MF200多频中波发射机自适应载波CIC内插滤波器设计

MF200多频中波发射机采用全新的数字调制器技术对音频信号及射频进行处理和分配控制,采用了自适应采样率转换方法对音频信号进行采样率提升同步至载波频域内。针对信号采样率转换及高频音频信号抽样量化失真的问题,采用了CIC数字内插滤波器设计方案。方案对异步采样率转换输出后的音频信号进行固定8倍内插,将音频信号采样率自适应变换到载波频率上,并在调制器音频处理板FPGA上实现。实际测试表明,该方案可以有效解决高频率音频信号抽样量化失真问题,同时,解决了数字调制器中音频信号自适应采样率二次转换问题,可以满足不同载波频率对音频信号采样率转换的需求,进一步提升了发射机的信号失真度指标。

The MF200 multi-frequency medium wave transmitter uses the new digital modulator technology to process the audio signal and distribute the radio frequency.The adaptive sampling rate conversion method is used to synchronize the sampling rate of the audio signal to the carrier frequency domain.The CIC digital interpolation filter design scheme is adopted for the problem of signal sampling rate conversion and high-frequency audio signal sampling and quantization distortion.The scheme performs a fixed eight times interpolation on audio signal output by Asynchronous Sample Rate Converters(ASRC),adaptively transforms the audio signal sampling rate to carrier frequency,and implements it on the FPGA of modulator audio processing board.The actual test on the transmitter shows that the scheme can effectively solve the problem of sampling and quantization distortion of high-frequency audio signal.At the same time,the scheme solves the problem of secondary sampling of adaptive sampling rate of audio signal in the digital modulator which can meet the requirements of different carrier frequencies for sampling rate conversion of audio signal and further improved the signal distortion index of the transmitter.