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## lab report 2

1 review
by: bmatthew Notetaker

47

8

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# lab report 2 ECE 3120

bmatthew Notetaker
Clemson

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lab report example
COURSE
electric circuit
PROF.
Staff
TYPE
Class Notes
PAGES
6
WORDS
KARMA
25 ?

## 8

1 review
"Eugh...this class is soo hard! I'm so glad that you'll be posting notes for this class"
Reid Jones

## Popular in Electrical Engineering

This 6 page Class Notes was uploaded by bmatthew Notetaker on Thursday March 10, 2016. The Class Notes belongs to ECE 3120 at Clemson University taught by Staff in Spring 2016. Since its upload, it has received 47 views. For similar materials see electric circuit in Electrical Engineering at Clemson University.

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## Reviews for lab report 2

Eugh...this class is soo hard! I'm so glad that you'll be posting notes for this class

-Reid Jones

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Date Created: 03/10/16
BJT Common­Emitter Circuit Voltage Gain   ABSTRACT: A 2n3904 NPN transistor was used to create a Bipolar Junction Transistor (BJT) Common  Emitter (CE) amplifier.  We need to analysis how the bias of the circuit and the values of the  resistors in the circuit affect the voltageVgain A . INTRODUCTION: A BJT common­emitter (CE) amplifier circuit is shown in Figure 1, it is a very common  amplifying a AC signal and still play a vital role in several audio applications.  This specific  amplifier uses a voltage dividing resistor network to bias the BJT.  In this experiment, we need  to explore how the voltage gain of the circuit is affected by changing the values of the emitter  and collector resistors, how input signals can lead to distorted output signals as the gain and Q­ point change.                                                                       Figure 1: Common­emitter circuit with emitter bypass capacitor BACKGROUND: The 2n3904 NPN transistor we used is a three­terminal device. It has three basic configurations  are appropriately called common emitter, common collector (emitter follower), and common  base. The configuration or amplifier is used in a particular application depends to some extent  on whether the input signal is a voltage or current and whether the desired output signal is a  voltage or current. From Figure 1, The signal from the signal source is coupled into the base of the transistor  through the coupling capacitor C  , w1ich provides dc isolation between the amplifier and the  signal source. The dc transistor biasing is established by R  and R1, and i2 not disturbed when  the signal source is capacitively coupled to the amplifier. The collector current (IC) in a BJT  depends on the β of the transistor, the transistor temperature, and the circuit elements.  Selecting the proper biasing network and resistors keeps the collector current and the voltage  gain relatively constant. The key elements that stabilize the circuit to changes in the transistor β  are the emitter resistor, R ,Eand the values of the bias resistors, R  and1R . To k2ep the high  gain of the C  Eircuit, the emitter resistor is usually bypassed by a large capacitor C . ThisE capacitor C iE generally large, 10μF or greater, and allows most of the ac current through R  to  E flow to ground. The small­signal voltage gain, A  = v /V ,oofsthe circuit is defined as the ratio of output signal  voltage to input signal voltage. In this experiment, without CE the voltage gain is determined by  the ratio of R Land R ,Ewhere R  isLthe total ac load resistance. In order to make the input signal, V , sSall enough to prevent distortion of the amplifier output,  use the voltage divider circuit shown in Figure 2, The voltage divider circuit shown in the Figure  2 divides input voltage from FGEN by 100:1.Thus, to get VS = 0.02VP­P, set FGEN to provide  2.0VP­P as input to the voltage divider.                                                                                Figure 2: Voltage divider network to generate Vs EXPERIMENTAL PROCEDURE AND RESULTS: Before the lab, we use the B2SPICE to simulate the circuits 10 times with various R  aCd R , Eith and  without C  , which are shown in figure 5,6,7,8,9,10 for the (1),(2),(3). E (1). R  = 3.9kΩ R  = 1kΩ (2). R  = 3.9kΩ R  = 200Ω (3). R  = 3.9kΩ R  = 10kΩ (4). R  = 1kΩ R C E C E C E C E = 1kΩ C  E (5). RC = 20kΩ R  =E1kΩ  When we do the lab experiment,  for experiment part I:  (1),We used the curve tracer and measure the β of the transistor at a collector current of about  1.0mA and V  ofCEbout 5 V. Set  I MAX = 20 ma, V MAX = 10V, use the 2N3904 transistor for this  part of the experiment.  (2), Set up the amplifier circuit shown in figure 3 with V  = CC.0V. Use the DMM to measure V C0  and V E0.                                            Figure 3: Common­emitter circuit for                              Figure 4: The common emitter circuit            Q­point measurement. For experiment  part II:  (1),We built the circuit shown in Figure 4 , for ac measurements by adding the capacitors (use  47µF) and sinusoidal input of 2VP­P 1kHz applied to the voltage divider circuit, R  and R .  S1 S2 Measure V  anO V  withSthe oscilloscope(with capacitor, C  and withouE capacitor, C ). Measure E V Owhile R  iC varied from 1kΩ to 20kΩ using the resistance decade box. Determine the voltage  gain, A V= V /O . S  (2), Set R C= 3.9 kΩ using a fixed resistor instead of the resistance decade box. Connect the  emitter bypass capacitor C  as sEown Figure 2. With R  = 3.9 kΩ aCd C  connected and Eithout C E measure V  anO V  for S  valueE from 200 Ω and 10kΩ.  (3) Set R  Eo 1kΩ and connect C  as shEwn in Figure 2. Vary the input signal frequency from 10  Hz to 50k Hz and use the oscilloscope to see how the magnitude of the output signal varies.                  Figure 5: R  = 3.9kΩ R  = 1kΩ without C .                                Figure 6: R  = 3.9kΩ R  = 1kΩ C E E  C E with C =22uF. E                           Figure C: R  = 3.9EΩ R  = 200Ω withouE C .                       C  Figure 8:E R  = 3.9kΩ R E  200Ω with C =22uF.                          Figure 9:R  = 3.9kΩ R  = 10kΩ without C Figure10：R  = 3.9kΩ R  = 10kΩ with C =22uF. C E E                           C          E    E  DISCUSSION OF EXPERIMENTAL RESULTS: From the lab experiment, we recorded the value of  V O­PP and V S­PP to calculate the voltage gain A ,  V which is A  V V /VO.  She table 1 is set R  = 3.C kΩ, measure V  and V  foO R  valuSs from E00  Ω and 10kΩ. From the table we can see when the Rc is constant ,the RE is bigger, the amplitude of the  output voltage is smaller, and without CE, the amplitude of the output voltage is bigger than with C E The result is similar to the V­t plot is shown in figure 5,6,7,8,9,10.so we can sEe a e function C  is  capacitor is placed across E  to short the ac current.                      With                   Without  R E(Ω) CE   CE   Output Output wavefor wavefor VO­ m VO­ m   PP(V) shape A V PP(V) shape A V 0.1001 4.10491 140.221 200 6 clipping 8 3.298 clipping 1 0.2579 Sinusoid 7.49941 150.892 500 8 al 9 4.904 clipping 3 0.1321 Sinusoid 3.83541 Sinusoid 127.381 1K 3 al 4 4.573 al 6 0.0471 Sinusoid 50.9142 3K 6 Flat 1.36894 1.782 al 9 0.0251 0.70952 0.9360 Sinusoid 26.3667 6K 1 Flat 2 2 al 6 0.0186 0.54037 Sinusoid 20.5043 8K 7 Flat 6 0.7115 al 2 0.0160 0.46637 0.5721 Sinusoid 16.6316 10K 9 Flat 7 3 al 9                                   O     C table 1: V  vs R CONCLUSIONS: From this experiment, we can learn how the value of the resistor Rc andER  affect the output  voltage shape and amplitude, and the voltage gain, V . For this lab, we can’t summarize the  formula of the connection of E  CR  toV  . We can roughly determine how the E  and c  impact  on the AV  This is important for us to understand the what the voltage gain really is and how to  use it to design special function circuits in the future.

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