lab 7

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C

ENEE 3517 – Electronics Lab 7

Differential Amplifier

In this lab, we w i l l work with the following BJT differential amplifier. Use R E = 1K,

RC = 1K, VCC = VEE = 5V.

A differential amplifier with resistive load, biased by a resistor and a voltage source

In the Lab:

Biasing:

1. Build the differential amplifier, by connecting both inputs v1 and v2 to the

ground.

2. Measure the DC v o l t a g e s at the emitter and collectors, and confirm that the transistors are in active mode.

3. Measure the exact values of the two R the emitter and collector currents.

Small-Signal:

resistors and of R E , and calculate

1. Connect the first input to the signal generator and supply a sinusoid with frequency 1KHz, and peak 100mV. Connect the second input to

the ground.

2. View the voltages signals at each one of the two outputs (i.e., at the collectors) using the oscilloscope. Observe any differences between the

two signals, even if these differences are small.

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For the Report:

As a l w a y s , remember that the following are o n l y guidelines and that all

necessary parts as listed in the syllabus have to be included in the report.

1. From your measurements, find β, and t h e small signal parameters, gm,

rπ.

2. Calculate the input differential resistance.

3. Based on y o u r s m a l l -signal measurements, determine what y o u r common-mode input (small s i g n a l ) an d what your differential

i n p u t (small signal) are.

4. Based on your measurements, d e t e r m i n e what the differential gain is (considering both the case of differential output and single-

ended output), and also what the common-mode gains (differential and

single- ended) are.

5. Calculate the theoretical values of the gains in 4.

6. Simulate the differential amplifier, and d e t e r m i n e the gains in 4. Compare them w i t h the t h e o r e t i c a l results, and the results obtained

from the measurements.