Patent ID: 7388413

Claim:
A ramp generator comprising: a capacitor with a first terminal and a second terminal; an operational amplifier configured to provide a periodic ramp signal at an output terminal, wherein a non-inverting input terminal is coupled to a reference voltage and an inverting input terminal is coupled to a current source; a switch array configured to couple the capacitor between the inverting input terminal and the output terminal of the operational amplifier, wherein the switch array periodically reverses polarity of the capacitor between the inverting input terminal and the output terminal of the operational amplifier by coupling the first terminal of the capacitor to the inverting input terminal of the operational amplifier while the second terminal of the capacitor is coupled to the output terminal of the operational amplifier during a first duration of a period and coupling the second terminal of the capacitor to the inverting input terminal of the operational amplifier while the first terminal of the capacitor is coupled to the output terminal of the operational amplifier during a second duration of the period, and wherein the capacitor does not substantially discharge in a transition between the first duration and the second duration of each period; and a flip-flop circuit configured to control the switch array, wherein the flip-flop circuit outputs two alternately active signals with frequencies determined by a clock signal and the clock signal is generated by comparing the periodic ramp signal to a bias voltage.