Demodulator is ideal for medical ultrasound systems

30th January 2007

Analog Devices

ES Admin

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The AD8339 from Analog Devices is a quad programmable I&Q demodulator with phase shifter that is ideally suited for medical ultrasound systems. In ultrasonic beam-forming applications like continuous wave Doppler ultrasound, the AD8339 reduces board space by as much as 75 percent compared to competing devices by replacing the large crosspoint-switch matrices and analog delay lines typically used in phased-array beam forming.

The AD8339 consumes just 73mW/channel, which is 30 percent less than competitive solutions, allowing medical instrument manufacturers to provide CW Doppler capabilities in portable and battery-powered equipment. Alternately, the power savings of the new device enables designers to increase the channel density of cart-based ultrasound systems, which often use hundreds of phase shifters per unit.

When transmitting and receiving Doppler ultrasound signals, variables such as tissue density, fluid viscosity, and rate of fluid movement create signals with exceptional dynamic range requirements. The AD8339 achieves a large dynamic range of 158 dB/Hz and features 22.5-degree phase steps, which compensates for signal latency caused by physiological variables to ensure accurate, time-aligned ultrasound images.

The AD8339 features a simple three-wire SPI (serial peripheral interface) interface for digital control of channel selection and phase states by system computer commands. A single synchronized common LO (local oscillator) input for all channels enables precise phase locking to the system clock. The new device features a quadrature phase error of ±0.5°, and I&Q amplitude imbalance of 0.25 dB. The LO frequency range is 100 MHz and the basic RF input frequency range is 25 MHz.

The new phase shifter works well with Analog Devices’ AD8332, AD8334 and AD8335 VGAs, the AD8021 high-speed voltage-feedback amplifier, the AD7686 and AD7693 PulSAR(R) analog-to-digital converters and the AD9510 clock distribution IC.

The AD8339 quad-programmable I&Q demodulator and phase shifter is sampling now and will be available in full production quantities in the June 2007. The device is priced at $11.95 in 1,000-piece quantities. The AD8339 is available in a 40-lead LFCSP (lead-frame chip-scale package).