CRO and functional generator physics

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CRO AND Functional
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Functions
By abdul wahab raza
10/15/2019
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Content
The Three Systems ......................................................................................................................6
Vertical System and Controls...........................................................................................................6
Horizontal System and Controls.......................................................................................................6
TYPES AND FUNCTIONS ...............................................................................................................7
Cathode-ray oscilloscope (CRO):...................................................................................................7
Dual-beam oscilloscope: .....................................................................................................................8
The dual-beamanalogoscilloscopecandisplaytwosignalssimultaneously.A special dual-
beamCRT generates anddeflectstwoseparate beams.Multi-trace analogoscilloscopescan
simulate adual-beamdisplaywithchopandalternate sweeps—butthose featuresdonotprovide
simultaneousdisplays.(Real time digital oscilloscopesofferthe same benefitsof adual-beam
oscilloscope,buttheydonotrequire adual-beamdisplay.) The disadvantagesof the dual trace
oscilloscope are thatitcannotswitchquicklybetweentraces,andcannotcapture two fasttransient
events. A dual beam oscilloscope avoids those problems...............................................................8
Analog storage oscilloscope[: ..............................................................................................................8
Digital oscilloscopes:...........................................................................................................................9
Mixed-signal oscilloscope:......................................................................................................9
Mixed-domainoscilloscopes:..................................................................................................9
Handheld oscilloscopes:......................................................................................................................9
Working:...................................................................................................................................11
Function generator controls ..........................................................................................................12
Typesof functiongenerator 13

CR-OSCILLOSCOPE
An oscilloscope, previously called an oscillograph,[1][2] and informally known as a scope or o-
scope, CRO (for cathode-ray oscilloscope), or DSO (for the more modern digital storage
oscilloscope), is a type of electronic test instrument that graphically displays varying
signal voltages, usually as a two-dimensional plot of one or more signals as a function of time.
Other signals (such as sound or vibration) can be converted to voltages and displayed.
Oscilloscope Systems and Controls

Analog and digital oscilloscopes have some basic controls that are similar, and some that are
different. We’ll look at the basic systems and controls that are common to both. Understanding
these systems and controls is key to using an oscilloscope to tackle your specific measurement
challenges. Note that your oscilloscope probably has additional controls not discussed here.
The Three Systems
A basic oscilloscope consists of three different systems – the vertical system, horizontal system,
and trigger system. Each systemcontributes to the oscilloscope’s ability to accurately
reconstruct a signal.
The front panel of an oscilloscope is divided into three sections labeled Vertical, Horizontal,
and Trigger. Your oscilloscope may have other sections, depending on the model and type.
When using an oscilloscope, you adjust settings in these areas to accommodate an incoming
signal:
 Vertical: This is the attenuation or amplification of the signal. Use the volts/div
control to adjust the amplitude of the signal to the desired measurement range.
 Horizontal: This is the time base. Use the sec/div control to set the amount of time
per division represented horizontally across the screen.
 Trigger: This is the triggering of the oscilloscope. Use the trigger level to stabilize a
repeating signal, or to trigger on a single event
Vertical System and Controls
Vertical controls are used to position and scale the waveform vertically, set the input coupling,
and adjust other signal conditioning. Common vertical controls include:
 Position
 Coupling: DC, AC, and GND
 Bandwidth: Limit and Enhancement
 Termination: 1M ohm and 50 ohm
 Offset
 Invert: On/Off
 Scale: Fixed Steps and Variable
Horizontal System and Controls
An oscilloscope’s horizontal systemis most closely associated with its acquisition of an input
signal. Sample rate and record length are among the considerations here. Horizontal controls
are used to position and scale the waveform horizontally. Common horizontal controls include:

 Acquisition
 Sample Rate
 Position and Seconds per Division
 Time Base
 Zoom/Pan
 Search
 XY Mode
 Z Axis
 XYZ Mode
 Trigger Position
 Scale
 Trace Separation
 Record Length
 Resolution
TYPES AND FUNCTIONS
Cathode-ray oscilloscope (CRO):
Example of an analog oscilloscope Lissajous figure, showing a harmonic relationship of 1
horizontal oscillation cycle to 3 vertical oscillation cycles.

For analog television, an analog oscilloscope can be used as a vectorscope to analyze complex
signal properties, such as this display of SMPTE color bars.
The earliest and simplest type of oscilloscope consisted of a cathode ray tube, a
vertical amplifier, a timebase, a horizontal amplifier and a power supply. These are now called
"analog" scopes to distinguish them from the "digital" scopes that became common in the
1990s and later.
.
Dual-beam oscilloscope:
The dual-beam analog oscilloscope can display two signals simultaneously. A special dual-
beam CRT generates and deflects two separate beams. Multi-trace analog oscilloscopes can
simulate a dual-beam display with chop and alternate sweeps—but those features do not
provide simultaneous displays. (Real time digital oscilloscopes offer the same benefits of a dual-
beam oscilloscope, but they do not require a dual-beam display.) The disadvantages of the dual
trace oscilloscope are that it cannot switch quickly between traces, and cannot capture two fast
transient events. A dual beam oscilloscope avoids those problems.
Analog storage oscilloscope[:
Trace storage is an extra feature available on some analog scopes; they used direct-view
storage CRTs. Storage allows a trace pattern that normally would decay in a fraction of a second
to remain on the screen for several minutes or longer. An electrical circuit can then be
deliberately activated to store and erase the trace on the screen.

Digital oscilloscopes:
While analog devices use continually varying voltages, digital devices use numbers that
correspond to samples of the voltage. In the case of digital oscilloscopes, an analog-to-digital
converter (ADC) changes the measured voltages into digital information.
Mixed-signal oscilloscope:
A mixed-signal oscilloscope (or MSO) has two kinds of inputs, a small number of analog
channels (typically two or four), and a larger number of digital channels(typically sixteen). It
provides the ability to accurately time-correlate analog and digital channels, thus offering a
distinct advantage over a separate oscilloscope and logic analyser. Typically, digital channels
may be grouped and displayed as a bus with each bus value displayed at the bottom of the
display in hex or binary. On most MSOs, the trigger can be set across both analog and digital
channels.
Mixed-domain oscilloscopes:
A mixed-domain oscilloscope (MDO) is an oscilloscope that comes with an additional RF input
which is solely used for dedicated FFT-based spectrum analyzer functionality. Often, this RF
input offers a higher bandwidth than the conventional analog input channels. This is in contrast
to the FFT functionality of conventional digital oscilloscopes which use the normal analog
inputs. Some MDOs allow time-correlation of events in the time domain (like a specific serial
data package) with events happening in the frequency domain (like RF transmissions).
Handheld oscilloscopes:
Further information: Oscilloscope types § Handheld oscilloscopes

Handheld oscilloscopes are useful for many test and field service applications. Today, a hand
held oscilloscope is usually a digital sampling oscilloscope, using a liquid crystal display.
.
The isolation available is categorizedas shown below:
Overvoltage
category
Operating voltage
(effective value of
AC/DC to ground)
Peak instantaneous
voltage (repeated 20
times)
Test
resistor
CAT I 600 V 2500 V 30 Ω
CAT I 1000 V 4000 V 30 Ω
CAT II 600 V 4000 V 12 Ω
CAT II 1000 V 6000 V 12 Ω
CAT III 600 V 6000 V 2 Ω

Function generator
ICs. A function generator is usually a piece of electronic test equipment or software used to
generate different types of electrical waveforms over a wide range of frequencies. Some of the
most common waveforms produced by the function generator are the sine wave , square wave,
triangular wave and sawtooth shapes. These waveforms can be either repetitive or single-shot
(which requires an internal or external trigger source).[1] Integrated circuits used to generate
waveforms may also be described as function generator
Working:
Simple function generators usually generate triangular waveform whose frequency can be
controlled smoothly as well as in steps.[3] This triangular wave is used as the basis for all of its
other outputs. The triangular wave is generated by repeatedly charging and discharging
a capacitor from a constant current source. This produces a linearly ascending and descending
voltage ramp. As the output voltage reaches upper or lower limits, the charging or discharging
is reversed using a comparator, producing the linear triangle wave. By varying the current and
the size of the capacitor, different frequencies may be obtained. Sawtooth waves can be
produced by charging the capacitor slowly, using a current, but using a diode over the current
source to discharge quickly - the polarity of the diode changes the polarity of the resulting
sawtooth, i.e. slow rise and fast fall, or fast rise and slow fall.
A 50% duty cycle square wave is easily obtained by noting whether the capacitor is being
charged or discharged, which is reflected in the current switching comparator output. Other
duty cycles (theoretically from 0% to 100%) can be obtained by using a comparator and the
sawtooth or triangle signal. Most function generators also contain a non-linear diode shaping
circuit that can convert the triangle wave into a reasonably accurate sine wave by rounding off
the corners of the triangle wave in a process similar to clipping in audio systems.

A typical function generator can provide frequencies up to 20 MHz. RF generators for higher
frequencies are not function generators in the strict sense since they typically produce pure or
modulated sine signals only.
Function generators, like most signal generators, may also contain an attenuator, various
means of modulating the output waveform, and often the ability to automatically and
repetitively "sweep" the frequency of the output waveform (by means of a voltage-controlled
oscillator) between two operator-determined limits. This capability makes it very easy to
evaluate the frequency response of a given electronic circuit.
Some function generators can also generate white or pink noise.[citationneeded]
More advanced function generators are called arbitrary waveform generators (AWG). They
use direct digital synthesis (DDS) techniques to generate any waveform that can be described
by a table of amplitudes.
A DDS function generator
Function generator controls
In addition to a selection of the basic waveforms
that are available, other controls on the function
generator may include:
 Frequency: As would be expected, this control alters the basic frequency at which the
waveform repeats. It is independent of the waveform type.
 Waveform type : This enables the different basic waveform types to be selected:
 Sine wave

 Square wave
 Triangular wave
DC offset: This alters the average voltage of a signal relative to 0V or ground.
Duty cycle: This control on the function generator changes the ratio of high voltage to
low voltage time in a square wave signal, i.e. changing the waveform from a square wave
with a 1:1 duty cycle to a pulse waveform, or a triangular waveform with equal rise and fall
times to a sawtooth.
Types of function generator
There are a number of ways of designing function generator circuits. However there are two
main approaches that may be used:
 Analogue function generator: This type of function generator was the first type
to be developed. First models appeared in the early 1950s when digital technology was not
widely used.
Despite the fact that they use analogue technology, these analogue function generators
offer a number of advantages:
 Cost effective: Analogue function generators are very cost effective, being at the
lower end of the function generator price range.
 Simple to use: Analogue function generators provide an effective test instrument that
is able to meet most user needs, while remaining simple and easy to use.
 Maximum frequencies: The analogue function generators do not have the high
frequency limitations on non-sinusoidal waveforms such as triangles and ramps as do the
digital function generators.
Digital function generator: As the name indicates, digital function generators
utilise digital technology to generate the waveforms. There are a number of ways in which
this can be done, but the most versatile and most widely used technique for digital function

generators is to use direct digital synthesis, DDS.
DDS uses a phase accumulator, a look-up table containing a digital representation of the
waveform, and a DAC. The phase accumulator moves another position each time it receives
a clock pulse. The next position in the look-up table is then accessed giving the digital value
for the waveform at that point. This digital value is then converted into an analogue value
using a digital to analogue converter, DAC.
Sweep function generator: A sweep function generator is simply one that can
sweep its frequency. Typically the more versatile sweep function generators utilise digital
technology, but it is also possible to use analogue versions as well.
Sweep function generators may be able to sweep over ranges of up to 100:1 or more,
although this is very dependent upon the actual generator type in question. Speed of the
sweep may also be important. Another feature that may be of importance is whether the
sweep is linear or logarithmic. Some function generators may have a switch for this

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