| 摘要 |
PURPOSE:To select the optimum cutoff frequency by providing a control means which determines the reference frequency corresponding to an ultrasonic transmission frequency and divides the frequency band of Doppler shift signals and outputs the filter processing information selecting the optimum cutoff frequency. CONSTITUTION:A controller 18 calculates and determines the reference frequency in response to the probe frequency and sends the information of the reference frequency and the information to uniformly divide the frequency band of Doppler shift signals into N to a unit controller 21. The unit controller 21 determines the band W of the Doppler shift signal for the reference frequency of a probe 1 used and the value of N to be uniformly divided into and controls the filter characteristic of a digital filter 8. An ultrasonic Doppler processor UD2 holds the detected output signal fed from a detector 6 as a sample with an S/H circuit 11, the unnecessary frequency component is removed from the hold signal by a band-pass filter 12, and it is frequency-analyzed by an FFT circuit 14 after amplification by an amplifier 13 to obtain the Doppler shift signal. |
