Apparatus and methods are provided for reducing coherent noise in
measurements of repetitive analog signal waveforms by digital signal
averagers. Coherent noise is repetitive and synchronous with the signal
waveform and is therefore undiminished by conventional signal averaging
techniques. A major source of coherent noise is the repetitive voltage
transitions that occur within the digital signal averager itself. The
apparatus and methods of the present invention introduce a known and
variable phase offset during the signal averaging process between the
signal waveform being measured and the internally generated coherent
noise, thereby allowing such coherent noise to be averaged, and therefore
reduced, during the signal averaging process. Consequently, the apparatus
and methods of the present invention allow greater signal-to-noise ratio
and signal dynamic range than with the prior art.