Complex phase-locked loop demodulator for low-IF and zero-IF radio receivers

A complex demodulator for demodulating an RF signal converted to digital I and Q IF signals, the complex demodulator comprising:

• a phase output node;
• an amplitude output node;
• a numerically controlled oscillator (NCO) for generating first and second NCO output signals in quadrature centred at the IF frequency;
• a first digital multiplier having a first input for receiving the digital I IF signal, a second input for receiving the first NCO output signal and an output for produce an output signal;
• a second digital multiplier having a first input for receiving the digital Q IF signal, a second input for receiving the second NCO output signal and an output for produce an output;
• a difference combiner for processing the outputs of the first and second digital multipliers to provide a phase signal at the phase output node, the phase signal being coupled to the NCO through a feedback loop to control the NCO frequency, the feedback loop exhibiting a first order loop characteristic in combination with the NCO;
• and
• a circuit for processing the digital I IF signal and the digital Q IF signal based on the first and second NCO output signals to provide an amplitude signal at the amplitude output node, the circuit including a third digital multiplier having a first input for receiving the digital I IF signal, a second input for receiving the second NCO output signal and an output for produce an output signal;
• a fourth digital multiplier having a first input for receiving the digital Q IF signal, a second input for receiving the first NCO output signal and an output for produce an output signal;
• and a sum combiner coupled to the outputs of the third and fourth digital multipliers for providing the amplitude signal at its output.