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

Abstract

A carrier recovery circuit, adapted to a demodulation circuit according to a quasi-coherent detection method for generating baseband signals by way of quadrature detection on a received signal having an intermediate frequency, rotates phases of baseband signals; detects a phase error and an amplitude error; controls a bandwidth of a loop filter based on its difference, eliminates a high-frequency component from the phase error; and performs phase rotation based on the phase error eliminating its high-frequency component. It 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 reducing bandwidth of the loop filter upon determining that the amplitude error decreases due to a reduction of the bandwidth of the loop filter. This optimizes the bandwidth of the loop filter to follow variations of the C/N ratio of the received signal, improving bit error rate.