Medical Electronics
New digital demodulator and JESD204B ultrasound analog front end reduces data rates and interface routing up to 80 per cent
A design based on digital demodulator and JESD204B interface for multiple channel ultrasound receive systems is introduced. The design reduces the data rates and simplifies board routing between the Analog Front End (AFE) and digital processing circuits up to 80 per cent. Hugh Yu, Gina Kelso and Ashraf Saad, Analog Devices, tells us more
A
s medical ultrasounds are widely used in the medical diagnostics field, doctors have
ever increasing demands for higher image quality of the ultrasound image systems, and one of the key techniques for image quality improvement is to enhance the signal-to-noise ratio of the receiving channel. As the number of receiving channels in a system doubles, the signal-to-noise ratio should improve by 3dB in theory. Therefore, increasing the number of system channels has become the easiest and most effective method to strengthen the signal-to-noise ratio. At present, 128-channel has become the mainstream configuration for middle to high level medical ultrasound equipment, and 192 or more channels will become the next trend for premium systems. With the increase in the number of channels, the data rates between the analog front-end and back-end digital processing as well as the physical connections sharply increases. They also cause the number of digital circuit device interfaces, the processing power, the costs, the design complexity of the entire receiver circuit, and the corresponding power consumption to increase as well.
System architecture
An ultrasound system is composed of a probe (transducer), transmitting circuit, receiving circuit, back-end digital processing circuit, control circuit, display module, etc. The digital
processing module usually comprises a FPGA, which generates the corresponding waveforms according to the current configuration and control parameters of the system. The transmit circuit’s driver and the high voltage circuit then generate a high voltage to excite the ultrasound transducers. It converts voltage signal into ultrasound waves that enters the human body while receiving the echoes produced by the tissues. Then the echoes are converted into a voltage signal and transmitted to a transmitting/receiving (T/R) switching circuit. The analog voltage signal after signal conditioning, gaining, and filtering is passed to the integrated ADC of the AFE and then converted into digital data, which is then transmitted through a JESD204B interface to the back-end digital parts for the corresponding processing to eventually create the ultrasound image.
JESD204B interface
The AD9671 digital output complies with the JEDEC Standard JESD204B, serial interface for data converters. The AD9671 supports single, dual, or quad lane interfaces. It can connect to an FPGA with a maximum data output rate of 5.0 Gbps. In terms of current AFE and ADC in multichannel ultrasound system applications, LVDS has replaced the parallel output interface. However, for the 128-channel or higher ultrasound system, the large amount of LVDS wire connections for the ADC output is still a headache for the
design engineers. With LVDS, there are 10 pairs of wires for one octal AFE in a current ultrasound system. For a 128-channel ultrasound system, 128/8 × 10 = 160 pairs of LVDS data, and clock wires are required to be connected to the FPGA.
As the JESD204B uses a 16-bit digital output format and uses 8B/10B encoding, the output data rate for an octal AFE with 14-bit resolution, 40 MSPS ADC the sampling rate is 20 × 40 × 8 = 6.4 Gbps. The maximum data rate of each lane of the AD9671 JESD204B interface is 5.0 Gbps, so only two pairs of data lanes are needed to implement an 8-channel AFE data output. So for a 128-channel ultrasound system, only 128/8 × 2 = 32 pairs of output data lanes are required as compared to 160 pairs of the LVDS wires; 80 per cent of the physical interface routing is eliminated.
Conclusion
A multichannel ultrasound system design based on AD9671, an octal AFE with digital demodulator and JESD204B interface, was introduced in this article. The application advantages and benefits of using such an AFE with digital demodulator and JESD204B interface in an ultrasound system are effectively analysed respectively. Comparing with most of current RF beamforming and LVDS interface- based designs, both the data rate and interface routing between the analog front end and digital processing parts are reduced 80 per cent. If the two methods are combined together in an analysis, the physical connections would be reduced even further. Therefore, the system design can effectively simplify the circuit design and software processing complexity by reducing the required board area for data interface routing, the computational complexity requirement, as well as the system design costs.
128-channel ultrasound system block diagram
www.cieonline.co.uk www.analog.com
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