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SBE202 Electronic Devices and Circuits (Lab) - … Electronics (Lab) The Story of a deciBel Outline...

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SBE202 Electronics (Lab) SBE202 – Electronic Devices and Circuits (Lab) Tutorial 3 Islam S. Badreldin Biomedical Engineering Department Faculty of Engineering Cairo University October 30, 2011
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Page 1: SBE202 Electronic Devices and Circuits (Lab) - … Electronics (Lab) The Story of a deciBel Outline 1 The Story of a deciBel 2 Introduction to SPICE SPICE AC Analysis 3 Using the …

SBE202 Electronics (Lab)

SBE202 – Electronic Devices and Circuits(Lab)

Tutorial 3

Islam S. Badreldin

Biomedical Engineering DepartmentFaculty of Engineering

Cairo University

October 30, 2011

Page 2: SBE202 Electronic Devices and Circuits (Lab) - … Electronics (Lab) The Story of a deciBel Outline 1 The Story of a deciBel 2 Introduction to SPICE SPICE AC Analysis 3 Using the …

Copyright

Copyright c© 2011 Islam S. Badreldin. Some rights reserved.

This work is licensed under a Creative CommonsAttribution-Share Alike 3.0 License

Page 3: SBE202 Electronic Devices and Circuits (Lab) - … Electronics (Lab) The Story of a deciBel Outline 1 The Story of a deciBel 2 Introduction to SPICE SPICE AC Analysis 3 Using the …

Outline

1 The Story of a deciBel

2 Introduction to SPICESPICE AC Analysis

3 Using the Oscilloscope and the Function Generator

Page 4: SBE202 Electronic Devices and Circuits (Lab) - … Electronics (Lab) The Story of a deciBel Outline 1 The Story of a deciBel 2 Introduction to SPICE SPICE AC Analysis 3 Using the …

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

Page 5: SBE202 Electronic Devices and Circuits (Lab) - … Electronics (Lab) The Story of a deciBel Outline 1 The Story of a deciBel 2 Introduction to SPICE SPICE AC Analysis 3 Using the …

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)

Page 6: SBE202 Electronic Devices and Circuits (Lab) - … Electronics (Lab) The Story of a deciBel Outline 1 The Story of a deciBel 2 Introduction to SPICE SPICE AC Analysis 3 Using the …

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

Page 7: SBE202 Electronic Devices and Circuits (Lab) - … Electronics (Lab) The Story of a deciBel Outline 1 The Story of a deciBel 2 Introduction to SPICE SPICE AC Analysis 3 Using the …

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

Page 8: SBE202 Electronic Devices and Circuits (Lab) - … Electronics (Lab) The Story of a deciBel Outline 1 The Story of a deciBel 2 Introduction to SPICE SPICE AC Analysis 3 Using the …

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)

Page 9: SBE202 Electronic Devices and Circuits (Lab) - … Electronics (Lab) The Story of a deciBel Outline 1 The Story of a deciBel 2 Introduction to SPICE SPICE AC Analysis 3 Using the …

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

Page 10: SBE202 Electronic Devices and Circuits (Lab) - … Electronics (Lab) The Story of a deciBel Outline 1 The Story of a deciBel 2 Introduction to SPICE SPICE AC Analysis 3 Using the …

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

Page 11: SBE202 Electronic Devices and Circuits (Lab) - … Electronics (Lab) The Story of a deciBel Outline 1 The Story of a deciBel 2 Introduction to SPICE SPICE AC Analysis 3 Using the …

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

Page 12: SBE202 Electronic Devices and Circuits (Lab) - … Electronics (Lab) The Story of a deciBel Outline 1 The Story of a deciBel 2 Introduction to SPICE SPICE AC Analysis 3 Using the …

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

Page 13: SBE202 Electronic Devices and Circuits (Lab) - … Electronics (Lab) The Story of a deciBel Outline 1 The Story of a deciBel 2 Introduction to SPICE SPICE AC Analysis 3 Using the …

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

Page 14: SBE202 Electronic Devices and Circuits (Lab) - … Electronics (Lab) The Story of a deciBel Outline 1 The Story of a deciBel 2 Introduction to SPICE SPICE AC Analysis 3 Using the …

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

Page 15: SBE202 Electronic Devices and Circuits (Lab) - … Electronics (Lab) The Story of a deciBel Outline 1 The Story of a deciBel 2 Introduction to SPICE SPICE AC Analysis 3 Using the …

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

Page 16: SBE202 Electronic Devices and Circuits (Lab) - … Electronics (Lab) The Story of a deciBel Outline 1 The Story of a deciBel 2 Introduction to SPICE SPICE AC Analysis 3 Using the …

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

Page 17: SBE202 Electronic Devices and Circuits (Lab) - … Electronics (Lab) The Story of a deciBel Outline 1 The Story of a deciBel 2 Introduction to SPICE SPICE AC Analysis 3 Using the …

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


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