Patent ID: 7391242

Claim:
A sawtooth waveform generator comprising: an operational amplifier that generates a ramp voltage on an output terminal; a timing circuit that controls the risetime of the ramp voltage generated by the operational amplifier, the timing circuit comprising: a capacitor having a first terminal and a second terminal; a timing resistor connected to an input terminal of the operational amplifier; and a switching circuit that operates during a first interval to connect the first terminal of the capacitor to the output of the operational amplifier and to connect the second terminal of the capacitor to the input terminal of the operational amplifier and the timing resistor, and that operates during a second interval to connect the second terminal of the capacitor to the output of the operational amplifier and to connect the first terminal of the capacitor to the input of the operational amplifier and the timing resistor; and a control circuit that controls the switching circuit, the control circuit responsive to the ramp voltage to cause the switching circuit to switch at a predetermined voltage level and responsive to a voltage level on the first terminal of the capacitor to select which of the first terminal and the second terminal of the capacitor to connect to the output terminal of the operational amplifier.