Abstract: A pull-up circuit comprises an operational amplifier which forms part of a feedback circuit, acting to bring a pull-up circuit output equal to a reference voltage input. The pull-up circuit may form part of a USB transceiver for incorporation in a USB Device. When the supply voltage of the USB Device is sufficiently high, it is used to provide the required pull-up voltage, with the feedback circuit including the operational amplifier the USB Device is not high enough to provide the required pull-up voltage. In that case, the USB bus voltage is used to generate the reference voltage which is used as an input to the feedback circuit.

Abstract: A charge pump comprises a single voltage multiplier stage (1) which converts an input voltage (VDD) into an output voltage (Vo) under control of a clock signal (Q, Qn; CLKO). An oscillator (2) receives the input voltage (VDD) to generate the clock signal (Q, Qn; CLKO) having a repetition period (Tr1, Tr2) which is substantially proportional to a squared input voltage (VDD2).