Day 7

Today we did a Time Varying signals lab, a BJT Curve tracer lab, and learned the superposition, linearity, and source transformation analysis techniques.

The purpose of this lab is to learn how to use the Analog Discovery to apply and measure time varying signals as well as using the oscilloscope to measure the time varying signals.

Since the resistances are are equal, through voltage division we expect the output voltage to be half of the voltage source thus the voltage signals will be half of the amplitude. 

Here is a picture of our circuit layout.

The three images above are the measurements from the oscilloscope. Input voltages are as follows: sinusoidal = 2V at 2kHz, triangular = 3V at 1kHz, and rectangular = 2.5V at 500Hz. The amplitude on the sinusoidal wave was at the expected 1V and the same can be said for the triangular and rectangular waves as they too have half the input voltage amplitude.


Next we began the BJT Curve Tracer Lab. The objective of this lab is to find the collector current vs. collector voltage. We were given a 2N3904 transistor.

Above is the schematic we followed to build the circuit.

Using the waveform generator we created a Gummel plot of the combined collector and base currents vs. the base-emitter voltage as shown above.

Above we learned that in a linear circuit we can assume a voltage at V_0 and work backwards to calculate the voltage source. The fraction that we are off in our voltage is equal to the fraction we are off in the V_0.

Next we learned the superposition principle where we set a power source to zero then solve for current, then set the other power source to zero and find its corresponding current. We can then add up the currents for the true current of the original circuit.

Here we learned that we can transform sources based on the resistances to what an opposite equivalent power source if it were in series/parallel with that resistor to then simplify to a very simple equivalent circuit.