WIDEBAND CAPACITIVE SENSING USING SENSE SIGNAL MODULATION

摘要

In described examples, wideband capacitive sensing (10) (single-ended or differential) is based on a modulated sense (capacitance) signal. A carrier/drive signal path (23, 34, 35) modulates a reference signal (31) with a carrier signal (21) (such as fixed frequency or spread spectrum) to generate a carrier/drive signal (32), driven (with optional pre-scaling) (34, 35) out through an output node (A) to sense capacitor(s) (12). A sense signal path (43, 44, 45, 24) receives at an input/summing node (B) up-modulated sense capacitance signal(s) (41), corresponding to measured capacitance up-modulated to the carrier frequency and, after filtering (optional) (43, 44) and amplification (45, 46), demodulates (24) the up-modulated sense capacitance signal with the carrier signal to generate a demodulated sense capacitance signal (49) corresponding to measured capacitance, which can be converted to sensor data. Sense signal path amplification (45) can use charge amplification (capacitor feedback) (45, 46) 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.