An input signal is applied to a ratiometric gain/attenuator circuit. A nulling circuit is arranged to null the input signal with an output from the ratiometric gain/attenuator circuit. The ratiometric gain/attenuator circuit may include a gain stage in series with a ratiometric attenuator. By implementing the attenuator ratiometrically, the gain may be compensated with reference to a ratio of component values. A limiting stage with an absolute reference may precede the gain stage, and a pair of detector cells may arranged at the inputs to the nulling circuit.