1 Signals and Instruments

MEASUREMENTS FOR ELECTRONICS AND

TELECOMMUNICATION AREA

ș. l. dr. ing. Ioana Marcu

Email: [email protected]

Grades Rules:

• 40% Lab

• 40% Final exam

• 20% Lab examination

• 10% Written test paper

Promovability conditions:

• Lab >=5

• Final exam > 16 din 40

• Lab examination >=5

• Written test paper >=5

mailto:[email protected]



Măsurări în Electronică şi Telecomunicaţii

GENERAL INFORMATION ABOUT METC

1. First specialized course – VERY IMPORTANT!!!

2. The information → very useful for the following years.

3. Course atendance: not mandatory but strongly encouraged!

4. Exam grade depends on the degree to understand this course

not on its memorization!

5. All the necessary explications are presented throughout this

course.

6. Problems similar to those solved at course are possible

subjects for final exam.

Măsurări în Electronică şi Telecomunicaţii

COURSE CONTENT

1. Signals and instruments for signals generation/measurement

2. Oscilloscope (scope)

3. Voltage and electrical currents measurement

4. Impedances measurement

5. Frequency and time measurement

Course support:

ham.elcom.pub.ro/Metc

Measurements for Electronics and Telecommunication Area

1. Signals and instruments for signals measurements


ELECTRONIC MEASUREMENT SYSTEMS

Measurements imply connection between signal generators and acquisition equipment.

Generated signals can be classified:

analog signals;

digital signals;

modulated signals;

noisy signals or intentionally distorted.

Examples of acquisition instruments:

scopes

spectrum analyzers, etc.


ELECTRONIC MEASUREMENT SYSTEMS

SIGNALS – DEFINITION + CLASSIFICATION

physical quantity used for:

messages transmission or storage;

systems tests.

mathematically = time dependency;

Signals used for systems tests are described by time-depended functions.


Classification:

Deterministic signals

Random signals


SIGNALS – DEFINITION + CLASSIFICATION

SIGNALS USED IN ELECTRONICS AREA

cover a large frequency domain:

Audio-frequency signals (AF)

frequency range between a couple of Hz and approx. 20 kHz;

can be heard by human ear.

Radio-frequency signals (RF)

frequencies over 100kHz;

used for information transmission through radio methods → broadcasted with different antennas;

upper limit: a couple of GHz. Measurements for Electronics and Telecommunication Area

PERIODIC SIGNALS

T = repetition period of the signal

EXAMPLE:

Sine wave

,x t kT x t k Z

+A

0

–A

T

t


PERIODIC SIGNALS

One-way rectified sine wave

REDRESOR

MONO-

ALTERNANŢĂ

ONE-WAVE

RECTIFIER


PERIODIC SIGNALS

Full-wave rectified sine wave

REDRESOR

DUBLĂ-

ALTERNANŢĂ

FULL-WAVE

RECTIFIER


PERIODIC SIGNALS

Square wave

two levels;

representation in binary form

of digital signals;

two logical values: “0” and “1”.

Symmetric square:

amplitude: A+ = A–;

period: equal periods for both states.

t


PERIODIC SIGNALS

Triangular and saw-tooth signals:

Periodic square impulses:

t t

t


PARAMETERS OF PERIODIC SIGNALS

T [s] – signal’s repetition period;

A+ [V] – positive peak amplitude;

A– [V] – negative peak amplitude;

Avv [V] – peak-peak amplitude:

vvA A A



RMS – root mean square:

= effective voltage = continuous voltage that produces the same average power through a 1Ω resistance with the corresponding period signal.

= for sine wave:

21t T

ef

t

A x t dtT

2ef

AA



Average value (mean value):

0

1t T

t

A x t dtT

A0 – mean

t

A+

A–

0



Square impulses:

=η [s] - duty

= tc [s] – rise time.

tc – rise time

tc

A

0.9A

0.1A

0

t

T τ

A

T


SINE WAVE - PARAMETERS

A – amplitude

ω - pulsation [rad./sec.]

T - period

+A

0

–A

T

t

( ) cos( )x t A t

2 f 1

fT



φ – initial phase;

Comparing two sine waves with the same frequency:

φ = φ1 – φ2

= phase difference.

1 1 1

2 2 2

cos

cos

x t A t

x t A t

φ



RMS (Root Mean Square):

Peak-peak

amplitude:

2ef

AA

2vvA A

T

t AVV

A

Aef = 0,707 A


CIRCUIT BEHAVIOR FOR SINE WAVE

Linear circuits

LINEAR

CIRCUIT

y(x) = a·x + b



Non-linear circuits

NON-LINEAR

CIRCUIT

- limitation -



Non-linear circuits

NON-LINEAR

CIRCUIT

2( ) 1,2 0,6 0,1y x x x



Modulators circuits

to transmit a signal by radio means a low-frequency signal (modulator signal) will modify one parameter of a much high-frequency sine wave (carrier signal) → modulation process.

Achieved signal has high frequency and carries the useful information → this signal is called

modulated signal.


MODULATED SIGNALS

Modulation types:

Amplitude modulation (MA);

Frequency modulation (MF);

Phase modulation (MP).

Frequency-modulated signal

Amplitude-modulated signal

Modulator signal

Carrier signal


SINE WAVE GENERATORS

A. Audio-frequency generators

larger frequency domain than audio range;

from 0,1 Hz up to 1MHz (even 10MHz);

rather simple generators with two adjusting elements (decade and continuous steps):

frequency

amplitude.


Audio-frequency generators

Quality parameters:

Distorsion factor:

- gives a degree for similarities between generated signal and a pure sine wave.

Precision and resolution for frequency range;

Stability of generated frequency;

Control of generated amplitude;

Output impedance (thousand, hundred ohms).


Radio-frequency generators

B. Radio-frequency generators

100kHz - 100MHz;

maximum limit can be extended;

AM and FM capabilities;

have low-frequency generator for modulator signal;

a digital frequency measurement equipment can be used for exact control over carrier frequency.


FUNCTION GENERATOR


FUNCTION GENERATOR - PARAMETERS














SCOPE DISPLAY

Sine wave with 1V amplitude

Cy = 0.1V/div 10 divisions (out of graticule)


SCOPE DISPLAY


Cy = 0.2V/div 5 divisions (out of graticule)


SCOPE DISPLAY


Cy = 0.5V/div 2 divisions

A=2div =1V


SCOPE DISPLAY

Signal’s frequency measurement

Turn Cx [s/div] until one period of the signal appears.


SCOPE DISPLAY




SCOPE DISPLAY




SCOPE DISPLAY



T=5,6 div.Cx

f=1/T


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1 Signals and Instruments