# High pass active filter circuit

High pass filter attenuate or reject all frequencies below critical frequency and pass all above frequencies. Critical frequency fc where filter gain is -3dB or 0.707 . When output of RC series circuit is across R or resistor then it acts as high pass filter. Active high pass filter is combination of RC / RLC/ RL/ LC circuit and a active gain device (Operational amplifier or transistor amplifier) . Here we share active high pass circuit examples.

## High Pass active filter

Above circuit is first order active high pass filter using OPA2348 operational amplifier. Frequency response is given in graph -3dB gain is 6 kHz to 10 kHz. but critical frequency of RC circuit R1 and C1 is 20.4kHz. this difference is actually caused by Av = 2.7 gain of operational amplifier.

Fc = 1/ (2 \pi RC)

Critical frequency of active high pass filter when unity gain amplifier

Av = 1