Clipper circuits are used to remove parts of a signal that are above or below a defined reference level. There are several types of clipper circuits: unbiased positive and negative clippers which clip either the positive or negative portions of a signal, and biased positive and negative clippers which use an external bias voltage to adjust the clipping level. Unbiased clippers cut off either the positive or negative half of the input waveform based on the diode configuration. Biased clippers allow changing the clipping level by adjusting the bias voltage applied in series with the input signal and diode.