High Frequency Coded Signals

wistfultitleΗλεκτρονική - Συσκευές

24 Νοε 2013 (πριν από 3 χρόνια και 10 μήνες)

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Ultrasound Microscopy and
High Frequency Coded Signals

Antti Meriläinen, Edward
Hæggström


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Using high frequency acoustic
waves for mm
-
/µm
-
scale imaging


Method is non
-
destructive


It “Sees” inside the sample


Ultrasound images differences of
acoustic impedances

Ultrasound Microscopy

What it is?

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Ultrasound Imaging

TOF
image

Amplitude

image

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Ultrasound Microscopy

Basic techniques

Phase Arrays



Single transducer
pulse
-
echo

http://en.wikipedia.org/wiki/Ultrasonic_testing

http://www.nde.com/phased_array_technology.htm

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Focused Ultrasound Transducer

[Yu, Scanning acoustic microscopy and its
applications to material
characterization
, 1995]

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TX


Pulser
, delta spike excitation


Gated sinus wave


For high frequencies ~1 GHz


RX


Protection circuit & Pre
-
amplifier


(Envelope detector / pulse shaper)


Oscilloscope




Tx
/Rx for USM


Camacho
, J.,
Fritsch
, C.: ‘
Protection

circuits

for
ultrasound

applications

Ultrasonics
,
Ferroelectrics

and
Frequency

Control
, IEEE
Transactions
, 2008, 55, (5), pp.1160
-
1164

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Delta spike excitation


Stress for transducer and sample


Energy/amplitude variation with high PRF



Gated sinus


Stress for transducer and sample


Uncertainty of Time
-
of
-
Fly (TOF)


Depth resolution

Challenges with current
techniques

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Coded

USM


Coded signals



Electronics


Signal generation


Switch and timing


Preamplifier



Signal Synthesis



Ultrasound measurements



RF
-
design


Components


PCB layout

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Tx

signal is wave packed


Frequency can be programmed


Phase can be programmed


Envelope (amplitude over time)
can be programmed


Example linear frequency
modulation (LFM)/chirp



Coded Signals

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Cross Correlation

dt

descript depth resolution

dt

depends on bandwidth

dt

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Coded Signal and SNR

SNR =10

SNR =1

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Arbitrary waveform generators


Digital to Analog converter (DAC)


Bandwidth up to 120 MHz (2 GS/s)


If you have money: 5.6 GHz (24 GS/s)


High frequency signal generators


Output: continuous sine wave


Frequency range up to 4+ GHz


Narrow modulation bandwidth (less than 1
kHz)

Signal generation

Numerical vector to Electric signal

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Modulation = change carrier wave by signal


Amplitude modulation (AM)


Quadrature amplitude modulation (QAM)


Frequency modulation (FM)


Phase Modulation (PM)


Many other ….


Modulation techniques

Modulation

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AM:




QAM:







QAM / IQ
-
modulation



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TRF370417 Modulator



Arbitrary/modulation bandwidth
is 2*120 MHz


dt

= 4.2ns


Center output frequency is set
by Local oscillator



Output Bandwidth is NOT
maximum output frequency

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Modulator outputs

1 cm

Lo

Q

I

RF Out

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Carrier Feedthrough and
Sideband Suppression

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Preamplifier

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Amplification


Cascade design


Voltage range


Max/Min signal input strenght


Impedance maching


Input impedance


Output impedance


DC
-
blocks


Capacitors and inductos for high frequencies


Same component can be tunet for different band



Preamplifier Design

Modulator
-
>
Attenuator(
-
60 dB)
-
>
Preamplifier(+55 dB)

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Receiving during
transmission is impossible


Transducer delay line gives
time limit for coded signal


Typically 0.3


5 µs


Signal generator limits coded
length 8 µs


Maximize signal time and
minimize switching time


Switch and Timing

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Switch Circuit

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Power handling


Bandwidth


Attenuation


Insertion loss (Smaller is better)


Isolation (Higher is better)


Switching time


Glitch


AC/DC coupling


Control voltages

Switch designing

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Circuit based on AVR
µController


Programmable


Predictable


Timing resolution is
62.5 ns


AVR trigs AWG and
oscilloscope and
controls the switches


Timing

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Timing Circuit

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Coded

USM


Coded signals



Electronics


Signal generation


Switch and timing


Preamplifier



Signal Synthesis



Ultrasound measurements



RF
-
design


Components


PCB layout

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I and Q are numerical signals that can be generated
by Matlab


Signal generation

How to generate I and Q

RF


LO
sin

LO
cos

X

X

Q

I

LP

LP

Matlab

RF

LO
sin

LO
cos

X

X

Q

I

+

Modulator

AWG

I & Q

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Results with 100


300 MHz

27
/15

Transmitted
signal

Received A
-
line

B
-
scan
image

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Signal
-
to
-
noise ratios (SNR) of surface echoes were estimated to compare
coded excitation and delta spike excitation


Preliminary results showed that coded chirp signal excitation increased mean
SNR (16
±
3) dB for 75 MHz transducer

Results from 2010: 30


70 MHz Coded signal

Pulse
-
echo

measurement

using

a

coded

5

V
pp

chirp

signal

excitation

at

30
-
70

MHz

(left)

and

a

33

V
pp

delta

spike

excitation

(right)
.

The

coded

excitation

increased

mean

SNR

(
16
±
3
)

dB
.

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Higher frequency and coded
signals


Higher frequency gives resolution


Modulator shift arbitrary band (Not increase bandwidth)


Coded signals may improve SNR/CNR


Cross correlation is sensitive for noise which has same
band than signal


Bad modulator can generated ”noise” (
Feedthrough
)


Effective bandwidth can be tuned by arbitrary code


Transducer bandwidth



Attenuation in immersion liquid


Arbitrary codes able
multitone

transmission



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RF design


Impedance matching


Single
-
end vs. Differential signals


Available IC components:


Amplifiers


Attenuators


Switches


Modulators / Demodulators


Power detector


Clock generator (PLL/VCO)

All components are SMD


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Single
-
End vs. Differential signals



Differential signals:


Single supply


No ground loops


Longer signal path


Reduces common
-
mode noise
(noise from ground)


Paired signal is required


Single


Simpler design


(Dual supply)

There is amplifiers for conversion

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Available IC components


Amplifiers


Low noise (Pre. Amp.)


Noise figure <1dB


Gain ~20dB


Gain blocks


50 Ω line driver


Power amplifier (Linear amplifier)


Differential amplifier


Variable gain amplifier (VGA)




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Available IC components


Modulators

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Available IC components


Modulators