performance

The INA118 provides low noise in most applications. For differential source impedances less than 1 k

Ω, the

INA103 may provide lower noise. For source impedances greater than 50 k

Ω, the INA111 FET-Input

Instrumentation Amplifier may provide lower noise.

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