Method and circuit for cancelling out comparator-delay in the relaxation oscillator

A method of compensating for comparator propagation delay within a relaxation oscillator, comprising:

• selectively charging and discharging a first capacitor coupled between a first node and a ground voltage;
• receiving a voltage across the first capacitor at a first input of a comparator, the first input coupled to the first node, wherein, during operation, transitions in an output signal of the comparator are delayed relative to transitions in the signal on the first node by a comparator propagation delay;
• selectively supply power to the capacitor using a first plurality of current sources, the current sources switched based on an output of the comparator;
• generating a compensation voltage proportional to the comparator propagation delay using a propagation delay integrator;
• and
• shifting a voltage on the capacitor by the compensation voltage.

A relaxation oscillator with comparator propagation delay compensation, comprising:

• a first capacitor coupled between a first node and a ground voltage;
• a comparator having a first input coupled to the first node, wherein,
• a first switch selectively connecting a first current source to the first node;
• a second switch selectively connecting a second current source to the first node;
• a second comparator coupled between a second node and the ground voltage;
• a third switch selectively connecting a third current source to the first node;
• a fourth switch selectively connecting a fourth current source to the first node;
• a fifth switch selectively connecting a fifth current source to the first node;
• and
• a sixth switch selectively connecting the second node to the first node, wherein closing the sixth switch results in a voltage shift at the first node,
• wherein the first, second, fourth and fifth switches are switched in tandem based on transitions in an output of the comparator, and
• wherein third and sixth switches are switched in tandem based on a propagation delay through the comparator, wherein the voltage shift compensates for the propagation delay.