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Digital Modeling of Analog Effect Circuits

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While SPICE circuit simulation software gives researchers and industry accurate information regarding the behavior and characteristics of circuits, the auditory effect of SPICE circuit simulation on audio circuits is not well documented. This project takes a thoroughly analyzed and popular

While SPICE circuit simulation software gives researchers and industry accurate information regarding the behavior and characteristics of circuits, the auditory effect of SPICE circuit simulation on audio circuits is not well documented. This project takes a thoroughly analyzed and popular audio effect circuit called the Ibanez Tubescreamer and simulates its distortion effect on a .wav file in order to hear the effect of SPICE simulation. Specifically, the TS-808 schematic is drawn in the SPICE program LTSPICE and simulated using generated sinusoids and recorded .wav files. Specific components are imported using .MODEL and .SUBCKT to accurately represent the diodes, bipolar transistors, op amps, and other components in order to hear how each component affects the response. Various transient responses are extracted as .wav files and assembled as figures in order to characterize the result of the circuit on the input. Once the actual circuit is built and debugged, all of the same transient analysis is applied and then compared to the SPICE simulation figures gathered in the digital simulation. These results are then compared along with a subjective hearing test of the digital simulation and analog circuit in order to test the validity of the SPICE simulations. The digital simulations reveal that the distortion follows the signature characteristics of Ibanez Tubescreamer which shows that SPICE simulation will give insight into the real effects of audio circuits modeled in SPICE programs. Diodes--such as Silicon, Germanium, Zener, Red LEDs and Blue LEDs--can dramatically change the waveforms and sound of the inputs within the circuit where as the Op-amps--such as the JRC4558, TL072, and NE5532--have little to no effect on the waveforms and subjective effects on the output .wav files. After building the circuit and hearing the difference between the analog circuit and digital simulation, the differences between the two are apparent but very similar in nature--proving that the SPICE simulation can give meaningful insight into the sound of the actual analog circuit. Some of the differences can be explained by the variance of equipment and environment used in recording and playback. Since this project did not use high fidelity audio recording equipment and consistency in the equipment used for playback, it is uncertain if the simulation and actual circuit could be classified as completely accurate. Any further work on the project would be recording and playing back in a constant environment and looking into a wider range of specific components instead of looking into one permutation.

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2015-12

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Multilevel resistance programming in conductive bridge resistive memory

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This work focuses on the existence of multiple resistance states in a type of emerging non-volatile resistive memory device known commonly as Programmable Metallization Cell (PMC) or Conductive Bridge Random Access Memory (CBRAM), which can be important for applications such

This work focuses on the existence of multiple resistance states in a type of emerging non-volatile resistive memory device known commonly as Programmable Metallization Cell (PMC) or Conductive Bridge Random Access Memory (CBRAM), which can be important for applications such as multi-bit memory as well as non-volatile logic and neuromorphic computing. First, experimental data from small signal, quasi-static and pulsed mode electrical characterization of such devices are presented which clearly demonstrate the inherent multi-level resistance programmability property in CBRAM devices. A physics based analytical CBRAM compact model is then presented which simulates the ion-transport dynamics and filamentary growth mechanism that causes resistance change in such devices. Simulation results from the model are fitted to experimental dynamic resistance switching characteristics. The model designed using Verilog-a language is computation-efficient and can be integrated with industry standard circuit simulation tools for design and analysis of hybrid circuits involving both CMOS and CBRAM devices. Three main circuit applications for CBRAM devices are explored in this work. Firstly, the susceptibility of CBRAM memory arrays to single event induced upsets is analyzed via compact model simulation and experimental heavy ion testing data that show possibility of both high resistance to low resistance and low resistance to high resistance transitions due to ion strikes. Next, a non-volatile sense amplifier based flip-flop architecture is proposed which can help make leakage power consumption negligible by allowing complete shutdown of power supply while retaining its output data in CBRAM devices. Reliability and energy consumption of the flip-flop circuit for different CBRAM low resistance levels and supply voltage values are analyzed and compared to CMOS designs. Possible extension of this architecture for threshold logic function computation using the CBRAM devices as re-configurable resistive weights is also discussed. Lastly, Spike timing dependent plasticity (STDP) based gradual resistance change behavior in CBRAM device fabricated in back-end-of-line on a CMOS die containing integrate and fire CMOS neuron circuits is demonstrated for the first time which indicates the feasibility of using CBRAM devices as electronic synapses in spiking neural network hardware implementations for non-Boolean neuromorphic computing.

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2015