Patent ID: 8755242

Claim:
A method of operating a high voltage generating circuit comprising: using an adjustable oscillator to generate a first pumping clock signal by delaying a clock signal by a first delay time; performing a first charge pumping operation using a first high voltage pump circuit in response to the first pumping clock signal; using a first adjustable delay circuit to generate a second pumping clock signal by delaying the first pumping clock signal by a second delay time; performing a second charge pumping operation using a second high voltage pump circuit in response to the second pumping clock signal; generating an output voltage in response to the first and second charge pumping operations; using a level detector to detect a level of the output voltage; and activating the adjustable oscillator when the level of the output voltage is not greater than a target voltage, else inactivating the adjustable oscillator when the level of the output voltage is greater than the target voltage.