a switchable analog signal inverter is suitable for inverting an input d . c . voltage , for example the d . c . voltage from a digital to analog converter , thereby halving the size of the dac . the inverter includes a capacitor having one side alternately switchable between a reference voltage point and an output terminal and another side alternately switchable between the reference voltage point and an input signal terminal , and switching means for selectively reversing the phasing of the switching between the reference voltage and the input signal . in one embodiment the inverter comprises a double pole reversing switch having inputs connected to a signal input terminal and to a reference voltage point and a capacitor connected by a change - over switch to first and second outputs of the reversing switch and by another change - over switch to a signal output terminal or to the reference voltage point . the reversing switch is operable in response to a polarity change signal to reverse the signal applied to the first and second outputs and thereby determine the polarity of the voltage pumped by the capacitor to the output terminal by clocking the change - over switches . the switches may be implemented by field effect transistors .