RC oscillator in which a portion of charging current is shunted away from capacitor

摘要

An analog oscillator for an integrated circuit operates at low frequency with reduced sensitivity to noise and can be implemented with a capacitor that takes up a small amount of die space. The oscillator charges a capacitor by generating a current with a charge current source and then shunting a portion of the current away from the capacitor with a shunt current source. The current sources are implemented in bipolar transistors which are operated at high current to reduce sensitivity to noise. The capacitor is charged slowly by a small difference current which is equal to the difference between the current from the charge current source and the current from the shunt current source. A Schmitt trigger comparator compares the capacitor voltage to a reference voltage and controls a discharge current source which discharges the capacitor. The current sources include current mirrors and are temperature compensated.