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UNIVERSITY OF CALIFORNIA AT BERKELEY
College of Engineering
Department of Electrical Engineering and Computer Sciences
EE140: Lab 1
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 low frequency performance by measuring the DC
bias current, common mode and differential voltage gains, and the offset voltage.
Figure 1: Lab 1 Op-Amp
Preliminaries
For this lab, the only things that you need to know about bipolar transistors are:
1) Ic = IS(eVbe/Vt-1)
2) IB = IC/
3) gm = IC/VT
4) ro = VA/IC
5) r = VT/IB =  /gm
You can get the values for IS, , VA and from the datasheets (or the spice models below, which
come from the datasheets)
http://www.fairchildsemi.com/ds/2N/2N3904.pdf
http://www.fairchildsemi.com/ds/2N/2N3906.pdf
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)
The only difference between our simple low frequency small signal model for the BJT and the
MOSFET is the addition of r between the base and emitter. When we drive the base with a
voltage source, this is irrelevant.
Note that for large signal analysis when calculating bias points, the base and emitter will never
be more than ~0.7 volts apart if the base/emitter diode is forward biased.
Prelab and Homework 5
1. Read all the lab tutorials in the course handouts section on the course website.
2. Differential amplifier analysis. Assuming R1 = R2 = 1kΩ and Rtail = 5.1kΩ.
a. Plot Vtail, Itail, IC2, IB2, gm2, and Vout1 versus the input common mode voltage
for Vi,CM= -9 to 9V. (if you do it right, this is just 2 curves with many different
axis labels)
b. Calculate and label the values at Vi,CM={-7, 0, 7} volts.
c. Calculate the value for ro2 at Vi,CM={-7, 0, 7} volts. Do we need to consider ro2
when calculating the first stage gain?
d. Calculate the value for the first stage differential voltage gain, AVDM1, at Vi,CM={7, 0, 7} volts
e. Use HSPICE and .OP to verify all of your hand calculations at Vi,CM={-7, 0, 7}
volts. Comment on any values that are different by more than 10%.
3. Second stage analysis.
a. Calculate the collector current IC3 required for the PNP BJT drives the second
stage output to Vout2 = {-8, 0, 8} volts.
b. Calculate the base/emitter bias voltage VBE3 required to achieve those 3 output
bias voltages, and the corresponding output resistance ro3 and input resistance r
of Q3 at those bias voltages. Do we need to consider the output resistance of Q3
in the voltage gain calculation of the second stage? Do we need to consider the
input resistance of Q3 in the voltage gain calculation of the first stage?
c. Calculate the second stage gain AV2 at Vout2 = {-8, 0, 8} volts.
d. Use HSPICE and .OP to verify your hand calculations at Vout2 = {-8, 0, 8} volts.
Comment on any values that are different by more than 10%.
4. 2 stage analysis.
a. What is the current through R1 that is necessary to produce Vout2 = 0 (you
calculated the necessary Vbe3 in the last problem)? How does that compare to the
current is flowing out of the base of Q3, Ib3?
b. What value of Vi,CM will give the right current through R1 to set Vout2=0?
c. In question 2, you calculated the values of Vout1 at Vi,CM = {-7, 0, 7}. How far are
these values from the value for Vout1 necessary to give Vout2 = 0? You know the
first stage voltage gain at these common mode input points. Calculate the input
offset voltage (i.e. the differential input voltage necessary to set Vout2=0) at VI,CM
= {-7,0,7}.
d. Use HSPICE and .DC to sweep the positive input (which one is it?) from -9 to 9
volts in 1mV steps, while keeping the negative input constant at {-7, 0, 7} volts.
i. Plot the tail voltage and first and second stage output voltages.
ii. On a separate plot, plot Vout2 and use the “measure/point” command in
awaves to label the gain at Vout2 = {-8, 0, 8} volts on each of the three
curves. How do these gains compare to the product of the corresponding
gains that you calculated above? Do all of them exist? Why not?
iii. When Vout2=0, what is the positive input voltage? The difference between
the positive and negative inputs is the input offset voltage. How does it
compare to the values that you calculated above?
5. Feedback
a. Use two 10k resistors to put the amplifier into feedback with a gain of (positive)
two. Use HSPICE to plot the input/output, sweeping the input from -9 to 9. Use
“measure” in awaves to find the gain at Vout={-8, 0, 8} volts.
b. Use two 10k resistors to put the amplifier into feedback with a gain of minus 1.
Use HSPICE to plot the input/output, sweeping the input from -9 to 9. Use
“measure” in awaves to find the gain at Vout={-8, 0, 8} volts.
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 first stage of the circuit in Figure 1using R1 = R2 = 1kΩ and RS = 5.1kΩ.
Measure the actual value of the resistors that you use. Measure the beta of each of the
transistors.
R1
R2
Rtail
Q1 beta
Q2 beta
Q3 beta
Vcc
Vee
3. Tie the two inputs together and use a voltage source to set an input common mode voltage of
{-7, 0, 7}. Measure the tail current and IC2 at each bias point.
4. Add a small resistor Rb2 between the voltage source and the base of Q2. Measure the first
stage differential gain and the base current at ViCM = {-7,0,7}. Note “small resistor” means
one that gives you a measurable voltage drop (so that you can calculate the base current and
the differential input voltage) without affecting the common mode input very much, or
dropping Q2 out of the forward active (high gain) region of operation. You may need to
change the value of Rb2 at different common mode bias points. Note that at each bias point
you are measuring 3 voltages (and a resistor value). Use that data to calculate the currents
and gain, and use the shaded area to write your results from prelab for comparison.
ViCM
V(Rtail) V(R1)
V(Rb2) Rb2
Itail
IC2
IB2
AVDM1
-7
0
7
5. Build the second stage by itself. Hook a voltage source up to the base of Q3 through a
small resistor Rb3. Measure the base voltage and base current required to set the output to {8, 0, 8} volts.
Vout2
VBE
V(Rb3)
IC3
IB3

-8
0
8
6. Connect the first and second stages. Use a voltage source to find the input common mode
voltage that gives an output equal to zero. Add a small resistor to the base of Q2 and
estimate the first and second stage gains (note: measure the changes in the two output
voltages, with and without the resistor).
ViCM
V(Rb2)
AVDM1
AV2
Vout1
Vout2
7. 4155 Measurements
a. Common Mode Response
i. Use the HP4155 Parameter Analyzer to measure Vtail, Vout1, and Vout2 vs. ViCM:
connect Vin1 to Vin2 and sweep the input from -9V to 9V. Use a VM (voltage
measurement) terminal to measure voltages. Do not forget to include ground
while using the parameter analyzer.
ii. graph AVCM vs. ViCM
b. DC Offset Voltage
i. Use the Parameter Analyzer to measure Vouta and Vout2 vs. V+. Connect V- to a
voltage source = {-7, 0, 7} (ideally do this for all integer voltages in this range –
depends on what the 4155 is happy with). Sweep V+ from -9V to 9V.
Use a VM (voltage measurement) terminal to measure Vtail, Vout1, and Vout2.
Use this data to estimate the first and second stage gains and input offset voltage
vs. input common mode voltage.
ii. Graph AVDM1, AVD2 and Vos vs. ViCM.
8. Differential Mode AC Response
a. Tie V- to ground. Use the function generator to apply a small amplitude 1kHz
sine wave to V+. Make sure to add an offset on the sine wave to keep the output
centered near zero. Make sure the disable button is off.
b. Use the oscilloscope to measure the peak-to-peak voltage of V+ and Vout1 and
Vout2.
c. Estimate AVDM1 and AVD2 at ViCM=0
V+,pp
V+, offset
Vout1,pp
Vout2, pp
Vout2, offset AVDM1
AVD2
9. Resistive Feedback
i. Use two 10k resistors to put the amplifier into gain of 2 and gain of -1
configurations. Measure the resistors before you put them in the circuit. Use
the oscilloscope to verify that the output is stable in each feedback configuration
when the input is grounded. If the output is ringing, slap a 1uF capacitor
between the output and ground.
ii. Using the Parameter Analyzer, sweep Vin1 from -9V to 9V.
iii. What is the input base current and closed loop gain at Vout2 = {-8, 0, 8}?
Rf1
Rf2
Vout2
-8
0
8
Postlab and due dates
TBD.
Vfb = Vb1
Ib1
AVCL