Wideband Capacitive Sensing Using Sense Signal Modulation

Wideband capacitive sensing (single-ended or differential) is based on a modulated sense (capacitance) signal. A carrier/drive signal path modulates a reference signal with a carrier signal (such as fixed frequency or spread spectrum) to generate a carrier/drive signal, driven (with optional pre-scaling) out through an output node (to sense capacitor(s)). A sense signal path receives at an input/summing node up-modulated sense capacitance signal(s), corresponding to measured capacitance up-modulated to the carrier frequency, and, after filtering (optional) and amplification, demodulates the up-modulated sense capacitance signal with the carrier signal, to generate a demodulated sense capacitance signal corresponding to measured capacitance, which can be converted to sensor data. Sense signal path amplification can use charge amplification (capacitor feedback), or transimpedance amplification (resistor feedback). For differential capacitive sensing, differential carrier/drive signals are driven to differential sense capacitors, and the resulting up-modulated sense capacitance signals are summed at the input/summing node.