UNIVERSITY OF CALIFORNIA AT BERKELEY College of Engineering Department of Electrical Engineering and Computer Sciences EE140: Lab 1 Due: Saturday March 15th, 2008 8am in the HW drop box Instruction For this lab, you may consult the professor, the TAs, the textbook, and any other inanimate objects, with the exception of your peers' lab reports, for reference. You may obtain data in pairs, but must submit your own written report. Be concise. Objective This lab focuses on the analysis of a simple two stage bipolar op-amp, shown in Figure 1 below. Your goal will be to characterize the circuit’s overall performance by measuring the DC bias current, common mode and differential voltage gains, and the offset voltage. This lab also introduces feedback and the effects of resistive load on an amplifier. Figure 1: Lab 1 Op-Amp Prelab 1. Read all the lab tutorials in the course handouts section on the course website. 2. 3. Hand-calculate the DC bias conditions for R1 = R2 = 1kΩ and RS = 5.1kΩ. This includes finding I1, I2, I3, and Vout. For NPN use Is = 6.734fA, and for PNP use Is = 1.41fA. 4. SPICE it. Verify the DC bias conditions you found in your hand calculations. Find the common mode gain vs. the common mode input voltage (Acm vs. Vin,cm), the offset voltage (Vos) vs. Vin,cm, the differential voltage gain (Adm) vs. Vin,cm. The offset voltage (Vos) of an op-amp is defined as the voltage required on the non-inverting terminal to make Vout equal to Vin,cm. See section 13.2 in Razavi for additional details. Use the following SPICE models for your simulation: NPN model Q2N3904 .model ee140_npn npn (Is=6.734f Xti=3 Eg=1.11 Vaf=74.03 Bf=416.4 Ne=1.259 Ise=6.734 Ikf=66.78m Xtb=1.5 Br=.7371 Nc=2 Isc=0 Ikr=0 Rc=1 Cjc=3.638p Mjc=.3085 Vjc=.75 Fc=.5 Cje=4.493p Mje=.2593 Vje=.75 Tr=239.5n Tf=301.2p Itf=.4 Vtf=4 Xtf=2 Rb=10) PNP model Q2N3906 .model ee140_pnp pnp (Is=1.41f Xti=3 Eg=1.11 Vaf=18.7 Bf=180.7 Ne=1.5 Ise=0 Ikf=80m Xtb=1.5 Br=4.977 Nc=2 Isc=0 Ikr=0 Rc=2.5 Cjc=9.728p Mjc=.5776 Vjc=.75 Fc=.5 Cje=8.063p Mje=.3677 Vje=.75 Tr=33.42n Tf=179.3p Itf=.4 Vtf=4 Xtf=6 Rb=10) Lab 1. Check your kits to make sure you have the following 1 2 2 1 PNP model Q2N3906 NPN model Q2N3904 1kΩ 5.1kΩ Figure 2: BJT Pin Configuration 2. Build the circuit in Figure 1using R1 = R2 = 1kΩ and RS = 5.1kΩ. 3. Measurements a. DC Biases i. Ground the inputs and measure I1, I2, I3, and Vout. b. Common Mode Response i. Use the HP4155 Parameter Analyzer to measure Vout vs. Vin,cm: connect Vin1 to Vin2 and sweep the input from -9V to 9V. Use a VM (voltage measurement) terminal to measure Vout. Do not forget to include ground while using the parameter analyzer. c. DC Offset Voltage i. Use the Parameter Analyzer to measure Vout vs. Vin,cm. connect Vin1 to Vin2 and sweep the input from -9V to 9V. Use a VM (voltage measurement) terminal to measure Vout. Do not forget to include ground while using the parameter analyzer. ii. Graph Vos vs. Vin,cm. d. Differential Mode Response i. Tie Vin2 to 0V. ii. Use the function generator to apply a 50mV amplitude 1kHz sine wave to Vin1. Make sure to add an offset equal to your extracted the Vos for Vin,cm = 0V. iii. Make sure the disable button is off. iv. Use the oscilloscope to measure the peak-to-peak voltage of Vin1 and Vout. v. Repeat with Vin2 = -1V and 1V. vi. Estimate Adm for the circuit for Vin,cm = -1V, 0V, 1V e. Resistive Feedback i. Connect a 510Ω resistor between Vout and Vin2. ii. Using the Parameter Analyzer, sweep Vin1 from -9V to 9V. iii. Now disconnect the feedback resistor and connect it between Vout and Vin1. iv. Sweep Vin2 from -9V to 9V. f. Varying the Resistive Load. i. Keep R1 a constant 1KΩ while varying R2. Extract Acm and Vos for several different R2 values. ii. Repeat the measurements for a constant R2 of 1KΩ while varying R1. Postlab 1. Provide two schematics of the circuit, one with the hand calculated and the other with simulated DC bias voltages and nominal currents. How do the measured values of currents compare with your hand calculations and SPICE simulation? 2. Use your measurements to extract Acm vs. Vin,cm. How do your results compare to the SPICE simulation? 3. How close are your measured values of Vos to your simulated ones? (Error percentage) Why does our circuit have an offset? 4. Estimate the the differential mode gain from your data. 5. Find the gain for the two feedback circuits. Are they different? Explain. 6. Graph Acm vs. R1 (holding R2 constant) and Acm vs. R2 (holding R1 constant). 7. How well does this circuit work as an op-amp? How can we improve the performance of this circuit (without scraping the entire circuit)? Deliverables (by 8am on Saturday, March 15th in the homework drop box.) Prelab: spice deck, hand calculations, plots of Acm vs. Vin,cm, Vos vs. Vin,cm, Adm vs. Vin,cm. Lab: values/graphs for, Vos vs. Vin,cm, Adm vs. Vin,cm Postlab: schematic x2, Acm vs. Vin,cm, Acm vs. R1, Acm vs. R2, postlab questions Remember to explain, or at least try to explain, all discrepancies between your calculations and measurements. Note: No late reports accepted. Legibility is required. Succinctness is strongly encouraged.