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)
### Features and Benefits
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 CSP_BGA
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 mV p-p, 750 mV p-p, or 450 mV p-p
Flexible active input impedance matching
Variable gain amplifier (VGA)
Attenuator range: 45 dB, linear in dB gain control
Postamp gain (PGA): 21 dB, 24 dB, 27 dB, or 30 dB
Antialiasing filter (AAF)
Programmable second-order low-pass filter (LPF) from 8 MHz to 18 MHz or 13.5 MHz to 30 MHz and high-pass filter (HPF)
