Basic circuit for silicon cochlea

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 Bandpass Fil e : Design and Implemen a ion in a 0.35m CMOS 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 o Use in Bionic Ea s”, IEE Jou nal o Solid S a e Ci cui s, Vol. 38, No. 1, 2003 [5] Kendall Su: “Analog Fil e s, Second Edi ion”, Kluwe Academic Publishe , 2003