A sigma-delta ADC using a passive RC filter as an integrator

摘要

A sigma-delta analogue-to-digital converter (ADC) converts an analogue input Vs at node 511 to a pulse stream Vp at node 516 having a frequency that varies inversely with the analogue input voltage (figures 4 and 5). The input analogue signal and the feedback pulse signal are combined in a simple low-pass filter network 530 which acts as an integrator because its cutoff frequency is much lower than the pulse frequency. An operational amplifier is not required in the integrator or elsewhere in the converter, which uses inexpensive comparators 535 and 570. The sigma-delta modulator has a high bandwidth and has low magnitude and phase errors.  The pulse feedback may comprise mulitple bits (figure 13). The ADC may be used in am electronic control unit (ECU) for a motor vehicle.