| 摘要 |
PURPOSE:To obtain a desired dynamic range by composing a TGC circuit by dividing into a first TGC circuit which performs the variable control of a gain setting an echo signal with high amplitude from the shallow part of an organism as a target, and a second TGC circuit which performs the variable control of the gain with low amplitude at entire depth setting the echo signal from the deep part as a main target. CONSTITUTION:An ultrasonic wave signal is transmitted at the leading edge of a trigger signal for transmission where it changes from 0 to 1. When transmission is completed, each oscillator immediately receives an ultrasonic echo signal from the organism. The first TGC circuits A1-An perform the variable control of the gain only for the period of time t1 from the transmission when the echo signal with high amplitude arrives, and vary the gain from 0(dB) to GA(dB) according to a gain function fA(t). Also, the second TGC circuits B1-Bn perform the variable control of the gain extending over the period of time t2 from the transmission to the next transmission, and vary the gain from 0(dB) to GB(dB) according to a gain function fB(t). As a result, the integrated dynamic range of the first and second TGC circuits goes to GA+GB, then, the gain control of the echo signal can be performed within the range. |
