Frequency Transformations

Until now, only filters using the low pass configuration have been examined. In this section, transforming the low-pass prototype into the other configurations: high pass, band pass, bandreject (notch) and all pass will be discussed.

Low Pass to High Pass

The low-pass prototype is converted to high-pass filter by scaling by 1/s in the transfer function. In practice, this amounts to capacitors becoming inductors with a value 1/C, and inductors becoming capacitors with a value of 1/L for passive designs. For active designs, resistors become capacitors with a value of 1/R, and capacitors become resistors with a value of 1/C. This applies only to frequency setting resistor, not those only used to set gain. ...

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