Thesis - Department of Electronic & Computer Engineering

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19.2Response Time V.S. Network Size N1918.8Response Time (ms)18.618.418.2180 10 20 30 40 50 60 70 80 90 100NFig. 2.4 Response time changes with network size N2.4 Related WorksLazzaro’s circuit [8] was the first hardware model of a winner-take-all network,which consists of only O(N) of interconnect. Each cell suppresses the outputs of allother cells through a global nonlinear inhibition. Since then, many improvements andvariations of this network with addition of positive feedback and lateral connectionshave been described.2.4.1 J. LazzaroIn Lazzaro’s design, a global nonlinear inhibition is computed by a single wire.Each cell contributes to this global inhibition, and each cell receives the same global16
inhibition. Due to the fact that each cell contributes to inhibit itself without any compensation,this circuit has a low resolution of 10% or so. The final outputs of the circuitare solely decided by the input conditions.2.4.2 Add self-excitationLazzaro’s circuit is enhanced through the addition of a current mirror to each cellto realize excitatory feedback (self-excitation). For example, J. A. Starzyk and X. Fangproposed such a circuit which can improve both the speed and resolution of the originalWTA circuit.To mediate the competition between potential winners, hysteresis can be added tothe WTA circuit by adding local feedback to the winning node in the array. The additionof hysteresis enhances the present winning stimulus so that it resists the selectionof a new winner unless the stimulus has a value much larger than the present winner[9]. This has been used for analog VLSI selective attention system.2.4.3 Add lateral excitationAfter lateral excitation is added to the WTA circuits through resistive networks, thewinner is no longer restricted to the one who has the largest input, but depends on thespreading inputs in the neighborhood around the neuron. This kind of competition israther close to the cortical competition. There are some implementations which canmake it difficult for the network to leave the WTA region [10][11].17
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Page 5: activities. The basin of attraction
Page 9 and 10: It is interesting to note that whic
Page 11 and 12: Although there is no saturation in
Page 13 and 14: • Response time of the system;As
Page 15: e verified by computer simulation (
Page 19 and 20: tion. Thus the power consumption is
Page 21 and 22: Let∆be the minimum time necessary
Page 23 and 24: The sender initiates the sequence b
Page 25 and 26: Here in Table 1 is the comparison o
Page 27 and 28: source cell will be broadcast on th
Page 29 and 30: At this point, it seems appropriate
Page 31 and 32: detected, all the potential spikes
Page 33 and 34: InitializationFor each timestep ε
Page 35 and 36: global inhibition BusActivity to fr
Page 37 and 38: Spikes from the winnerATpTTT n T n+
Page 39 and 40: the network will either work at WTA
Page 41 and 42: The computer simulation results for
Page 43 and 44: 5.5 Steady State AnalysisAs demonst
Page 45 and 46: all the losers. To ensure that all
Page 47 and 48: 10090θ=θ mThe necessary condition
Page 49 and 50: 100Necessary conditions to exhibit
Page 51 and 52: The response time is estimated in t
Page 53 and 54: 5.6.2 Further study on the non-arbi
Page 55 and 56: 100Response time V.S. equivalent ga
Page 57 and 58: cell will never collide with each o
Page 59 and 60: ps ( i) = ( 1 - ϕ i)δ( s)for s =
Page 61 and 62: These results show that the collisi
Page 63 and 64: 5.7.4 SummaryCompared with the Pois
Page 65 and 66: 6. ConclusionsIn this thesis, a cla
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In this thesis, we consider only a
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v i() t≤I i----------- ( 1 - e1 -
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If a+ b - 1≥0, then τ---- d [ v
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If a+ b - 1 > 0, since v i() t > 0
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whereV ˙ i () t=max( v i ()0 t , )
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θ t s Nf f wp ct(%) p cl(%) p cw(%
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10. “WTA networks with lateral ex
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Thesis - Department of Electronic & Computer Engineering

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