M3 - Low Noise CMOS Simulation of Outer Hair Cell

Low Noise CMOS Simulation of Outer Hair Cell Activity in the

M li C hlMammalian Cochlea

K A R E N J U Z S W I KR O B E R T L I T T R E L L

E D W A R D T A N GE D W A R D T A N G

Cochlea & MEMS Transducer

Picture courtesy of NSF

Outer Hair Cells

Tectorial Membrane

Inner Hair Cell

Basilar Membrane•Outer Hair Cell Feedback

Basilar Membrane•Enhance Sensitivity

•Tectorial Membrane & OHC Outer Hair Cell•2nd Order System Model

•Inner Hair Cell Sensing

Animation courtesy of http://147.162.36.50/cochlea/cochleapages/theory/main.htm

Goals & Specificationsp

T t th i f OHC tiTest theories of OHC operationBuild a better transducerModeling the 2nd order system of tectorial membrane and OHC

Specifications

B d idth H kHBandwidth 20Hz – 20kHz

Max Adjustable Gain 40 dB

Input Referred Noise (1kHz) 38nV/√HzInput Referred Noise (1kHz) 38nV/√Hz

Max Input Signal 276 µV

Block Diagramg

Stage 1 – Beam Sensingg g

PMOS Differential A lifi

VDD

AmplifierNoise SourcesBiasing of InputSingle Ended Vin

Vout

gConversion

( )2 2 21/

8 (1 / )3 2 '

mbs meq white f

m ox

kT g g KFE E E f fg fC WLK

⎛ ⎞+= + Δ = + Δ⎜ ⎟

⎝ ⎠

Stage 2 – Beam Feedbackg

Transconductance amplifierTransconductance amplifierSubthreshold devicesFollower integratorAdjustable damping and time constant

+-

Q

G3

Adjustable damping and time constant

VDD+-

+-

Vin

Vout

Q

Tau TauG1

G2

V V VV- V+

Vb

VOUT

+-

2 2

1( ) 1 1sβ =

+ 2 2 1s sQ

τ τ+ +

Transconductance AmplifierAmplifier

Stage 3 – Drive Beam Actuationg 3

Buffer between output of second order system and p youtput impedanceSource follower topologyp gyCoupling capacitorAdjustable attenuationAdjustable attenuation

Circuit Performance

All specifications are exceededAt process corners, the time constant and quality factor show significant variation as cited by Lyon and Mead (1988)

Specifications Model

Bandwidth 20Hz – 20kHz 11Hz – 185kHz

Max Adjustable Gain 40 dB 49.5 dB

Input Referred Noise (1kHz) 38nV/√Hz 37.5nV/√HzInput Referred Noise (1kHz) 38nV/√Hz 37.5nV/√Hz

Max Input Signal 276 µV >1 mV

Total Area N/A 0 084 mm2Total Area N/A 0.084 mm2

Circuit Performance

Response of circuit can be adjusted with external voltage for specified natural Response of circuit can be adjusted with external voltage for specified natural frequency and quality factor

0

100Fn=1kHz, Q=5

0

50

e (d

B) Fn=1kHz, Q=1 Fn=10kHz, Q=5

Fn=10kHz, Q=1Input referred noise is below the self noise of a

-100

-50ai

n/N

oise

Input Referred Noise (dB re 1 V/√Hz)

n , Qpiezoelectric sensor

-150

100

Ga

Gain is 49.5 dB

100 102 104 106-200

Frequency (Hz)

Mimicking OHC Activityg y

Qualitative comparison: circuitry Vs OHC feedbackQualitative comparison: circuitry Vs. OHC feedback

40

n (d

B) Experimental Membrane Displacement

High Outer Hair Cell ActivityExperiments by C ( 8)

0

20al

ized

Gai

nModerate Outer Hair Cell Activity

Low Outer Hair Cell Activity

Cooper (1998) on a Guinea Pig

102 103 104

-20

Nor

ma

Effect of Feedback on a Second Order System

20

40

d G

ain

(dB

) Effect of Feedback on a Second Order System

High Feedback Gain

Moderate Feedback GainMagnitude of Feedback Transfer FunctionResponse of 2nd

order system

2 3 4

-20

0

Nor

mal

ized

Low Feedback GainModeled Circuit Transfer Function

order system

102 103 104

Frequency (Hz)

N

Questions?Questions?