| 摘要 |
PURPOSE:To reduce sampling frequency without injuring an information amount possessed by an ultrasonic signal, by taking out only the necessary band width of the ultrasonic signal while sampling only the signal in the band thereof. CONSTITUTION:An ultrasonic signal received by an element E and converted to an electric signal is amplified by an amplifier A and the amplified signal is sampled by a sampling means S after passed through a filter F having a pass band of (2/3)fc (frequency approximate to the center frequency of the ultrasonic signal)- (4/3)fc. The frequency of a sampling clock CT is (4/3)fc and a series of sampled data are sent to a shift register SR while alternately written in line memories LM1 or LM2 at every one transmission and reception and, after passes through a complementary device IP, obtained as input data to a phase adjusting adder. By this mechanism, when the center frequency is 3MHz, sampling frequency can be reduced to 4MHz. |
