Lab

Lab 1 - EE 420L

Authored by Hongzhong Li,

Today's date : 01/30/2015

Lab description - Basic RC circuits Analysis

For this first lab simulate, and verify the simulation results with experimental measurements, the circuits seen in Figs. 1.21, 1.22, and 1.24 (use a 1 uF cap in place of the 1 pF cap) of the book. Your results should be similar to, but more complete than, the simulation results seen on pages 17 - 23. In your report, and for each circuit, show the

Circuit schematic showing values and simulation parameters (snip the image from LTspice).
Hand calculations to detail the circuit's operation.
Simulation results using LTspice verifying hand calculations.
Scope waverforms verifying simulation results and hand calculations.
Comments on any differences or further potential testing that may be useful (don't just give the results, discuss them).

The Laboratory Report

1.21 -

Transient Analysis

Schematic	Simulation

Scope Waveforms:

A transient analysis is performed to see the relationship of voltage and current of the circuit as a function of time. By doing a transient analysis, we can determine output voltage, oscillation, and time delay, etc. This will allow us to see how the circuit behave under default initial conditions.

Another useful potential testing is the AC Analysis below:

Schematic	Simulation

Using the datas from above, we can plot the amplitude and phase response in excel:

We performed an AC analysis to see the relationship of voltage and current as a function of variable frequency within a specific range. By doing an AC analysis, we can determine the voltage gain, frequency response, bandwidth, and cut-off frequency. The amplitude and phase of output voltage at f=200Hz is at (-4.11dB, or 0.623 magnitude response). From the table of measurement, we know that the cut off frequency is at 159 Hz (-3 dB frequency, or 0.707 magnitude response). We also know that the response is decreasing significantly once it passes the cut off frequency (159Hz). If we increase the frequency by 10 (ex. 100Hz to 1k Hz), the magnitude response will decrease by 10 (ex. -1.5dB to -16dB). This means that this circuit is a low pass filter. (Passing frequency at 159Hz and cutting off any higher frequency signal)

1.22-

Transient Analysis

Schematic	Simulation

Scope Waveforms:

Similarily to 1.21, we will perform a AC analysis:

Schematic	Simulation

Using the datas from above, we can plot the amplitude and phase response in excel:

1.24

Schematic	Simulation

Scope Waveforms

Another useful testing is to simulate the delay and rise/fall time of the circuit.The output signal can be given by Vout= Vin (1-exp(-t/RC). The time constant is RC value. The delay time is when the Vout=50%|Vin|, td=0.7RC = 700us; and the rising time or falling time is the time it takes the output to be from the 10%|Vin| to 90% |Vin|, tr=2.2RC = 2.2 ms. The following simulations show that the increasing resistance or capacitance can make the time delay and rising or falling time longer

Schematic	Simulation

This concludes the lab, back up the file and email.

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