Ultrasound equipment with CW (continuous wave) Doppler measurement capabilities is used to measure blood flow where extremely faint signals are often present. Detection of limited level signals due to low blood volume or distance between the target and the transducer requires an extremely large dynamic range in the receiver signal chain, typically 160 dB/Hz. Current techniques using analog delay lines followed by a very high dynamic range I/Q (in-phase/quadrature) demodulator to extract the Doppler signal can be imprecise. Furthermore, these designs require significant board space, demand large power budgets, and are costly to implement.

The AD9276 and AD9277 octal ultrasound receivers allow system designers to provide CW Doppler, as well as PW (pulse wave) Doppler capabilities, in mid and high end cart-based ultrasound systems, while reducing overall system size, complexity, and power consumption. The AD9276 and AD9277 integrate gain, filtering, data conversion, and demodulation for Doppler signal processing on a single chip. These octal ultrasound receivers consume only 90 mW per channel when processing signals in CW Doppler mode and require 80% less board space than competing ultrasound receiver subsystems. They provide a variable gain range of up to 42 dB and a selection of antialiasing filter options, as well as the industry's lowest input-referred noise (0.75 nV/√Hz @ 5 MHz typ) when operating under real-world conditions. An SPI (serial port interface) allows designers to further customize the noise and power performance for any given imaging mode or probe. In addition, an integrated I/Q (in-phase/quadrature) demodulator with programmable phase rotation on each channel through the SPI port features 16 phase settings. This reduces size and power consumption while improving the performance of the CW Doppler signal path. Each LNA output drives an I/Q demodulator to produce an output dynamic range that typically exceeds 160 dB/√Hz.

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AD9276 and AD9277 Features

• 8 channels of LNA, VGA, AAF, ADC, and I/Q demodulator
• Input-referred noise: 0.75 nV/√Hz (gain = 21.3 dB) @ 5 MHz typ
• VGA attenuator range: –42 dB to 0 dB
• Single-ended input; V_IN maximum: 733 mV p-p/550 mV p-p/367 mV p-p
• Dual-mode active input impedance matching
• Antialiasing filter (AAF), programmable 2nd-order LPF from 8 MHz to 18 MHz
• AD9276: 12-bit 80 MSPS ADC
• AD9277: 14-bit 50 MSPS ADC

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