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BJT h-Parameters and Amplifier Characteristics Lab

h-parameters BJT device experiment examining transistor amplifier circuit behavior. The 2N4400 bipolar junction transmitter is utilized to verify theoretical material presented in the lecture course Analog and Semiconductor Devices through the use of laboratory measurement equipment and calculations.


Objectives:

1. To measure the static and dynamic h-parameters of a bipolar junction transistor (BJT).

2. To review the DC and AC characteristics of common emitter, common collector, and common base transistor amplifier circuits.



Equipment and Materials:
1. Curve tracer
2. DC power supply
3. Digital Multimeter
4. Function generator
5. Oscilloscope

6. 2N4400 BJT (2)
7. Assorted resistors and capacitors



Procedure:

1. Using the transistor curve tracer, determine hfe, hie, and hoe for each of two
2N4400 transistors at Ic - 1mA, VCE = 7.5V. Compare these values to those in the 2N4400 specifications.

2. For the circuit of Figure 1, determine the values of Rc and R1 such that the quiescent operating point is at Ic = 1mA, VCE = 7.5V.

3. With resistance values within 5% of those given or calculated for the circuit of Figure 1, use the small signal ac model and the measured h-parameters to calculate the following:

a. Zi (input impedance)

b. Zo (output impedance)

c. Av = Vo / Vin (ac voltage gain of the stage (RL = ∞))

d. Vt / Vs (ac voltage gain of the system (Rs = 1 KΩ, RL = 4.7 KΩ))

4. Construct the circuit of Figure 1.



5. Determine the quantities listed in Procedure 3 experimentally (f = 1kHz). Compare the measured and calculated values. Include percent error, using:


percent error (plus or minus) [((measured) - (calculated)) / (calculated)] x 100%

Explain significant difference.

6. Plot Vt / Vs versus frequency for 10 Hz ≤ f ≤ 10 MHz.

7. Repeat procedures 3 through 6 for circuit 1 while the emitter resistor is bypassed with a 10 microfarad capacitor. (Use resistive voltage divider between Vs, and Rs as required.)


8. In addition, calculate all low frequency breaks and the high frequency break due to CT.

9. Repeat procedures 3 through 6 for the circuit of Figure 2.

10. In addition, calculate all low frequency breaks and the high frequency break due to CT.



Procedure & Data:
1. In the given experiment two BJT h parameters and amplifier characteristics were examined. First the family of curves and transfer function curves were plotted using a curve tracer and hand plotted for data to be calculated. With the plotted data several hand calculations were performed and data produced (table 1) using the following equations.

Β = IC / IB (E.1)

hie = ΔVBE / ΔIB (E.2)

hoe = ΔIC / ΔVCE (E.3)


Table 1: Hand Calculated Data for 2N4400 BIT Transistors, Device Characteristics


Once the characteristics of the devices were calculated more hand calculations were performed to complete the given circuit (figure 1) with Ic = 1mA and VCE = 7.5V. Resistance values were found for each of the unknown resistors by using KVL and Ohms Law around the circuit. Next a small signal model was created and several calculations were performed. Zi, Zo, Av, Vt / Vs were hand calculated from the small signal model and recorded (table 2).


The circuit was then constructed with input frequency at f = 1kHz and tested for proper biasing measurements were taken and compared to the previous hand calculations in table 2. Data was then measured for the gain Vt / Vs, over a wide frequency range of 10Hz to 10MHz and plotted (chart 1).


Table 2: 2N4400 BJT Transistors Using Small Signal Model vs. Measured Data for Figure 1


In the next step, the circuit in figure 1 was modified by adding a bypass capacitor of 10μF in parallel to the resistor RE. Again hand calculations were performed; measurements were taken and compared as before (table 3).



Table 3: 2N4400 BJT Transistors for Modified Bypassed RE, Figure 1



* Conflicting measured data. Unable to determine without more laboratory circuit analysis.

Once both circuit configurations, bypassed and un-bypassed, were examined frequency breaks for both low and high frequencies were calculated (see attached lab notes, part 8).

For greater analysis of the BJT's characteristics another circuit configuration was constructed and analyzed (figure 2). The common collector circuit was first examined using hand calculations where several values for resistors needed to be calculated. Once all component values were known for the circuit the calculated data and measured data was collected and compared (table 4).


Table 4: Common Collector Amplifier Data Analysis, Figure 2


* Conflicting measured data. Unable to determine without more laboratory circuit analysis.

Once again the gain vs. frequency was examined and plotted (chart 4). Frequency breaks were calculated for both the low and high frequencies (see attached lab notes, Part 10).



Conclusion & Discoveries:

In analysis of the circuits the use of a small signal model provides one with a very powerful tool in which to see how specific devices are connected and in turn allows for a greater understanding of the circuits behavior.

It was found for the common emitter amplifier circuit, in bypassing the emitter resistor the gain for the circuit increased greatly when compared to the un-bypassed circuit configuration. This also provides a greater roll of on the low end by the addition of a pole and zero.

In the common collector amplifier a voltage divider network needed to be used in order to reduce the clipping effect caused by to much input voltage at the gate.

In closing by examining the effects frequency has on the BJT devices allows one to gain a better understanding for developing multistage configurations and other applications for the device.


Graphics and Data
Figure 1.0: BJT #1 Output Characteristics
Figure 1.1: BJT #1 Transfer Characteristics
Figure 2.0: BJT #2 Output Characteristics
Figure 2.1: BJT #2 Transfer Characteristics
Figure 3.0: Common Base Emitter, Freq. vs Gain
Figure 4.0: Common Base Emitter w/ Re Bypassed
Figure 5.0: Common Collector Amplifier, Freq. vs Gain
Lab Notes
Lab Notes Page 1
Lab Notes Page 2
Lab Notes Page 3
Lab Notes Page 4
Lab Notes Page 5
Lab Notes Page 6
Lab Notes Page 7

Electrical Engineering lab key words: BJT h-parameter, Amplifier Characteristics, Bipolar Junction Transistor, Common Emitter, Common Base, Common Collector, 2N4400, BJT measurements, transfer characteristics, Offset voltage, bias current, offset current, two port models, frequency response, transfer functions, nonlinear devices.

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