Download BJT Op Amp and Feedback - Electronic Circuits Laboratory | EE 371 and more Lab Reports Microelectronic Circuits in PDF only on Docsity! 1 University of Portland School of Engineering EE371 Electronics Laboratory Lab #3 BJT Opamp and Feedback Assigned: Mon, March 23, 2009 Due: Mon, April 20, 2009 (Check-offs on or before April 17, 2009) 1) Introduction: In Lab #3, you will be analyzing the inner workings of an actual BJT opamp. Then you will build and test your opamp in a unique closed-loop 2nd-order circuit configuration. Consider the BJT opamp circuit and its simple equivalent circuit both shown in Figure 1 below. All five BJT transistors, Q1-Q5, are contained within a single CA3096 chip. The output buffer stage is simply a 741 opamp configured in its unity-gain mode. For hand- calculations: 1) assume VBE-on=0.7V for all transistors:, 2) assume the 741 is an ideal opamp and, 3) assume that the dc value of VC5 = 0V. Q1 Q2 Q4Q3 VEE= -15V + VCC= +15V - R2 Q5 CC Vout - + 741 V- V+ R1 71.5kΩ 70kΩ 500pF + - v+ v- vout Above circuit is equivalent to: A(s) BJT Op Amp Figure 1. 2 2) Pre-Lab Exercises: A. Consider the BJT opamp, by itself, in its open-loop configuration as shown in Figure 1. 1. Determine the opamp’s transfer function, A(s)≈ωt/s, and SR using hand calculations. Record ωt and SR in your Summary Table. B. Next, consider the BJT opamp in the unique closed-loop 2nd-order low pass feedback circuit configuration shown in Figure 2 below. Set R1=R2=1kΩ, C1=1nF and C2=100nF. ~ C2 C1 R1 R2 vin vout + - A(s) BJT Op Amp Figure 3. BIG HINT: For this circuit… ( ) ( ) ( ) A s R R C C s R C R C R C s s R C s = + + + + = − 1 11 2 1 2 2 1 1 2 1 1 2 1 2β 1. Sketch the classic feedback diagram of this circuit (use the BIG HINT above). Include in your final report. 2. Determine Af(s) and LG(s). Include in your final report. 3. Use matlab (i.e., bode(Af)) to plot the Af(s) Bode Plot. Determine MP, ωp, and ωH using your "Calculator Sheet" (or matlab) and record in your Summary Table. 4. Use matlab (i.e., margin(LG)) to calculate the Gain Margin and Phase Margin and record in your Summary Table. 5. Use matlab (i.e., step(Af)) to plot the Step Response. Determine tr, tp and P0 using your "Calculator Sheet" (or matlab) and record in your Summary Table. 6. Change C2 to 1nF. Repeat Parts 1 through 5. (Note that since this is now an overdamped system, you will not need to calculate MP, ωp, tp or P0). 7. Include all your above annotated matlab plots in your final report.
