TS616_08 datasheet(29/37 Pages) STMICROELECTRONICS

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TS616

Choosing the feedback circuit

29/37

9.1

The bias of an inverting amplifier

A resistance is necessary to achieve good input biasing, such as resistance R, shown in

Figure 66.

The magnitude of this resistance is calculated by assuming the negative and positive input

bias current. The aim is to compensate for the offset bias current, which could affect the

input offset voltage and the output DC component. Assuming Ib-, Ib+, Rin, Rfb and a zero

volt output, the resistance R is:

R = Rin // Rfb

Figure 66.

Compensation of the input bias current

9.2

Active filtering

Figure 67.

Low-pass active filtering - Sallen-Key

From the resistors Rfb and RG, we can directly calculate the gain of the filter in a classic non-

inverting amplification configuration:

We assume the following expression as the response of the system:

Load

Output

Rfb

Rin

Ib-

Ib+

Vcc+

Vcc-

TS616

Load

Output

Rfb

Rin

Ib-

Ib+

Vcc+

Vcc-

TS616

Rfb

910

TS616

OUT

Rfb

910

TS616

OUT

--------

Vout

Vin

-----------------

-----

()

------------

-----------------------------------------

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