The RF receiver and pulser sections of a real-time B-mode scanning system have been designed, tested, debugged, and integrated with a 50 MHz transducer. The receiver section has a sensitivity of 100 microvolts on the front end and 60 dB of variable gain from the TGC amplifier sections (two are cascaded in series). Multiplexing and demultiplexing circuits have been designed and tested and are currently being integrated into a complete 2 channel system for testing. Once the mux and demux circuits are tested and characterized, the RF front end circuitry will be duplicated for 16 channels. The data acquisition system is capable of simultaneously sampling 8 channels at 250 MHz and 16 channels at 125 MHz. A real time digital beam forming architecture for a 50 MHz array has been designed and simulated. The system is based on oversampling sigma-delta A/D converter technology which samples at a (wavelength/32) time resolution for accurate time delays for steering and focusing. The sigma-delta A/D converter is integrated with a shift register, multiplexer and control logic to select the appropriate samples for the time delay. A MATLAB software library has been written for resolution , coverage, time delay (focusing and steering), and sampling frequency. In order to achieve the (wavelength/32) resolution, sampling rates on the order of 1 GHz are required. A circuit architecture has been defined and the system is currently being designed with high speed CMOS components that are capable of running at operating frequencies of several hundred MHz. ?
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