Patent ID: 7492229

Claim:
A circuit, comprising: a capacitor coupled to be alternatingly charged and discharged by first and second current sources; a first voltage follower circuit including a first bipolar transistor having a base coupled to the capacitor, the first bipolar transistor biased such that a voltage at an emitter of the first bipolar transistor follows a voltage on the capacitor; a current mirror having first and second current paths, the first current path coupled to the base of the first bipolar transistor, the first current path providing substantially all of a base current received by the base of the first bipolar transistor; and a switch coupled between the second current source and the capacitor, the switched coupled to be alternatingly opened and closed such that when the switch is opened, the first current source is coupled to charge the capacitor and when the switch is closed, the first and second current sources are coupled to discharge the capacitor, wherein the switch is coupled to be opened until the voltage on the capacitor is charged to a first threshold and wherein the switch is coupled to be closed until the voltage on the capacitor is discharged to a second threshold.