Circuit calibration using a time constant

A method comprising:

• providing a resistor in a first current path of a resistor-capacitor (RC) circuit;
• providing a variable capacitor in a second current path of the RC circuit;
• providing a virtual ground on one side of the variable capacitor;
• activating a switch for a period of time;
• comparing a voltage VR across the resistor to the ground with a voltage VC across the capacitor to the virtual ground after the period of time;
• and
• changing a value of the variable capacitor if the voltage VR and the voltage VC are not the same after the period of time.

A circuit comprising:

• a resistor in a first current path of an RC circuit;
• a capacitor in a second current path of the RC circuit;
• a current mirror in the first and second current path that is configured to maintain a substantially equivalent current in both the first current path and the second current path;
• and
• an operational amplifier having the resistor connected to an input thereof, and having the capacitor connected in a feedback loop of the operational amplifier.