A signal processing system to provide a control signal (Cs) to a power factor correction circuit, the signal processing system comprising: a nonlinear delta-sigma modulator, wherein: the nonlinear delta-sigma modulator includes: an input to receive an input signal (v(n)) to the nonlinear delta-sigma modulator; a combiner to receive the input signal (v(n)) and a feedback signal (f(y(n-1))) and generate a difference signal (d(n)) between the input signal (v(n)) to the nonlinear delta-sigma modulator and the feedback signal (f(y(n-1))); a loop filter to filter the difference signal (d(n)) and generate a filter output signal (u(n)); a quantizer coupled to the loop filter to receive and quantize the filter output signal (v(n)), generating a quantizer output signal (y(n)); and a feedback path coupled between the combiner and the quantizer to generate the feedback signal (f(y(n-1))), wherein the feedback path includes a nonlinear feedback model means that models nonlinearity of a nonlinear process of the power factor correction circuit; whereby the control signal (Cs) is based on the quantizer output signal (y(n)). a nonlinear delta-sigma modulator, wherein: the nonlinear delta-sigma modulator includes: an input to receive an input signal (v(n)) to the nonlinear delta-sigma modulator; a combiner to receive the input signal (v(n)) and a feedback signal (f(y(n-1))) and generate a difference signal (d(n)) between the input signal (v(n)) to the nonlinear delta-sigma modulator and the feedback signal (f(y(n-1))); a loop filter to filter the difference signal (d(n)) and generate a filter output signal (u(n)); a quantizer coupled to the loop filter to receive and quantize the filter output signal (v(n)), generating a quantizer output signal (y(n)); and a feedback path coupled between the combiner and the quantizer to generate the feedback signal (f(y(n-1))), wherein the feedback path includes a nonlinear feedback model means that models nonlinearity of a nonlinear process of the power factor correction circuit; whereby the control signal (Cs) is based on the quantizer output signal (y(n)). the nonlinear delta-sigma modulator includes: an input to receive an input signal (v(n)) to the nonlinear delta-sigma modulator; a combiner to receive the input signal (v(n)) and a feedback signal (f(y(n-1))) and generate a difference signal (d(n)) between the input signal (v(n)) to the nonlinear delta-sigma modulator and the feedback signal (f(y(n-1))); a loop filter to filter the difference signal (d(n)) and generate a filter output signal (u(n)); a quantizer coupled to the loop filter to receive and quantize the filter output signal (v(n)), generating a quantizer output signal (y(n)); and a feedback path coupled between the combiner and the quantizer to generate the feedback signal (f(y(n-1))), wherein the feedback path includes a nonlinear feedback model means that models nonlinearity of a nonlinear process of the power factor correction circuit; whereby the control signal (Cs) is based on the quantizer output signal (y(n)). an input to receive an input signal (v(n)) to the nonlinear delta-sigma modulator; a combiner to receive the input signal (v(n)) and a feedback signal (f(y(n-1))) and generate a difference signal (d(n)) between the input signal (v(n)) to the nonlinear delta-sigma modulator and the feedback signal (f(y(n-1))); a loop filter to filter the difference signal (d(n)) and generate a filter output signal (u(n)); a quantizer coupled to the loop filter to receive and quantize the filter output signal (v(n)), generating a quantizer output signal (y(n)); and a feedback path coupled between the combiner and the quantizer to generate the feedback signal (f(y(n-1))), wherein the feedback path includes a nonlinear feedback model means that models nonlinearity of a nonlinear process of the power factor correction circuit; whereby the control signal (Cs) is based on the quantizer output signal (y(n)).