ADC self-test using time base and current source

A constant current source, a stable time base and a capacitor are used to self-check operation of an analog-to-digital convertor (ADC) by charging the capacitor for a pre-determined amount of time to produce a voltage thereon. This voltage will be proportional to the amount of time that the capacitor was charged. Multiple points on the ADC transfer function can be verified in this self-check procedure simply by varying the amount of time for charging of the capacitor. Relative accuracy among test points may then be easily obtained. Absolute accuracy may be obtained by using an accurate clock reference for the time base, a known current source and capacitor value.