Application of an Adaptive Direct Current Offset Elimination Algorithm Based on FPGA in Orthogonal Demodulation

Abstract

In the coherent demodulation of the FM signal, an uncertain frequency deviation exists between the demodulated carrier and the modulated carrier, which will generate a direct-current (DC) offset in the demodulation signal and directly affect the performance of the system. An adaptive interference cancellation method based on least mean square (LMS) is proposed to eliminate the DC offset in this paper. Compared with the method of filtering the DC offset by using a high-pass filter, the LMS algorithm has low latency and low implementation cost. The method is implemented and verified on the field-programmable-gate-array (FPGA) platform by hardware description language. Simulation results show that the LMS algorithm can eliminate the DC offset from the demodulated signal within 1.5ms.