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