超声血流仪多普勒频移信号的数字化提取

Digital Extraction of Doppler Frequency-Shift Signal for Ultrasonic Blood Flow Meter

基于FPGA的多普勒频移信号数字提取,其数控振荡器NCO产生与发射信号同频率的离散正余弦波采样点。每来一个时钟脉冲,N位加法器将频率控制数据M与相位寄存器输出的累加相位数据相加,并将结果送相位寄存器输入端。相位寄存器每经过2N/M个fCLK时钟周期后回到初始状态,相应的正(余)弦查找表经一个循环回到初始位置,完成一个NCO信号频率周期。

The digital extraction of Doppler shift signal is based on FPGA. The numerically controlled oscillator （NCO） generates a discrete-time, discrete-valued sinusoidal （cosine） waveform which frequency is as same as the emissive waveform. Frequency controlled data （M） plus an accumulative phase data output by a phase register in an N-bit adder when a clock pulse comes, the result is sent to the input port of the phase register. The phase register returns to its initialize state after 2^N/M fCLK clock periods, the corresponding sinusoidal （cosine） lookup tables returns to its initialize state after a circle, then a NCO signal frequency period is completed.