Delta-sigma modulator to issue an analog representation of a physiological signal

A method for operating a physiological monitor comprising: detecting an analog signal from a patient, wherein the analog signal comprises a physiological waveform; converting the analog signal into a digital signal; demodulating the digital signal to produce at least two demodulated physiological signals; applying one of the demodulated physiological signals to a delta-sigma modulator (51) to provide an output signal; and filtering said output signal to provide an analog output filtered physiological waveform in real time.