Patent ID: 8368408

Claim:
An apparatus for measuring a time period, comprising: a constant current source; a current steering switch coupled to the constant current source; a capacitor coupled to the current steering switch, the capacitor having a known 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 circuit for controlling the current steering switch, wherein the current steering switch couples the capacitor to the constant current source when the circuit detects a start of an event and decouples the capacitor from the constant current source when the circuit detects an end of the event; 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 on the capacitor to a time value representative of a time period between the start and the end of the event, wherein the circuit for controlling the current steering switch, comprises: a first flip-flop having a clock input coupled to a first event signal edge indicating the beginning of the event; a second flip-flop having a clock input coupled to a second event signal edge indicating the end of the event; and 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 a control input of the current steering switch.