Lab Report Day Seven - Time-varying Signals, A BJT Curve Tracer

 

1. Time-varying Signals

In this lab, we first make some predictions about the output wave for the circuit below if R1 and R2 are identical. 

We guess that they would have the same shape, with different amplitude. The top three are the input wave, and the bottom three are the output waves. The amplitude of the output would be half of the input. 

 

First, we are going to measure the resistance of two resistors with same value. We get both of them have the same theoretical value, 1K ohm, and same true value, 978 ohm.

 

 

This is the set up of the experiment. 

 

This is the graph for the sine wave.  The frequency and period are its original value. The amplitude becomes half. 

 

 

This is the graph for the triangular wave. The frequency and period are its original value. The amplitude becomes half. 

 

This is the graph for the square wave.  The frequency and period are its original value. The amplitude becomes half. 

 

 

2. A BJT Curve Tracer

 

In this lab, we are going to investigate the collector current, IC vs. collector voltage, VCE characteristics of the BJT. We are going to use a breadboard, a 100K Ω Resistors, a 100 Ω Resistor, and a small signal NPN transistor.

 

The true value of the 100 ohm resistor is 99.5 ohm. % difference is (100-99.5)/100*100% = 0.5%

 

The true value of the 100K ohm resistor is 99.4 K ohm. % difference is (100K-99.4K)/100K*100% = 0.6%

 Here is the set up of our circuit.

 

Here are our first input wave (Channel 1) and second input wave (Channel 2).

  

Here is the oscilloscope of the wave it detected.

We can see that Ic vs Vce have 5 curves.

 Summary:

Today we learn some new methods of circuit analysis. We talk about linear circuit. Source transformation is a useful procedure replacing voltage source or current source. We do a Time-Varying signal lab to see how a voltage divider actually works, and we introduce BJT, and figure out how BJT works.