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

Objectives:

• To verify the operating point for a Beta Stabilized Biasing Network (Bias Point)

• To verify the operation of BJT inverter

• To introduce BJT as an amplifier using CEC, CCC and CBC.

1.- (HW) DC Biasing Analysis

Using simple Kirchoff's Laws and Ohm's Law, analyze the circuit shown in Figure # 1 and find VE, VC, VB ,VBE, VCE, , IB, IE, IC, RB, (assume VCC = 30 VDC, b = 180, VT = 26 mV).

Label this analysis - "Analysis #1 - DC Bias Calculation"
See the handout - "DC Bias"
 

Assemble this circuit on ORCAD and perform a bias point detail analysis. Use NS3904 for the BJT.  Show the calculated voltages and currents by appropriately placing IPROBEs and VIEWPOINTs on your schematic.  Label the circuit as "Circuit #1 - DC Bias Simulation"

 

Compare the DC Voltages and DC currents obtained from your hand calculation and ORCAD.  Why there are some differences?

2.- (HW) Inverter Simulation
 
 

Use SPICE to simulate the BJT inverter shown in Figure # 2. Use NS3904 for BJT.  Plot the value of the output voltage VC vs. the input voltage V2. Label this plot as "Plot #1 -Inverter Simulation". V1 is 5 V_DC.  Use "DC Sweep" to set  V2  from 0 to 5 Volts with an increment of 0.5 V_DC.  Indicate in the plot when the BJT is in the saturation, linear, or cut-off region.
 
 
 

3.- Verification for DC Biasing and Inverter

1. Build and test the circuit shown in Figure #1. Measure VE, VB, VC, VBE, IB, IE, and IC.  Put the measurement in Data Table #1 - DC Bias Measurement.

 
2. Build and fully test the circuit shown in Figure #2. Measure VC for V2 varying from 0 to 3 Volts with increments of 0.2 Volts. Put the measurement of V2 and VC in "Data Table #2- Inverter Measurement".  Plot the graph of VC vs V2.  Label this plot as "Plot #2 - BJT as an Inverter"

4. -  (H/W)  Analysis of BJT as an Amplifier

One of the famous BJT application is as amplifiers.  There are three basic configurations and each configuration has a specific application to electrical circuit.  The configurations are:
1) Common Emitter
2) Common Collector
3) Common Base

Further information can be read from the textbook in Chapter 4.11.
Using circuit of Figure #1, derive a formula and find the values for:
     i) Voltage Gain of Common Emitter
     ii) Voltage Gain of Common Collector
     iii) Voltage Gain of Common Base

     Hint:  To derive the voltage gain for each configuration, you need to follow these steps:
               1) Do a DC Bias Analysis (which you already did in Part 1)
               2) Draw a small signal analysis corresponding to each configuration.  For example small signal analysis for
                   CEC is different from small signal analysis for CCC.
               3) Find the expression for Voutput and Vinput.
                  4) Voltage Gain = Voutput / Vinput.
 
 
 

5. -  Verification of BJT as an Amplifiers

b)  By applying a sinusoidal signal (small signal) as the input, measure:

1. Voltage gain Avo (unloaded) for the circuit in Figure # 1 when operating in CEC.  Label the output plot as "Plot A - CEC Voltage Gain (Unloaded)"

 
2. Voltage gain Avo (unloaded) for the circuit in Figure # 1 when operating in CBC.  Label the output plot as "Plot B - CCC Voltage Gain (Unloaded)"

 
3. Voltage gain Avo (unloaded) for the circuit in Figure # 1 when operating in CCC.  Label the output plot as "Plot C - CBC Voltage Gain (Unloaded)"

1.  Connect a large capacitor between VCC and ground in order to remove all the noise from the source.
2.  Use a really small sinusoidal signal as your input.  Vinput < 100mVp.
3.  Check your DC Bias Voltages and Currents before measuring the small signal.  Make sure that the BJT  is operating in the correct Bias Point (DC) before doing any small signal measurement.  For example, VBE must be at least 0.6 V_DC.
4.  Use Vpp option in the oscilloscope to measure the Voutput and Vinput.
 
 
 

6.- Conclusion

1.  BJT has been shown to operate as an inverter.  Can BJT with a dc power supply (VCC) be used to control appliances that has ac power supply?  Elaborate.

2.  BJT must stay at one operating point (DC Bias) to operate as an amplifier.  Why?