Pll power supply filter (with pump) having a wide voltage range and immunity to oxide overstress

Abstract

A power supply filter capable of functioning with low power supply voltages includes a resistor-capacitor circuit coupled to a power supply line and a transistor for providing power to a target circuit, such as a phase-locked loop circuit, coupled between the resistor-capacitor circuit and the power supply line. The resistor-capacitor circuit is coupled to a charge pump controller to keep the transistor in a saturation state. The charge pump controller receives at least one clock signal that is coupled to at least one capacitive circuit. The at least one capacitive circuit includes at least two capacitors in series with a biased middle node located between the at least two capacitors in order to provide immunity to time dependent dielectric breakdown, the middle node coupled to approximately half the power supply line. A method of filtering noise from a power supply includes providing an N-channel source follower circuit coupled between the power supply and a target circuit, the N-channel source follower circuit including a resistor-capacitor circuit and a transistor with a threshold voltage. The method also includes maintaining the transistor in a saturation state through placing a charge pump in the N-channel source follower circuit, the charge pump receiving a first clock signal and a second clock signal, and allowing the voltage provided to a target circuit to exceed the voltage of the power line minus the threshold voltage while maintaining the transistor in a saturation state.