EE 420L Engineering Electronics II Lab 

Lab 1- Review of basic RC circuits

     

Francisco Mata Carlos

 email: matacarl@unlv.nevada.edu

 1/30/19

     

 

Pre-lab: Requirement:

 

Lab description:

For this lab the circuits shown in Fig. 1.21, 1.22, and 1.24 were simulated and verified with experimental measurements. These figures are from Dr. Baker’s CMOS book.

 

Requirements:

 

   

Experiment 1: Fig 1.21

Note: the values for resistor and capacitor used for the experimental portion were 1.197kΩ and 0.997𝞵F respectively

    

 

Hand Calculations:

Magnitude response:

Phase response:

 

 

LTspice simulation

 

Oscilloscope measurement

 

Vin on the plot above is the yellow trace which shows to be about 2.06V peak to peak, but the magnitude is about 1.06V. We can also see that at about 200Hz the output Vout (blue trace) is about 1.2V peak to peak, thus about 0.61V magnitude

 

 

Hand Calculations

LTspice simulations

Experimental

Vout magnitude

0.6226V

0.6227V

0.61V

Phase response

Time delay

 

 

 

 

AC Analysis

 

The AC simulation below is using the same value resistor and capacitor as the values used for the experimental set up. Also, a series resistance of 65 ohms was added to the voltage source to assimilate the impedance from the function generator.

 

 

Experimental Results:

 

Frequency

output Vpp 

Phase

input Vpp

10

2.08

7

2.2

100

1.64

37

2.2

1k

0.34

60

2.12

10k

0.043

-10

2.08

100k

0.0176

-160

2

1M

0.014

-160

2

 

 

 

The experimental results were very close to the LTspice simulation and the hand calculations

     
       
Below is a video showing the frequency response for the input and output for Experiment 1: Fig 1.21. This is a frequency sweep using the function generator;
the range is from 4Hz to 2KHz. In the video, it can be seen that the magnitud of the output signal (lavender) goes down as frequency increases.
The video was taken and edited by Bryan Kerstetter using an iphone. This is 720 resolution but a 4k video on You Tube can be seen here
 
If the video doesn't play then right click on it and click on "show controls" to see the Play button.
 

 

Experiment 2: Fig 1.22

   

Note: the values for resistor and capacitors used for the experimental portion were 1.197kΩ, 0.997𝞵F, and 2.088𝞵F

 

 

 

 

 

 

 


Hand Calculations:

Magnitude response:

 

 

Phase response:

 

 

LTspice simulation

 

Oscilloscope measurement

Vin on the plot above is the yellow trace which shows to be about 2.10V peak to peak, but the magnitude is about 1.08V. We can also see that at about 200Hz the output Vout (blue trace) is about 1.52V peak to peak and about 770mV magnitude

 

 

Hand Calculations

LTspice simulations

Experimental

Vout magnitude

0.6935V

0.703V

0.770V

Phase response

Time delay

 

 

 

AC Analysis

The simulation below shows the input and output in an ideal situation; however, this is not the case for a real circuit. The resistor and capacitors are the same value as the ones used experimentally.

 

Ideal Frequency Response

The input in the two simulation below stays constant unaffected from the impedance of the cables and function generator. The output in this case is 2/3 times the input at high frequencies.

 

For an ideal circuit at high frequencies the output is the ratio of the capacitors times the input voltage.

 

 

 

 

Non-Ideal Frequency Response

Due to the impediance from the function generator the input voltage decrements as frequency increases, which makes the output Vout go to zero. In this simulation 65 ohms was added in series to the voltage source. This set up explains why the experimental values for the input and output from the table go to zero.

  

 

Experimental Results:

Frequency

output Vpp

input Vpp

Phase, degrees

10

2.06

2.2

13

100

1.56

2.2

10

1k

1.36

2.08

2

10k

0.64

1

-10

100k

0.144

0.248

-155

1M

0.112

0.32

-180


       

From the information above we can see that different hand calculations can be used depending on the frequency. At high frequencies equation (3) can be used, but for lower frequencies equation (2) should be used. Also, by adding equipment impedances or resistances to the SPICE circuit as described above we can simulate a more realistic circuit.

   

 

Below is another video showing the frequency response for the input and output for Experiment 2: Fig 1.22. This is a frequency sweep using the function generator;
the range is from 20Hz to 7KHz. In the video, it can be seen that the magnitud for both the input and output signals go down as frequency increases. This is due to
the impediance from the function generator.
This video was also taken and edited by Bryan Kerstetter using an iphone. This is 720 resolution but a 4k video on You Tube can be seen here
 
If the video doesn't play then right click on it and click on "show controls" to see the Play button.

    

   

   

  

   

 

  Experiment 3: Fig 1.24

For 1.24 (use a 1 uF cap in place of the 1 pF cap)

 

 

 

 

 


Hand Calculations:

𝞃 = RC = (1k)(1𝞵F) = 1ms                5 𝞃 = 5ms

 

 

 

 

LTSpice simulations:

 

The simulation below shows the rise time of the output Vout. The duty cycle being used on this simulation is 50% with a period of 10ms. This set up was decide in order to see the rise time and to show that the pulse needs to stay on for at least 5RC (5𝞃) in order to be consider fully charged. The rise time shown below is about 2.19ms.

 

The simulation below shows the time delay of the output (Vout), which is about 715𝞵s.

 

Oscilloscope measurement

The information in the red box above shows in blue the rise time and the fall time, which is about 2.4ms. The time delay in yellow shows to be about 816𝞵s. This result is close to the LTspice simulation and hand calculations.

 

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