A positive clipper circuit passes a positive input signal voltage below its threshold and outputs a constant voltage for an input signal voltage above its threshold. A negative clipper does the same thing for negative voltages.
It is often implemented with diodes.
It's effect on a sine wave is to flatten the peaks.
Clipper circuit consist of a diode and a resistor.
Depending upon the direction of the diode(forward of reversed biased),it acts as a open switch(reversed biased) or closed switch(forward biased).Which can clipp the positive or negative part of input signal at the output.
It is used in wave shaping, basically a rectifier circuit...msg