US Patent 10141941 Differential PLL with charge pump chopping

According to a first example aspect there is provided a charge pump circuit that includes a first chopper circuit configured to switch first and second chopper circuit outputs between first and second chopper circuit inputs at a chopping frequency, wherein successive input signals at the first chopper circuit input are output alternatively at the first and second chopper circuit outputs in successive cycles of the chopping frequency and successive input signals at the second chopper circuit input are output alternatively at the second and first chopper circuit outputs in successive cycles of the chopping frequency. A differential charge pump is configured to receive the signals output from the first and second chopper circuit outputs and produce corresponding first and second charge pumped signals.