Outline - Nanyang Technological Universitynews.ntu.edu.sg/rc-VIRTUS/Documents/2014-S401.pdf · AFE Operation Principle Basic timing diagram for ultrasound analog front-end (AFE)

A High-frequency Transimpedance Amplifier for CMOS Integrated 2D CMUT Array towards 3D Ultrasound Imaging

Xiwei Huang1, Jia Hao Cheong2, Hyouk-Kyu Cha3, Hongbin Yu2, Minkyu Je4, and Hao Yu1* 1. School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore

2. Institute of Microelectronics, A*STAR (Agency for Science, Technology and Research) 3. Dept. of Electrical Engineering and Info. Tech., Seoul National University of Science and

Technology, Seoul, Korea 4. Dept. of Info. and Communication Engineering, Daegu Gyeongbuk Institute of Science and

Technology (DGIST), Korea

02-Oct-2014

Outline 1. Introduction 2. CMUT-array based Ultrasound Receiver 3. TIA Circuit Design and Implementation 4. Measurement Results 5. Conclusions

3D-UBM Introduction Glaucoma imaging by 3D ultrasound bio-microscope: High-frequency (>30MHz) high-resolution CMOS readout with integrated CMUT array

CMUT+ Analog front-end IC and supporting electronics

High-frequency High Bandwidth AFE

3-D Imaging 2-D Transducer Array

Receiving

Transmitting Targets

Ultrasound Imaging System

C

MU

T T

rans

duce

r ar

ray

HV

Tx/

Rx

Swit

ch

HV pulser

Digital Signal Processing and Control

Preamp

Analog Front-End

LPF

Imag

e P

roce

ssin

g/D

ispl

ay

Transmitted acoustic

wave

Received reflected acoustic

wave ADC

TGC (VGA)

Key components: CMUT array + analog-front-end (AFE)

Capacitive Micromachined Ultrasonic Transducer CMUT Device A transducer that converts ultrasound acoustic waves into electrical signals and vice versa The energy transduction is due to capacitance change between membrane and substrate Easier CMOS integration with wider bandwidth

(a) Diagram of CMUT array, (b) one CMUT element, (c) one CMUT cell, (d) cross-section view of CMUT cell, (e) top view of CMUT cells.

Table I. Design Parameters for in-house fabricated CMUT

Equivalent simulation model for CMUT

Parameter Values CMUT array (elements) 16×16 CMUT cells per element 20×20

CMUT cell geometrical profile

Width 28μm Depth 28μm

Thickness 3μm Gap size 0.1μm

CMUT element dimension 600μm×600μm CMUT excitation voltage (VP-P) 20V

Bandwidth 17.5-52.5MHz Capacitance variation 2.12aF/Pa

Capacitance per element (deflated) 44pF

C=44pF

R=4.785kΩ

L=31μH

C=1.6aF

i

(d) (e)

Trench Connection

CMUT-array based AFE Receiver

Rf

CMUT2_EN

OUT_EN

VBias

CMUT1

CMUT2

CMUT1_EN

Pulser1(Transmitter)

Pulser2(Transmitter)

TIARB CB

VBias

RB CB

Cparasitic

1. One preamplifier shared by two AFE channels considering bonding area constraint for 600μm×600μm CMUT element

2. Additional parasitic capacitance of 1pF included in simulation considering bonding for CMUT element and preamplifier

3. HV protection switch using HV double-diffused lateral MOS (DMOS) transistor to isolate preamplifier and avoid possible breakdown in transmission mode

AFE Preamplifier Circuit Specifications

Parameters Specs. Supply Voltage 6V

Gain 61.18dbΩ 3dB Bandwidth 52.5MHz

Input Referred Noise 1.15uArms Max Output Voltage 1VP-P

Output Load 3.2pF//310KΩ

Table. Design specs for preamplifier Preamplifier: trans-impedance amplifier (TIA) with specs by CMUT device and system dynamic range Receiving Bandwidth: 100% fractional bandwidth of the CMUT center frequency 35MHz Gain: output of the preamplifier able to produce a maximum of 1VP-P voltage to the TGC in next stage considering the maximum CMUT capacitance variation Input referred noise: determined by the case when the minimum acoustic-wave pressure echo signal is received Output load: determined by the input impedance of the next stage TGC on PCB

• Attenuation rate: -0.5 dB/MHz/cm • Target focal depth: 1.2 cm

• Input signal DR: centre frequency + focal depth (back and forth) = 35MHz*2*0.5*1.2= 42dB • 256 gray-scale display DR: 20*log(256)=48dB

=90dB

AFE Receiver DR

=> ADC: 6.02*10+1.76=61.96dB, TGC=90-61.96=28.2dB

AFE Preamplifier Circuit Design

Resistive feedback TIA schematic

MP1 MP2 MP3

MSW1

MSW2

MN1

MN2 MN4

MN3

MSW3

VDD

GND

IbiasRf

CMUT1

CMUT2

RX_IN_EN1

RX_IN_EN2

OUT_EN

Resistive feedback TIA Low-noise detection Ease of biasing high bandwidth capability

Rf = 1.15KΩ => Gain=20*log(1.15K)= 61.2dBΩ

( )parasiticCMUTINdBTIA CCR +=−

13,ω

2

_

2_

22_

2__

11

++×++=

fin

ampinampNRampNtotalinN R

CR

viiif

ω

Transimpedance Gain

3dB Bandwidth

Input Referred Noise

AFE Operation Principle

Basic timing diagram for ultrasound analog front-end (AFE)

AFE Implementation and Measurement

1. Tapeout Process: Global Foundry 0.18-μm Bipolar/CMOS/DMOS (BCD) 2. A unity gain analog buffer is included on chip for driving external load of the

probe with over 280MHz bandwidth 3. CMUT array wire boned on PCB within a barrel glued on the PCB (QFN24

package) 4. External power supply of 6V and 80μA input bias current

TIA testing chip photo TIA testing PCB photo

400μm

250μm

CMUT Array

AFE Preamplifier AC + Noise Measurement Results

Simulated closed-loop frequency response AC simulation vs. measurement Results

Input referred noise simulation result Input referred noise measurement result

Parameters Simulation Measurement Transimpedance Gain 61.18dBΩ 61dBΩ

-3dB Bandwidth 75MHz 100MHz Input Referred Noise 16.8pA/√Hz 27.5pA/√Hz

AFE Acoustic Measurement Setup

1. Immerse CMUT array in the vegetable oil contained in the barrel to mimic the underwater testing environment

2. Choose one CMUT element from the CMUT array for transmitting and provided it with 20V DC bias voltage

3. Choose one other CMUT element for receiving the acoustic wave resulting from the reflection at the oil-air layer interface

4. A hydrophone was immersed into the oil to measure the acoustic pressure as a reference to the TIA output voltage signal

AFE Preamplifier Acoustic Measurement Results

1. The delay of the received echo can show the pulse-echo distance, which is the depth of the oil inside the barrel

2. Our in-house fabricated CMUT device successfully generated a 6mV acoustic pulse with the triggering from external pulser

3. The peak-to-peak voltage of our first echo signal was about 7mV, which also successfully demonstrated the functionality of the developed TIA of the analog-front-end receiver

(a) CMUT transmitted acoustic pulse signal captured by hydrophone

(b) TIA received echo signals from CMUT.

Conclusions

A CMOS analog front-end (AFE) receiver integrated with CMUT array is demonstrated (0.18-µm BCD process) for high frequency 3D ultrasound imaging The primary component, a transimpedance amplifier (TIA), achieves 61dBΩ gain with 17.5MHz to 100MHz bandwidth, and low input referred noise of 27.5pA/√Hz The TIA was successfully integrated with CMUT and the receiving functionality has been demonstrated with a pulse-echo acoustic testing Our future work is to demonstrate the whole 3D ultrasound imaging system with digital image processing

References [1] P. Levesque and M. Sawan, “Novel low-power ultrasound digital preprocessing architecture for wireless display,” IEEE Trans. Ultrason. Ferroelectr. Freq. Control, vol. 57, no. 3, pp. 757-767, Mar. 2010. [2] I. O. Wygant, et. al., “An integrated circuit with transmit beamforming flip-chip bonded to a 2-D CMUT array for 3-D ultrasound imaging,” IEEE Trans. Ultrason. Ferroelectr. Freq. Control, vol. 56, no. 10, pp. 2145-2156, Oct. 2009. [3] K. K. Shung, J. Cannata, Q. Zhou, and J. Lee, “High frequency ultrasound: A new frontier for ultrasound,” Int. Conf. of the IEEE Engineering in Medicine and Biology Society (EMBC), pp. 1953-1955, 2009. [4] I. O. Wygant, et. al., “Integration of 2D CMUT arrays with front-end electronics for volumetric ultrasound imaging,” IEEE Trans. Ultrason. Ferroelectr. Freq. Control, vol. 55, no.2 pp. 327-342, Feb. 2008. [5] I. Ladabaum, X. Jin, H. T. Soh, A. Atalar, and B. T. Khuri-Yakub, “Surface micromachined capacitive ultrasonic transducers,” IEEE Trans. Ultrason. Ferroelectr. Freq. Control, vol. 45, no. 3, pp. 678–690, May 1998. [6] T. R. Gururaja, “Piezoelectric transducers for medical ultrasonic imaging,” IEEE Int. Symp. on Applications of Ferroelectrics (ISAF), pp. 259-265, 1992. [7] I. Kim, et. al., “CMOS Ultrasound Transceiver Chip for High-Resolution Ultrasonic Imaging Systems,” IEEE Trans. Biomed. Circuits Syst., vol. 3, no. 5, pp. 293-303, Oct. 2009. [8] G. Gurun, P. Hasler, and F. L. Degertekin, “Front-end receiver electronics for high-frequency monolithic CMUT-on-CMOS imaging arrays,” IEEE Trans. Ultrason. Ferroelectr. Freq. Control, vol. 58, no. 8, pp. 1658–1668, Aug. 2011. [9] L. R. Cenkeramaddi, A. Bozkurt, F. Y. Yamaner, and T. Ytterdal, “A low noise capacitive feedback analog front-end for CMUTs in intra vascular ultrasound imaging,” IEEE Ultrason. Symp. (IUS), pp. 2143-2146, 2007.

Thank you! http://www.ntucmosetgp.net

[email protected]

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