A DIGITAL 128-CHANNEL TRANSCUTANEOUS BLOOD-FLOWMETER

According to figure 1. the flowmeter is identical to the classical implementations äs far äs the RF stage. From there on the Video Signal is quantified and processed in discrete time and amplitude elements. The A/D Converter is set up in a tracking arrangement. The four least significant bits of the difference between the previously established phase image and the actual Signal ( see figure 2. ) are encoded within 50 nsec. The complete 10 bit phase image, however, is built up in a period of several hundred scans; fast enough to follow the low frequency components. On the other hand, the difference signal is fed forward to the following stages, thus performing first order clutter rejection. This dual mode Converter can be considered äs a synthesis of a velocity shaped sweep Integrator [5l and the linear ränge gate principle [1]. A digital highpass and hysteresis element reduce the doppler frequencies, established in each ränge bin, to a one bit discrete time representation. A demultiplexer plus a delay of the two quadrature paths yields a four bit word to be interpreted by the coincidence gate.