Patent ID: 7236113

Claim:
A capacitance-to-digital (CD) modulator for converting a sensor capacitance C S and a reference capacitance C R to a pulse code modulated (PCM) signal, the CD modulator comprising: a first stage sigma-delta integrator for selectively forming charge packets in C S and C R during a first phase, and integrating charge from C S and C R during a second phase to produce a first stage output V OUT1 , wherein the first stage sigma-delta integrator includes a feedback capacitor for having a capacitance C F1 ; a second stage sigma-delta integrator for sampling the first stage output V OUT1 , and integrating the sampled first stage output to produce a second stage output V OUT2 ; a quantizer for converting the second stage output V OUT2 to the PCM signal; and a sensor failure mode detection (SFD) circuit for deriving from V OUT1 an SFD signal that identifies failure modes of C S and C R , wherein the SFD signal is representative of a capacitance ratio C R /C F1 .