Transcapacitive charge measurement

摘要

A circuit for measuring a change in capacitive coupling between a transmitter electrode and receiver electrode includes a transmitter module that couples with the transmitter electrode and drives it with a plurality of positive and negative measurement cycles. A latched comparator has an input and an output, where the input couples with the receiver electrode. Upon enablement, the latched comparator determines if receiver electrode voltages satisfy an input threshold of the latched comparator and provides an output signal from an output based on this determination. A first counter is adjusted based on a first output signal of the latched comparator output during a positive measurement cycle. A second counter is adjusted based on a second output signal of the latched comparator during a negative measurement cycle. Measurement of change in capacitive coupling between the transmitter electrode and receiver electrode is based on counter values of the first and second counters.

主权项

1. A circuit for measuring a change in capacitive coupling between a transmitter electrode and receiver electrode, said circuit comprising:
a transmitter module configured for coupling with said transmitter electrode of a capacitive input device, said transmitter module configured to drive said transmitter electrode with a plurality of positive and negative measurement cycles, wherein a positive measurement cycle drives said transmitter electrode between a first voltage level and a second voltage level, and wherein a negative measurement cycle drives said transmitter electrode between said second voltage level and said first voltage level; a latched comparator, wherein said latched comparator comprises:
an input configured for coupling with said receiver electrode of said capacitive input device and, upon enablement, configured for determining if voltages from said receiver electrode satisfy an input threshold of said latched comparator, wherein said voltages correspond with said positive and negative measurement cycles; andan output configured for providing latched comparator outputs based upon said determining; a first counter wherein said first counter is incremented based on a first output value of said latched comparator output, wherein said first output value corresponds to a determination that a first voltage of said voltages satisfies said input threshold, and wherein said first voltage of said voltages corresponds to a positive measurement cycle of said plurality of positive and negative measurement cycles; and a second counter, wherein said second counter is decremented based on a output value of said latched comparator output, wherein said second output value corresponds to a determination that a second voltage of said voltages satisfies said input threshold, and wherein said second voltage corresponds to a negative measurement cycle of said plurality of positive and negative measurement cycles, and wherein said measurement of said change in capacitive coupling between said transmitter electrode and receiver electrode is based on counter values of said first and second counters.