Processor simplifies ultrasound system design

A novel analogue signal processing chip aims to simplify the development of continuous wave Doppler imaging in stationary and portable ultrasound systems.

Analog Devices reckons it has extended its leadership in analogue signal processing technology with an integrated circuit that simplifies the development of continuous wave (CW) Doppler imaging in stationary and portable ultrasound systems.

CW Doppler is an advanced Doppler technique, used in approximately 30% of today's cardiac ultrasound equipment that allows physicians to accurately assess the physical state of arteries, veins and blood vessels by quickly detecting blood flow and direction.

The demand for both portable and stationary CW Doppler ultrasound systems is growing, with annual global unit shipments expected to increase 15%, year to year, over the next five years.

These multichannel ultrasound systems are capable of using hundreds of phase shifters per unit.

Analog Devices' AD8333 is the industry's first dual-channel I/Q demodulator and phase-shifter for CW Doppler ultrasound.

The monolithic Doppler phase-shifter IC achieves a dynamic range of 161dB/Hz, which is equal to or exceeds the dynamic range of existing multichip solutions, while using less than 25% of the board space per channel and delivering a per-channel bill of materials savings of up to 75%.

"Because ABF analogue front ends typically comprise discrete crosspoint switches or custom ASICs, manufacturers have been forced to accept significant cost and board space penalties", said Jay Cormier, Product Line Director of the Linear Products Group at Analog Devices.

"The AD8333, by comparison, provides the same coherent summing and phase alignment of multiple input channels as competing products while consuming just 190mW per channel and significantly reducing circuit board area".

The frequency and wavelength of an electromagnetic field are affected by relative motion.

This is known as the Doppler effect.

In the field of continuous wave Doppler ultrasound, the source and receiver are stationary.

When transmitting and receiving Doppler ultrasound signals, variables such as tissue density, fluid viscosity, and rate of fluid movement create signals with very large dynamic range requirements.

In CW Doppler processing, the most demanding application in ultrasound, there is a particular need for large dynamic-range signal processing elements.

CW Doppler ultrasound systems require analogue beam forming (ABF) because the large dynamic range cannot be processed digitally.

Historically, an ABF front-end consisted of multiple low-noise amplifiers, analogue delay lines, and numerous crosspoint switch matrices.

The dual-channel AD8333 significantly alters this approach by replacing it with a programmable phase-shifting technique with an I/Q demodulator for each input channel, eliminating the need for multiple analogue delay lines and crosspoint switches.

The reduction in board space and low power allow for an increase in continuous wave functionality compared with the delay line approach.

The AD8333 is designed with 22.5-degree phase steps, allowing for accurate time alignment of multiple channels in continuous wave beam forming applications.

The amplifier offers parallel 4bit digital control of phase states, and provides accurate channel matching through a common LO interface.

Analog Devices offers a suite of products to complement the AD8333 and help customers complete the design of their medical ultrasound systems, including the AD8332 dual variable gain amplifier (VGA) or the AD8335 quad VGA, the AD9510 clock IC, the AD8021 high-speed amp and AD8016 line driver, and either the AD7665, AD7679, or AD7685 members of ADI's PulSAR family of analogue-to-digital convertors.

Whereas the power budget and board and cost savings enabled by the AD8333 optimise the development of advanced CW Doppler ultrasound equipment for both fixed and portable medical environments, the combination of I/Q demodulation and phase shifting also suits the AD8333 to other applications where measurement of phase shifts are required, including weather radar, adaptive antenna arrays, and automotive collision avoidance systems.

The AD8333 monolithic Doppler phase-shifter is currently sampling and will be in full production in August 2005.

The device is offered in a 5 x 5mm LFCSP (lead-frame chip scale package) and is priced at $8.95 each in 1000-unit quantities.

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