Patent ID: 7859321

Claim:
Apparatus comprising: a multistage charge pump having an output for connecting a load, said charge pump comprising m gain stages with m external stage capacitors, with m being an integer number larger than 1, for charging and discharging said external stage capacitors in order to provide an output voltage at said output which is approximately m times higher than a supply voltage of said charge pump, said charging and discharging being influenced by switches that are controlled by a switching signal having a switching frequency, at least one external reference capacitor, a monitoring circuit for monitoring temperature-induced changes of the value of said external reference capacitor, wherein the monitoring circuit comprises: a current source, first and second switches connected in series between a voltage source and said current source, a counter connected to said first and second switches to control said first and second switches, a plurality of resistors in a series configuration connected to said voltage source, and a plurality of comparators, each of said comparators including a first input connected to said at least one external reference capacitor and to a node between said first and second switches and a second input connected between adjacent resistors of said plurality of resistors, said comparators being connected to output signals that represent said temperature-induced changes of the value of said external reference capacitor, and means for adjusting said switching frequency in order to compensate variations of the gain of said charge pump that are caused by the changes of the value of said m external stage capacitors.