a circuit to generate a reference voltage from a power supply based on a predetermined voltage level , the reference voltage for use by a switched capacitor analog to digital converter includes a follower connected between the power supply and a current source to output the reference voltage . an amplifier is connected in a negative feedback arrangement with the reference voltage and the predetermined voltage level so as to provide an output , and a current sink is connected to the output of the amplifier . a charge pump provides the current sink with a voltage higher than the power supply , and the follower is driven based on the current sink . the charge pump includes a pair of series - connected switching legs , each switching leg being connected to a biasable capacitor , and being driven in diagonally complementary operation together with biasing of the capacitor , so as to provide the voltage for the current sink .