AN2400

Filter design

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Filter design

Here, a 6th-order low pass filter is used. A low pass filter passes all the signals below the

cutoff frequency and attenuates the signal above cutoff frequency. The reason behind using

a sixth order filter is to have a steeper slope and therefore a better frequency response. It is

created by cascading six first-order low pass filters as shown in figure below:

Figure 8.

Sixth order low pass RC-filter

Calculating resistance of low pass filter:

Cutoff frequency:

so:

R = 1 / (2

π C f

= 1 / (2

π (.01 µF) (8 kHz) )

= 1990

Ω

R = 1.9 k

Ω

1.9 k

Ω is not a standard value, so 1.8 kΩ is used.

RR

R

R

R

R

CC

C

C

C

C