The document discusses different types of oscilloscopes including dual trace CROs, dual beam CROs, digital storage oscilloscopes, and sampling oscilloscopes. A dual trace CRO uses a single electron beam but an electronic switch to display two input signals simultaneously. A dual beam CRO has two separate electron beams and deflection systems allowing two signals to be displayed together in real-time. Digital storage oscilloscopes digitize and store input signals, allowing slow signals to be analyzed. Sampling oscilloscopes take samples from input signals over multiple cycles to display high-frequency signals beyond the bandwidth of its amplifiers.

1. DUAL TRACE CRO
In dual trace CRO, two separate vertical input signals can be displayed simultaneously. The CRO consists of a
single beam CRT, single time base generator, and two identical vertical amplifiers with an electronic switch. The
output of the vertical amplifiers is connected to the electronic switch via a mode control switch.
Dual trace CRO is used to generate only one electron beam but display two traces. Thus the same electron beam is
used for generating both the traces to display two different input signals simultaneously.
Block Diagram ofDual Trace CRO
There are two separate vertical input channels, channel A and B. They use separate attenuator and preamplifier stage.
Because of this arrangement, it is possible to control the amplitude of each input independently.
After amplification, both the channels are applied to an electron switch. This switch will connect one channel at a
time to the vertical amplifier via a delay line.
The trigger selector switch S2 allows the circuit to be triggered by channel A or channel B or line frequency or signal
from an external source.
The Horizontal amplifier gets input either from channel B or from time base generator through switch S1 and S3
depending on the mode of operation.
Only in X-Y mode of operation, the input of the horizontal amplifier is from channel B. Otherwise it gets input from
time base generator.
In X-Y mode of operation, the time base generator is disconnected from the horizontal amplifier and channel B acts
as horizontal input. Channel A acts as a vertical input. It plots Y-input (Channel A) with respect to X-input (Channel
B).
It allows two modes of operations:

2. 1. The alternate mode.
2. The chopped mode.
Alternate Mode (ALT Mode)
In the alternate mode, the electronic switch connects the two channels A and B alternately in the successive cycles of
the time base generator. Thus two channels are alternately connected to the vertical amplifier.
The switching rate of the CRT is controlled by the sweep rate of the time base generator. Hence, the CRO alternately
displays the two vertical signals. Each vertical amplifier has its own calibrated input alternators and position controls
so that the amplitude of each signal can be separately adjusted.
Alternate Mode
The alternate mode is used for the high-frequency signal. Time base is set at high speed so that both the traces appear
as continuous trace instead of alternate trace.
Chopped (Chop) Mode
In the chopped mode, the electronic switch will make several transitions from one channel to the other during one
sweep.
A free-running oscillator is used to control the position of the electronic switch.
As the electronic switch is running at very high speed, each channel is displayed for a very short time.

3. Chop Mode
The switching rate of the electronic switch or chopping rate is approximately 100 kHz or 0.01 msec.
This is of greater use for simultaneous observation of the low-frequency signals, whose frequency is much lower
than the chopping frequency.
Dual Beam CRO
The dual beam CRO is built around a special CRT, which displays two completely independent beams.
It has two separate electron beams. Each electron beams has its own independent sets of vertical and horizontal
deflection plates.
The time base generator is common for both the channels and beams.
Block Diagram ofDual Beam CRO
Dual Beam CRO

4. If the two channels can have an independent time base circuit than they produce different sweep rates for an
individual channel. This will also increase the weight and size of an oscilloscope.
Each channel has separate attenuator, delay line, and amplifier.
Two methods are used for generating two electron beams within CRT.
 Using double electron gun
 Using a beam splitting method
In double electron gun generators two electron beam separately. So the brightness and focus of each electron beam
can be controlled separately. But it increases weight.
In the split beam method, the last anode has two apertures through which two beams emerge.
Difference between Dual Trace and Dual Beam CRO
Dual Trace CRO Dual Beam CRO
A single electron beam is used to display two traces.
Two electron beams are used to display two
signals.
One main vertical amplifier is used. Two main vertical amplifiers are used.
Two fast transient events cannot be captured. Two fast transient events can be captured.
Two signals cannot be displayed together in real-
time.
Two signals can be displayed simultaneously in
real-time.
The circuit operates either in alternate mode or
chops mod to obtain two traces using one electron
beam.
Two electron beams are obtained either by using
two-electron gun or by using the beam-splitting
technique.
The frequency of both the signals should be
multiple of each other for a stable display of both
the traces as both the signals are controlled by a
one-time base.
If two-time bases are used then the frequency of
both the signals should not be multiple of each
other for a stable display.

5. Digital Storage Oscilloscope
Definition: The digital storage oscilloscope is an instrument which gives the storage of a digital
waveform or the digital copy of the waveform. It allows us to store the signal or the waveform in
the digital format, and in the digital memory also it allows us to do the digital signal processing
techniques over that signal. The maximum frequency measured on the digital signal oscilloscope
depends upon two things they are: sampling rate of the scope and the nature of the converter. The
traces in DSO are bright, highly defined, and displayed within seconds.
Block Diagram of Digital Storage Oscilloscope
The block diagram of the digital storage oscilloscope consists of an amplifier, digitizer, memory,
analyzer circuitry. Waveform reconstruction, vertical plates, horizontal plates, cathode ray tube
(CRT), horizontal amplifier, time base circuitry, trigger, and clock. The block diagram of the digital
storage oscilloscope is shown in the below figure.
Digital Storage Oscilloscope Block Diagram
As seen in the above figure, at first the analog input signal is amplified by amplifier if it has any
weak signal. After amplification, the signal is digitized by the digitizer and that digitized signal
stores in memory. The analyzer circuit process the digital signal after that the waveform is
reconstructed (again the digital signal is converted into an analog form) and then that signal is
applied to vertical plates of the cathode ray tube (CRT).
The cathode ray tube has two inputs they are vertical input and horizontal input. The vertical input
signal is the ‘Y’ axis and the horizontal input signal is the ‘X’ axis. The time base circuit is
triggered by the trigger and clock input signal, so it is going to generate the time base signal which
is a ramp signal. Then the ramp signal is amplified by the horizontal amplifier, and this horizontal
amplifier will provide input to the horizontal plate. On the CRT screen, we will get the waveform
of the input signal versus time.

6. The digitizing occurs by taking a sample of the input waveform at periodic intervals. At the
periodic time interval means, when half of the time cycle is completed then we are taking the
samples of the signal. The process of digitizing or sampling should follow the sampling theorem.
The sampling theorem says that the rate at which the samples are taken should be greater than twice
the highest frequency present in the input signal. When the analog signal is not properly converted
into digital then there occurs an aliasing effect.
When the analog signal is properly converted into digital then the resolution of the A/D converter
will be decreased. When the input signals stored in analog store registers can be read out at a much
slower rate by the A/D converter, then the digital output of the A/D converter stored in the digital
store, and it allows operation up to 100 mega samples per second. This is the working principle of a
digital storage oscilloscope.
DSO Operation Modes
The digital storage oscilloscope works in three modes of operations they are roll mode, store mode,
and hold or save mode.
Roll Mode: In roll mode, very fast varying signals are displayed on the display screen.
Store Mode: In the store mode the signals stores in memory.
Hold or Save Mode: In hold or save mode, some part of the signal will hold for some time and
then they will be stored in memory.
These are the three modes of digital storage oscilloscope operation.
Waveform Reconstruction
There are two types of waveform reconstructions they are linear interpolation and sinusoidal
interpolation.
Linear Interpolation: In linear interpolation, the dots are joined by a straight line.
Sinusoidal Interpolation: In sinusoidal interpolation, the dots are joined by a sine wave.
Waveform Reconstruction of Digital Storage Oscilloscope

7. Difference between Digital Storage Oscilloscope and Conventional Storage
Oscilloscope
The difference between DSO and the conventional storage oscilloscope or analog storage
oscilloscope (ASO) is shown in the below table.
S.NO Digital Storage Oscilloscope Conventional Storage Oscilloscope
1
The digital storage oscilloscope collects
data always After triggering only, the conventional storage
oscilloscope collects data
2 The cost of the tube is cheap The cost of the tube is costlier
3
For higher frequency signals the DSO
produce bright images
For higher frequency signals the ASO cannot
produce bright images
4
The resolution is higher in digital storage
oscilloscope
The resolution is lower in conventional storage
oscilloscope
5 In DSO an operating speed is less In ASO an operating speed is less
Advantages
1. They possess infinite storage time.
2. It can be easily operated.
3. Digital storage oscilloscope allows flexible display property.
Applications
1. It is used in audio and video recording.
2. It is used in radio broadcasting for signal testing.
3. In circuit debugging, it is used for testing of the voltage of the signal.

8. Sampling Oscilloscope:
Definition: Sampling Oscilloscope is an instrument that is used to generate waveform by collecting
various samples of an electrical signal. It is basically an advancement of digital oscilloscope having
additional features for special purposes.
In sampling oscilloscope from various portions of the waveforms, different samples are taken, over
consecutive cycles and the overall image is shown on screen as a continuous wave. In order to create a
waveform around 1000 points are to be needed.
It is to be noted here that, before getting displayed, the resultant waveform is amplified with the help of
a low bandwidth amplifier. These instruments are used to observe high-frequency signal that lies
beyond 50 GHz range. A high-frequency waveform is achieved at the output of the oscilloscope as
compared to the slope sample rate.
Block diagram and Working of Sampling Oscilloscope
The figure below shows the block diagram of the sampling oscilloscope:
Here, as we can see the input signal is fed into the sampling gate. When the sampling pulse is provided
to the sampling gate, it gets open in order to sample the input waveform. It is noteworthy that sampling
is to be done in synchronization with the frequency of the applied input signal.
The vertical amplifier employed in the circuit delays the input signal and after amplification, the signal
is given to the vertical plates.
When the sampling cycle begins, the oscillator gets activated by the trigger pulses. Due to which, linear
ramp output voltage is produced. The signal generated from the ramp generator is then fed to the
voltage comparator unit.

9. Here, the ramp signal gets compared with the staircase signal, generated by the staircase generator.
During comparison when the amplitude of the two signals is equal, it advances the staircase by one
step. Thus generating a sampling pulse. This again opens the sampling gate and the cycle is repeated in
a similar manner.
The size of the steps generated by the staircase generator determines the resolutionof the image at the
output. When the size of the steps is smaller, the number of samples will be larger. Thus, the image
resolution will be higher.
The figure below shows the waveforms at the various blocks of the sampling oscilloscope:
The frequency of samples in the Sampling Oscilloscope can be as low as one-hundredth of the input
signal frequency. Thus we can say for the input signal frequency of 1 GHz only 10 MHz amplifier
bandwidth is needed.
Advantages of sampling oscilloscope
 It is advantageous using a sampling oscilloscope, as it can measure high-speed electrical signals.
 By using sampling techniques, the input signal can be instantly transformed into a signal in a
low-frequency domain. Further circuitry produces a highly efficient display.
 It has the ability to react and store information in the form of rapid bits.
Disadvantage of sampling oscilloscope
 Sampling oscilloscope allows the measurement to be done on signals having repetitive
waveforms.