Abstract: To correct non-linearity and noise in the conversion of a pulse code modulated signal (PCM) into a uniform pulse width modulated signal (UPWM), a model is made of the known non-linearity in the conversion by dividing a plurality of non-linearity components in the model, where the polynomial components are separately weighed with filter coefficients. The model is used as a basis for the construction of a filter of the Hammerstein type whose non-linear parts consist of a division of the PCM signal into a plurality of powers, and whose linear parts are approximated by means of the model made. With the circuit of the invention it is now possible to construct a purely digital amplifier which has a great efficiency, low weight, etc.