| 摘要 |
PROBLEM TO BE SOLVED: To hold an output signal at a constant value without producing amplitude change and accurately detect a signal component even if a signal level becomes small by square operation by performing synchronizing rectification and the square operation by a digital circuit. SOLUTION: An A/D converter 41 VD-converts a signal after passage of BPF 40 by a frequency mf (m: integer, and f: ultrasonic transmission frequency of a transmitter 31). A shift register 42 comprises resistors 421 -42m , the data of the resistor of each stage is shifted whenever conversion data is obtained, and m pieces of the conversion data taken every 1/mf cycle are stored. The multiplier 431 or 432 of a processor 43 a sin or cos function value shifting a phase each by 2π/m to the data stored to each stage of the shift register 42 respectively, and stores them to a memory for function value 433. After a multiplication value is added by adders 434, 435, squared by square devices 436, 437, after these square values are added by the adder 438, they are extracted by a square root device and amplitude is found by an amplitude calculator 440. |
