ECE-322 Lab Description
This lab builds on your experience in the ECE-321L lab. You will have more freedom in ECE-322L to design your 2.75 hours of lab work each week. These analog experiments will draw from circuits described and analyzed in the ECE-322 text: Microelectronics: Circuit Analysis and Design, by Prof. Don Neamen. You will simulate your experiments with SPICE prior to coming to lab. Your knowledge resources are the well-described text and web site searching on google if you want more information. The lag in lab work until the fourth week is done to allow time for the 322 lectures to get into material that supports the lab.
The semester outline is:
Semester week / Topic / LAB1 / No Lab
2 / “
3 / “
4 / Orientation
5 / Diode and Rectifiers / 1
6 / BJT characterization and common-emitter amp / 2
7 / Two-stage amps: Darlington pair CE amp. DC coupled and dual supply bias
8 / Fall Break -No Lab / 3
9 / MOSFET characterization and CS amplifier, CMOS inverter as Class A amp / 4
10 / Op Amp / 5
11 / IC biasing with Diff Amp, CMRR, Ad, Acm / 6
12 / Class AB power amp / 7
13 / Open Lab / 8
14-15 / Written EXAM
Lab Web Site: www.ece.unm.edu/electronics/eece322.html
After the first lab session, there will be much less detailed instructions than in previous labs. A topic circuit is given for each week, and you are to design not only that circuit, but how you use your time. The pre-design work will be written on a word document or equivalent using pasted figures, SPICE, and Excel where appropriate. Your real time lab notebook is a spiral bound book that you record results, observations, and thoughts during the lab.
The first meeting is an orientation similar to that in the ECE-321L lab. Safety is reviewed, lab groups defined, and SPICE will be reviewed. The lab will use AIM SPICE as the primary circuit simulator. If you have access to another version of SPICE at work, school, or home, then feel free to use it. An AIM SPICE tutorial and users guide will be on the course website. AIM SPICE uses a simple line code entry. Since our circuits are relatively simple, they can be encoded rapidly. Download: (1) Lab-0 Laboratory Safety and Orientation, (2) AIM SPICE Tutorial, (3) AIM SPICE User guide.
The first lab analyzes diodes used in rectifier circuits. Lab-2 will use a curve tracer to measure the relevant BJT characteristic curves. The curve tracer has two important uses: (1) you can measure small signal parameters such as b (hfe), rp (hie), ro (hoe), and (2) you can determine whether your transistor is failing. If a suspected failing transistor gives good characteristic curves, then it is good. The small signal parameters are essential to design amplifiers with specific goals, such as my common emitter amplifier must have a gain of 150, or it must have an input impedance of 10 kW. The link of the small signal parameters to the bias values of ICQ and VCEQ permeates your design. Any change in bias conditions changes the small signal parameters which changes your design goals for gain or input-output impedance.
Lab-2 begins the design phase of this lab experience. You will transition from previous directional lab sheets to an experience where you plan your own work activity. Details of planning work on a common-emitter amplifier are given for you to see an approach for the subsequent six labs. Planning your own time is more realistic and also good preparation for the two senior projects courses.
Labs 3-8 select specific circuits described in your textbook. You will plan your work with strong pre-lab activity.
LAB-1 Diodes and Rectifiers
Follow Instructions on the procedures located on the course website.
LAB-2 BJT Characterization and Common-Emitter Amp
Follow instructions on the lab sheet. The TA will show you how to use the curve tracer.
The common-emitter amplifier is the first active circuit you will build. An example of how you might approach that lab is given next. The procedure reviews the relevant reading material in the text and then decides what will be done to most efficiently use your time. Take notes as you read on topics to explore in lab.
Common-Emitter lab preparation and lab activity:
Reading: Transistor properties are described on pages 288-303 with emphasis on understanding BJT operation and characteristic curves. The CE amp is described in Chapters 5 and 6 in the text. A spec sheet for the BJT 2N2222 is given on page 395-396 (or look on line). Transistor properties are described on pages 288-303 with emphasis on BJT operation and characteristics curves. Estimates of the hybrid parameters are given on page 393. Use the scaled down hybrid-p model (Figure 6.13b) when you do the ac analysis of gain and terminal resistance since SPICE uses that. Let b » hfe, ro » 1/hoe, and rp » 1/hie. You can calculate VA from ro and ICQ, and independently estimate rp from rp = bVt/ICQ.
Biasing: Pages 303-327 show how to bias a BJT in its three configurations, CE, CC, and CB. Pages 335-346 show discrete biasing configurations: single base resistor in series with signal source (not recommended), capacitor coupled single base resistor (okay for learning but has large bias resistor), voltage divider biasing (Fig. 5.58), and dual supply biasing (Fig. 5.61). The voltage divider and dual supply bias circuits are more representative of real discrete and IC designs. The dual supply bias is used in integrated circuits since it can eliminate the large coupling capacitors.
Amplifier ac Properties: The primary relevant ac properties are the voltage gain Av, the gain frequency response, and the input or output resistance. An actual design situation may pick any of the four as a first order goal, but let’s assume that voltage gain is primary. In this design, you want Av as large as possible and good symmetrical swing range about the collector-emitter terminals (VCE).
Two Lab Circuits to build:
(1) Construct the CE circuit shown in Figure 5.55 and design for maximum voltage gain and symmetrical swing of the output sine wave. You will do this by writing the voltage gain expression from the hybrid-p model. Then you maximize the numerator and minimize the denominator. You will find this more challenging than first appears since some of the variables work against each other. Watch that VCEQ doesn’t become too small or too large to pass a reasonable sized sine wave signal.
(2) Construct the CE circuit shown in Figure 5.61 and design for maximum voltage gain. Don’t just copy the values from the book, but set voltage gain goals and the bias necessary to support that. Notice the design does not have a coupling capacitor. Notice what happens to Av if you bypass the emitter resistor with a large capacitor. You can understand the effect by observing the location of RE in the gain equation.
Data and Notebook Presentation: You will do the design and simulation prior to coming to class. The lab will do circuit construction, debugging, and measurements. Your prior design will dictate what you measure. You are to decide what is relevant. The TA will review your design at the beginning of the lab.
Comments on circuit design: The chronological order in the book explains biasing in Chapter 5 and ac analysis in Chapter 6. Your design may actually reverse that order. If voltage gain is a priority then you might first write Av as a function of the circuit variables. For example the gain expression of the circuit of Figure 5.55 is approximately
If your design spec was Av = -75, then you would insert values for b and rp and back calculate RL. You would then do the bias design with this value of RL. Your chosen bias current (ICQ) and the value of RL will decide VCEQ. You will find there are a variety of combinations and you will make tradeoffs to implement a design with large voltage gain and good symmetrical swing.
Trouble Shooting: Initially, you may find yourself inefficient and confused in seeking why your circuit isn’t working. You will be better with practice. Try these guidelines
1. Check the power supply voltage and the node where it enters the circuit.
2. Measure the dc node voltages on your circuit. The base, emitter, and collector dc voltages define the state of the transistor. VBE should be about 0.7 V, VBC should be reverse biased, and VCE should be well above the saturation value of 0.1 – 0.2 V. You can easily determine if your transistor is off, linear region, or saturated. If you suspect the transistor is defective, take it to the curve tracer and see if you can get a good family of curves. Another quick transistor check uses the DMM diode checker function. Turn the circuit power off and hook the DMM leads across the BE diode and again for the CB diode. You should get a diode result if they are good.
3. If other node voltages are not what you designed for check the wire connections. Be alert to connections that are intermittent due to a weakness in the mechanical structure of the connections. Proto-boards are not perfect! Do ohmmeter checks on the proto-board.
LAB-3 Two-stage amps: Darlington Pair amp, DC Coupled and Dual Supply Bias
Use Figure 6.73 (page 444) for the Darlington Pair circuit. Replace the constant current source symbol in the emitter of Q2 with a resistor that helps set the bias current.
LAB-4 MOSFET Characterization and CS Amplifier, CMOS Inverter as Class A Amp
Use the schematic in Figure 4.28 (Page 231). Don’t use the book’s values but design your amplifier for a large voltage gain and good symmetrical swing about the transistor. You will have to adjust for the particular current drive constant
after you measure its value in lab. Use an approximate value of Kn’ of 2.8 mA/V2 for your pre-lab calculations.
CMOS Inverter as amplifier: Use the 7400 hex inverter chip. Hint: measure the voltage transfer curve and look for a region where the input and output voltages are linearly related. Hint: what is significant about the point where VIN = VOUT ? Use a series coupling capacitor to drive the inverter with the signal source.
LAB-5 Op Amp
Use the text description of the op amp to investigate op amp configurations and their properties.
LAB-6 IC Biasing with Diff Amp, CMRR, Ad, Acm
Use the text description of the diff amp to investigate this wonderful circuit (Use VCC ≥ 10 V, your lab instructor will tell you why after the lab if you haven’t figured it out)
LAB-7 Class AB Power Amp
Use the text description of properties of this power output stage.
LAB-8 Open Lab; You Design Your Own Experiment
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