# Building all pass filter

#### DaniKowa

Joined Jul 1, 2021
41
Hi,

1) Supposing ti build a all pass filter to correct a phase signal (ex -90° to 0°or -180) .Is this correction is still fixed for all frequencies passing through the filter or not?

2) Is this filter buildable with discrete components instead the opamp?

#### crutschow

Joined Mar 14, 2008
27,950
.Is this correction is still fixed for all frequencies passing through the filter or not?
No, it varies with frequency.
Is this filter buildable with discrete components instead the opamp?
Yes.
But the opamp circuit will likely give a more ideal response.

Below is the LTspice simulation of an all-pass op amp filter:
Note that the phase varies from 180° to 0° as the frequency increases, while the amplitude is essentially constant.
If you interchange R1 and C1 the phase will vary from 0° to180° as the frequency increases.

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