Analysis Of A Diode Circuit Using SPICE

Analysis Of A Diode Circuit Using Spiceintroductionthe

The purpose of this experiment is to analyze a diode circuit using SPICE simulation, compare simulation results with hand calculations based on ideal and constant-voltage-drop (CVD) diode models, and verify these with laboratory measurements. Students are instructed to predict the diode's operating state, voltage, and current using different assumptions before conducting simulations and physical measurements.

The experimental procedure involves simulating the circuit with a standard 1N4148 diode model from the SPICE library and recording the diode voltage and current. Then, students modify the diode model by entering specific parameters (IS = 10^-15 A, N = 0.01) into SPICE, re-run the simulation, and again record the voltage and current across the diode. Additionally, they physically assemble the circuit with a 1N4148 diode and measure these parameters directly using a digital multimeter.

The report requires summarizing the objective, procedure, discussion of results, and conclusions. Specifically, students must compare the diode's state (on or off), voltage, and current obtained through hand calculations (ideal and CVD models), SPICE simulations with specified models, and actual laboratory measurements. Comments on the effects when setting N to an unrealistic value like zero should also be included, providing insight into the diode's behavior under various assumptions. Raw data, calculations, and supporting documentation are to be placed in an appendix.

Paper For Above instruction

The analysis of diode circuits is fundamental in understanding nonlinear electronic components and their behavior in various circuit configurations. This experiment leverages both theoretical calculations and practical measurements, supplemented with SPICE simulations, to develop a comprehensive understanding of diode operation under different modeling assumptions.

At the core of the experiment is the comparison between ideal diode assumptions and more realistic models involving constant-voltage-drop (CVD) approaches. An ideal diode is characterized as a perfect switch, conducting with zero voltage drop when forward-biased and not conducting at all when reverse-biased. In contrast, the CVD model acknowledges a more realistic forward voltage (~0.7 V for silicon diodes), affecting the current flow and circuit response accordingly.

The simulation begins with the standard 1N4148 diode model from the SPICE library. Using this model, the software calculates the operating point—state, voltage, and current—based on the circuit parameters provided. This initial step verifies the baseline performance and provides preliminary data to compare with hand calculations. It allows for quick visualization of how the diode behaves under specified bias conditions.

Subsequently, the diode model's parameters are manually adjusted to reflect specific physical characteristics—namely a saturation current (IS) of 10^-15 A and an emission coefficient (N) of 0.01—by editing the device model in SPICE. These parameters influence the exponential I-V characteristic, yielding different simulation results that more accurately mimic actual diode behavior. By comparing these outcomes to the previous models, students can observe the sensitivity of circuit response to diode parameters and better understand the nonlinear nature of diodes.

Complementing the simulations, physical assembly of the circuit with a real 1N4148 diode provides empirical data. Measurement of the diode voltage and current with a multimeter offers a tangible reference point, highlighting discrepancies or confirmations of simulated predictions. Variations between simulation and measurement can be attributed to component tolerances, measurement inaccuracies, and assumptions made during modeling.

Analysis of the experimental results involves detailed comparison across the different techniques. The hand calculations assuming an ideal diode predict a sharp ON/OFF state, while CVD calculations incorporate a fixed forward voltage, leading to different predicted currents and voltages. SPICE simulation results validate these predictions, with the behavior influenced by the diode model parameters. The actual measurements reveal the real-world diode performance, often lying between the ideal and more realistic models.

One significant aspect of this experiment is analyzing the effect of unrealistically low N values, such as zero. Setting N to zero chemically removes the exponential term's influence, leading to a flat I-V characteristic, which is physically impossible but serves as an educational artifact to illustrate the importance of the emission coefficient in diode modeling. Such modifications emphasize the need for accurate parameter choice in circuit simulations.

Overall, this experiment provides insight into the nonlinear behavior of diodes, the importance of accurate modeling, and how simulation tools like SPICE can effectively predict real-world circuit performance. The combined approach enhances conceptual understanding, preparing students to design and analyze diode-based circuits effectively.

References

• Sedra, A. S., & Smith, K. C. (2014). Microelectronic Circuits (7th ed.). Oxford University Press.
• Razavi, B. (2001). Design of Analog CMOS Integrated Circuits. McGraw-Hill Education.
• Weste, N. H. E., & Harris, D. (2011). CMOS VLSI Design: A Circuits and Systems Perspective. Addison-Wesley.
• Nashelsky, L. (2012). Electronic Devices and Circuit Theory. Pearson.
• Hayes, J. R., & Van Valkenburg, M. E. (1971). Digital Circuit Analysis and Design. Addison-Wesley.
• PSpice User Guide. (2020). Cadence Design Systems.
• Bell, D. A. (2014). Operational Amplifiers: Theory and Design. Wiley.
• Streetman, B. G., & Banerjee, S. K. (2015). Solid State Electronic Devices (7th ed.). Pearson.
• Millman, J., & Grabel, A. (1987). Microelectronics. McGraw-Hill Education.
• Kirk, W. (2010). Introduction to Circuit Analysis and Design. CRC Press.