Experiment 7 - Bipolar Junction Transistor Characteristics

W.T. Yeung, W.Y. Leung, and R.T. Howe

UC Berkeley EE 105

In this lab, you will determine the I_C - V_CE characteristics of a BJT in several regions of operation. The large signal parameters will be determined experimentally. You will then derive the large signal model for the BJT in each region of operation. The key concepts introduced in this laboratory are:

The 4 regions of operations of the BJT

Determination of the region of operation based on the voltages V_BE and V_CE

Determination of large signal parameters such as and V_A.

H & S Chapters 7.1 - 7.4

Write down the complete Ebers-Moll Equations

Write down the simplified equations appropriate for the forward active and reverse active regions. From these equations, derive the Ebers-Moll large-signal model for each region of operation.

Shown below is the complete Ebers-Moll model for the bipolar junction transistor. You will find all the parameters for this model in this experiment. You might find it useful to tabulate your data into a table such as Table1.

FIGURE 1.

Table 1: Regions of Operations and Measurements
	Forward Active	Saturation	Cutoff	Reverse Active
VBE
VBC
IB
IC
		NA	NA
		NA	NA
IES or ICS		NA	NA

1. Connect the M3500 (NPN1)on Lab Chip 2 as shown in Fig. 2. Let R_C =5k, R_B = 1 M, and R_E = 100 . Let V_CC = 5V.

FIGURE 2.

2. Increase V_BB until I_C = 0.5mA. Measure V_BE and V_BC. What region of operation is the transistor operating in? Measure I_B, the base current and compare that to the collector current. What is ? Once is found, you can calculate .

It is often more convenient and sometime, more accurate to measure the current by measuring the voltage across the resistor through which the current flows, using Ohm's Law

3. Draw the simplified Ebers-Moll model for the BJT in this region of operation and find its parameters.

4. While keeping the voltage V_BB constant at 4V, vary V_CC from 0V to 6V. This should take the transistor through 2 regions of operation. Note the base current I_B. Make a careful plot of I_C vs. V_CE. You will need to take many points of I_B and I_C at low V_CE due to the steep slope of the curve. Note V_BE and V_BC at saturation. Draw the simplified Ebers-Moll model for the BJT in the saturation region. From this plot, find the early voltage V_A. Does the Ebers-Moll model predict the correct behavior?

5. Change V_BB to -3V. How much collector current flows? Does it agree with the Ebers-Moll model? What region of operation is this? What is V_BE and V_BC? Draw the simplified Ebers-Moll model for the BJT in this region of operation.

6. Interchange the collector and the emitter and let V_BB be 4V. Measure V_BE and V_BC. What region of operation is the transistor operating in? Measure I_B, the base current and compare that to the collector current. What is ? Draw the simplified Ebers-Moll model for the BJT in this region and find its parameters

1. Load the program PBJT6 into the HP-4145

2. Place the Lab Chip 2 into the test fixture and make the proper connections with the SMUs.

3. At the Source Setup Screen, change the start value of the base current to be the base current you found in procedure 3.1.4.

4. Run the test program and note the curves traced out by the 4145.

5. Using the marker and cursor, find the Early voltage, V_A for the curve corresponding to the base current you observed in procedure 3.1.4.

FIGURE 3.

6. You can find by comparing the collector current with its corresponding base current. Find the value of for the base current you found in procedure 3.1.4. How do they compare?

7. Get a hardcopy of the I_C - V_CE curve.

8. Interchange the connection for the collector and emitter and repeat the experiment. Find _R and V_AR.

9. Get a hardcopy of the I_C - V_CE curve.

10. Make hardcopies of both measurements. How do they compare?

1. Load the program PDIODE,

2. Connect the base and the emitter od Lab Chip 2 to the appropriate SMUs as described by the SOURCE SETUP SCREEN.

3. The program will plot the current as a function of the base-emitter voltage on a log scale. Using the equation for a forward biased diode, determine I_ES.

4. Interchange the connections and repeat the experiment to find I_CS.

5. Get a hardcopy

Perform a SPICE analysis using the parameters you found. The circuit is shown below. You will need to perform a nested sweep. V_CC will vary from 0 to 5 V and I_B will vary with the initial base current from procedure 3.1.4 in steps of 10 A. Plot I_C vs. V_CE. Fill in the parameters for the M3500 in the data sheet in the Appendix.

FIGURE 4.

Using the program PBJT and PDIODE, modify them to find the parameters for the pnp transistor M3511 (PNP)on Lab Chip 1 (collector = pin 27, base = pin 26, emitter = pin 25).

FIGURE 5.