All-Pass Filter (1st Order)

This is a 1st order ALL pass filter circuit. All frequencies are allowed at the same gain by this circuit. Here is the schematic diagram of the circuit:

All-Pass Filter (1st  Order)

We can change the signal’s phase using this circuit. This circuit can be used to correct the phase of the signal as well. At F(90) this circuit has a 90° phase shift. At high frequencies the phase shift is 180° and 0° at dc. The component values  R1 = R2 = R3 = R, with F(90) = 1/(2pR*C1) . F(90) is the frequency where we expect for 90 degrees phase shift. [Source: Texas Instruments Application Note]