| 摘要 |
An ultrasonic imaging system which utilizes two summation channels to provide increased bandwidth employs two demodulation stages in each receive channel. The first demodulator receives digital signals from an analog-to-digital converter and demodulates those signals to baseband, thereby producing an in-phase component and a quadrature component. The in-phase and quadrature components are demodulated by the second demodulator, forming a total of four signals which are filtered and combined to form two sets of complex signals. One set corresponds to the upper or high frequencies and the other set corresponds to the lower frequencies. Each band is treated separately in a subsequent phase rotation. The phase changes reflect those required by the center frequency of each of the subbands. The upper band signals are coherently summed in one summation channel, while the lower band signals are coherently summed in another summation channel. The coherently summed upper and lower band signals are then reconstituted into one composite baseband signal.
|
