EEN1026 Electronics II – Assignment Objective:
To design JFET and high-frequency BJT amplifiers circuits using both hand analysis and computer software simulations.
CAD Tool:
OrCAD PSpice 9.1 (Student Version)
Grouping:
2 students per group
Instructions: 1. Print a copy of this page, fill in your details and sign.
2. Submit this page together with the complete report containing hand analysis th and simulation results to Dr. Guo Xiaoning before Friday 7 January 12noon (any late submission will result in zero marks). Be sure to hand in the two reports at the same time to avoid mix-ups. Rules & Regulations 1. Assignment report must be handwritten and the final calculated results must be highlighted (underlined or use different colours, colours, etc.). 2. Assignment report must be arranged according to the order of assignment questions. 3. All schematic diagrams and simulated graphs/waveforms must be printed directly from the PSpice simulation software. Copy-and-paste screenshots will not be accepted. Before printing
Question 1 – JFET Amplifier Question Objectives - To gain an understanding of electronic circuit design procedures. - To develop a working knowledge of CAD tools and device models. - To compare theoretical performance with simulated results. - To design electronic circuit to meet specific application requirements. Project Description Design a Junction Field Effect Transistor (JFET) common-source amplifier that meets the required specifications. Heavy emphasis is placed on the theory and comparison with simulation results. (Note that Assignment Question 1 is an open-ended problem. Therefore, different students are expected to get different results.)
Required Specifications Voltage Gain: Input Resistance: Load Resistance: Supply Voltage: Output Voltage Swing: Input Signal Frequency:
At least 10 At least 100 kΩ 100 kΩ 30 V 10 V peak-to-peak or more 1 kHz sinusoidal
A DC loadline can be drawn passing two points, (V GS(Max), ID(Max)) and (VGS(Min), ID(Min)) which are located on the TC Max and TCMin curves. This loadline can be represented by I D mV GS c , where m is the slope and c is the intercept point on the I D axis of the loadline. By choosing suitable I D(Max) and ID(Min) values, the biasing resistance values can be found analytically or graphically to satisfy the required specifications. You may choose to use the common source JFET amplifier topology (voltage-divider bias) as given in Figure 1-2 or any JFET amplifier you like, as long as the designed amplifier fits the required specifications.
(v) (vi) (vii)
(viii) (ix)
(x)
Find the value of c. [With the loadline equation. Graphical approach is not suitable.] Derive the required circuit equations based on Figure 1-2. Find the required biasing resistors. [Note the required input resistance and the around center-Q condition, i.e. V DSQ 0.5(V DD – V SQ). V SQ = I D RS , not the value from Figure 1-2.] Find the required coupling/bypass capacitors. [f cutoff = 1/2πReqC eq << f operating] Analyze the voltage gain and the maximum output voltage swing for the two extreme cases, TC Max and TCMin. [Use graphical approach with the plotted TC graph. Transfer V gs (V gs = V GSQ + vgs(ac)) to I d . For forward workout, V gs I d … V ds v RL(ac). Check the allowable V ds swinging range. If V ds swing is out off range, use reverse workout first then forward, i.e. allowable V ds … V gs I d … V ds v RL(ac). vgs must be symmetrical.] If the required specifications cannot be met, go back to step (i), choose new values for ID(Max) and ID(Min), and repeat the design process. [Note on the change of the gain and voltage swing with respect to the change of I D(Max) and I D(Min) values.]
3. Using PSPICE software, simulate the amplifier performance using a 1 kHz sinusoid signal. (i) Set the amplitude of the source signal set to a value that gives maximum voltage swing at the load resistor without noticeable distortion. State the amplitude used in
Question 2- High-frequency BJT Amplifier Question Objectives -To gain an understanding of electronic circuit design procedures. -To develop a working knowledge of CAD tools and device models. - To compare theoretical performance with simulated results. Project Description Design a Bipolar Junction Transistor (BJT) amplifier. Compare the hand analysis with simulation results. Brief Theoretical Background (You should refer to Chapter 2 for other information)
The performance of a BJT amplifier at high-frequency operation can be analyzed using the hybrid-π model. The hybrid-π parameters can be calculated with the h-parameters and other parameters which can be found in datasheet. gm
r b 'e
I C V T h fe gm
h
, where V T = 26 mV at room temperature
(ii) Find h fe, hie, hoe, hre and C obo values from the graphs in the datasheet at the calculated value in step 1(ii). Find f T value also. [Use typical f T value if any.] (iii) Calculate gm value with the calculated IC value in step 1(ii). (iv) Calculate r b’e, r bb’ , r b’c, gce and C e values. [Note that the calculation for gce value may have large error. Let the value stays here.] 3. Hand calculation for |A V|, |AVS| and |Zi| (i) Draw an AC equivalent circuit for the circuit in Figure 2-1. (ii) Draw a model circuit with hybrid-π model for the circuit in Figure 2-1. Justify via calculation which parameters can be neglected. [Normally, r ce is a few tens of kΩ.] (iii) Write down the equations for AV‟, AV (=Vo /Vi), Yi (=1/Zi) and AVS (=Vo /Vs). [Derivations are not required. For reducing calculation work, A V‟ can be simplified, justify via calculation which terms in the A V‟ equation can be neglected.] (iv) Determine the values of |A V|, |AVS| and |Zi| at 100 kHz, 1 MHz, 10 MHz and 100MHz. Record their values in Table 2-1. [Since the calculations need quite a large number of working steps, systematic calculation work is necessary, either to reduce mistakes during calculations or to be easily read by reader. Tables will be useful for this purpose with the necessary notes (e.g. how to perform the calculations, formulas for intermediate equations/terms/factors) at the bottoms of the tables. Make sure these notes are clear and readable.]
Table 2-1: Hand analysis results
Table 2-2: PSpice simulation results
Frequency 100 kHz 1 MHz 10 MHz 100 MHz
|AV|
|AVS|
|Zi|
Appendix - Basic PSpice Revision
You probably already have some experience using PSpice, from your Electronics I course. As you know, PSpice is a popular simulation tool from OrCAD. The PSpice Student Version is the professional version with a limited parts library and a limited circuit size. Nevertheless, this limited version is more than sufficient for our academic purpose. Please refer to your Electronics I assignment for detail steps in creating the schematic, setting up the required stimulus, etc. Preliminary question: Where do I get the PSpice 9.1 Student Version software?
You may search for the keyword “ PSpice Student Version” using any search engine on the internet. You will find many websites that offer free download link of this software. Analyses Required
There are many analyses that you can perform with PSpice. However, for this assignment, you only need to use 4 types of analyses:
gm can be viewed in the simulation output file when bias point details analysis is performed (*.OUT). You can view the .OUT file by clicking the circled button in the OrCAD PSpice A/D Demo window.
Transient
Transient analysis is a kind of analysis that sweeps the time variable. The results of transient analysis will be a graph that time as its x-axis, with different voltage/current levels as the yaxis. This analysis allows you to see how signal affects the voltage/current of different node/branch in the circuit with respect to time. Refer to Figure A-2 for a sample transient analysis output. A similar analogy is your oscilloscope that captures the time domain waveform. Note: By checking "Detailed Bias Pt." option in the transient analysis setup, g m can be viewed in the simulation output file (*.OUT). Acknowledgement
Acknowledgement is given to Cadence for the free PSpice 9.1 Student Version software. Reference [1] OrCAD PSpice user‟s guide
Appendix – Sample Schematic and Waveforms
Figure A-1: Example of PSpice Schematic printout
Figure A-2: Example of PSpice generated waveforms
