Original Publication Date: 1987-Jun-01
Included in the Prior Art Database: 2005-Feb-01
Fig. 1 shows a partial schematic of the analog comparator. The principle used to make the voltage comparison is charge transfer or charge coupling across a switched inversion capacitor. A standard CMOS process does not provide the ability to fabricate parallel-plate gate oxide capacitors, and the comparator shown in Fig. 1 uses an N-channel MOSFET transistor for the implementation of the capacitor. The gate of the transistor forms the upper plate of the capacitor, and the shorted drain-source node forms the lower plate. The device becomes a parallel-plate gate oxide capacitor whenever the gate voltage exceeds the drain-source voltage by at least one device threshold voltage. (Image Omitted) There are three such capacitors used in the analog comparator shown in Fig. 1. They are labeled devices 5, 7, and 'c'.