The AD9675 is designed for low cost， low power， small size， and ease of use for medical ultrasound. It contains eight channels of a variable gain amplifier （VGA） with a low noise preamplifier （LNA）， a continuous wave （CW） harmonic rejection I/Q demodulator with programmable phase rotation， an antialiasing filter （AAF）， an analog-to-digital converter （ADC）， and a digital high-pass filter and RF decimation by 2 for data processing and bandwidth reduction. Each channel features a maximum gain of up to 52 dB， a fully differential signal path， and an active input preamplifier termination. The channel is optimized for high dynamic performance and low power in applications where a small package size is critical. The LNA has a single-ended to differential gain that is selectable through the serial port interface （SPI）。 Assuming a 15 MHz noise bandwidth （NBW） and a 21.6 dB LNA gain， the LNA input SNR is 94 dB. In CW Doppler mode， each LNA output drives an I/Q demodulator that has independently programmable phase rotation with 16 phase settings. Power-down of individual channels is supported to increase battery life for portable applications. Standby mode allows quick power-up for power cycling. In CW Doppler operation， the VGA， AAF， and ADC are powered down. The ADC contains features to maximize flexibility and minimize system cost， such as a programmable clock， data alignment， and programmable digital test pattern generation. The digital test patterns include built-in fixed patterns， built-in pseudorandom patterns， and custom user-defined test patterns entered via the SPI.