A dual beam oscilloscope can display two signals simultaneously using a CRT that generates and deflects two separate electron beams. It avoids issues with dual trace oscilloscopes that time share a single beam. A dual trace oscilloscope displays two signals by rapidly switching a single beam between the two input channels. Sampling oscilloscopes convert fast signals to low frequency domains by taking samples over successive cycles. Digital storage oscilloscopes digitize input waveforms and store them in memory for display, allowing non-repetitive signals to be observed. Oscilloscope probes come in passive and active varieties, with 1x, 10x, and 100x attenuation ratios for passive probes and integrated circuits in active probes for improved performance

1. OSCILLOSCOPES TYPES
-Venumaheswar Rao
KITS Warangal

2. DUAL BEAM OSCILLOSCOPE

3. Multi-Input Oscilloscope
 Oscilloscopes can have multiple input and display facilities.

4.  The most common one is of –TWO INPUTS.

5.  There are two types of multi input oscilloscope.
Single beam oscilloscope
Double beam oscilloscope
How a double beam oscilloscope looks like

6. Dual Beam Oscilloscope
 The dual beam analog oscilloscope can display two signals
simultaneously.
 A special dual beam CRT generates and deflects two beams
separately.
 Unlike an ordinary Dual trace oscilloscope which time
shared a Single electron beam, thus loosing about 50% of
each signal, a dual beam oscilloscope simultaneously
produced two separate electron beams capturing entirely of
both signals.
 Also Dual trace oscilloscope cannot capture two fast
transient events, as it cannot switch quickly enough
between traces. So to avoid these problems Dual beam
oscilloscope is used.

7. Construction
 The dual beam oscilloscope has two separate electron
beams and therefore two completely separate vertical
channels.
 Each channel consists of a pre amplifier and attenuator.
 There is a single set of horizontal plates and single time
base circuit.
 The sweep generator drives the horizontal amplifier which
in turn drive the plates.
 The horizontal plates sweep both the beams across the
screen at the same rate.

8. Dual beam oscilloscope with independent time base

9. Dual beam oscilloscope with common time base

10. Modes of operation
 There are two methods used for generating the two
electron beams with in the CRT.
1) Double gun tube.
2) Split beam.
A. Double gun tube:
This method allows the brightness and focus of
each beam to be controlled separately but it is
bulkier than a split beam.

11. B. Split beam:
1. In this method single electron gun is used.
2. A horizontal splitter plate is placed between the
last anode and the γ deflection plate.
3. This plate is held at the same potential as the
anode, and it goes along the length of tube,
between the two vertical deflection plates which
isolates the channel.

12. Disadvantages
 This arrangement has half the brightness of single
beam.
 The two display may have noticeably different
brightness.

13. DUAL TRACE OSCILLOSCOPE

14. Why Dual Trace?
 Unlike single trace oscilloscope, dual trace oscilloscope can
display two traces on the screen, allowing you to easily
compare the input and output.
 For Example: input and output of an amplifier.

17. Difference between DTO and Dual Beam Oscilloscope
 A dual-trace oscilloscope should not be confused
with a dual-beam oscilloscope.
 Dual-beam oscilloscopes produce two separate
electron beams on a single scope, which can be
individually or jointly controlled.
 Dual-trace refers to a single beam in a CRT that is
shared by two channels.

18. DTO Working modes

20. Block Diagram

21. Dual Trace Oscilloscope Works in Following two modes
 Alternate mode
 Chopped mode
Alternate Mode:
In alternate mode an electronic switch alternate
between signal A&B.

22.  In this an electronic switch alternates between
channels A and B, letting each through for one cycle
of horizontal sweep.
 The display is blanked during the fly back and hold-
off periods, as in a conventional oscilloscope.
 The screen will show a stable display of both the
waveform at channels A and B.
 The alternate mode cannot be used for displaying
very low frequency signals.

23. Chopped Mode
In the chopped mode the switch free runs at very high
frequency.

24.  In this mode the electronic switch free runs at a high
frequency of order of 100kHz to 500 kHz.
 The result is that small segments from channels A
and B are connected alternately to the vertical
amplifier, and display in the screen.
 If the chopping rate is much faster than the
horizontal sweep rate, the display will show a
continuous line for each channel.
 If the sweep rate approaches the chopping rate then
the individual segments will be visible, and the
alternate mode should not be used.

26. Typical Applications
 Troubleshoot electro optical and electrical systems.
 Observe a triggered event separately or relative to
the trigger itself.
 Use with analog light meter output to visualize
intensity of a source.
 Check response of a silicon, InGaAs, or avalanche
photo diode.
 Analyze signals produced by function generators.
 Evaluate system performance.

27. SaMPLING OSCILLOSCOPE
Definition:
The sampling oscilloscope is a special type of digital
sampling oscilloscope which is used to examine a
very fast signal. In other words, The sampling
oscilloscope receives various electrical signal and
then togetherly display the signals on the screen.

28. Working
 It works on the principle of stroboscopic light in
which sample is taken at different portions of the
waveform, over successive cycles, and then the total
picture is stretched, amplified by relatively low
bandwidth amplifiers, and display as the continuous
wave on the screen.
 The sampling techniques of the oscilloscope convert
the input signal into the low-frequency domain. The
low-frequency signal has a highly efficient domain.
The sampling oscilloscopes in not used for displaying
the transient signals.

29. Block Diagram of Sampling Oscilloscope

30. Description
 The input signal is applied to the delay line where the signal
is delayed.
 The signal delay means the precise time difference develops
between the input and output signal.
 The output obtains from the delay line passes to the diode
sampling gate.
 The sampled signal received from the diode gate stores in
the capacitor.
 Then it is fed to the amplifier for amplification and then
given to the vertical axis of the display screen.

31.  The single feedback is used from the amplifier to
the diode gate. The feedback shows that the voltage
stored on the capacitor increases only by the
change in internal signal between each sample.

32. Waveforms
 The staircase waveform is shown in the figure below. The waveform
shows that it is reset after several numbers of steps. Thus, more than
1000 points are used on the screen for creating the waveform. The
staircase waveform is used in the cathode ray tube. It is used for
removing the spot on the screen.

33. Advantages & Disadvantages
 The advantage of the sampling oscilloscope is that it can
measure the very high-speed event with the help of the
instrument having lower bandwidth.
 The disadvantage of the oscilloscope is are that it can
only measure the repetitive or continuous signal. The
frequency range of the oscilloscopes depends on their
design.

34. DIGITAL STORAGE OSCILLOSCOPE(DSO)

35. Description
 In DSO, the waveform to be stored is digitized, stored in
a digital memory and retrieved for display on the storage
oscilloscope.
 Figure shows the block diagram of DSO as consists of,
1. Data acquisition
2. Storage
3. Data display.

36. Data Acquisition
 Data acquisition is earned out with the help of both analog to digital
and digital to analog converters, which is used for digitizing, storing
and displaying analog waveforms. Overall operation is controlled by
control circuit which is usually consists of microprocessor.
 Data acquisition portion of the system consist of a Sample-and-Hold
(S/H) circuit and an analog to digital converter (ADC) which
continuously samples and digitizes the input signal at a rate
determined by the sample clock and transmit the digitized data to
memory for storage.
 The control circuit determines whether the successive data points are
stored in successive memory location or not, which is done by
continuously updating the memories.

37. Storage
 When the memory is full, the next data point from the ADC
is stored in the first memory location writing over the old
data.
 The data acquisition and the storage process is continues
till the control circuit receive a trigger signal from either the
input waveform or an external trigger source. When the
triggering occurs, the system stops and enters into the
display mode of operation in which all or some part of the
memory data is repetitively displayed on the cathode ray
tube.

38. Data Display
 In display operation, two DACs are used which gives horizontal and
vertical deflection voltage for the CRT Data from the memory gives
the vertical deflection of the electron beam, while the time base
counter gives the horizontal deflection in the form of staircase
sweep signal.
 The screen display consist of discrete dots representing the various
data points but the number of dot is very large as 1000 or more that
they tend to blend together and appear to be a smooth continuous
waveform.
 The display operation ends when the operator presses a front-panel
button and commands the digital storage oscilloscope to begin a
new data acquisition cycle.

39. Advantages
 Allows for automation.
 In this, slow traces like the temperature variation
across a day can be recorded.
 With colour Bigger and brighter display, to
distinguish multiple traces.
 peak detection.

40. Applications of cro
(Phase & frequency)
• It may also be used to observe a voltage-versus-
voltage pattern by eliminating the time parameter.
The resulting pattern is referred to as a Lissajous
pattern.
• Applying two ac waveforms to both the horizontal
and vertical amplifiers, you can observe a Lissajous
pattern on the screen.

41.  If one of the input waveforms is completely known,
the frequency, phase, and magnitude relationships
between the two waveforms may be measured from
the pattern.
 When both applied waveforms are sinusoidal, the
resulting Lissajous pattern may take many forms
depending upon the frequency ratio and phase
difference between the waveforms.

42. Frequency Measurement
 To determine the frequency ratio, draw horizontal and
vertical lines through the center of the pattern.
 The ratio of the number of horizontal axis crossings to
the number of vertical axis crossings determines the
frequency ratio.
 This ratio is given as
where fx and fy are the frequencies of the two waveforms.

43. Examples

44. Examples

45. Phase Measurement
 In this condition the phase difference will be,

46. Examples

47. Oscilloscope Probes
 Oscilloscope probes may be categorized into two main types,
and they can fall into one of two main areas:
 Passive oscilloscope probes: This type of probe is the
one that is in most widespread use. It only includes passive
elements and may provide 1:1, i.e. straight through
connectivity from the point under test, to the scope input.
Other types may provide a defined degree of attenuation.
 Active oscilloscope probes: As indicated by the name,
this type of scope probe has active components incorporated
within the probe itself. This enables greater levels of
functionality and higher levels of performance to be attained.
However they are much more expensive and normally
reserved for more exacting or specialist requirements.

48. Passive oscilloscope probes
 The great majority of test scope probes used with
oscilloscopes are the passive variety. They enable a
wide range of measurements to be made, and cover
most applications. In addition to this, passive test
probes are far cheaper than active ones as would be
expected.
 Scope probes are generally classified according to the
level of attenuation of the signal they provide. Types
including 1X (giving a 1 : 1 attenuation ratio), 10X
(giving a 10 : 1 attenuation ratio) and 100X (giving a
100 : 1 attenuation ratio) are available:

49. 1X scope probes
 The most basic form of oscilloscope probe, or scope probe, is what is often
termed the 1X probe. It is so called because this type of scope probe does
not attenuate the incoming voltage as many other probes do. It consists of a
connector to interface to the oscilloscope (generally a BNC connector), and
a length of coax which is connected to the probe itself. This comprises a
mechanical clip arrangement so that the probe can be attached to the
appropriate test point, and an earth or ground clip to be attached to the
appropriate ground point on the circuit under test.
 The 1X probes are suitable for many low frequency applications. They
typically offer the same input impedance of the oscilloscope which is
normally 1 M Ohm. However for applications where better accuracy is
needed and as frequencies start to rise, other test probes are needed.

50. 10X scope probes
 To enable better accuracy to be achieved higher levels of
impedance are required. To achieve this attenuators are
built into the end of the probe that connects with the
circuit under test. The most common type of probe with a
built in attenuator gives an attenuation of ten, and it is
known as a 10X oscilloscope probe. The attenuation
enables the impedance presented to the circuit under test
to be increased by a factor of ten, and this enables more
accurate measurements to be made. In particular the
level of capacitance seen by the circuit is reduced and
this is reduces the high frequency loading of the circuit
by the probe.

52. 10X scope probes
 As the 10X probe attenuates the signal by a factor of ten, this
obviously means that the signal entering the scope itself is reduced.
This has to be taken into account. Some oscilloscopes automatically
adjust the scales according to the probe present, although not all are
able to do this. It is worth checking before making a reading.
 The 10X scope probe uses a series resistor (9 M Ohms) to provide a
10 : 1 attenuation when it is used with the 1 M Ohm input
impedance of the scope itself. A 1 M Ohm impedance is the standard
impedance used for oscilloscope inputs and therefore this enables
scope probes to be interchanged between oscilloscopes of different
manufacturers.
 10X oscilloscope probes also allow some compensation for
frequency variations present. A capacitor network is embodied into
the probe as shown. The capacitor connected to ground can then be
used to equalise the frequency performance of the probe.

53. 100X scope probes
 Although they are not as common as the 1X and 10X
scope probes, 100X probes and other values including
20X and 1000X are also available. These oscilloscope
probes tend to be used very high voltages need to be
monitored and a high degree of attenuation is required
or if very low levels of loading are needed. These probes
are not common and tend to be quite specialized.
 If they were used for normal applications, the 100X
attenuation would result in very small signal levels being
presented to the input of the oscilloscope and as a result,
noise on the input amplifiers of the scope would tend to
be visible.

54. Active oscilloscope probes
 Although 10X probes are widely used because of their
superior response, they are not able to provide all the
performance that may be needed for some applications.
By using active electronic circuits in the remote end of
the oscilloscope probe it is possible to offer very high
levels of performance.
 Active oscilloscope probes use specially developed
integrated circuits. By placing these chips right at the
point at which the signal is probed, it enables the signal
to be preserved during its transition from the point at
which it is sampled to the input of the oscilloscope, in
some instances using differential techniques.

55. Active oscilloscope probes
 In this way the signal integrity it maintained, despite the
fact that it may have a fast rise time, may have a low
signal level, or require a high input impedance at the
point at which it is sampled. Not only is the input
resistance very high, but more importantly the input
capacitance is very low. With capacitance normally
providing the limiting factor, the reduction in
capacitance enables sensitive waveforms to be measured
far more accurately.
 Although active probes are more expensive than their
passive cousins, they offer a better level of performance
that may be essential in some circumstances.