Basic ci cui o silicon cochlea
227
BASIC CIRCUIT FOR SILICON COCHLEA
D. u ako á, P. K užlic
Dep . o Mic oelec onics, Slo ak Technical Uni e si y, Ilko io a 3, B a isla a
daniela.du acko a@s uba.sk, pe e .k uzli[email p o ec ed]
Summa y Cochlea implan s es o e pa ial hea ing o people wi h se e e o p o ound senso ineu al dea ness. Low-powe
wide-dynamic- ange sys ems a e ha d o build. The biological cochlea is one o he mos awesome examples o such
sys em. I can sense sounds o e 12 o de s o magni ude in in ensi y wi h powe dissipa ion o ew ens o mic owa s. In
his pape , an analog band pass il e is implemen ed in AMS 0.35m CMOS echnology. We used he Sallen-Key opology
in he il e .
1. INTRODUCTION
The human ea ansduces ai bo ne sounds
in o a neu al signal which is subsequen ly
p ocessed by a la ge a ie y o neu ons in he
b ains em be o e being passed on o highe le els o
neu al p ocessing. The cochlea implan is a de ice
ha bypasses a non unc ional inne ea and
s imula es he hea ing ne es wi h pa e ns o
elec ical cu en s so ha speech and o he sounds
can be expe ienced by p o oundly dea people [1].
They mimic he unc ion o he ea in s imula ing
neu ons in he cochlea as he esponse o sound.
Fig. 1: (a) The human ea . (b) The uncoiled cochlea wi h
he basila memb ane and an exagge a ed, schema ic
ep esen a ion o he memb ane displacemen due o a
pu e one o a ela i ely low equency. The dashed lines
ep esen he maximum displacemen o he basila
memb ane and he solid line is a snapsho . [2]
Human ea s hea only sounds wi h equencies
be ween 10Hz and 20 kHz. Bu human speech can
be ecognized jus by hea ing sounds wi h
equencies in much smalle in e al, om 1 kHz o
5 kHz. The e o e we will use a band pass il e ha
will pass only equencies om his in e al.
2. BAND PASS FILTER IN ELECTRONIC
COCHLEA
Th ee s ages ansduce he sound in o ol age
spikes on he audi o y ne e ibe s. The i s s uc u e
o impo ance is he cochlea, a luid- illed, coiled,
bony s uc u e in he inne ea . The cochlea is di ided
in wo by basila memb ane. Sound c ea es p essu e
wa es in he luids o he cochlea and he cochlea
il e s his wa e, so ha di e en sound equencies
will cause di e en pa s o he basila memb ane o
ib a e mos . The second s age in he ansduc ion
p ocess consis s o an a ay o inne hai cells, which
sense he ib a ion o he basila memb ane along he
memb ane. The hi d s age in he ansduc ion
p ocess is implemen ed by he spi al ganglion cells
which make synap ic con ac s wi h inne hai cells
and whose axons o m he audi o y ne e.
Fig. 2: Bionic ea o e iew.
Fig. 2 shows an o e iew o a common signal-
p ocessing chain. Sound is i s sensed by a
mic ophone. P e-emphasis and gain con ol a e hen
pe o med on he inpu pa h. Band pass il e s hen
di ide he sound in o di e en equency bands. The
en elope o each channel is hen de ec ed. The
dynamic ange o each channel is comp essed o i
in o he pa ien ’s dynamic ange. Finally, he signal
om each channel a e modula ed and sen o he
elec odes o s imula e he emaining neu ons o he
pa ien [4].
Cu en sys ems use a DSP-based p ocesso
ha may be wo n as a pack on he bel o as a
Behind-The-Ea uni . The challenge now is o mo e
o designs ha can be ully implan ed. Reducing he
powe o he bionic ea is one o he keys o mo ing
o a ully implan ed sys em and p o ides an impo an
mo i a ion o his wo k.
Ad ances in Elec ical and Elec onic Enginee ing 228
Fig. 3: Sallen-Key band pass il e .
The Sallen-Key il e is a popula il e due
o i s e sa ili y and ease o design. The Sallen-Key
band pass il e ( ig. 3) was designed in AMS 0.35
m CMOS echnology. De ices R1 and C1
ep esen a low pass il e and de ices C2 and R2
ep esen a high pass il e . Resis o s R4 and R5
se s he gain o he wo s age ope a ional ampli ie .
The ci cui was simula ed by he CADENCE ools.
The ans e unc ion o he band pass il e is he
ollowing [5]:
( )
2
0
0
2
0
ws
Q
w
s
Q
w
G
sH
BP
+








+








=
We eadily iden i y he ollowing exp essions o
he h ee pa ame e s:
21321
21
0
CCRRR
RR
w+
=
,
12132311
21321
21
1111
CRCRCRCR
CCRRR
RR
Q
µ
−
+++
+
=
,
12132311
11
1111
CRCRCRCR
CR
G
µ
µ
−
+++
=
.
Fig. 4: The ou pu esponse o he designed il e .
Fig. 4 show he equency cha ac e is ic o
he designed band pass il e . You can see ha we
o ien ed on he egion abou 3.5 kHz, wha is
equency band co esponding wi h he human
speech. We used a ansien analysis. We applied a
ec angle pulse on he inpu pin o he il e and we
obse e he ol age on he ou pu pin.
3. CONCLUSION
Mo ing bionic ea s om sys ems ha a e
pa ially wo n ou side he body o ue implan s ha
a e ully embedded inside he body equi es
o e coming a numbe o echnical obs acles. One
impo an obs acle in ol es ways o subs an ially
lowe he powe o he signal p ocessing. A i s s ep
in ha di ec ion is explo ing and cus omizing il e
echnologies. These il e s ha e o ope a e wi h la ge
dynamic ange and use minimal powe . A
unc ionally simple, analog il e o elec onic
cochlea was p esen ed. The band pass il e was
designed and implemen ed in AMS 0.35m CMOS
echnology. The u u e wo k is adding swi ched
capaci o elemen s o he schema ic and ab ica es he
chip.
Acknowledgmen
This wo k has been suppo ed by he Minis y o
Educa ion o he Slo ak Republic unde G an
No. 1/2046/05.
REFERENCES
[1] R. Sa peshka , R. F. Lyon, C. Mead: “A
Low-Powe Wide-Dynamic-Range Analog
VLSI Cochlea”, Analog In eg a ed Ci cui s
and Signal P ocessing, Vol. 16, pp. 245 -
274, 1998
[2] A. Van Schaik: “An analog VLSI Model o
Pe iodici y Ex ac ion in he Human
Audi o y Sys em”, Analog In eg a ed
Ci cui s and Signal P ocessing, Vol. 26, pp.
157 - 177, 2001
Basic ci cui o silicon cochlea
229
[3] L. Quin anilla, J. A ias, L. En iquez, J.
Vicen e, J. Ba bolla, D. Vazquez, A.
Rueda: “A Swi ched Opamp-Based
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echnology”, Analog In eg a ed Ci cui s
and Signal P ocessing, Vol. 34, pp. 201 -
209, 2003
[4] C. D. Sal house, R. Sa peshka : “A P ac ical
Mic opowe p og ammable Bandpass Fil e
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S a e Ci cui s, Vol. 38, No. 1, 2003
[5] Kendall Su: “Analog Fil e s, Second
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