Texas Instruments | AFE5812 Ultrasound Analog Front End for Industry Applications | Application notes | Texas Instruments AFE5812 Ultrasound Analog Front End for Industry Applications Application notes

Texas Instruments AFE5812 Ultrasound Analog Front End for Industry Applications Application notes
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AFE5812 Analog Front End for Industry Ultrasound
Xiaochen Xu
Key Words
advanced fabrication techniques at a much higher
cost. While a higher frequency acoustic wave is easily
attenuated in medium as listed in Table 1.
NDT, Sonar, High Frequency Ultrasonic Receiver
Introduction
Ultrasound is a sound wave, and the sound wave's
frequency is typically higher than the audible range of
20KHz. Ultrasound imaging is used in both medical
and industry applications. Medical ultrasound imaging
systems use frequencies that range from 1-MHz to 20MHz, with sub-millimetre resolution for evaluating
internal organs. Industry ultrasound imaging systems
can be used for seafloor mapping (<1m resolution) to
tiny defect (<50um) detection in silicon wafers. As a
result of broad applications, industry ultrasound
requires a wider frequency range, for example 20-KHz
to 100-MHz. Both industry and medical ultrasound
systems use a similar architecture. To achieve a
desired image resolution or field of view, a single
channel or up to thousands of channels can be
selected.
Similar to any imaging modality, image quality is an
important topic in medical ultrasound imaging.
Common criteria, such as spatial resolution and
imaging penetration, are settled primarily by the
transducer characteristics and acoustic wave
propagation theories. Both axial (RA) and lateral
(RL)resolutions for an ultrasound image are linearly
proportional to the acoustic wavelength in the medium:
Table 1. Acoustic Properties of Solid and Liquid
Name
Longitudinal
Velocity c
[m/s]
Density
ρ
[Kg/m3]
Z = ρc
[Rayl]
Attenuation
Coefficient
[dB/MHz×cm]
at 1 MHz
Water
1480
1000
1.48×106
0.0022
Sea
Water
1530
1025
1.57×106
0.002~0.006
6
Aluminum
6374
2700
17.1×10
0.01
Castor
Oil
1480
969
1.43×106
0.553
Air
343
1.31
450
11.98
When the media is inhomogeneous, partial energy of
the acoustic wave can be reflected at a boundary of
two media. The unreflected acoustic wave continues
with its propagation until it gets reflected at the next
boundary, or attenuated completely.
The reflection(R) and transmission(T) coefficients are
determined by the difference of acoustic impedances
(Z=ρc) of these two media, where ρ and c are the
density and sound velocity of media respectively,
assuming the wave propagation direction is
perpendicular to the boundary.
(1)
(3)
(4)
where
•
•
•
•
•
Industry Requirements
c is the sound velocity in the medium
f is the ultrasound frequency
Zf the focal distance
2r the transducer aperture
τ-6dB the –6 dB duration of the received echo
when a transducer is excited by an impulse
signal.τ-6dB proportionally equals to the N
period of the received echo
(2)
Hence, higher frequency operation achieves better
resolution. In practice, it is not feasible to improve
image quality by only increasing the transducer
frequency. A higher frequency transducer requires
thinner piezoelectric material, which demands more
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Two cases can be observed to understand the
demanding requirements from industry applications:
one is the sonar application using a range of 20-KHz
to 50-KHz signals for seashore mapping, which
requires signal detecting from 100s meters or even
kilometers away after high attenuation. The other case
is Non-Destructive Testing (NDT), where 10~50MHz
signals are used to detect tiny defects in high speed
train rail, oil pipe, and silicon wafer.
A large mismatch between the metal and air or oil
coupling layer leads to extremely high reflection, for
example, strong signals at the surface in NDT.
AFE5812 Analog Front End for Industry Ultrasound Xiaochen Xu
Copyright © 2018, Texas Instruments Incorporated
1
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Meanwhile, huge attenuation in Sonar and tiny defect
in NDT result in very weak received signal. Both of
these cases demonstrate the fundamental challenges
of industry applications, a wider frequency range, a
wider dynamic range, and from –40°C to +85°C
operation temperature range in the field. TI has been
working on addressing these applications over the
years.
TI’s medical ultrasound analog front ends, such as the
AFE5805 and AFE5808 families, has gained great
success in medical applications. These devices mainly
target hospital applications, which only require a
commercial temperature range, for example, 0 to
70°C. Additionally, medical applications do not require
the wide range of frequencies and dynamic ranges as
industry applications do. Thus, some trade-offs were
made for medical ultrasound analog front ends. The
AFE5808 and AFE5805 families are not perfect fits for
handling sonar frequency lower than 100KHz and
extreme high amplitude signals over 2 Vpp.
In the past several years, the success of highly
integrated medical ultrasound AFEs drive industry
designers to seek suitable single chip AFEs. With
more than 10 years of expertise, TI has leveraged on
medical applications, and released the AFE5812
device to address market needs. The AFE5812 was
designed in TI’s proprietary BiCMOS process and
CMOS process. The device includes an amplifier die
(LNA, VCAT, PGA and LP filter) and an ADC die to
achieve the best performance with the lowest power.
Then, advanced package technology was used to
deliver a single chip solution. Based on the millions of
AFEs’ production experience, the AFE5812 supports a
full industry temperature range from –40°C to +85°C.
The AFE5812 device has been successfully used in
>50 MHz ultrasound imaging systems and <100 KHz
sonar systems.The AFE5812 device has three core
improvements compared to the previous medical
AFEs.
The first improvement is the AFE5812 device is
designed to achieve much wider operation frequency.
The used bipolar transistors have very low 1/f noise
and very high ft. As a result, the signal chain of
AFE5812 device can support wide industry
applications ranging from less than 20-KHz to more
than 50-MHz. Even though the AFE5812 device's ADC
operates from 10-MSPS to 65-MSPS, advanced signal
processing can be used for signals outside of the
Nyquist frequency range. For example undersampling
techniques have been successfully deployed in
telecommunication applications.
2
Secondly, in many industry applications, performance
is the biggest concern rather than power consumption.
Typically, the maximum accepted signal is limited by
the AFE’s power supply and transistor’s threshold
voltage . The AFE5812 device’s LNA is based on a 5V supply compared to 3.3-V supply used in the
AFE5808/5 family. Thus, the AFE5812 device’s power
consumption is slightly higher than the medical AFEs.
As a return, the AFE5812 device can maintain stability
as long as input signal amplitude is below 4Vpp. In
most industry applications, like NDT, the maximum
signal is at the surface between the transducer and the
object. These signals do not carry useful information,
but these signals can saturate front ends and trigger
unexpected AFE behaviors. The AFE5812 device’s
high tolerable signal range ensures a fast and
consistent overload recovery performance. This has
been proven in extreme applications like oil pipe
inspection.
Lastly, the AFE5812 device has built-in digital I/Q
demodulator and decimator. The demodulator and
decimator moves the computation extensive
operations from FPGAs to on-chip custom logics. The
demodulator and decimator also significantly reduce
the total output data amount, especially for sonar
applications. ADC can oversample <100 KHz signal at
10 MSPS, and the on-chip decimation operation highly
improves the SNR. As a result, the output SNR is
close to 16-bit <1-MSPS ADC’s.
Summary
TI’s latest AFE5812 device solves the challenges from
industry ultrasound applications. NDT, sonar, high
frequency ultrasound, industry inspection and et cetera
are just a few solution examples. Higher integration
and lower power analog front-end solutions are still
being developed for both medical and industry
ultrasound receivers. These receivers ease the system
design and reduce time to market. Newer AFE58JD28
and AFE58JD32 devices continue to support both
medical and industry applications.
References
Xiaochen Xu, etc.“Challenges and Considerations of
analog front ends design for portable ultrasound
systems”, 2010 IEEE Utlrasonics symposium.
Ziad O. Abu-Faraj, etc. “Handbook of Research on
Biomedical Engineering Education and Advanced
Bioengineering Learning”, ISBN. 978-1466601222,
2012.
AFE5812 Analog Front End for Industry Ultrasound Xiaochen Xu
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