Abstract: The present invention provides an analog to digital converter including an integrator for charging and discharging a capacitor according to two currents of opposite direction containing a component of the analog input signal which is continuously connected. Also, a control circuit periodically switches on one current which remains until the integrator output reaches a reference level at which time the opposite direction current is switched on. A number of such cycles forms an integration period closely approximating a predetermined period. The control circuit measures the total amount of time of the integration period and also the accumulative amount of time that current flow is in a predetermined direction. From these two times, a digital representation of the analog input signal is calculated. The next integration period begins at the end of the previous to achieve a maximum conversion rate for a given integration period.