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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.
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:
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)
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).
* 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.
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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