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# High-Pass Filters (HPF) - Active High Pass Filter and Passive High Pass Filter

B.Sc (Hons, USJ) (Polymer Science and Technology, Chemistry, Physics)
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Last Updated On : January 20, 2023
Published Date : July 25, 2022

A high-pass filter is a filter that significantly attenuates or rejects all frequencies below fc (critical frequency) and passes all frequencies above fc. The pass band of a high-pass filter is all frequencies above the critical frequency.

## Active high pass filters

### Calculation of transfer function of an active high-pass filter

Let’s take,

To remove complex numbers in the equation, the 4th power of the complex part is taken and takes the 4th root. This mathematical operation can be done separately for two complex parts.

To remove the other complex part in the equation, the same operation can be done.

Therefore, the voltage gain of an active high pass filter can be written in,

The above equation gives the transfer function of an active high-pass filter. The voltage gain at each ω (Angular frequency of the signal) value can be calculated using the above equation.

#### Calculation of voltage gain at different ω (frequency) values using the transfer function of an active high-pass filter

• When ω <<< ωc

• When ω = ωc

• When ω >>> ωc

## Passive high pass filters

### Calculation of transfer function of a passive high-pass filter

Take

To remove the complex part in the equation, the same operation that was done on the transfer function in the active filter can be used here.

The above equation gives the transfer function of a passive high-pass filter. The voltage gain at each ω (Angular frequency of the signal) value of a passive high-pass filter can be calculated using the above equation.

#### Calculation of voltage gain at different ω (frequency) values using the transfer function of a passive high-pass filter

• When ω >>> ωc

• When ω = ωc

• When ω <<< ωc

## References and Attributes

### Figures:

The cover image was created using an image by Tide He from Pixabay