circuits laboratory

EE2002 Circuits Laboratory James Lamberg

Load-Line Method and Clipper Circuits

James Lamberg University of Minnesota Circuits Lab Section 4

Abstract

We are trying to better understand the current versus voltage aspects of an incandescent lamp using the load-line method and the voltage-limiting aspects of diodes using clipper circuits. We can then apply these concepts to real-life situations. We find that the incandescent lamp’s current varies with the square root of the voltage applied and that diodes limit voltage to the drop of the diode and clip input waves to that drop. Introduction: In this experiment, we are trying to better understand how incandescent lamps work as well as how diodes clip input waves. We will first set-up the experiment, obtain data, and analyze our data. For the incandescent lamp, we first draw a circuit diagram of the experiment and then set-up our diagram. We will use a variable- voltage source, an ammeter, a voltmeter, and the incandescent lamp. We then run the experiment, varying the voltage across the lamp and measuring the current into the lamp. We then analyze the data using the load-line method and determine the correct operating points for the data given to us. For the diode circuit, we again begin with a circuit diagram and then set-up our experiment. We will use a resistor, diodes, a function generator input source, and an oscilloscope. We then run the experiment with a fixed voltage and view the input and output waves on the oscilloscope. We then use diode analysis to determine the clipped voltage of the input signal waveform. Theory: For the incandescent lamp, we first draw the circuit diagram:

Fig. 1: Incandescent Lamp Circuit Diagram

In the diagram, V_Variable is the variable voltage source, V_Ammeter is the ammeter, R_Light is the incandescent lamp, and l_Volt_Meter is the voltmeter. (See last page). Next, we use Kirchhoff’s voltage lab to get the load-line equation:

!

VSS

= R " iD

+VD

We assume that

!

VSS

and

!

R are given and we want to find

!

iD

and

!

VD for the diode.

We have a relationship between the two unknowns graphically, by doing an experiment or with previous knowledge of the incandescent lamps characteristics. Then we graph the load line using the intercepts of the

!

iD

and the

!

VD axis. The intersection of the load

line and the incandescent lamp’s characteristic curve is the operating point we want to find. For the diode and input waveform, we first draw a circuit diagram:


Fig. 2: Clipper Circuit Diagram In the diagram, l_Scope_Input and l_Scope_Output are the two voltages the oscilloscope will read. R is the resistor. D_Neg is the diode that clips negative waves and Vn is the voltage source so negative voltage can be limited at any point. D_Pos is the diode that clips positive waves and Vp is the corresponding voltage source for positive wave clipping. V_Wave_Gen is the function generator input signal. (See last page). Next we use diode analysis for the clipper circuit. The resistor will not cause a voltage drop; it will only reduce current (Ohm’s Law) so the diodes do not go into their breakdown range. The diode connected to the positive lead of the function generator (D_Pos, forward biased) will cause a voltage drop since it is not an ideal diode but is a silicon 1N4148. This will limit positive input wave voltage to the drop of the diode, which is usually 0.6 or 0.7 volts. We can connect a second diode in parallel with the first diode but connect it to the negative lead of the function generator (D_Neg, forward biased for negative voltages). This again will limit the wave voltage, but instead of limiting the positive waves it will clip the negative waves to the value of the voltage drop through the diode. Both of these occur because the diodes are set up as half-wave rectifiers in the circuit and will not allow the opposing wave (negative for a positive forward biased diode and positive for a negative forward biased diode).

Now, we can add additional voltage sources after the diodes to limit the voltage to a larger variety of values. The limiting voltage will be the sum of the drop through the diode and the new voltage source in series with the diode. The input waveform will be clipped at the limiting voltage. This is then shown graphically on the oscilloscope. Experiment & Data: For the incandescent lamp, an ohmmeter connected to the leads of the lamp was used to determine the lamp resistance of 245Ω. Next, Figure 1 was constructed using a solder-less breadboard and wires. The voltage was then varied from about 0-30 and the corresponding current was measured. This is the data from that measurement: Current (mA) V (Volts)

0.000 0.000 0.662 0.160 3.560 1.850 4.880 3.130 6.870 5.480 8.500 7.730 9.570 9.350

11.290 12.190 13.080 15.420 14.500 18.180 15.320 19.840 16.200 21.700 17.110 23.700 17.880 25.400 18.570 27.000 19.970 30.300

This data was then plotted on a TI-89 calculator. Here is the graph in MATLAB:


Fig. 3: Lamp Characteristic Next, we use the given data and the load-line method to determine the operating points for the data:

!

VSS

= R " iD

+VD

40V = R " 0A+ VD, V

D= 40V

20V = R " 0A +VD, V

D= 20V

40 = 4000 " iD

+ 0, iD

= 0.01mA

20 = 2000 " iD

+ 0, iD

= 0.01mA

Now we determine the equations for the two load lines:

!

Slope1 =0 "0.01

40 " 0= "0.5mA

Slope2 =0 "0.01

20 "0= "0.25mA

i1

= "0.5 #V +10mA

i2

= "0.25 #V +10mA

Now we graph these two load lines and determine the operating points where the load lines intersect the incandescent lamp’s characteristic curve.

Fig. 4: Operating Points From the graph, we find that the operating points are: Operating Point 1: (7.73V, 8.50mA) Operating Point 2: (5.25V, 7.37mA) Next, we use in resistor in series with the lamp and ammeter. For the first run, we use a 4000Ω resistor and apply 40.0 Volts. Then we view our results from the voltmeter and ammeter: Operating Point 1: (7.70V, 8.44mA) Next we use a 2000Ω resistor and apply 20.0 Volts to get: Operating Point 2: (5.66V, 7.35mA) For the diode circuit (voltage clipper), we constructed four different circuits. In the first circuit, the resistor was a 21.5kΩ resistor and there was only one diode, which was forward biased to allow only the positive voltage of the input waveform. The function generator was set to a sine wave with peak at 8 Volts. Here is the diagram:

Fig. 5: Circuit Diagram for 1st Clipper We then view the oscilloscope connected at Vin and Vout to view the clipping of the wave:

Fig. 6: Input and Output for 1st Clipper Then we graph these two together to see the clipping voltage better:


Fig. 7: Input vs. Output for 1st Clipper From this, we see that the positive wave is clipped at 0.91 Volts. We do the same experiment again, but reverse the diode so it allows positive and clips the negative portion of the wave: Here is the diagram along with the results:

Fig. 8: Circuit Diagram for 2nd Clipper

Fig. 9: Input and Output for 2nd Clipper

Fig. 10: Input vs. Output for 2nd Clipper From this, we see that the negative wave is clipped at 0.89 Volts. Now we repeat the 1st clipper circuit but add in the necessary voltage source in series after the diode to limit positive voltage to 2 Volts. Here is the diagram along with the results:

Fig. 11: Circuit Diagram for 3rd Clipper

Fig. 12: Input and Output for 3rd Clipper

Fig. 13: Input vs. Output for 3rd Clipper To get a clip at +2 Volts, we needed to add in a 1.1V source after the diode, which gave a 0.9V voltage drop. This added up to +2 Volts and from Figure 13, we can see that it in fact does clip the waveform at +2 Volts. Next, we need to clip both the positive and negative voltages of the input waveform at 2 Volts. To accomplish this, we use the same circuit we did in the 3rd Clipper, but put another diode and voltage source, in the other direction, connected in parallel. Here is the diagram, along with the results:

Fig. 14: Circuit Diagram for 4th Clipper


Fig. 15: Input and Output for 4th Clipper

Fig. 16: Input vs. Output for 4th Clipper To get a clip at +2 Volts, we needed to add in a 1.1V source after the positive diode (D_Pos), which gave a 0.9V voltage drop. This added up to +2 Volts. For the negative diode (D_Neg), we needed to add a 1.3V source after it since it had a different voltage drop. We can then see from Figure 16 that the voltage was clipped at both positive 2 volts and negative 2 volts. Lastly, we change the function generator waveform to the triangle wave and the square wave and view the results on the oscilloscope.

Fig. 17: Input and Output for 4th Clipper and a triangle wave input

For the triangle wave, the positive and negative is clipped and it looks similar to the sine waveform we initially used.

Fig. 18: Input and Output for 4th Clipper and a square wave input

For the square wave, the voltage is limited below the input voltage peaks. This will then drop the peak voltage to the limiting voltage. The oscilloscope shows a similar square wave that is limited at +2V and –2V. Error: There may have been error in the electronic instruments, the devices (such as diodes), and the connections. There may also have been human error in measurement. Any of these could change the results of the experiment but do not drastically effect the overall results and concepts. Conclusion: For the incandescent lamp, we found measured that two operating points to be: Operating Point 1: (7.70V, 8.44mA) Operating Point 2: (5.66V, 7.35mA) Theoretically, we were supposed to get: Operating Point 1: (7.73V, 8.50mA) Operating Point 2: (5.25V, 7.37mA) Since these values are very close given the error in the experiment, we can conclude that the load-line method works for the incandescent lamp and the current vs. voltage relationship is correct. For the clipper circuits, we found that a diode will limit an input waveform depending on the bias of the diode. A diode connected to the positive lead of the input voltage source and biased to allow current to travel to the negative


lead will clip positive voltage to the voltage drop of the diode. The same is true for a diode biased the other way.. It will limit negative voltage to the voltage drop of the diode. We can then put voltage sources in series after the diodes to increase the voltage that the wave will be limited to. These were shown on the oscilloscope. From this, we can conclude that the clipper circuits do work and our diode analysis is correct. We can also check our analysis by using different wave functions such as triangle and square waves.

Acknowledgments: C. Hacker, University of Minnesota Electrical Engineering Student B. Pokorny, University of Minnesota Teaching Assistant References: Electronics, Second Edition by Allan R. Hambley 2000: Pages 134-145 The Math Works, Inc: MATLAB 5.2.1 http://www.mathworks.com

Fig. 1: Incandescent Lamp Circuit Diagram

Fig. 2: Clipper Circuit Diagram


Bipolar Junction Transistors

James Lamberg University of Minnesota Circuits Lab Section 4

Abstract

We are trying to better understand the collector current versus collector-emitter voltage aspects for a 2N3393 Bipolar Junction Transistor (BJT). We are also trying to obtain values for the transistor current gain and small signal resistance from these and similar measurements. From this, we can create a circuit to make a Light Emitting Diode (LED) blink at 5 Hz and also create a “Current Mirror” circuit. Introduction: We began by forward biasing the 2N3393 BJT and taking measurements for the collector current and the collector-emitter voltage for several fixed base current values. We used these numbers to plot the BJT’s output characteristics. We then used similar collector-emitter voltages and corresponding base currents to plot an

!

ic

versus

!

iB

graph (collector versus base currents). We used this data to calculate the small-signal common-emitter current gain at different values of collector-emitter voltage as well as the small-signal output resistance for several values of collector current. We then constructed a similar circuit using the 2N3393 BJT and used an oscilloscope to measure the small-signal common-emitter current gain and the small-signal input resistance. We then compared this data to that of the previous circuit. We were then given a circuit to construct, which was driven by a triangle wave such that the 2N3393 BJT would be in the cutoff region at one extreme and saturated at the other. We then determined the common-emitter current gain and the collector-emitter saturation voltage. Using the previous circuit with some modifications, we were able to

incorporate a LED so that it would blink at a rate of 5Hz. Lastly, we used two 2N3393 BJTs to create a current mirror. We then measured the collector current for both BJTs and found the ratio between them. Theory: For the first part, we construct the circuit shown below and take measurements at the ammeter and voltmeter.

FIG. 1: BJT Circuit #1 DC This was the same circuit that would have been used in the second part, but we used similar values for the collector-emitter voltages and their corresponding base currents. We used all of this data to construct a collector current versus collector-emitter voltage graph. We did this for different values of base currents using Ohm’s Law.

!

iB

=VB

RB

=VB

100k", for

!

VB ranging from 1

volt to 5 volts, giving

!

iB

ranging from

!

10µA to

!

50µA . We then plotted collector current versus base current for the values we calculated previously. We then found


the small-signal common-emitter current gain using:

!

Gain = " =ic

iB

=#i

c

#iB

Since we’re using small signals, we must use the change in the values. This can be accomplished by choosing two points for the same fixed

!

VBE

. To calculate the output resistance, we use Ohm’s Law:

!

Rout

=VOut

ic

Again, we are using the change in the values so we use two points with the same fixed base current

!

iB

. For the next part, we use the following circuit:

FIG. 2: BJT Circuit #2 Sine Wave Here we have a sine wave as the input. We also set the DC offset to allow the small signal something larger (DC signal) to ride on. Measurements were taken with an oscilloscope. Although we wanted to use ammeters, the oscilloscope measured voltages and we used the corresponding resistors to determine the current at each branch of the 2N3393 BJT:

!

ic

=VC

1k" and

!

iB

=VB

100k" with

!

Gain = " =ic

iB

, where

!

VC

and

!

VB are the

respective collector and base voltages measured. Measurements were taken for values of

!

VCC

at 5V, 10V, and 15V using the MATH function of the oscilloscope. The MATH function will find the difference in the two point voltages (lead one minus lead two), giving us the necessary values for

!

VC

and

!

VB. To

calculate the small-signal input resistance of the 2N3393 BJT, we use the following Kirchoff’s Voltage Law (KVL) equation around the input loop:

!

"Vin# "i

B$100k%# "i

B$R

B= 0

Where the 10Ω resistor was removed since it does not make up a significant part of the equation (very small value). Next, we take these values and compare them to those obtained in the first part of the experiment. We were then given a circuit containing a 2N3393 BJT and told to drive it with a triangle wave:

FIG. 3: BJT Circuit #3 Triangle Wave To get the desired situation, we must lower the

!

VCC

so that the BJT saturates at one extreme and increase the

!

Vin

so that the BJT is in cutoff at the other extreme. To find the common-emitter current gain, we start with

!

VCE

which was measured via the oscilloscope. We again found the voltage drops across the base and collector resistors and divided by their resistance values to get the current. Gain was calculated as usual:

!

Gain = " =ic

iB

Using this idea of saturation and cutoff for the 2N3393 BJT, we can construct a circuit that will allow an LED to blink at a rate of 5Hz.

FIG. 4: BJT Circuit #4 Blinking LED


Here we replace the input (base) resistor with a smaller one. This will allow for a larger current flow through the base (using Ohm’s Law), which will therefore allow for the correct current to flow through the diode and cause it to emit light. The idea behind this comes from the KVL equation around the output loop:

!

VCC

=VCE

+ iC" 1k#( )

When the positive part of the wave is shown at the input, the base current will be positive so the collector current will be positive as well as large.

!

VCE

will then be small so the LED will get sufficient current to emit light since:

!

" # iB

= iC$ i

E= i

LED and the diode

current will be around 20mA without drawing more than 1mA from the signal generator. When the negative peak enters, the base current will be negative and the collector current will be negative and large. Therefore, most of the voltage will be dropped at

!

VCE

so not enough current will reach the LED (and it will not emit light). We were again given a circuit to construct as shown below:

FIG. 5: BJT Mirror Circuit Here, we use two ammeters (Amm1 and Amm2) to obtain values for the collector current for each 2N3393 BJT. We then determine the ratio using the following formula:

!

Ratio =iC1

iC2

which should be about 1.

Experiment & Data: Taking measurements for the collector current and the collector-emitter voltage and varying the input voltage from 0 to 10 volts, we got this data: 1V, 10

!

µA 2V, 20

!

µA

!

VCE

(V)

!

iC

(mA)

!

VCE

(V)

!

iC

(mA) 0.02 0.012 0.02 0.051 0.04 0.056 0.04 0.182 0.08 0.220 0.08 0.888 0.10 0.395 0.10 1.338 0.12 0.472 0.23 2.110 0.15 0.545 0.33 2.120 0.33 0.596 1.33 2.140 1.20 0.599 2.08 2.150 2.00 0.603 5.35 2.190 4.13 0.608 6.28 2.200 6.47 0.614 7.51 2.220 7.65 0.617 9.85 2.240 8.93 0.621 10.60 2.260

10.04 0.623 3V, 30

!

µA 4V, 40

!

µA

!

VCE

(V)

!

iC

(mA)

!

VCE

(V)

!

iC

(mA) 0.03 0.22 0.02 0.180 0.08 1.61 0.03 0.427 0.10 2.03 0.05 0.864 0.17 3.49 0.07 1.459 0.34 3.67 0.20 5.080 0.75 3.69 0.53 5.250 1.30 3.71 1.04 5.280 2.48 3.75 1.46 5.310 3.16 3.77 2.65 5.360 4.93 3.81 4.37 5.450 8.02 3.89 6.44 5.540 9.30 3.93 8.68 5.650

10.70 3.97 10.32 5.730 5V, 50

vce (V) ic (mA) 0.02 0.216 0.04 0.768 0.11 4.29 0.19 6.38 0.39 6.81 1.72 6.92


3.09 7.02 5.55 7.18 7.70 7.34 9.60 7.48

10.66 7.59 Plotting this data for each fixed base current value, we get:

FIG. 6: Collector Current vs. Collector-Emitter Voltage

We can also plot this data for a fixed

!

VCE

to get the base current versus the collector current. Here is the data and plot for this:

!

VCE

=0.10

!

VCE

=0.33

!

iC

(mA)

!

iB

(µA)

!

iC

(mA)

!

iB

(µA) 0.395 10 0.596 10 1.338 20 2.120 20 2.030 30 3.600 30 3.200 40 5.100 40 4.000 50 6.620 50

vce=4.0

ic (mA) ib (µA) 0.607 10 2.156 20 3.800 30

5.410 40 7.900 50

FIG. 7: Collector Current vs. Base Current

Now we calculate the small-signal common-emitter current gain at different values of collector-emitter voltage:

!

" =#i

C

#iB

!

VCE

= 0.33V "2.12mA #0.596mA

20µA#10µA=152.4

!

VCE

=1.33V "3.71mA # 2.14mA

30µA #20µA=157.0

!

VCE

= 2.5V "5.36mA # 3.75mA

40µA# 30µA=161.0

!

VCE

=1.5V "6.92mA # 5.31mA

50µA# 40µA=161.0

Now we calculate the small-signal output resistance:

!

ROut

="V

Out

"iC

!

ROut

=0.33V " 0.22V

2.12mA " 2.11mA=11k#

!

ROut

=1.04V " 0.53V

5.28mA " 5.25mA=17k#

!

ROut

=8.02V " 4.93V

3.89mA " 3.81mA= 38.625k#

!

ROut

=1.33V "0.33V

2.14mA "2.12mA= 50k#

!

ROut

=5.35V " 2.08V

2.70mA " 2.15mA= 81.75k#

!

ROut

=9.85V " 7.51V

2.24mA "2.22mA=117.5k#

!

VCE

=1.0

!

VCE

=2.0

!

iC

(mA)

!

iB

(µA)

!

iC

(mA)

!

iB

(µA) 0.597 10 0.603 10 2.135 20 2.148 20 3.700 30 3.74 30 5.275 40 5.279 40 6.840 50 6.96 50


Many of the values range from 10-100kΩ. Next, we use Circuit #2 from FIG. 2. We change

!

VCC

to 5V, 10V, and 15V and measure the base and collector voltages from the 2N3393 BJT. We measure this using the MATH function of the oscilloscope to get:

!

VCC

=15V "VB

= 2.08V and VC

= 3.50V

!

VCC

=10V "VB

= 2.08V and VC

= 3.31V

!

VCC

= 5V "VB

= 2.08V and VC

=1.438V We then use Ohm’s Law with the base resistance of 100kΩ and collector resistance of 1kΩ to get:

!

VCC

=15V

!

VCC

=10V

!

VCC

=5V

!

iB

20.8µA 20.8µA 20.8µA

!

iC

3.5mA 3.31mA 1.438mA Gain 168.27 159.135 69.135

Now we do a KVL around the input loop without the 10Ω resistor since it is not significant. This gives the small-signal input resistance:

!

"Vin# "i

B$100k%# "i

B$R

B= 0

!

2 " 20.8µA #100k$"20.8µA # RB

= 0

!

RB

= 3846" Here is a table of the BJT characteristics we have obtained so far:

!

VCC

=15V

!

VCC

=10V

!

VCC

=5V

!

iB

20.8µA 20.8µA 20.8µA

!

iC

3.5mA 3.31mA 1.438mA Gain 168.27 159.135 69.135

0.33V 1.33V 2.5V

Gain 152.4 157.0 161.0 1.5V

Gain 161.0 0.33V 1.04V 1.33V

!

ROut

11kΩ 17kΩ 50kΩ 5.35V 8.02V 9.85V

!

ROut

81.7kΩ 38.6kΩ 117.5kΩ Next we examine circuit #3 from FIG. 3. We wanted to create a situation

where the device would be both in the cutoff region at one extreme and saturation at the other extreme. To do this, we turned

!

VCC

down to 0.2V, saturation. To get cutoff, we increased the amplitude of the wave by adjusting the output level of the signal generator. Using the oscilloscope leads, we got:

!

VC

= 990mV and

!

VB

=13.44V using the Peak-to-Peak function on the scope. We then divide by the corresponding resistors and determine the gain:

!

iB

=13.44V

100k"=134.3µA

!

iC

=990mV

1k"= 990µA

!

" =iC

iB

=990µA

134.3µA= 7.36

Here is a graph of the input (triangle wave) and the output (cutoff/saturation).

FIG. 8: Input & Output for Cutoff/Saturation Circuit

Next, we use this idea to make an LED blink at 5Hz. The LED needs about 20mA to emit light so we needed to lower the base resistance:

!

iE

= 20mA " ic

= # $ iB

iB

=20mA

#=20mA

160=125µA

So a 2.2kΩ resistor will work sufficiently well if we use an input of about 8V. The LED blinked at 5Hz with good emission of light using this setup. Here is a graph of the input (triangle wave) and the output (LED blinks at peak)


FIG. 9: Input & Output for Blinking LED Circuit

The last circuit we examine is from FIG. 5, the current mirror. Data is obtained via ammeters:

R=0Ω

!

iC

1 1mA 2mA 3mA

!

iC

2 69.0mA 69.0mA 69.0mA

!

iC

1 4mA 5mA 6mA

!

iC

2 69.0mA 69.0mA 69.0mA

!

iC

1 7mA 8mA 9mA

!

iC

2 69.0mA 69.0mA 69.0mA

!

iC

1 10mA

!

iC

2 69.0mA

!

Ratio =iC1

iC2"1 for all of the data taken

when there was a 1kΩ resistance at the two emitter ends of the BJTs. When there was no resistance, the current in BJT

!

Q1 did not affect that of BJT

!

Q2.

This is because there is a mismatch between the two collector currents with respect to the reference. Error: There may have been error in the electronic instruments, the devices (such as BJTs), and the connections. There may also have been slight human error in measurement. Any of these could change the results of the experiment but did not drastically affect the overall results and concepts. Conclusion: Through correct circuit design, one can take many useful measurements from a Bipolar Junction Transistor such as currents and voltages at various points in the circuit. This data can be used to construct graphs of the BJT such as its output characteristics and base current versus collector current relationship. One can also find the gain of the transistor in different circuits as well as the small-signal input resistance. One can use the switching capabilities of the BJT to make an LED blink as well as use the BJT to make a current mirror and, of course, as an amplifier. Acknowledgments: D. Smith, University of Minnesota Circuit Laboratory Instructor C. Hacker, University of Minnesota Electrical Engineering Student B. Pokorny, University of Minnesota Teaching Assistant References: University of Minnesota EE2002 Laboratory Manual: Pages 9-10

R=1000Ω

!

iC

1 1mA 2mA 3mA

!

iC

2 0.98mA 1.98mA 2.97mA

!

iC

1 4mA 5mA 6mA

!

iC

2 3.94mA 4.98mA 5.88mA

!

iC

1 7mA 8mA 9mA

!

iC

2 6.88mA 7.88mA 8.85mA

!

iC

1 10mA

!

iC

2 9.97mA


Electronics, Second Edition by Allan R. Hambley 2000: Pages 212-279 The Math Works, Inc: MATLAB 5.2.1

http://www.mathworks.com Beige Bag Software: P-Spice Lite http://www.beigebag.com

Revised 1/24/02

University of Minnesota

Department of Electrical andComputer Engineering

EE 2002 Laboratory Manual

An Introductory Circuits/ElectronicsLaboratory Course

2Revised 1/24/02

Introduction

You will find this laboratory to be different than those you have experienced up to this time. Itwas designed with several objectives in mind. First, it is intended to supplement the lecturecourse EE2001 and can only be carried out with the maximum benefit if you are acquaintedwith the topics being discussed there. Second, it is intended to develop your self-confidence inlaboratory procedures and in drawing conclusions from observations. As a consequence theinstructions are very spare and assume you will be able to extract conclusions from eachexperiment and will relate parts of the total lab to each other without being explicitly asked todo so.

Important Points

- Your grade in this course will depend principally on your in-lab work.

- You are expected to maintain a lab notebook. It must contain a running account of theexperiment. It is not intended to be a book into which you copy notes previously gathered on theback of an envelope. It must however be legible and coherent. Write in such a way that anotherperson could perform the same experiment based on your account, and this same person couldunderstand the conclusions that you drew from your data. It is not necessary to hide your mistakes. Ifyou make a mistake in an entry simply draw a line through that entry and start over - you will not bepenalized for this.

- The lab notebook should have the following characteristics:- It should be a bound notebook (spiral bound is OK).- Lab entries should be dated, and should include:- Complete circuit diagrams.- Explanation of circuit, methods, procedures, etc.- All calculations for designs.- All measurements (including component values).- All analysis and comparisons of data with theory.

Homework

There is no formal lab homework or pre-lab work in this course, but it will pay great dividendsfor you to make a careful reading of the experiment description before arriving in thelaboratory. You will also note that some parts of the "experiments" involve analytical workwhich can be better done elsewhere. Most problems students have with this course are due tolack of preparation prior to coming to lab. If after reading through the lab and consulting therelevant section of your EE2001 text you do not understand something, seek out either yourTA or the faculty member in charge of the lab.

If you do not spend at least 30 to 40 minutes studying the experiment, making notes,circuit diagrams, calculations, etc. in your laboratory notebook, prior to coming into thelab, you will not finish the experiments.

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It will be obvious to everyone in the class, including your classmates, your TeachingAssistant, and your Professor, that you have come in unprepared.

And you will receive no extra help for such poor performance.

MILESTONES

In each experiment there will be a few “milestones”. These are specific tasks that must beaccomplished and demonstrated to the TA or professor before going on to the next item. Allmilestones must be completed or you will not pass the course. If the milestones are notcompleted by the end of the quarter you will receive an F for the course. While the milestonesare not a part of the grade formula, delays in milestone completion will unavoidably delay thesubmission of your lab notebook with the corresponding grade penalty.

Lab notebooks and lab reports will not be accepted if the milestones for thecorresponding lab have not been completed.

Grades will be determined from the following components of the course:

Lab Notebooks - 30%Lab Practical Exams - 40% Take them seriously, they are forty minutes to one

hour in duration and they account for a significantportion of your final grade.

Lab Reports - 30%

Lab notebooks will be collected up to three times during the quarter. They will be due asspecified in the EE 2002 Schedule.

Lab reports will be collected approximately one week after scheduled completion of thecorresponding lab.

You will be given a schedule during the first week of class which will contain all labpractical exam dates as well as notebook and lab report due dates.

- Late Penalties. The penalties for late notebooks or lab reports are as follows:

1 or 2 days late: 3% deducted from your FINAL SCORE.

3 or 4 days late - an additional 3% deducted from your FINAL SCORE.

and so on...

- Check the class website for separate document detailing the requirements for the lab reports.

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Lab Housekeeping Rules

• No food or drink is to be brought into the lab and most importantly is not tobe placed on the lab benches.

• At the conclusion of each laboratory session, all cables, etc. are to bereturned to the proper wire racks and any borrowed equipment (thereshould be no borrowed equipment without the approval of the TA) returnedto its proper location. The only items on the lab bench when you leaveshould be the equipment normally found on each bench.

• The TA will record a demerit against your record in his gradebook each timeyou fail to meet the above standards. Four or more demerits at the end ofthe term after grades have been computed will result in a grade reduction ofone level (A to A-, A- to B+, etc.).

• If for some reason, you find the lab bench does not meet the abovestandards when you first come in, inform your TA immediately. You are stillresponsible for leaving the lab bench neat when you leave.

• Only students registered for lab courses scheduled in this laboratory courseare allow entry to this lab. You will use your U-card each time you enter.Under no circumstance is the lab door to be propped open by any means.

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Experiment #1: Orientation andFamiliarization with Equipment

Session #1

DemonstrationThe instructor will demonstrate the use ofthe digital meter for voltage, current andresistance measurements. In particular theinfluence of the meter on the quantity beingmeasured will be emphasized. Proceduresand expectations for this course will bediscussed.

Experiment #2: DC Measurements

Sessions #2 and #3

Experiments1. Measure the voltage of a nominal 1.5VAAA cell to the nearest mV.

2. Determine experimentally the value ofresistor that, when place across the cell,will make a measurable change in themeasured cell voltage. Calculate theinternal resistance of the cell.

3. Measure the voltage range of each of thepower supply outputs. A later experimentwill require a voltage which can beadjusted over the range 0 to 40V. Decidehow you would provide such a voltage.

4. Set a power supply output to the valueof the cell voltage measured in item 1.Determine the change in this voltage whenthe supply is loaded with the resistor usedin item 2.

5. Design a circuit to light the red light-emitting diode (LED). The LED currentmust be about 15 mA (no more!). Thediode voltage will be about 1V but youmust not connect a voltage source directly

to the diode because the current is a verystrong function of this voltage and chancesare that the diode current would exceed themaximum allowed.NOTE: The short lead of the diode is thecathode, i.e. the negative lead.__________________________________MILESTONE #2-1: Demonstrate yourLED circuit to your instructor, makingsure that meters are connected to showdiode current and voltage and that there isno possibility of exceeding the specifiedmaximum diode current.__________________________________

DemonstrationThe instructor will demonstrate the use ofthe oscilloscope and the signal generator tomeasure periodic waveforms and to displayone variable versus another (x-y mode).

Experiments6. Connect a voltage divider to an outputof the power supply. Design it to give anoutput that is 1/3 of the supply voltage andso that neither the power ratings of theresistors nor the current rating of thesupply are exceeded. The voltage outputof the divider must not change by morethen 1% when loaded with 10KΩ.

7. Design a current divider that willprovide a 1/3 - 2/3 current split. Observethe current and power limitations as youdid in the previous item. Another designconstraint is that the current metersinserted to measure the current divisionratio must not upset this ratio.

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__________________________________MILESTONE #2-2: Demonstrate yourcurrent divider. Show that the currentmeters have no effect on the currentdivision.__________________________________8. Construct a non-trivial resistive circuitwith at least 2 loops and at least 3 resistorsin each loop. Verify Kirchhoff's laws forthis circuit. Notice that this item is more"open ended", i.e. there is more room forindividual initiative. These lab instructionswill be increasingly presented in this mode.__________________________________MILESTONE #2-3: Demonstrate yourworking circuit. Be prepared to show oneor two branch voltages and how theycompare to those calculated in your notes.__________________________________

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Experiment #3: Circuit Theorems

Session #4

Experiments1. Construct a resistive circuit containingseries and parallel branches and a DCvoltage source. Measure the voltage at atleast 2 nodes (relative to a reference node)as a function of the source voltage.Measure the current in at least 2 branchesas a function of the source voltage.

2. Construct the circuit shown below.

Verify the superposition theorem for atleast 2 nodes and 2 branches.

3. Design and construct another resistivenetwork containing 3 voltage sources.Determine selected node voltages andbranch currents analytically andexperimentally.

4. Construct the circuit shown.

Determine, experimentally and analytically.the Thevenin equivalent at the port shown.

MILESTONE #3-1: Explain to yourinstructor how you carried out item 4 andthe data that you obtained.

Experiment #4: I-V Curves and LoadLines

Session #5

DemonstrationThe instructor will demonstrate the smallsignal resistance versus dc current level fora diode and will discuss the load linemethod.

Experiments1. Measure the current vs. voltage relationof the incandescent lamp supplied.

2. Using your data from item 1 and theload line approach, determine the lampcurrent expected for the following valuesof power supply voltage and series resistor.

Voltage Resistance 40.0 4000 Ω 20.0 2000 Ω

3. Check the results of item 2 by directmeasurement.

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4. Build this circuit and, driving it with thesignal generator, display on the scope theoutput voltage versus the input voltage.

5. Change the circuit so that it limits fornegative input voltages.

6. Change the circuit so that it limits at+2 V.

7. Change the circuit so that it limits at+2V and also at -2V.__________________________________MILESTONE #4-1: Demonstrate yourcircuit of item 7.__________________________________

8. Show the influence of your circuit ofitem 7 on various input periodicwaveforms.

Experiment #5: Diodes andRectification

Session #7

Experiments

1. Measure the current-voltage relation forthe 1N4740 Zener diode over its entireallowable ranges of voltage and current.Obtain a collection of data points.

2. Use the data of item 1 to determine thesmall signal resistance of the diode atforward currents of 10, 20 and 30 mA.

3. Devise a large-signal model for yourZener diode, applicable in the reversebreakdown region for currents from 10 to50 mA.

4. Examine the output of this circuit for 1KHz sinusoidal input amplitudes from 0.5to 5V.

5. Investigate the following power supplycircuit (known as a “bridge” circuit).

6. Determine the effect of placing a largecapacitor across the load of the circuit ofitem 6. Make certain you observe theproper polarity when connecting thecapacitor.__________________________________MILESTONE #5-1: Demonstrate theload voltage of the circuit of item 6, withand without the “filter” capacitor.__________________________________

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Experiment #6: BJT Characteristicsand Amplifiers

Demonstration – session #8The instructor will demonstrate variousmethods of biasing bipolar junctiontransistors.

Experiments

1. Measure the 2N3393 collector currentversus collector-emitter voltage for severalfixed values of base current.

2. Design an arrangement to measure thecollector current versus base current forseveral fixed values of collector-emittervoltage for the 2N3393. (see milestonebelow)

__________________________________MILESTONE #6-1: Explain yourproposed circuit to your instructor beforetaking any measurements.__________________________________

3. From the data obtained calculate thesmall-signal common-emitter current gainat different values of collector-emittervoltage. Also calculate the small-signaloutput resistance at several values ofcollector current.__________________________________MILESTONE #6-2: Report the values initem 3 to your instructor and explain howthey were obtained.__________________________________

Demonstration – session #9

The instructor will demonstrate BJTamplifier circuits.

Experiments

4. Using the techniques of thedemonstration, design a circuit to measurethe small-signal common-emitter currentgain and the small-signal input resistance ofthe 2N3393. Make those measurements atseveral levels of collector current.__________________________________MILESTONE #6-3: Collect your valuesfrom items 3 and item 4 into a table andshow them to your instructor. Demonstrateyour circuit design of item 4.__________________________________

5. Build the circuit shown, drive it with atriangular wave, and display the outputvoltage versus the input voltage for aninput swing sufficient to cutoff the deviceat one extreme and saturate it at the other.Determine the common-emitter currentgain and the collector-emitter saturationvoltage.

6. Design and build an arrangement toswitch an LED on and off at 5 Hz. Thediode current should be about 20 mA whenon. Do not draw more than 1 mA from thesignal generator.

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__________________________________MILESTONE #6-4: Demonstrate thecircuit of item 6 to your instructor.

7. For the “current mirror” shown in thediagram below, determine the ratio of Ic1to Ic2 for Ic1 ranging between 1 and 10mA. First do these measurements for R=0,then for R=1 KΩ. (Q1,Q2 are 2N3393)

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Experiment #7: MOSFETCharacteristics and Amplifiers

Session #10

Experiments The experiments below all involvemeasurements on a MOSFET. You willuse the MOSFETs contained on the 74C04hex inverter chip. The diagram for one ofthe 6 inverters is shown below.

1. Measure ID versus VDS for various

values of VGS. Do this for one n-channel

and one p-channel device.

(Homework) Determine thetransconductance of each device at severaldrain current levels.

2. Determine the threshold voltages ofone n-channel and one p-channel device.__________________________________MILESTONE #7-1: Explain to yourinstructor how you deduced the thresholdvoltages. Show your data.__________________________________

(Homework) Use the data of item 1 todetermine the conductance parameters (K)for the 2 devices. Using a reasonable value

of carrier mobility, determine the oxidethickness for the 2 devices.

(Homework) Determine the channellength modulation parameter (λ) for the n-channel MOSFET using the data from step

3. Using VDD = 5V measure the outputvoltage vs the input voltage over the range0 to 5V. Use your oscilloscope in both thetime base mode and the x-y mode. Sketchthe data in your lab notebook.

__________________________________MILESTONE #7-2: Demonstrate yourcircuit and its operation to your instructor.

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Experiment #8: Op Amps

Session #12

1. To ensure that the output of theamplifier is zero when the differential inputis zero ("offset nulling") the scheme shown

is used. (The potentiometer is adjusted toforce the output to zero when the inputterminals are both zero.) Design andconstruct a non-inverting amplifier with avoltage gain of approximately 10, null itsoffset and measure the gain over thecomplete range of input voltages.

2. Power the opamp with +5 and –5V andmonitor its output when one input isgrounded and the other varied a few mVon either side of zero. Plot this data.

3. Repeat with the roles of the inputterminals interchanged. Plot this data.

4. Design and construct a comparatorcircuit which will indicate whether anunknown voltage is greater than or lessthan a given reference voltage. The lattershould be capable of being varied between-5 and +5 V.

__________________________________MILESTONE #8-1: Demonstrate howyour circuit can convert a 1 kHz sine waveto a square wave with a variable dutycycle. Also show your plots from Items 2and 3.__________________________________

5. To your comparator circuit of Item 4add green and red LED's so that the greenlights up when the input voltage is less thanthe reference and the red when it is greater.__________________________________MILESTONE #8-2: Demonstrate yourcircuit from Item 5.__________________________________

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Session #13

6. Using resistors in the few KΩ range,design a voltage divider to provide anoutput of about 5V from a 15V source.

7. Determine the load on the divider whichwill drop the output voltage to 50% of theno load value. What is the significanceof this load?

8. Construct a 741 buffer (unity gain, non-inverting amplifier) to insert between theoutput of the divider and the loaddetermined in Item 7. Repeat loadmeasurement of Item 7. What is thesignificance here?

9. The thermocouple is a two-terminaldevice commonly used to accuratelymeasure temperatures. It is comprised oftwo dissimilar metallic wires joinedtogether to form a junction. Anytemperature difference in this circuitinduces a small voltage. This is known asthe Seebeck Effect discovered in 1821.

Your task is to design an opamp interfacebetween your thermocouple and theDVOM such that the DVOM reads directlyin degrees F. (For example, 1 mV perdegree F) You must then accuratelymeasure the temperatures of variousobjects in the room.__________________________________MILESTONE #8-3: Demonstrate yourcircuit to your instructor and explain itsoperation.__________________________________

10. Design and implement a circuit whichwill indicate with LED's whether atemperature is above or below roomtemperature (RT). Red must representtemperatures higher than RT and Greenshould represent the opposite.

__________________________________MILESTONE #8-4: Demonstrate yourcircuit to your instructor and explain itsoperation.__________________________________

Instructions for Written (Formal) Laboratory Reportsin EE20002, 2006, 3006, 3101, 3102, and 3105

Written reports for these undergraduate laboratories and separate and distinct from the labnotebooks you have been keeping. These are formal reports which are to be prepared from thedata you have collected and recorded in your lab notebooks. The lab reports should be type-written and tables and graphs should be produced on commercial graphing software or handdrawn in ink on commercial graph paper. The written reports should consist of four sections:

1. Abstract2. Introduction3. Main Body (you should use a more descriptive title specialized to the subject)4. Conclusions

1) Abstract

The abstract should be a brief (<200 words) description of the experiment and what it taught.Generally, an abstract should not include references to specific data. Below is an example of anabstract for a technical paper taken from a journal called Applied Physics Letters (don't worry ifyou cannot understand it):

A novel dual laser ablation process that leads to particulate-free film growth ispresented. A pulsed CO2 laser and an excimer (KrF) laser have been spatially

overlapped on a Y2O3 target with a temporal delay between the pulses. The

particulate density of the films grown by this method are at least three orders ofmagnitudes maller than the particulate density of a single excimer laser ablatedfilm of similar thickness. In addition, a time of flight ion probe study indicates asixfold enhancement of the plume species kinetic energies under dual laserablation. Th degree of plume excitation is observed to depend strongly on thedelay between laser pulses. (S. Witanachchi, K. Ahmed, P. Sakthevel, and P.Mukherjee, Appl. Phys. Lett., 66, (1469 (1995)

While you are probably not familiar with terms such as ''plume species' or 'laser ablation', youshould be able to pick up the main points that the authors intend to address in their paper: thatthey have a new technique for depositing films by laser ablation, and that the particulate size inthe films is quite a bit smaller. Notice that the authors conveyed this information without citingspecific data from their experiment.

2) Introduction

The introduction to your report should tell the reader the motivation for the experiment and moreabout the specifics of the experiment than the abstract has told. Some references to specific datamay be helpful. Most scientific and engineering papers include an instruction which starts withcitations of previous work by the authors and others and then goes on to describe each phase ofthe experiment. since you will probably not be citing previous work in your report, yourintroduction should concentrate on the narrative description of the steps in the experiment. Let's

say that your experiment involved investigating various manufacturer's volt-ohm meters(VOM's) for their suitability in making measurements of high impedance sources. The abstractcould be very short:

Introduction

One of the primary tools of the test engineer is an affordable VOM if the DC-50MHz range. We have tested several of the more popular and widely availablemodels. Namely, the Acme model 1000, the Testing Instruments model 5011, andthe Applied Electronics model 102. Each of the instruments was characterized bymaking a series of measurements on a calibrated source. Two parameters wereused as a basis of comparison: the input impedance as a function of frequencyand the absolute accuracy of the instrument given the known input impedance.Price-performance comparisons were made based on these two parameters only.The three instrument's performance were found to roughly correlate with cost.Since the three instruments vary considerably in price, the user can use the datapresented here to make a cost-effective purchasing decision.

Notice that the main purpose of the introduction is to spell out the motivation and then brieflydescribe the method undertaken. The example above is on the short side. You may want toinclude certain important aspects of the conclusion - for example, so and so's VOM is by far themost accurate but also cost ten times as much as the others, and would only make sense in a labwhere high precision measurements are routinely make, etc.

In these undergraduate laboratories, the experiments are only based on a few hours of laboratorytime and are consequently very short compared with most tasks undertaken by professionalscientists and engineers. As a consequence, the amount of data reported is relatively small andthis can make writing both an abstract and an introduction seem like overkill. If yourintroduction seems redundant, double check to see if you have put too much in the abstract; andremember the following: the introduction should give the motivation for the experiment, itshould outline the steps in the experiment, and it should hint at the conclusion.

3) Main Body of the Report

The main body is where you get specific. You may wish to divide the main body into subsectionssuch as "Experimental Setup", Measurements Taken", etc. or you may wish to write the mainbody in a more narrative style. The important thing is that the main body should support theclaims you made in the abstract by describing the experimental setups and listing tables orgraphs of data. While it should be the longest part of the write-up, if you have done a good job oftaking data, you will find it the easiest to write.

4) Conclusion

The conclusion should clearly state what was accomplished in the experiment. For instance, ifthis is a report on the "Design of a DC to 100 MHz Amplifier with 10db Gain", the conclusionshould unambiguously state that " yes, we did build an amplifier to specification or " no, we

were not successful, and why our approach was/wasn't successful. Since many people only readabstracts and conclusions of technical papers (don't assume your TA will only read these parts) itis your job to write the conclusions in such a way that it will convince a skeptical reader that thedata in the main body supports your claims.

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