Three-phase low noise charge pump and method

Abstract

A low noise charge pump circuit includes a first terminal of a first flying capacitor selectively coupled to a first voltage during a first recharging phase and a second terminal of the first flying capacitor selectively coupled to a second voltage during the first recharging phase. The second terminal of the first flying capacitor is coupled to a precharge control circuit during a first parasitic capacitance precharging phase that occurs after the first recharging phase to cause the voltage of the first terminal of the first flying capacitor to equal an output voltage. The first terminal of the first flying capacitor is coupled to an output conductor conducting the output voltage during a first discharging phase that occurs after the first parasitic capacitance precharging phase. The second terminal of the first flying capacitor is coupled to a discharge control circuit which increases the voltage of the second terminal of the first flying capacitor during the first discharging phase until the output voltage is equal to a regulated value.

Description

BACKGROUND OF THE INVENTION [0001] The present invention relates generally to charge pumps, and more particularly to an improvement which provides substantially reduced output noise compared to prior charge pumps. [0002] On-chip generation of an internal supply voltage at a value greater than the power supply voltage rail VCC has been one approach to providing rail-to-rail operation of an operational amplifier. However, generation of such an internal supply by means of a charge pump circuit has been problematic due to the large amount of output noise (at the charge-pump clock frequency) produced by known charge pumps. [0003] A standard charge pump circuit is a two-phase circuit including two “flying capacitors” and one “reservoir capacitor” which operate to store and maintain the output voltage of the charge pump circuit. FIG. 1A shows a standard charge pump circuit 1, which includes an amplifying circuit 2 having an output 3 connected to a control terminal of a controlled current s...

AI Technical Summary

Benefits of technology

The present invention provides an improved charge pump circuit with reduced output noise. The circuit includes a first flying capacitor and a second flying capacitor that are selectively coupled to a first voltage and a second voltage during a recharging phase to avoid noise spikes on the output conductor. The circuit also includes a precharge control circuit and a discharge control circuit to regulate the output voltage. The three-phase charge pump circuit includes a reservoir capacitor and switching circuits for selectively coupling the first and second flying capacitors to the first and second voltages during the recharging phases to avoid noise spikes. The circuit can produce a low noise output voltage on the output conductor with reduced noise on the output.

Problems solved by technology

However, generation of such an internal supply by means of a charge pump circuit has been problematic due to the large amount of output noise (at the charge-pump clock frequency) produced by known charge pumps.

A drawback of prior art two-phase charge pump circuit 1 is that it has a fast, noise-producing transient process between its above mentioned first and second phases, during which the top plate of one of the flying capacitors is connected to reservoir capacitor Cout at the same time the voltage across the associated parasitic capacitor connected between the bottom plate of that flying capacitor and ground (i.e., the integrated circuit substrate) is still at 0 volts.

This causes a fast negative-going spike in Vout, which constitutes the noise above mentioned noise.

This can typically result in negative noise spikes of roughly 70 millivolts.

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