SBE202 Electronics (Lab)
SBE202 – Electronic Devices and Circuits(Lab)
Tutorial 3
Islam S. Badreldin
Biomedical Engineering DepartmentFaculty of Engineering
Cairo University
October 30, 2011
Copyright
Copyright c© 2011 Islam S. Badreldin. Some rights reserved.
This work is licensed under a Creative CommonsAttribution-Share Alike 3.0 License
Outline
1 The Story of a deciBel
2 Introduction to SPICESPICE AC Analysis
3 Using the Oscilloscope and the Function Generator
SBE202 Electronics (Lab)
The Story of a deciBel
Outline
1 The Story of a deciBel
2 Introduction to SPICESPICE AC Analysis
3 Using the Oscilloscope and the Function Generator
SBE202 Electronics (Lab)
The Story of a deciBel
The deciBel I
Once upon a time, engineers were disappointed by the unitlessratio of powers
Power transfer is a ratio defined by Pout
Pin
So, engineers started to use the Bel unit
1 Bel = log(Pout
Pin)
SBE202 Electronics (Lab)
The Story of a deciBel
The deciBel II
Numerical Example
If we have a ratio of 0.9, it can be expressed as
log(0.9) = −0.046Bel
SBE202 Electronics (Lab)
The Story of a deciBel
The deciBel III
As engineers started to use the Bel unit, they were more andmore disappointed as the numbers were too small
0.9 = -0.046 Bel and 1.7 = 0.23 Bel
So, engineers again decided to start using a better unit, thedeciBel (dB)
1 dB = 10 log(Pout
Pin)
Now engineers are happy, as 0.9 = -0.46 dB and 1.7 = 2.3 dB
SBE202 Electronics (Lab)
The Story of a deciBel
The deciBel IV
The dB
Finally, when we use the amplitude instead of the power, we have
1dB = 10 log(Pout
Pin)
= 10 log((Aout
Ain)2)
= 20 log(Aout
Ain)
SBE202 Electronics (Lab)
Introduction to SPICE
Outline
1 The Story of a deciBel
2 Introduction to SPICESPICE AC Analysis
3 Using the Oscilloscope and the Function Generator
SBE202 Electronics (Lab)
Introduction to SPICE
SPICE AC Analysis
The SPICE AC Analysis allows us to determine and plot theFrequency Response of linear circuitsFrequency Response means how the linear circuit responds todifferent sinusoidal inputs with different frequenciesThe Sinusoidal Fiedelity property of linear systems is thecornerstone behind SPICE AC Analysis
SBE202 Electronics (Lab)
Introduction to SPICE
SPICE AC Analysis
Start a new simulation using the following codeThis code tells SPICE to calculate the circuit response todifferent sinusoids with unity amplitude and varying frequenciesThe frequencies are 501 points of frequency linearly spacedbetween 1 Hz and 100 Hz
SBE202 Electronics (Lab)
Introduction to SPICE
SPICE AC Analysis
As we can see from the simulation result, this first-order RCcircuit attenuates the high frequenciesThis is why this circuit is called a lowpass filter
SBE202 Electronics (Lab)
Introduction to SPICE
SPICE AC Analysis
We can convert this figure to logarithmic scaleFirst, ask SPICE to calculate the voltage in dB using the DB()
function
SBE202 Electronics (Lab)
Introduction to SPICE
SPICE AC Analysis
Then convert the X-axis to a logarithmic scaleWe can see the -20 dB/decade, characteristic of first-orderlowpass filters
SBE202 Electronics (Lab)
Using the Oscilloscope and the Function Generator
Outline
1 The Story of a deciBel
2 Introduction to SPICESPICE AC Analysis
3 Using the Oscilloscope and the Function Generator
SBE202 Electronics (Lab)
Using the Oscilloscope and the Function Generator
Using the oscilloscope, we can see how the voltage differencebetween any two points in the circuit is changing over timeThe first step to do with an oscilloscope is to calibrate itUsing the function generator, we can have a voltage source withits voltage varying over timeFunction generators can produce different functions, typicallysquare waves, triangular waves, and sinusoidal waves
SBE202 Electronics (Lab)
Appendix
For Further Reading
Further Reading
Contributors.SPICE Basics.Available Online: http://www.ecircuitcenter.com/Basics.htm
Richard C. Dorf, James A. Svoboda.Introduction to Electric Circuits.6th Edition. John Wiley & Sons.
Wikibooks Contributors.Practical Electronics.Available Online:http://en.wikibooks.org/wiki/Practical Electronics
