What type of circuit is used to clamp or restrain a waveform to a fixed DC potential?

A clamping circuit is designed specifically to shift the entire waveform to a fixed DC level while preserving its shape. It does this by adding or subtracting a constant voltage, effectively "clamping" the waveform at a specified level. This is useful in various applications where it is necessary to ensure that the signal does not exceed a certain voltage range, such as in signal conditioning or waveform shaping.

The other options each serve different purposes. A timing circuit would be used to generate or manage time-based signals, while a shaping circuit alters the characteristics of a waveform, such as its rise and fall times or duty cycle, without necessarily clamping it to a fixed DC level. A filter circuit, on the other hand, is designed to allow certain frequencies to pass while attenuating others, and does not perform the function of restricting a waveform to a specific DC potential. Thus, the clamping circuit is the correct choice for the described function.