AN3984 datasheet(7/46 Pages) STMICROELECTRONICS

Part #	AN3984

Description	The purpose of this document is to provide a tool to calculate

PDF	46 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

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7 / 46 page

AN3984

First-order filter design (LPF and HPF)

Doc ID 022240 Rev 1

7/46

First-order filter design (LPF and HPF)

The preliminary step to obtain the coefficients for the first-order low-pass filter or high-pass

filter is to define three constants obtained from the filter parameters:

Equation 7

In a first-order filter both the coefficients a2 and b2 are null.

The denominator coefficients are identical for both an LPF and an HPF designed for the

same cutoff frequency and they are computed as follows:

Equation 8

The numerator for an LPF can be calculated as follows:

Equation 9

The numerator for an HPF can be calculated as follows:

Equation 10

The coefficient used in APWorkbench can be calculated by applying these formulas:

Equation 11

()

⋅

tan

()

−

()

Coefficien

t a

Coefficien

t b

Coefficien

−

AN3984 Datasheet(PDF) 7 Page - STMicroelectronics