A method for closed loop operation of a capacitive accelerometer, the capacitive accelerometer comprising: a proof mass moveable along a sensing axis in response to an applied acceleration; and first and second fixed capacitive electrodes (104, 106) arranged symmetrically either side of the proof mass along the sensing axis with a gap defined between each of the first and second fixed capacitive electrodes (104, 106) and the proof mass under zero applied acceleration; the method comprising: applying a first drive signal V 1 to the first fixed capacitive electrode and a second drive signal V 2 to the second fixed capacitive electrode, the first and second drive signals each having a periodic waveform varying in amplitude between zero and a maximum value V ref; and sensing a displacement of the proof mass and applying pulse width modulation to the first and second drive signals with a constant frequency f mod and a variable mark/space ratio so as to provide a net electrostatic restoring force on the proof mass for balancing the inertial force of the applied acceleration and maintaining the proof mass at a null position; characterised by: applying a voltage offset V ref /2 to the proof mass; and applying the pulse width modulation such that the first and second drive signals have a waveform that varies so that when either one of the first and second drive signals is at V ref or zero the other drive voltage is at V ref /2. a proof mass moveable along a sensing axis in response to an applied acceleration; and first and second fixed capacitive electrodes (104, 106) arranged symmetrically either side of the proof mass along the sensing axis with a gap defined between each of the first and second fixed capacitive electrodes (104, 106) and the proof mass under zero applied acceleration; the method comprising: applying a first drive signal V 1 to the first fixed capacitive electrode and a second drive signal V 2 to the second fixed capacitive electrode, the first and second drive signals each having a periodic waveform varying in amplitude between zero and a maximum value V ref; and sensing a displacement of the proof mass and applying pulse width modulation to the first and second drive signals with a constant frequency f mod and a variable mark/space ratio so as to provide a net electrostatic restoring force on the proof mass for balancing the inertial force of the applied acceleration and maintaining the proof mass at a null position; characterised by: applying a voltage offset V ref /2 to the proof mass; and applying the pulse width modulation such that the first and second drive signals have a waveform that varies so that when either one of the first and second drive signals is at V ref or zero the other drive voltage is at V ref /2. applying a first drive signal V 1 to the first fixed capacitive electrode and a second drive signal V 2 to the second fixed capacitive electrode, the first and second drive signals each having a periodic waveform varying in amplitude between zero and a maximum value V ref; and sensing a displacement of the proof mass and applying pulse width modulation to the first and second drive signals with a constant frequency f mod and a variable mark/space ratio so as to provide a net electrostatic restoring force on the proof mass for balancing the inertial force of the applied acceleration and maintaining the proof mass at a null position; characterised by: applying a voltage offset V ref /2 to the proof mass; and applying the pulse width modulation such that the first and second drive signals have a waveform that varies so that when either one of the first and second drive signals is at V ref or zero the other drive voltage is at V ref /2. applying a voltage offset V ref /2 to the proof mass; and applying the pulse width modulation such that the first and second drive signals have a waveform that varies so that when either one of the first and second drive signals is at V ref or zero the other drive voltage is at V ref /2.