Octal Ultrasound AFE with JESD204B

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.

APPLICATIONS

* Medical imaging/ultrasound

* Nondestructive testing (NDT)

* 8 channels of LNA, VGA, AAF, ADC, and digital RF decimator

* Low power:

- 150 mW per channel, TGC mode, 40 MSPS

- 62.5 mW per channel, CW mode

* 10 mm × 10 mm, 144-ball CSPBGA

* TGC channel input referred noise: 0.82 nV/√Hz, maximum gain

* Flexible power-down modes

* Fast recovery from low power standby mode: 2 μs

* Low noise preamplifier (LNA)

* Input referred noise:

0.78 nV/√Hz, gain = 21.6 dB

* Programmable gain: 15.6 dB, 17.9 dB, or 21.6 dB

* 0.1 dB compression: 1000 mVP-P, 750 mVP-P, or 450 mVP-P

* Flexible active input impedance matching