Patent ID: 8854119

Claim:
A circuit, comprising: a charge pump having an input node for receiving an input voltage, a capacitor, a transistor switching circuit having an output coupled to the capacitor, a supply node for receiving a charging current applied to an input of said switching circuit and an output node for outputting an output voltage, wherein the charge pump is configured to generate a voltage difference between the input node and the output node; a first level shifter having a first node coupled to the output node and a second node, the first level shifter configured to apply a first voltage variation to the output voltage in response to a bias current received from a current source; a second level shifter having a third node coupled to the input node and a fourth node, the second level shifter configured to apply a second voltage variation to the input voltage; a voltage follower configured to set the voltage at the second node substantially equal to the voltage at the fourth node and to provide the difference current flowing through the second level shifter; and a current multiplier configured to generate the charging current in response to the difference current provided by the voltage follower; wherein the current source comprises: an operational amplifier having a positive input node, a negative input node and an output node, a third transistor and a third resistor, wherein the positive input node is configured to receive a reference voltage, the negative input node is coupled to a source of the third transistor, the output node is coupled to a gate of the third transistor, and the third resistor is coupled between the source of the third transistor and a reference potential line so as to provide the bias current flowing through the third transistor.