EE100B Lab Report 7

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EE100B Lab Report 7: Basic Output StagesAndrew Yu

860998961

Zaza Nguyen

860967146

Sec 23

3-8-2013


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Abstract:

The objective of this lab is to familiarize us with the basic output-stage

topologies. In this lab, we will focus on Class-A and Class-B Follower examples. In

each follower, we will also be focusing on DC Bias and Signal operation of that class.

Procedures:

Class-A Follower:

We will be using Figure 1, Q2 and the associated components supply a constant

current to the follower Q1 to assemble the circuit for the lab in order to obtain

datas.

Figure 1: Class-A BJT Follower with Emitter-Current Bias

Resistors R3 and R4 serve to equalize the currents in D1 and Q2 whose junctions are

likely to be quite different in size. Resistor Rs serves simply to allow one to monitor

the bias current directly. Resistor R1 represents the internal resistance of a typicalsignal source.

1. DC Bias:

Assemble circuit from Figure 1 with S grounded and no load connected tonode B.

Adjust the supplies to 5V as closely as you can. Measure voltages at nodes A,B, C, D, E and F.


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Estimate collector current of Q1 and its 2. Signal Operation:

Edit circuit to: R2 = 1k, RL = 10k, and node S connected to a functiongenerator providing a 0.2 Vpp triangle wave at 1kHz.

Measure voltages at nodes S, A, and B with oscilloscope; calculate voltagesgains from S to B (VB/Vs) and A to B (VB/VA). Measure input resistance at A.

Observe nodes S and B; both oscilloscope channels direct-coupled with zerovolts at the screen center. Raise input voltage until first the output waveform

is chipped at one peak, then the other. Peak output voltages at each case?

Class-B Follower;

1. DC Bias:

Assemble circuit in Figure 2 with node S grounded. RL 10k, and supplies at+/-5V.

Figure 2: Class-B Complementary BJT Output Stage

Use multimeter to measure the voltages at nodes A, B, C, and D to verify thatthere is no standing bias current in the circuit.

2. Signal Operation:

Change to 0.2 VPP triangle wave applied to node S initially and a load 10kconnected to node B.

Measure nodes S, A, and B with the two-channel oscilloscope. Increase input signal with nodes S and B displayed on oscilloscope (noting

the peal value of the signal at S for which output at node B is just noticeable).

Increase input amplitude until 1VPP output is observed at S and A. Observing node B, increase input signal until output peaks just begin to limit.

Note their value and corresponding peak values at nodes S and A.

Estimate device at the peaks.


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Data Analysis:

Class-A Follower:

DC Bias

Voltages: [V]

Signal

Operation

Voltages [V]

A -0.018 S 0.2

B -0.64 A 0.02

C 4.93 B 0.019

D -4.93

E -4.32

F -4.89

Vin = -0.695 VPP = 9.201V

Iin = 0.148mA VPP = 10.2V

Figure 3: When the frequency in the multimeter is still at 1kHz.


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Figure 4: This shows when we raise the input voltage.

When we consider and at the current levels measured, we notice that the

currents in D1 and Q2 are nearly the same (due to R3 and R4).

R1 = 4.7k

Class-B Follower:

DC Bias

Voltages: [V]

Signal

Operation

Voltages: [mV rms]

A -4.13 A 4.8

B -4.76 B 4.8

C 4.89 S 4.8

D -4.79

When is noticeable when the VPP is about 1.201V.

We considered the values of input resistance and gain


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Figure 5: When the frequency is at 1kHz.

Figure 6: When we increase the frequency

Conclusion:

In this lab, we have successfully completed the understanding of Class-A and

Class-B followers by recreating the schematic and obtaining data to analyze. This lab

has helped us understood the basic output-stage circuits where we used a PNP and

non BJT transistors as well as a diode to create the schematic. We were to obtain the


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different voltages values at different nodes of the schematic, where we noticed the

values were similar to each other, and adding them together would give it a 0V. We

also used the function generator as well as the oscilloscope to obtain a graph of the

signal for both Class-A and Class-B follower. At this part, we can analyze the graph

and see how it changes by raising input voltages until the waveform is chipped at

one peak. We also obtain = 1.201V from estimating at the peaks.

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EE100B Lab Report 7