Patent ID: 8022714
Filing Date: 2011-09-20
Classification: G01R,G04F

Abstract:
1. An apparatus for measuring capacitance, comprising: a constant current source; a current steering switch having a control input, wherein the current steering switch is coupled to the constant current source; a capacitor coupled to the current steering switch, the capacitor having an unknown value of capacitance, wherein a voltage on the capacitor increases substantially linearly in time when the current steering switch couples the constant current source to the capacitor; a first flip-flop having a clock input coupled to a clock having a known precision time period, wherein the first flip-flop determines a beginning of the precision time period; a second flip-flop having a clock input coupled to the clock, wherein the second first flip-flop determines an end of the precision time period; an AND gate having a first input coupled to a Q-output of the first flip-flop, a second input coupled to a Q-not output of the second flip-flop and an output coupled to the control input of the current steering switch, wherein the capacitor is coupled to the constant current source at the beginning of the known precision time period and is decoupled from the constant current source at the end of the known precision time period; an analog-to-digital converter (ADC) for converting the voltage on the capacitor to a digital representation thereof; and a digital processor for converting the digital representation of the voltage to a capacitance value.