ECT 2036 Circuits and Signals

ECT2036: Circuit and Signals SIG2

Experiment SIG2: Circuit analysis using ORCAD Pspice

PRECAUTIONARY STEPS:

1. Read this experiment sheet thoroughly and carefully before coming to your lab session. 2. Take precautions for safety. Also handle equipment carefully to prevent any damages. 3. Try to get as much of the analysis done during the lab session. 4. Close all running programs other than the OrCAD-PSpice program. 5. Seek the approval of your results for each part of the experiment from your lab supervisor before moving to the next one. 6. The lab report should include the graphs, calculations of the resistance values of Part 4.0, comments and analysis of the findings. 7. Appendix A on page 5 provides some guidelines and examples on how to solve Part 4.0.

1.0 Objectives:

(i) To understand the concept of electronic circuit simulation using a software like OrCAD-Pspice (ii) To design passive and active low pass filter circuits for various orders. (iii) To apply the simulation conditions for passive and active low pass filter circuits for AC sweep analysis. (iv) To analyze the simulation results for passive and active low pass filter circuits. (v) To evaluate the performances of active Butterworth and Chebyshev low pass filter circuits from the simulation results (vi) To prepare report from the simulation results of the design of active Butterworth and Chebyshev low pass filter circuits

2.0 Introduction:

Methods of circuit analysis vary widely depending on the complexity of the problem. Whereas some circuits require nothing more complicated than the writing of a single equation for their solution, others may require several equations to be solved simultaneously. When the response of a circuit is to be performed over a wide range of frequencies, the work is often both tedious and time consuming. In many cases the problem to be solved requires that the students have an understanding of which basic laws and principles are involved in the solution. In some cases, if the topology of a network is known, along with complete descriptions of the circuit elements, computer programs can be used to perform the analysis. Such programs have been under development for several decades. Dr.Spice and OrCAD- PSpice are among the powerful programs that are capable of solving many types of electrical networks under a variety of conditions.

1/6 ECT2036: Circuit and Signals SIG2

3.0 Procedure: Start OrCAD-Pspice A/D Click start  Programs  OrCAD demo  Capture CIS demo

Part I: Variable Component Sweep Analysis Step 1: From the menu bar click: File  New  project Step 2: Put name as “Project I”  select “Analog Mixed-signal circuit wizard” OK. (For the circuit as in Figure 1) PARAMETERS: Resistance = 20 R1 L1 out Resistance 10mH IC = -90mA

C1 2u , IC = 10v 0 Figure 1

Step 3: Add these functions to your library: (Analog ; Source ; Special ; Sourcstm & Eval) . Step 4: Draw the circuit as shown in Figure 1: Components needed are as follows:  Analog (R-var, L , C)  Special (PARAM)  Ground (0/source). {from the vertical menu}  Output (Offpageleft-R). {from the vertical menu “<

 A simulation result shows the transient response with difference value of resistance R Step 9: OPTIONS  Click FFT icon to see the frequency domain picture  Change the increment to a small value to see more patterns

Part II: Design of Passive Low Pass Filter Step 1: Open a new project named project 2 for the circuit Figure 2.

R1 L 1 Out 10 10m  H

V1 10Va C1 c 1000 0 u Figure 2 Step 2: Instruct OrCAD to perform AC Sweep analysis with a frequency sweep variable that is to be varied from 1Hz to 1 KHz at 100 points. Step 3: Run simulation. Step 4: Click trace  click Vout. Step 5: A result of low pass filter is displayed.

Part III: Design of 1 st Order Butterworth Low Pass Filter Step 1: Open a new project named project 3 for the circuit in Figure 3.

R 1 82

1Va V 0 7 5 c + 1 + V 3 VCC VCC 6 + - 0 A74 ou 2 1 1 t

- - 4 V 15Vd V 15Vd V c 2 c 3 C 0.01 0 0 1 u 0 VCC - Figure 3

Step 2: Instruct OrCAD to perform AC Sweep analysis with a frequency sweep variable that is to be varied from 500Hz to 500 KHz at 1000 points. Step 3: Run simulation. Step 4: Click trace  click Vout. Step 5: A result of low pass filter is displayed. *μA741 can be selected from the Eval library.

4.0 Laboratory Assignment

Second order low pass filter 00 Table 1: Higher order low pass filter parameters. 1st stage 2nd stage 3rd stage Overall pass- Order RB/RA f’ RB/RA f’ RB/RA f’ band gain (dB) Butterworth 3 - 1 1.000 1 - - 6.0 4 0.152 1 1.235 1 - - 8.2 5 - 1 0.382 1 1.382 1 10.3 6 0.068 1 0.586 1 1.482 1 12.5 2dB Chebyshev 3 - 0.322 1.608 0.913 - - 8.3 4 0.924 0.466 1.782 0.946 - - 14.6 5 - 0.223 1.437 0.624 1.862 0.964 16.9 6 0.879 0.321 1.637 0.727 1.901 0.976 23.2 Note: Normalized cut-off frequency, f’ = 1/[2RC  desired cut-off frequency]

(i) Design a 1st, 3rd and 5th order Butterworth low pass filter where the cut-off frequency is 20 kHz. (ii) Design a 1st, 3rd and 5th order 2dB roll-off Chebyshev low pass filter where cut-off frequency is 20 kHz. (iii) Write your own conclusions and comment your results.

Important points to be noted:

 You are given one week to prepare and submit your lab report to the lab staff.  Reports can be handwritten or typed. Neatness and carefulness will be taken into account in the marking of your report.  You MUST use the FOE lab report cover template. The template can be downloaded at http://foe.mmu.edu.my/lab/Docs/Student_Lab-Report_cover-1.doc  Prepare your own lab report and use your own findings from the simulation results.  Please be instructed that plagiarism is an academic offence and if similar reports are found, you should be required to give an explanation for the similarities and no marks will be given for both the original and the copied ones.  Late submission of your lab report will not be usually entertained unless if there is any emergency cases and strong proof for late submission. Otherwise, automatically awarded 0 (zero) mark for the late submission.  This lab report carries 5% of the total course marks.

Appendix A

Guidelines for Part 4.0:

 Higher-order filters may be constructed by cascading a combination of 1st and 2nd order filter sections (stages). The basic structure of 1st order and 2nd order low pass filter sections is shown in Figure A1:

R R A B V V V o V o i i

Figure A1a: 1st order low pass filter network. Figure A1b: 2nd order low pass filter network

 The block diagrams in Figure A2 illustrate the schemes for a higher-order low pass filter. Odd-order filters are obtained by cascading a 1st order section with one or more 2nd order sections. For example, a 5th order low pass filter can be built by cascading a 1st order section with two 2nd order sections.

1st order 2nd order

3 rd Order Filter

1st order 2nd order 2nd order

5 th Order Filter

Figure A2: Block diagram illustrating the higher-order low pass filters

 The values and parameters in Table 1 can be used to design the required filters in your assignment. Apply the following relationship: 1 f   2RC  fc

where, fc, is the given cut-off frequency.

 Design examples:

1) Third order Butterworth filter: To design a third order Butterworth low pass filter with a cut-off frequency of 19.4 kHz. Set C = 0.01F for all the calculations. By referring to Table 1, it is simple to determine that the selected resistance value should be 820 for all 1st and 2nd stages of filters. 1 R   820 2  0.01 19.4k 2) Fifth order Butterworth filter: To design a fifth order Butterworth low pass filter with a cut-off frequency of 19.4 kHz. Set C = 0.01F in all the calculations. By referring to Table 1, you can determine the suitable resistance values.

3) Third order Chebyshev filter To design a third order Chebyshev low pass filter with a cut-off frequency of 21.4 kHz. Set C = 0.01F in all the calculations. The first stage of the resistance value is calculated as follows: 1 R   2310  2200 2  0.01  21.4k  0.322 By referring to Table 1, you can determine the suitable resistance values.

4) Fifth order Chebyshev filter To design a fifth order Chebyshev low pass filter with a cut-off frequency of 20.1 kHz. Set C = 0.01F in all the calculations. The first stage of the resistance value is calculated as follows: 1 R   3551  3600 2  0.01  20.1k  0.223 By referring to Table 1, you can determine the suitable resistance values.