The phase angle of the resulting output signal at ƒc is +45 o. The cut-off frequency, corner frequency or -3dB point of a high pass filter can be found using the standard formula of: ƒc = 1/(2πRC). The frequency range “below” this cut-off point ƒc is generally known as the Stop Band while the frequency range “above” this cut-off point is generally known as the Pass Band. This lower cut-off frequency point is 70.7% or -3dB (dB = -20log V OUT/V IN) of the voltage gain allowed to pass. This filter has no output voltage from DC (0Hz), up to a specified cut-off frequency ( ƒc ) point. We have seen that the Passive High Pass Filter is the exact opposite to the low pass filter. However, to reduce the loading effect we can make the impedance of each following stage 10x the previous stage, so R 2 = 10*R 1 and C 2 = 1/10th of C 1. In practice, cascading passive filters together to produce larger-order filters is difficult to implement accurately as the dynamic impedance of each filter order affects its neighbouring network. The cut-off frequency point for a first order high pass filter can be found using the same equation as that of the low pass filter, but the equation for the phase shift is modified slightly to account for the positive phase angle as shown below.

However in practice, the filter response does not extend to infinity but is limited by the electrical characteristics of the components used. The frequency response curve for this filter implies that the filter can pass all signals out to infinity. It has a response curve that extends down from infinity to the cut-off frequency, where the output voltage amplitude is 1/√ 2 = 70.7% of the input signal value or -3dB (20 log (Vout/Vin)) of the input value.Īlso we can see that the phase angle ( Φ ) of the output signal LEADS that of the input and is equal to +45 o at frequency ƒc. Here the signal is attenuated or damped at low frequencies with the output increasing at +20dB/Decade (6dB/Octave) until the frequency reaches the cut-off point ( ƒc ) where again R = Xc. The Bode Plot or Frequency Response Curve above for a passive high pass filter is the exact opposite to that of a low pass filter.

Bode plot multisim tutorial