Reducing noise in a capacitive sensor with a pulse density modulator

An apparatus for measuring a capacitive sensor output, comprising:

• an excitation source configured to apply an excitation signal to a capacitor of the capacitive sensor which causes generation of a modulated signal from a baseband signal, wherein the excitation signal is of a carrier frequency which is higher than frequency content of the baseband signal;
• a demodulator configured to demodulate the modulated signal to generate an intermediate signal representative of a capacitance of the capacitor wherein the demodulator is configured to demodulate based, at least in part, on the excitation signal;
• and
• a pulse density modulator configured to:
• convert the intermediate signal into a pulse-density modulated output signal with a pulse-density modulator;
• and
• shape a noise transfer function of the pulse-density modulator to have an approximate zero at the carrier frequency.