A signal processing circuit (10) performs a sample and hold (16) of an input signal (14) and stores a maximum value of the input signal (18). A guardband signal (21) is developed that is less than the maximum value that is stored. The input signal is compared to the guardband signal to determine if the input signal is above or below the guardband signal. A threshold signal (25) is developed by taking a percentage of the maximum value that is stored. The input signal is compared to the threshold signal to regenerate the input waveform. If the input signal is below the guardband signal and above the threshold signal, the sample and hold circuit is reset to acquire a new maximum value of the input signal so that a new threshold can be used for regenerating the input signal.