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15/9/2011 1 OSCILLOSCOPE & OSCILLOSCOPE & SIGNAL GENERATOR SIGNAL GENERATOR OSCILLOSCOPE & OSCILLOSCOPE & SIGNAL GENERATOR SIGNAL GENERATOR LECTURER: NURHANUM BINTI OMAR LECTURER: NURHANUM BINTI OMAR CHAPTER 3 3.1.1 Define of Oscilloscopes Oscilloscope is a device that allows the amplitude of electrical signals, whether they be voltage, current, power, etc., to be displayed primarily as a function of time ( the basic instrument for the study all types of waveforms).

Chapter 3 Ee101

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Page 1: Chapter 3 Ee101

15/9/2011

1

OSCILLOSCOPE & OSCILLOSCOPE &

SIGNAL GENERATORSIGNAL GENERATOR

OSCILLOSCOPE & OSCILLOSCOPE &

SIGNAL GENERATORSIGNAL GENERATOR

LECTURER: NURHANUM BINTI OMARLECTURER: NURHANUM BINTI OMAR

CHAPTER 3

3.1.1 Define of Oscilloscopes

Oscilloscope is a device that allows the amplitude of electrical

signals, whether they be voltage, current, power, etc., to be

displayed primarily as a function of time ( the basic instrument for

the study all types of waveforms).

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3.1.2 Explain the functions of

Oscilloscope

The main functions of oscilloscope are:

i. Measure the voltage (AC or DC)

ii. Measure the time and frequency

iii. Measure the phase differential between two

waveforms

3.1.3 Classify types of Oscilloscope

(analogue and digital)

Oscilloscopes can be classified into two categories:

i. Analogue

→ Works with con&nuously variable voltages.

→ Works by directly applying a voltage being measured to an

electron beam moving across the oscilloscope screen.

→ The voltage deflects the beam up and down propor&onally,

tracing the waveform on the screen.

→ This gives an immediate picture of the waveform.

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3.1.3 Classify types of Oscilloscope

(analogue and digital) (cont…)

ii. Digital

→ Works with discrete binary numbers that represent voltage

samples.

→ Samples the waveform and uses an analog-to digital

converter (or ADC) to convert the voltage being measured

into digital information.

→ It then uses this digital informa&on to reconstruct the

waveform on the screen.

3.1.4 Block diagram of an analogue

oscilloscope.

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3.1.5 Block diagram of an digital

oscilloscope.

3.1.6 Basic functional block diagram

of an analogue oscilloscope

• When you connect an oscilloscope probe to a circuit, the voltage

signal travels through the probe to the vertical system of the

oscilloscope.

• Depending on how you set the vertical scale (volts/div control), an

attenuator reduces the signal voltage or an amplifier increases the

signal voltage.

• Next, the signal travels directly to the vertical deflection plates of

the cathode ray tube (CRT).

• Voltage applied to these deflection plates causes a glowing dot to

move. (An electron beam hitting phosphor inside the CRT creates

the glowing dot.) A positive voltage causes the dot to

move up while a negative voltage causes the dot to

move down.

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3.1.6 Basic functional block diagram

of an analogue oscilloscope (cont…)

• The signal also travels to the trigger system to start or trigger a

‘horizontal sweep’. Horizontal sweep is a term referring to the action of

the horizontal system causing the glowing dot to move across the screen.

• Triggering the horizontal system causes the horizontal time base to move

the glowing dot across the screen from left to right within a specific time

interval.

• Many sweeps in rapid sequence cause the movement of the glowing dot

to blend into a solid line. At higher speeds, the dot may sweep across the

screen up to 500,000 times each second.

• Together, the horizontal sweeping action and the vertical deflection

action trace a graph of the signal on the screen. The trigger is necessary

to stabilize a repeating signal. It ensures that the sweep

begins at the same point of a repeating signal.

3.1.7 Basic functional block diagram

of an digital oscilloscope

• Some of the systems that make up digital oscilloscopes are the same as

those in analogue oscilloscopes. However, digital oscilloscopes contain

additional data processing systems.

• With the added systems, the digital oscilloscope collects data for the

entire waveform and then displays it.

• When you attach a digital oscilloscope probe to a circuit, the vertical

system adjusts the amplitude of the signal, just as in the analogue

oscilloscope.

• Next, the analogue-to-digital converter (ADC) in the acquisition system

samples the signal at discrete points in time and converts the signals

voltage at these points to digital values called sample points.

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3.1.7 Basic functional block diagram

of an digital oscilloscope (cont…)

• The horizontal systems sample clock determines how often the ADC takes

a sample.

• The rate at which the clock "ticks" is called the sample rate and is

measured in samples per second.

• The sample points from the ADC are stored in memory as waveform

points. More than one sample point may make up one waveform point.

• Together, the waveform points make up one waveform record. The

number of waveform points used to make a waveform record is called

the record length.

• The trigger system determines the start and stop points of the record.

The display receives these record points after being stored in memory.

3.1.8 Advantages and disadvantages

digital oscilloscope

Advantages Disadvantages

High-accuracy measurements Can be more costly

Display storage Can be less intuitive to operate because

they typically have more features)

Bright, well-focused display at virtually

sweep speed

Pre-trigger viewing capability

Peak/glitch detection

Automatic measurements

Computer, printer/plotter connectivity

Waveform processing capability including

waveform math functions

Display modes like averaging and infinite

persistence

Self calibration

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3.1.9 Advantages and disadvantages

analogue oscilloscope

Advantages Disadvantages

Familiar controls Low accuracy

Instantaneous display updating for real-

adjustments

Display flicker and/or dim display

Direct, dedicated controls for No pre-trigger viewing capability

Adjustments like vertical sensitivity,

time base speed, trace position and

trigger level low cost.

Limited bandwidth

Higher cost of ownership

Limited measurement capability

3.2 Front Panel of an Analog

Oscilloscope

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• POWER SWITCH ON/OFF

Main power switches of the instrument. When this switch is turned

on, the LED above the switch is also turned ON

• POWER LAMP

This LED lamp lights when power is turned ON

• INTENSITY KNOB

It can control the brightness of the spot or trace.

• FOCUS KNOB

After obtaining appropriate brightness with intensity, adjust focus

for clearest line

3.2.1 Explain function of Display

Controls

• TRACE ROTATION KNOB

This knob is used to correct the horizontal trace when it becomes

slanted with respect to the horizontal scale, due to the effect of

magnetic fields

• SCALEILLUM KNOB

This is used to adjust scale brightness. If this knob is turned

clockwise, brightness is increased. This feature is useful for

operation in dark places, or when taking pictures

• CAL 0.5V TERMINAL

Outputs a 0.5V p-p 1 KHz rectangular wave for calibrating probes

GND TERMINAL

This is a grounding terminal

3.2.1 Explain function of Display

Controls (cont…)

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• CH1 INPUT CONNECTOR

This is a BNC connector used for vertical input CH1. The signal applied to

this connector when in the X-Y mode becomes the X-axis signal.

• CH2 INPUT CONNECTOR

This is a BNC connector used or vertical input CH2. The signal applied to

this connector when in the X-Y me ie becomes the Y-axis signal.

• AC-GND-DC SWITCH

Select following input coupling options for CH1 and CH2

AC: blocks dc signal component allowing only AC signal to pass into

attenuator

GND: input signal is switch off and attenuator is grounded

DC: dc coupling, all signal are directly connected to attenuator

3.2.2 Explain function of Vertical

Controls

• VOLTS/DIV SELECTOR SWITCH

This is a step attenuator switch adjusting the vertical deflection sensitivity.

Set to the position which displays the input signal at the most convenient

height on the CRT.

• VARIABLE KNOB

The fine adjustment is used for varying the vertical-axis deflection

sensitivity continuously. If this knob is completely counter clockwise the

vertical sensitivity is reduced to less than 1/2.5 of VOLTS/DIV switch

setting. This knob is used for comparing two waveform and rise time

measurement. However this knob is normally in the locking position.

• PULL X5 MAG

When the pull x5 Mag is pulled out, the vertical axis gain is magnified 5

times, the maximum sensitivity becomes 1mV/div

3.2.2 Explain function of Vertical

Controls (cont…)

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• 20MHz BANDWIDTH

The frequency bandwidth of vertical axis is limited to 20MHz. This knob

can be used when you cannot synchronize the signal by high frequency

noise or expanded trace.

• ALT/CHOP

When the vertical mode is in dual, this button can display ALT and CHOP

mode. ALT mode is a sequential display mode with one cycle of signal

between CH1 and CH2. CHOP mode is a sequential display mode with a

frequency step of approximately 220MHz between CH1 and CH2.

• POSITION

Used to move the CHI or CH2 trace up or down on the CRT screen

3.2.2 Explain function of Vertical

Controls (cont…)

• INVERT SWITCH

When the invert push button is pressed, the polarity of the input signal

applied to CH2 is inverted. This function is convenient when 2 waveforms

of difference are compared, or for displaying the CHI and CH2 difference

waveform using ADD.

• MODE SELECTOR SWITCH

Selects vertical axis operating mode

CHI: only the signal applied to CH1 is displayed on the screen

CH2: only the signal applied to CH2 is displayed on the screen

DUAL: when both CH1 and CH2 buttons are pushed in the signals applied

to CH1 and CH2 input are displayed on the screen

ADD: display the algebraic sum of the CHI and CH2 input voltage

3.2.2 Explain function of Vertical

Controls (cont…)

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• A TIME/DIV

Selects sweep speed from 0.05μs/div to 0.2μs/div in 21 calibrated steps.

• HORIZONTAL POSITION

The trace can be moved in a horizontal direction. Tuning this knob

clockwise moves the trace towards the right, turning the knob is counter

clockwise moves the trace towards the left.

• PULL X10 MAG

When pulled out, the trace will be magnified by a factor of 10 times. The

sweep time becomes 1/10 of the indicated on-the time/div switch, (e.g.

100μs/div becomes 10μs/div for X10 MAG). To magnify a portion of a

waveform: Move the waveform of interest to the centre gratitude on the

horizontal scale.

3.2.3 Explain function of Horizontal

Controls

• A, B, ALT (H DISPLAY)

This switch selects the sweep method of A, B. When both A and B buttons

are pushed in, it was display B sweep which was duplicated by A sweep

and 2 trace of B sweep simultaneously.

• X-Y

Displays the CH1 and CH2 input signal as an X, Y graph. The vertical

deflection signal is applied to the CH1 input and the horizontal deflection

signal is applied to the CH2 input. The CH2 Vertical position control is used

for the positioning the X, Y display on the vertical axis the horizontal

position control positions the X, Y display on horizontal axis of CRT.

• TRACE SEPERATION

This trace separation controls the vertical position interval of A sweep and

B sweep at the sweep mode is A ALT B.

3.2.3 Explain function of Horizontal

Controls (cont…)

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• DLY POS

Adjusts to starting with B sweep during the A sweep periods.

• VARIABLE

When this knob is turned all the way clockwise (cal) the sweep is indicated

by the A time/diy switch, if the knob is turned all the way counter

clockwise the sweep is less than ½ of the A time/div setting. During normal

operation, this knob is turned to the CAL position.

3.2.3 Explain function of Horizontal

Controls (cont…)

• B TRIS'D

This knob selects between continuous delay and triggered delay. For

continuous delay (normal state), the B sweep starts immediately after the

sweep delay time determined by A time/div switch (19) and delay pos (25).

For triggered delay (the knob is pushed), the sweep starts with B trigger

signal after the continuous delay time.

• TRIGGER SOURCE SELECTOR SWITCH

Selects sweep trigger signal source.

INT: The input signal applied to CH1 or CH2 becomes the trigger signal

CH2: The input signal applied to CH2 becomes the trigger signal

LINE: The power line frequency becomes the trigger signal source

EXT: The external signal applied to EXT input becomes the trigger signal.

This is used when the trigger signal is external the vertical

input signal

3.2.4 Explain function of Trigger

Controls

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• TRIG LEVEL KNOB

This control sets the amplitude point on the trigger waveform that will

start the sweep.

Pull Slope knob

Selects the polarity of the slope the trigger source waveform will start the

sweep.

(+) Slope is selected when the pull slope knob is in normal position

(-) Slope is selected when the pull slope knob is pulled out.

• HOLD OFF

By the operation of Hold Off, complicated repetitive signals can be

captured.

3.2.4 Explain function of Trigger

Controls (cont…)

• TRIG-MODE SWITCH

Auto: Sweep continuously runs in the auto sweep mode. A trace will be

displayed even when there is no input signal or when the input waveform

is not triggered. A stationary waveform will be displayed when the input

waveform is properly triggered.

Norm: A trace will be displayed only when the input waveform is present

and is properly triggered. There will be no trace displayed on the CRT if

there is no input signal or if the input signal is not synchronized. Normal

sweep is used when the input signal's frequency is less than 2LHz.

TV-H: Effective when trig mode is set to TV, and is used when the

horizontal of the TV signal is to be synchronized.

TV-V: Effective only when trig mode is set to TV, and is used when the

vertical of the TV signal is to be synchronized.

*Both TV-V and TV-H are synchronized only when the trigger

signal is (-).

3.2.4 Explain function of Trigger

Controls (cont…)

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• Probe is more than a cable with a clip-on tip.

• It is a high-quality connector, carefully designed not to pick up stray

radio and power line noise.

• Probes are designed not to influence the behaviour of the circuit

you are testing.

• However, no measurement device can act as a perfectly invisible

observer.

3.3.1 Define of Oscilloscope Probes.

3.3.2 Classify types of Oscilloscope

Probes.

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3.4.1 Prepare procedure for calibrate

Oscilloscope.

• Turn on oscilloscope. Allow it to warm up for approximately 10

minutes. Letting the oscilloscope warm up prevents damage to its

cathode ray tube.

• A green light is show on the CRT screen when the oscilloscope is

ready. The green light should run across the screen horizontally and

should be in the centre of the screen.

• Adjust the position knob on the oscilloscope by and turn it

clockwise or counter clockwise until this line is at the centre of

the screen. If the line shows up as a green dot moving across the

screen, adjust the time/div knob until the dot appear as a line and

then centre it.

3.4.1 Prepare procedure for calibrate

Oscilloscope.

• Usually an oscilloscope has two channels CH1 and CH2. Connect

your oscilloscope probe to CH1.

• Find the voltage selector switch and set it to AC volts.

• Find CAL connector. It looks like a small enclosed hook, similar to

the eye of a needle.

• Attach the oscilloscope probe to CAL connector. Ground the

ground wire. A peak to peak square wave one volt above the centre

division and one volt below the centre division. This means the

oscilloscope is correctly calibrated at 2 Vpp.

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3.4.2 Connection between Signal Generator

and Oscilloscope for signal

measurement.

3.4.3 Using Oscilloscope To Measure

Voltage, Frequency, Time And Phase Angle

• Voltage (V) :

= No. vertical division x volt/div

x probe { x1 or x10 }

• Period, T (s) :

= No. Horizontal division x

time/div

• Frequency measurement,

f(Hz):

= 1 / period

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3.4.3 Using Oscilloscope To Measure

Voltage, Frequency, Time And Phase Angle

• Using oscilloscope to measure voltage

If the setting VOLT/DIV = 1V.

Voltage peak-to-peak = Volt/Div X Div

Example :

Voltage peak–to-peak = Volt / Div X Div

= 1 Volt / Div X 10 Div

= 10 Vp-p

3.4.3 Using Oscilloscope To Measure

Voltage, Frequency, Time And Phase Angle

• Using oscilloscope to measure frequency

If the setting TIME/DIV = 0.2ms.

Frequency= 1 / T

Where T = Time / div x Div

So, Frequency = 1

[Time / div] x div

Example :

Frequency = 1

[Time / div] x div

Frequency = 1

0.2ms x 10 div

Frequency = 500 Hz

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3.4.3 Using Oscilloscope To Measure

Voltage, Frequency, Time And Phase Angle

a) Voltage measurement (V)

(i) V = 4 x 2 x 1 = 8 Vpp (ii) V = 2 x 2 x 1 = 4 Vp

b) Period (s) = 4 x 1 ms/div = 4 ms

c) Frequency measurement (Hz) = 1/T = 1/4ms = 1 kHz

3.4.3 Using Oscilloscope To Measure

Voltage, Frequency, Time And Phase Angle

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3.4.4 Evaluate the specification of

analogue Oscilloscope

To use an analogue oscilloscope, three basic setting accommodate an

incoming signal:

a. The attenuation or amplification of the signal

Use the volt/div control to adjust the amplitude of the signal before it

is applied to the vertical deflection plates.

b. The time base

The time/div control to set amount of time per division represented

horizontally across the screen.

c. The trigger of the oscilloscope

Use the trigger level to stabilize a repeating signal, as well as

triggering on a single event. Also adjust the focus and

intensity controls to create a sharp and visible display.

3.5 Introduction to signal generator

• A signal generator is a test device which generates an alternating

voltage signal suitable for test purposes.

• The signal generator is used primarily in the alignment of tuned

circuits.

• A signal generator is classified according to its frequency and is one

of two types: audio frequency or radio frequency.

a. Audio frequency generators produce signals with a frequency

range from 20 Hz to 20 kHz.

b. Radio-frequency generators produce signals covering a range of

frequencies from 10 kHz to 10 GHz.

• Many radio-frequency generators have audio outputs separately

available through front panel jacks. These outputs are

normally 100 Hz and 400 Hz.

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3.5.1 Audio signal generators.

• Audio signal generators produce stable audio-frequency signals

used for testing audio equipment.

• Video signal generators produce signals which include the audio

range and extend considerably further into the RF range.

• These generators are used in testing video amplifiers and other

wideband circuits.

3.5.2 Classify types of signal generator.

• Audio signal generators produce stable audio-frequency signals

used for testing audio equipment.

• Video signal generators produce signals which include the audio

range and extend considerably further into the RF range.

• These generators are used in testing video amplifiers and other

wideband circuits.

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3.5.2 Classify types of signal generator.

• Video signal generator :

A device which outputs predetermined video and/or television

waveform and other signals used to stimulate faults in, or aid in

parametric measurements of television and video systems.

• Pitch generator:

- A types of signal generator optimized for use in audio and

acoustics applications.

- Sophisticated pitch generators will also include sweep generators

a function which varies the output frequency over a range.

- Pitch generators are typically used in conjunction with sound

level meters, when measuring the acoustics of a room or a sound

reproduction system, and/or with oscilloscopes or

specialized audio analyzers.

3.5.2 Classify types of signal generator.

• Arbitrary waveform generators (AWG):

- Sophisticated signal generators which allow the user to generate

arbitrary waveforms, within published limits of frequency range,

accuracy and output level.

- Unlike function generators, which are limited to a simple set of

waveforms; an AWG allows the user to specify a source

waveform in a variety of different ways.

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3.5.3 Explain Standard Signal Generators.

• Produces known and controllable voltages

• Used as power source for measurement of gain, signal to noise ratio,

bandwidth, standing wave ratio, and other properties.

• Extensively used in testing of radio receiver and transmitter.

• The output signal can be Amplitude Modulated (AM) or Frequency

Modulated (FM).

3.5.4 Explain Function Generators.

• Produce different waveforms of adjustable frequency

• Common output waveform are sine, square, triangular and saw tooth

• The frequency may be adjusted, from a fraction of a hertz to several

hundred kHz

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3.5.5 Front Panel of a Signal Generators.

3.5.5 Front Panel of a Signal Generators.

Frequency Selection Group

� Range switch: Provide seven fixed decades of frequency

� Multiplier: Variable potentiometer allowing frequency setting

between fixed range.

Sweep Group

� The sweep group can frequency sweep any of its function outputs.

� It could be swept up or down in frequency using linear or log sweeps.

� Unlike function generators, there are no annoying discontinuities or

band-switching artifacts when sweeping through certain frequencies.

� Two sweep marker frequencies can be specified.

� When the sweep crosses either of the marker frequencies, a TTL

transition is generated at the rear-panel output to allow

synchronization of external devices.

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3.5.5 Front Panel of a Signal Generators.

Amplitude Modulation Group

� To provide 20dB of attenuation of the output waveform selected by

function switch.

DC offset Group

� To allow the DC level of the output waveform to be set as desire.

Output Group

� Used to adjust the amplitude of the generator’s out signal.

� The group consists of the amplitude control knob, the three

attenuation buttons and the fused 50Ω BNC connector.

Function or Waveform group

� To provide selection of desired output waveform.

(Square, triangle and sine waveforms are provided)

3.5.5 Front Panel of a Signal Generators.

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3.5.6 Connection Between Signal Generator

& Oscilloscope For Signal Measurement

� Connect the oscilloscope probe and signal generator.

� Switch on the signal generator and adjust the output level to produce

a visible signal on the oscilloscope screen.

� Adjust TIME/DIV and VOLTS/DIV to obtain a clear display and

investigate the effects of pressing the waveform shape buttons.

� The rotating FREQUENCY control and the RANGE switch are used

together to determine the frequency of the output signal.

3.5.6 Connection Between Signal Generator

& Oscilloscope For Signal Measurement

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THANK YOU