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[...]... filterbank must be of constant Q This is a significant drawback for applications where a realistic, OHC -based, AGC needs to be incorporated Fig 12 Modelling BM filtering via neuromorphic (filter-cascade) and bio-inspired (filterbank) architectures Fig 13 Dilating-biquads filterbank; adapted from Lin (Lin et al., 1992a) 442 Biomimetic Based Applications 3 Increasing the performance: 1993 - 1998 1993 & 1994:... that particular biquad topology, the Q was obtained through the addition of positive-feedback currents (marked Ifb in Fig 19) which contributed additional shot noise As it will be shown later on, his 1998 effort employed a different biquad topology (based on the DIFF2 structure which was discussed by Lyon in 1992 (Lyon, 1991)), although the WLR topology remained the same 448 Biomimetic Based Applications. .. parallel to tiny cochlea cascades whose corner frequencies overlapped by 1 octave This particular architecture may be viewed as a 452 Biomimetic Based Applications hybrid of an architecture that has many parallel filters in a filterbank and one that has one filter-cascade with all filters in serial Even though he partly deviated from a purely neuromorphic BM structure, he showed that by adopting this... reported up to that date) Bor also provided a table with the errors from the measured peak gains and peak frequencies (i.e CF) from theoretical values Yet, no IHC, neuron or OHC -based AGC circuits were designed 446 Biomimetic Based Applications Fig 17 Measured a) amplitude and b) phase responses from 8 taps of a 32-section SC filtercascade; from Bor (Bor and Wu, 1996) Within Carver Mead’s group, Rahul... was based on the pioneering contributions of Douglas Frey (Frey, 1993;Frey, 1996)on the systematic synthesis of the so called log-domain filters published only a year before The rationale behind this is that the signal is firstly compressed to an intermediate nonlinear voltage according to the logarithmic I-to-V relationship of WI MOS devices The compression generally leads to 444 Biomimetic Based Applications. .. 450 Biomimetic Based Applications Fig 22 Furth’s wide linear range OTA implementation The voltage VGo sets the gain of the Gilbert Multiplier Cell, Vsat is the biasing of the level shifter transistor, whereas Vcas is the biasing of the low-voltage current mirror; adapted from Furth (Furth and Andreou, 1996b) realized that in order to locally control the pseudo-resonant gain at the output of a particular... Because of the fact that the compression law is based on the natural logarithm, the resulting filters were called log-domain filters Toumazou’s design demonstrated a simulated input DR of 80dB, while dissipating a mere 125 nW/pole Toumazou’s contribution was quite valuable at the time, because a) it revealed the potential of current-mode design within the particular cochlea application and b) it showed... of potassium conductances create the downswing (i.e de-activation through re-polarization) Here, the membrane of the neuron was modelled by the membrane capacitance Cmem and the membrane leakage current is controlled by the current Ileak In the absence of any input (i.e Iex = 0) the membrane (Vmem) potential is drawn to its resting potential controlled by V– Excitatory inputs add charge to 458 Biomimetic. .. charge to 458 Biomimetic Based Applications Fig 30 (a) Circuit details of the VLSI neuron (b) Example of the response of the membrane potential (Vmem) and the output signal (Vout) to a DC input current (Iex); from Van Schaik (Schaik, 2001) Cmem, whereas inhibitory inputs discharge Cmem If the excitatory input (Iex) becomes larger than Ileak then Vmem will rise from its resting potential Vmem is then... 2002, David Graham with Paul Hasler from Georgia Tech presented a new very compact second-order section for cochlea modelling with high overall performance (Graham and 460 Biomimetic Based Applications Hasler, 2002) Their design was based on the DIFF2 structure discussed by Lyon in 1992 and on the autozeroing second-order section presented by the authors in (Hasler et al., ) The basic building block . 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