A comparator for comparing a first input voltage with a second input voltage and generating a corresponding output voltage, the comparator comprising:
- a first input terminal for receiving the first input voltage;
- a second input terminal for receiving the second input voltage;
- an output terminal for outputting the output voltage;
- a first supply rail for providing a first supply voltage;
- a second supply rail for providing a second supply voltage, the comparator further comprising:
- a follower stage comprising:
- a first follower stage supply terminal coupled to the first supply rail;
- a second follower stage supply terminal coupled to the second supply;
- a follower stage input terminal coupled to the second input terminal;
- and
- a follower stage output terminal for providing a follower stage output voltage;
- an inverter stage comprising:
- a first inverter stage supply terminal coupled to the first supply rail;
- a second inverter stage supply terminal coupled to the follower stage output terminal;
- an inverter stage input terminal coupled to the first input terminal;
- and
- an inverter stage output terminal for providing an inverter stage output voltage and coupled to the output terminal;
- signal conditioning means coupled between the inverter stage output terminal and the comparator output terminal, a controllable switching device arranged to couple the first follower stage supply terminal to the first supply rail, the switching device being controllable to switch between:
- first state, in which the switching device electrically connects the first follower supply terminal to the first supply rail;
- and
- a second state, in which the switching device electrically disconnects the first follower supply terminal from the first supply rail;
- control means arranged to control the controllable witching device;
- and
- filtering means arranged between the inverter stage output terminal and the comparator output terminal to filter at least one frequency component from the output voltage,
- wherein the control means includes an oscillator having an output arranged to control the switching device to alternate between the first and second states, the oscillator output includes a fundamental frequency, and the filtering means is arranged to filter out at least the fundamental frequency,
- wherein the inverter stage output voltage has a first range, in use, determined by the voltage applied to the first supply rail and by the follower stage output voltage, and the signal conditioning means is adapted to generate, from the inverter stage output voltage, a comparator output voltage at the comparator output terminal having a second range, where the second range is larger than the first range, wherein said second range extends substantially from a voltage supplied to the first supply rail to a voltage supplied to the second supply rail, wherein the signal conditioning means comprises a further follower stage, an analog to digital converter, and an inverter connected in series between the inverter stage output terminal and the comparator output terminal, and
- wherein the inverter stage comprises an enhancement mode field effect transistor (FET).