ENS1253- Electrical Engineering 1B

Assignment

Electrical Engineering

Design Phases for Mosfet Designed using Multisim

Table of Contents

Introduction

This report deals with the analysis of Mosfet circuit designed using multisim software and sharing the experience while constructing the circuit. Before sharing the experience gained and the lessons learned lets have a brief discussion about multisim software.

Brief Overview about Multisim software

Multisim is a SPICE simulator software, which is used for the design and analysis of analog and digital circuits and testing them in real time world. Via Multisim software it becomes easier to test the circuit designed on paper and view its frequency response in stipulated environment. The main advantage of Multisim software is that, it provides an analogy for wide variety of circuit components along with several tests i.e AC analysis, DC analysis, Transient analysis, DC sweep analysis and even Monte Carlo simulation. The figure below shows the screenshot of Multisim software.

Design Phases

For this purpose, the Mosfet circuit was designed using the Multisim software for the following design phases listed below:

• Transient Analysis
• DC analysis
• AC analysis.

Simulation Results

The circuits are shown in tabular format below:

The main points to consider were that, during DC analysis capacitor are open circuited and during AC analysis, capacitor gets short circuited, but here we are considering the low frequency analysis not midband frequency analysis because generally in midband frequency analysis, the capacitor are short circuited.

The graphs obtained for all the three cases are shown in tabular format below:

The above graphs were obtained using the direct option available via the multisim software i.e Transient Analysis, DC analysis and the AC analysis. The main purpose of the design was to actually calculate the Q point through DC analysis and the input impedance, phase margin and the gain margin through AC analysis.

One more main advantage of Multisim software is that, the results could be obtained directly by using the transfer characteristics as shown below.

For Q Point:

Q point is obtained using the DC analysis. The Q point is simply given as (Drain Current and Gate to Source voltage) i.e Q(I_D, V_GS)

Where,

I_D = Drain Current, V_GS = Gate to source voltage.

The simulation results are shown below:

Now, clearly in this case, the drain current is 666.619 uA and Gate to source voltage is

 -7.00057.

So, in this case:

Q point is Q(66.619 uA, -7.00057 V)

For the AC characteristics:

For this case, the results could be simply obtained by using the transfer characteristics option available in the multisim software.

The transfer characteristics are shown below:

Clearly from the Mosfet Transfer Function Analysis, we obtain the following results for the input impedance and the output impedance as shown below:

• Input Impedance = 18 K
• Output Impedance = 15 K.

Issues Encountered during the Construction of Circuit

Issues

The main issues encountered during the construction of circuit using the Multisim software was that, it was strictly told not to use oscilloscope to view the graphs. Via Oscilloscope it would have been easy to analyse the circuit, but without the oscilloscope it was little tough and the research was required to obtain the results. Apart from that there was little variation among the theoretical and practical results. There was variation of about 20% in the cases obtained. The variation was calculated in the form of percentage error using the formula shown below:

% Variation = * 100%

Where,

True value = Theoretical Value

Measured Value = Practical value

Another main issue which was obtained in the construction of circuit was during AC analysis, as we were doing the lower frequency analysis instead of Midband Analysis, where the capacitors are not short circuited, so the circuit diagram for AC as well as the transient analysis obtained was similar infact the same, which has been analysed in the design phases.

Lessons Learned

The main lessons which were learned during the construction of circuit using the Multisim software was about better research i.e without proper research, it is not possible to obtain the desired results of circuit analysis using the Multisim software. Another important lesson learned from the construction of circuit was that its essential to do hand calculations accurately before doing the actual implementation and there is always some error obtained during the measurement of theoretical and practical values. However the practical values differs on each measurement and the accuracy can be obtained by measuring the multiple values and taking average of it.

Experience

The main purpose of this design was to understand the concept of Mosfet as an amplifier and to obtain the AC and the DC analysis results. The experience was good, infact I came to know that doing the calculations by hand takes more time as compared by multisim software directly. If knowledge regarding the use of multisim software is proper, then its just a easy task. Apart from that, it was more of a learning experience, as I came to know that the graphs can be viewed even without using the oscilloscope.

Apart from that, I gained experience about designing a proper test plan and the test strategy. In this case, the proper test strategy was that to first analyze the circuit by hand and then go for the actual implementation. The proper test plan indicates the schedule, estimates of the theoretical values beforehand, so that it becomes easier to test the ckt in real time environment.

Conclusion

The above report focuses on discussing about the construction of circuit and lessons learned along with the experience gained during the design phase. For this purpose, the Mosfet circuit was chosen and analysed using the multisim software. Relevant screenshots are attached in the report, wherever required.

References

Kholiddinov, I., Komoliddinov, S., & Tychiev, Z. (2021). ANALYSIS OF CALCULATION OF DIFFICULT ELECTRICAL CIRCUITS IN THE MULTISIM SOFTWARE. Universum:Technical Sciences, 83(2-4). https://doi.org/10.32743/unitech.2021.83.2-4.11-15

Li, P. (2014). Electronic Circuit Teaching Aided by MultiSim Virtual Simulation Software. Advanced Materials Research, 933, 703–707. https://doi.org/10.4028/www.scientific.net/amr.933.703

Ni, H. J. (2014). AC-DC-AC Frequency Control System Simulation Analysis. Applied Mechanics and Materials, 536-537, 1110–1113. https://doi.org/10.4028/www.scientific.net/amm.536-537.1110

Sullivan, P. J., Xavier, B. A., Costa, D., & Ku, W. H. (1996). Silicon MOSFET distributed amplifier. Electronics Letters, 32(12), 1106. https://doi.org/10.1049/el:19960699

Appendix

Hand calculations for obtaining the Q point using the DC analysis are shown below:

DC ckt diagram

Here,

Q point = Q (ID, VGS)

Where,

ID= Drain Current

VGS= Gate to source voltage.

Procedure for calculation of drain current

By applying the entire procedure, we get the Q point as: Q(667.1 uA, -8.7V)