Carrier recovery circuit and demodulation circuit under quasi-coherent detection method

A carrier recovery circuit adapted to a demodulation circuit according to a quasi-coherent detection method, said carrier recovery circuit comprising:

• a phase rotator that rotates a phase of a baseband signal detected from a received signal;
• a phase error detector that detects a phase error included in the baseband signal with the rotated phase;
• an amplitude error detector that detects an amplitude error included in the baseband signal with the rotated phase;
• a loop filter that eliminates a high-frequency component from the phase error;
• a loop filter controller that controls a bandwidth of the loop filter based on the phase error and the amplitude error;
• and
• a phase rotation controller that controls the phase rotator based on the phase error eliminating its high-frequency component,
• wherein the loop filter controller expands the bandwidth of the loop filter when a difference between the phase error and the amplitude error is greater than a predetermined threshold, whilst the loop filter controller reduces the bandwidth of the loop filter upon determining that the amplitude error decreases due to a reduction of the bandwidth of the loop filter.

A demodulation circuit comprising:

• a reference oscillator that carries out free-running oscillation on a reference signal with a reference frequency;
• a quadrature detector that demodulates a received signal having an intermediate frequency with the reference signal so as to generate baseband signals whose phases are orthogonal to each other;
• an A/D converter that performs A/D conversion on the baseband signals;
• a phase rotator that rotates the phases of the digitized baseband signals;
• a phase error detector that detects a phase error included in the baseband signals with the rotated phases;
• an amplitude error detector that detects an amplitude error included in the baseband signals with the rotated phases;
• a loop filter that eliminates a high-frequency component from the phase error;
• a loop filter controller that controls a bandwidth of the loop filter based on the phase error and the amplitude error;
• and
• a phase rotation controller that controls the phase rotator based on the phase error eliminating its high-frequency component.

A carrier recovery method adapted to a demodulation circuit according to a quasi-coherent detection method, said carrier recovery method comprising:

• rotating a phase of a baseband signal detected from a received signal;
• detecting a phase error included in the baseband signal with the rotated phase;
• detecting an amplitude error included in the baseband signal with the rotated phase;
• controlling a bandwidth of a loop filter based on the phase error and the amplitude error, thus eliminating a high-frequency component from the phase error;
• and
• controlling phase rotation based on the phase error eliminating its high-frequency component.

A demodulation method according to a quasi-coherent detection method using a loop filter, said demodulation method comprising:

• demodulating a received signal having an intermediate frequency with a reference signal having a reference frequency, thus generating baseband signals whose phases are orthogonal to each other;
• performing A/D conversion on the baseband signals;
• rotating phases of the digitized baseband signals;
• detecting a phase error included in the baseband signals with rotated phases;
• detecting an amplitude error included in the baseband signals with rotated phases;
• controlling a bandwidth of the loop filter based on the phase error and the amplitude error;
• and
• controlling phase rotation based on the phase error whose high-frequency component is eliminated by the loop filter.