Building flexibility into electronic
design of ultrasound systems
Rob Reeder, Analog
31 May 2010
In today’s electronics marketplace, portability and
performance are key metrics for system designers. Portability pushes the
boundaries of applications to satisfy the desire for complex tools that
are consumer 'pocketable', while performance
needs dictate the dynamic range of the overall system.
range, or lower noise, provides higher quality sound or images that
allow for better results. Providing end-users with high-performance,
portable applications places increased demands on the system designer
and on the components used within the system.
This article reviews the up-front
considerations that must be addressed to offer portable,
performance-based products that provide system designers with the
flexibility required to bring new products to this global market.
For many years, manufacturers
implemented these complicated systems by designing their own custom
ASICs. This solution usually consisted of two ASICs that encompassed
most of the TGC and Rx/Tx paths, as shown in Figure 1 below.
Figure 1. The ASIC
This approach was common before multichannel VGAs, ADCs, and DACs
became widely available. The custom circuits, which allowed designers to
incorporate low-cost, flexible functions, provided cost savings over
time because incorporating much of the signal chain minimized the number
of external components. Unfortunately, as time went on the technology
available in these lithographies showed its age in both scale and power consumption.
ASICs have a high number of gates, but their digital technology is not
optimized to successfully implement analogue functions such as high
performance ADCs. ASICs also paint the system designer into a corner due
to the limited number of suppliers.
Although high-performance imaging can be
achieved using this partitioning method, it is not optimal in terms of
portability, size, and power consumption. The advent of quad and octal
TGCs, ADCs, and DACs allowed both the size and power to be reduced
without compromising performance, bringing new system approaches and new
players into these markets.
Multichannel components allow the designer
to put devices closer together, increasing the number of channels in the
system; they also allow the designer to divide the sensitive circuits
between two or more boards to complete the system. This allows for
effective reuse of the electronic circuits over many platform
As a side note: as channel counts increase, this leads
to dynamic range improvement. Effectively, noise can be treated as
uncorrelated in the system. By doubling the number of channels in a
system the noise is halved and the dynamic range increases by 3 dB.
Therefore, a 64-channel system can add as much as 6-dB improvement in
dynamic range over a 16 channel system.
Today, IC manufacturers are able to
integrate complete multichannel TGC paths, as shown in Figure 2 below.
Multichannel, multi-component integration makes the design approach
easier, reducing PCB size and power dissipation without sacrificing
performance. As higher level integration schemes become more
predominant, advantages once again follow in cost, size, and power
reduction, leading to less heat in the system and longer battery life.
Figure 2. Commonly
sought multi-component integrations.
Ultrasound system design
A good example of an application where
this is used is in ultrasound subsystems such as Analog Devices’
AD9272/AD9273, which integrates the LNA/VGA/AAF/ADC and crosspoint
switch, implements the complete time-gain compression (TGC) path, the
most common receiver path found in an ultrasound system.
The two devices
offer the system designer the flexibility to trade performance for power
consumption: the high-performance AD9272 features low noise (0.75nV/rt-Hz),
while the low-power AD9273 consumes only 100 mW per entire TGC channel
at 40 MSPS. The pin compatible-devices employ serial I/O to keep the pin
count low. Housed in a compact, 14-mm × 14-mm × 1.2-mm package, they
reduce per-channel area and power dissipation by more than 33% as
compared to multi-chip solutions.
Most ultrasound companies acknowledge
that their intellectual property (IP) lies within the probe and
beamformer technology. Multichannel ICs are quickly becoming commodity
devices, putting an end to high cost components and the endless tweaking
and optimization of individual TGC path to complete the system and get
that extra bit of performance or savings in power.
Other portions of the
ultrasound system are being considered for further integration; studies
have shown that if the front-end electronics were closer to the probe,
less probe loss and better signal sensitivity would occur, allowing
system designers to relax the requirements on the front-end components
(LNA/VGA). Integration of these portions of the signal chain might prove
Practically speaking, the AD9272/9273
offers doctors and medical practitioners the opportunity to use devices
that make more accurate diagnoses available, much sooner. The
portability of the device enables it to be used in ambulances, field
hospitals, clinics, rescue crews and doctors’ offices, as well as
enabling bedside imaging for patients. Crucially, it also allows for
quicker results, at much lower costs. Moreover, it is also able to offer
improved image quality, reliability and a much longer battery life.
With so many applications becoming
realised in ultrasound, the demand for both performance and portability
is high. Performance driven applications, such as cardiology and 4-D
image processing, contain the largest number of channels, features, and
options. Power is not a driving factor because these systems are used at
the patient’s bedside, operating room suite, or nurses’ triage, but
performance is key as these systems are used for human diagnoses.
Portable ultrasound offers a different array of application
opportunities, especially in locations where reliable electrical power
is scarce or does not exist, such as remote village clinics, emergency
medical services, animal farming, bridges, and large machinery
Figure 3. Portable
ultrasound systems used for large animal farming and breeding.
*S*System photo courtesy of E.I.
Ultrasound systems can generally be
split into three classes: high-end, mid-range, and low-end. High-end
ultrasound systems are at the forefront of the most recent technology
and market features, produce the best images, and are more expensive.
Mid-range systems generally have a sub-set of the features that a
high-end ultrasound system offers without much sacrifice in image
quality. Low-end systems are scaled down even further and, in some
cases, serve a particular application, be it clinical or otherwise. As
technology advancements are made, trends show the low-end systems are
beginning to catch up on the image quality, making diagnoses precise,
noninvasive, and timely.
Ultrasound covers a wide range of
varying applications, so the tradeoffs a system designer must make have
increased. Each modality has limitations that are defined generally by
performance vs. power. Today these challenges have been met with
components that allow the designer to scale the performance vs. power
ratio within the IC, thus cutting down on time to market. The AD927x
from Analog Devices offers a host of configurability within the IC to
scale input range, bias, sample rate, and gain. Depending on which
imaging modality or probe type is required, the system designer can
literally system-scale the design appropriately in real-time, offering
the maximum performance at minimum power.
In a typical application, images from a
5-MHz probe producing a 0.5-Vpp signal are to be acquired. If the LNA
that has 0.86-nV/rt-Hz of noise, or 1.4-nV/rt-Hz for the entire channel,
is source terminated with 50 ohms, the input dynamic range of the system
would be 92 dB, producing a noise figure (NF) of 3.8 dB. This translates
to an output dynamic range of 66.3 dB, allowing the system designer to
maintain optimum performance while only dissipating 191 mW/channel at
If the system performance exceeded
expectations, the system designer might decide that a 2-dB reduction in
input dynamic range could be justified in the system if 50 mW channel
could be saved. The system designer could experiment with gain, bias,
termination, and other parameters to see if this is feasible, but
changing all these metrics to understand the system tradeoffs can be
A configuration tool, such as the one
Analog Devices makes for its AD927x family, makes it convenient for the
system designer to evaluate performance, as shown in Figure 4 below. Here, all
the features have been put in place, allowing the system designer to
make these tradeoffs quickly and system scaling to be pushed down into
the IC level directly. This alleviates the designer from changing real
hardware and producing cumbersome image processing tests to validate
these tradeoffs. Furthermore, the configuration tool will translate the
optimized configuration parameters to digital settings and generate a
file that can replicate the part final configuration setup for the
Figure 4. AD9272/9273
medical ultrasound configuration tool for an integrated Rx Channel
Advances in integrated multichannel
devices are pushing system flexibility even further today. New
innovative products and configuration tools make the system designer’s
life easier without a doubt. This provides a means of developing
diversified ultrasound products that are configurable and scalable,
depending on the imaging modality, when it comes to performance vs.
Rob Reeder, senior converter applications engineer, Analog
Rob Reeder is a senior converter
applications engineer working in the high-speed signal processing group
at Analog Devices in Greensboro, NC. Rob has been published numerous
papers and articles about applying converters, converter testing, and
converter applications. Rob Reeder can be reached at
The author would like to give a special
thanks to our product development engineer, Gina Kelso, for creating the
AD927x family configuration tool and gui.
1. Brunner, Eberhard, “How
Ultrasound System Consideration Influence Front-End Component Choice,”
Analog Dialogue 36, Part 1 (2002).
2. Kisslo, Joseph A. and David B. Adams,
Principles of Doppler Echocardiography and the Doppler Examination #1,
London: Ciba-geigy, 1987
3. Kuijpers, F. A., “The
role of technology in future Medical Imaging,”
Medicamundi, 1995, Vol. 40, No. 3, Philips Medical Systems.
4. Bandes, Alan, “How
Are Your Bearings Holding Up? Find Out with Ultrasound,”
Sensors Magazine, July, 2006, pp. 24-27.
5. Meire, Hylton B. and Pat Farrant,
Basic Ultrasound, Wiley, 1995, pp. 1-66.
6. Reeder, Rob. “Ultrasound Portable
Partitioning,” Medical Design Technology, February 2008.
Rob and Corey Petersen, “8-Channel 12-Bit, 10-50-MSPS Front End: The
AD9271—A Revolutionary Solution for Portable Ultrasound,” Analog
Dialogue 41, July 2007.
8. ADI AD927x Configuration Tool. For a
copy please send an email to highspeed.converters @ analog.com