1. A charge pump comprising: an up input and a down input to the charge pump;
an output having an output capacitance to be charged in response to the up input and discharged in response to the down input;
a fixed current source that sources a relatively constant source current to a first junction node;
a variable current source that sources a varying source current to a second junction node, wherein the varying source current varies in response to a control voltage;
a first driver transistor, coupled to conduct current between the first junction node and the output in response to the up input;
a second driver transistor, coupled to conduct current between the second junction node and the output in response to the down input;
a first series transistor, coupled to conduct current between the first junction node and an intermediate node in response to the up input being inactive;
a second series transistor, coupled to conduct current between the second junction node and the intermediate node in response to the down input being inactive;
a sampling capacitor for storing a sampled charge, generating the control voltage to the variable current source; and
a sampling switch coupled to conduct current between the intermediate node and the sampling capacitor when the up input and the down input are inactive, whereby the intermediate node is coupled to the sampling capacitor to adjust the varying source current.
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