The George Washington University
School of Engineering and Applied Science
Department of Electrical and Computer Engineering
 ECE 20 - Spring 2001

Experiment # 6 (Part II)

Bipolar Junction Transistors
Common Collector (CC)








Equipment:
You must make up a complete equipment list and have your instructor review it before you start.
 

Objectives:

Figure # 1






1.- (HW) Analysis

In Exp. #5, the DC Bias Analysis and general formula for Unloaded Voltage Gain (Avo) for circuit of Figure #1 were calculated.  The more detailed analysis analysis on Common Collector Amplifier for this circuit will be conducted in this section.

When this circuit is operated in CCC:

    1. Find ROUT
    2. RIN
    3. Unloaded Voltage Gain, Avo
    4. Av (RL=ROUT)
    5. Ai (RL=ROUT).
    6. Maximum input voltage vin max that the amplifier can accept before the output distorts (unloaded).
To get a credit for this analysis, you must show all the steps below:
1.  Do DC Bias Analysis
2.  Draw Small Signal Equivalent circuit for CCC
3.  Find Rin, then Rout @Vin=0
4.  Find Vout and Vin to get Av
5.  Find Av @ RL=Rout
6.  Find Ai
7.  Find Vinmax

The text book and lab handout should give you a good example on how to perform the analysis.
 

2.- Verification

Build and fully test the circuit shown in Figure #1. By applying a sinusoidal signal such that the small signal approximation holds, measure:

    1. RIN (input impedance) and ROUT (output impedance) of the assembled circuit.  Read the lab handout to properly understand how to measure Rin and Rout.

      2.  
    2. Unloaded Voltage gain, Avo.  Label the plot - "Plot 2a - Avo for CCC"

      3.  
    3. Voltage Gain for RL equal to 2*ROUT, ROUT, ROUT /2, and ROUT /4.  Print the output plot for each case and label each plot as "Plot 2b - Av @ RL= [RL value] for CCC"

      4.  
    4. Find the maximum input voltage that the amplifier can accept before the output distorts (Unloaded case). Print the plot and label it as "Plot 2c - Vin max before output distorts for CCC"

      5.  
    5. Determine the phase relationship between the input and output voltages.
Hint: Connect a large capacitor between VCC and ground in order to remove all the noise from the source. The noise is amplified and mixes with the output due to the input AC signal vs.
 
 
 

3.- (HW) Design of Current Amplifier

In this section you are asked to design a Current Amplifier.   Current Amplifier is one application of Common Collector.  You can use Class A, Clas B or Class AB to design your amplifier.  Use ORCAD to verify that all the specifications have been achieved.
 

Design Specifications of the Amplifier

VCC  = 24 VDC ± 0.5 VDC

Vin     =  250 mVsin

Ai       =  20 @ 5 kHz

RL     <  100 W
 
 
 

4.- Assembly, Test and Verification of Specifications

Build and test your design. Measure and verify that your design meets all the given specifications.

  1. Measure all the necessary DC bias points with no small signal input (Vs).

    2.  
  2. Connect the small signal input and measure Av, Rin (input impedance) and Rout (output impedance) of the assembled circuit (unloaded).

    3.  
  3. Find the maximum input voltage (Vin max) that the amplifier can accept before the output distorts.

    4.  
  4. Measure the phase relationship between the input and output voltages.

    5.  
  5. Print out the output plot of Vout and Vin.  Label this plot "Plot 4a - Design of CEC - Vout and Vin)". Annotate in the plot the Voltage gain Av you get from the circuit.

    6.  
  6. Use music as the Vinput and use speaker as the R Load.  What is your observation?

 
 

5.- Conclusion

  1. Compare the measured results to your design calculations and specifications. Explain any differences.

    2.  
  2. What can you say about the general characteristics of CCC amplifier( Rin, Rout, Av, Ai etc)