The Delta-Sigma or Sigma-Delta analog-to-digital converter works on the principle of oversampling, whereby a low-resolution ADC repeatedly samples the input signal in a feedback loop. In many cases, the ADC used is nothing more than a comparator (a 1-bit ADC!), the output of this ADC subtracted from the input signal and integrated over time in an attempt to achieve a balance near 0 volts at the output of the integrator. The result is a pulse-density modulated (PDM) bitstream of 1-bit digital data which may be filtered and decimated (converted to a binary word of multiple bits):



Explain what this PDM bitstream would look like for the following input voltage conditions:



Vin = 0 volts

Vin = VDD

Vin = Vref