Patent ID: 6900672

Claim:
A voltage ramp generator capable of linearly discharging a capacitor for slew rate control of a power driving stage, comprising; a cascoded current source that is coupled to an output voltage of the capacitor, a first supply voltage, and a second supply voltage, said cascoded current source comprising: a current mirror, coupled to the first supply voltage; a first cascode devise coupled between a mirror leg of the current mirror and the output of the capacitor; and a first biasing device for biasing the first cascode device coupled between a reference leg of the current mirror and the second supply voltage, wherein the current mirror and the first cascode device operate in a high resistance region as the output voltage of the capacitor falls from a third voltage to ensure a high impedance of the output voltage of the capacitor until the output voltage of the capacitor reaches a first interim voltage, and wherein when the output voltage of the capacitor reaches the first interim voltage the first cascode device operates in a low resistance region, the current mirror continues to operate in the high resistance region and an output impedance of the cascoded current source coupled to the capacitor decreases, but the output voltage being at or below the first interim voltage does not require that the output voltage be as high an impedance to continue linearly discharging the capacitor to the first supply voltage.