40

30

R =

L

50kΩ

20

10

R =

L

5kΩ

0

R =

L

500kΩ

–10

–20

C =

L

10nF

C =

L

1nF

C =

L

100pF

100

1k

10k

100k

1M

10M

Frequency (Hz)

3

4

INA138

f

–3dB

=

f

–3dB

1

2 R C

π L L

V

O

R

C

L

L

13

INA138, INA168

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SBOS122E – DECEMBER 1999 – REVISED DECEMBER 2017

Product Folder Links: INA138 INA168

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Copyright © 1999–2017, Texas Instruments Incorporated

Typical Applications (continued)

8.2.2 Output Filter

Figure 12. Output Filter

8.2.2.1 Design Requirements

Filter the output of the INA1x8 devices.

8.2.2.2 Detailed Design Procedure

A low-pass filter can be formed at the output of the INA1x8 devices simply by placing a capacitor of the desired

value in parallel with the load resistor. First determine the value of the load resistor needed to achieve the

desired gain. Refer to the table in Figure 9. Next, determine the capacitor value that will result in the desired

cutoff frequency according to the equation shown in Figure 12. Figure 13 illustrates various combinations of gain

settings (determined by RL) and filter capacitors.

8.2.2.3 Application Curve

Figure 13. Gain vs Frequency