In this paper, a neuromorphic crossbar circuit with binary memristors is proposed for speech recognition. The binary memristors which are based on filamentary-switching mechanism can be found more popularly and are easy to be fabricated than analog memristors that are rare in materials and need a more complicated fabrication process. Thus, we develop a neuromorphic crossbar circuit using filamentary-switching binary memristors not using interface-switching analog memristors. The proposed binary memristor crossbar can recognize five vowels with 4-bit 64 input channels. The proposed crossbar is tested by 2,500 speech samples and verified to be able to recognize 89.2% of the tested samples. From the statistical simulation, the recognition rate of the binary memristor crossbar is estimated to be degraded very little from 89.2% to 80%, though the percentage variation in memristance is increased very much from 0% to 15%. In contrast, the analog memristor crossbar loses its recognition rate significantly from 96% to 9% for the same percentage variation in memristance.

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Abstract:In this paper, we propose a reconfigurable charge pump (RCP) circuit that could change its architecture according to sunlight variation. In strong sunlight, the RCP works by the parallel mode that can maximize the output current. In moderate sunlight, the RCP changes to the serial-parallel mode. When sunlight becomes weak, the RCP runs by the serial mode to keep its output voltage around the target voltage. Compared with the fixed-mode circuit that maintains the serial mode all the time regardless of sunlight variation, the RCP can generate 2.5 times larger output current and has power efficiency better by 24%, in strong sunlight. The area penalty and overhead in power efficiency of the RCP are only 15.8% and 1.2%.

In this paper, the non-linearity in memristor's current-voltage relationship that can affect half-selected cells is analyzed. From the simulation, for the V(DD)/2 scheme, if the non-linear coefficient is larger than 8, unwanted resistance loss during the write time can be suppressed less than 10%. Comparing the V(DD)/2 and V(DD)/3 scheme, the V(DD)/2 scheme can reduce the current consumption by 2 orders of magnitude with little larger resistance change in half-selected cells than the V(DD)/3.