Abstract: A proximity switch using logic means to detect a difference in capacitance. A bias capacitance and a sensing capacitance are charged by a first voltage source, each through one of a first pair of FET devices matched for transconductance, during a charge interval. During a detection interval the capacitances are discharged to ground potential or to a second voltage source of opposite polarity than the first voltage source, each through one of a second pair of FET devices also matched for transconductance. The difference in discharge rate between the bias and sensing capacitance, which is a measure of the capacitance of each, is detected by a cross coupled latch (RS flip-flop), setting the latch in a particular state. A second cross coupled latch stores the data thus obtained for utilization. The proximity switch circuit may be embodied as part of an MOS LSI integrated circuit, except for the bias and sensing capacitances, or may be constructed of discrete bipolar devices.