Analog Vs Digital Oscilloscope by fjzhangxiaoquan

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									            Analog Vs Digital Oscilloscope
The goal of this article is to compares and analyzes choose a
new oscilloscope that would be good for you and to compare
and contrast between Instek GOS-6112 100 MHz Analog
Oscilloscope and Agilent U1604A Handheld Digital oscilloscope
(40 MHz). There are hundreds of different models to choose
from with widely varying costs and specifications. I can not
possibly tell you what the best oscilloscope would be. There are
a lot of factors that come into play.

Most people want one oscilloscope and they want the best
oscilloscope. Some people believe the more that you spend the
better is the oscilloscope and that is not always the best
option. Other people believe the cheap option; cheap is not
always the best. The more time you spend doing research, the
more money you save, the better the quality and the more
technical specifications you get. If you can not afford a new
oscilloscope then buy a used oscilloscope and make sure it has
been recently calibrated before you buy and all the controls
move. After you purchased oscilloscope you next purchase
might be a function generator.

The factors involved that whether one oscilloscope is better
than other and why are: bandwidth, number of channels,
sampling rates, memory depth, resolution and accuracy (display
capacity), triggering capability, probe requirement,
connectivity and analysis capability.
In the above figure showing Instek GOS-6112 100MHz Analog
Oscilloscope and for about £531.20 ($1,035) you can buy it. In
the figure to the right showing Agilent U1604A Handheld
Digital Oscilloscope and for about £1,134.46 you can buy it.

The Handheld Digital Oscilloscope is small-size, less heavy,
easy to carry, high-performance and high-price then 100MHz
Analog Oscilloscope. Both Analog and Digital Oscilloscopes are
used to display and analyze the waveform of electronic signals.
The 100MHz Analog Oscilloscope has more mechanic switch
(for example: trigger) then the Digital Handheld Oscilloscope.

Both Analog and digital oscilloscopes are used in laboratories,
education, industries etc... However, the Handheld Digital
Oscilloscopes are used at a customer’s site. Both Analog and
digital oscilloscopes are used electronics technicians and
engineers, students, lecturers, scientists etc.

Oscilloscope types include, analog, digital, PC, handheld, mixed
signal, digital (storage, sampling and phosphor). The work you
are require to do and location will determine what type of
oscilloscope is best to use.

Digital oscilloscopes can display signal that may happen only
once and Analog Oscilloscopes display signals as they happen.

The History of the Cathode Ray Tube

Karl Ferdinad Braun: The great Germany inventor and he
displayed the first oscilloscope (Brun tube) in 1987.
Bandwidth

The bandwidth is the difference in frequency between the
highest and lowest frequency roll-offs where response has
fallen by – 3dB. However, modern oscilloscopes respond to DC
(which is 0 Hz), then they are said to be DC coupled and the
bandwidth is simply the highest frequency of operation (roll-
off).

Today a 20MHz oscilloscope is the slowest oscilloscope
(1/20MHz=50ns) that you could buy. A 40 MHz handheld
digital oscilloscope will display 40 MHz waveforms and a 100
MHz Analog oscilloscope will display 100 MHz waveforms, are
not at its correct amplitude (29% error), but attenuated by
71% of its true amplitude (- 3 dB point).

Distortion of 29%, because as the frequency increases, the
gain (output/input) decreases and making the display less
accurate. For example, a Sawtooth wave has componets at 2, 4,
6, 8, 10 … times the fundamental frequency. As the frequency
increases these components become smaller, a 2KHz Sawtooth
wave will contain components at 2KHz, 4KHz, 6KHz, 8KHz,
10KHz… Hence, a sufficient number of these harmonics must
be present to accurately represent this sawtooth wave.

Therefore, 100 MHz Analog oscilloscope has a larger
bandwidth then 40 MHz handheld digital oscilloscope and it will
display more accurate. A useful rule of thumb is that you
should purchase an oscilloscope with a bandwidth 5 times
higher than the maximum frequency signal you will require
(Oscilloscope Bandwidth Required = Frequency Component of
Measured Signal * 5). However, high bandwidth oscilloscopes
are expensive because higher bandwidth will likely provide
more accurate reproduction of your signal.

Number of Channels

Most oscilloscopes in use today are dual-channel models.
Before you purchase an oscilloscope make sure if it is a 2 or 4
channels. Single-channel oscilloscopes can display one waveform
at once, dual-channel oscilloscopes can display two waveforms
at once and 4-channels oscilloscopes can display four
waveforms at once.

The 4-channel oscilloscopes are use to view the relationship of
several signal and it allow to make precision measurements fast
and efficiently. The 100 MHz Analog and Handheld Digital
oscilloscope are both dual-channel. For Handheld Digital
oscilloscope, when use two channels at maximum sampling rate,
the DAC converts the signal in each channel in turn and
resulting in a half of the digitizing rate per channel compared
with that available when using one channel.

For a 4-channel Digital oscilloscope, when use four channels at
maximum sampling rate, the DAC converts the signal in each
channel in turn and resulting in a quarter of the digitizing rate
per channel.

Sample Rate

The sample rate is the rate at which the input signal is
converted to a digital signal and sampling rate is the inverse of
the resolution. For example, if you are interested in 20ns
resolution between point A and B, then the sampling rate that
can provide this resolution is 1/20ns = 50*10^6 sample/sec.

The faster the oscilloscope can sample, the more accurately
(greater the resolution) it can represent fine details in a fast
signal and less likely that critical information or event will be
lost. The minimum sample rate may also be important if you
need to look at slowly changing signals over longer periods of
time. Remember that the Nyquist theorem says that the signal
must be sampled at least twice as fast as its highest
frequency. If waveforms are periodic then you can save money
by selecting an oscilloscope that provides equivalent time or
random periodic sampling.
The main advantage of Handheld Digital Oscilloscope over
100MHz Analog Oscilloscope are the memory depth, 200*10^6
sample/sec (5ns resolution), and you can use Dual Waveform
Math (DWM) and Fast Fourier Transform (FFT) function to
perform quick waveform analyses in both time and frequency
domains.

DWM function to perform math functions for signal addition
and subtraction from multiple channels and FFT function allows
you to view the waveform in a frequency domain using four
windowing techniques (Rectangular, Hanning, Hamming and
Black-Harris).

Free dynamic range (SFDR) is the difference (in dB) between
the signal power and the power of the highest harmonic in the
band of interest as shown in the spectral plot of figure on the
right (result of calculating the FFT of a signal and a few of the
measurements).

Memory Depth

The Handheld Digital Oscilloscope is up to 250 times the
memory depth with 125 kilobytes of memory depth per channel
and you can capture long time spans and non-repeating signals
while maintaining a maximum sampling rate of 200 MSa/s.
The memory depth is the number of samples which can be
stored in memory, memory depth and sampling are related.
Memory depth required depends on the time selected need to
measure and the time resolution require.

The digital storage oscilloscopes (DSOs) store captured
samples in a buffer memory and for a given sampling rate, the
size of the buffer memory determines how long it can capture
a signal for before the memory is full. The memory depth
benefits are fast sampling at long timebases, timebase zoom,
and memory segmentation to let you capture a sequence of
events.

However, high-speed waveform memory is expensive because it
takes time to process a longer memory.


Display Capability
Both Analog and Digital Oscilloscopes allow you to display phase
shift, rise time, fall time, delay, pulse width, duty cycle,
frequency and period. If the oscilloscope stop work, you can
not repair it and you need to send it to the manufacture
because the manufacture want you to go back there to use
their service and repair, and oscilloscopes are not water
resistant.

The Handheld Digital Oscilloscope comes with a color display to
allow you to quickly and clearly identify your signal between
two channels.
The large 4.5 inch LCD display with 320 x 240 resolutions
extends the simplicity and makes it easier for you to see more
information.

The 100 MHz Analog Oscilloscope provides a high intensity 6-
inch retangular type cathode-ray tube with red internal
graticule. It displays clear readable traces even at high sweep
speeds. Internal graticule lines eliminate parallax-viewing error
between the trace and the graticule line.
It has two-channel, dual-sweep and each channel has 11 basic
deflection factors from 2mV to 5V per division. The horizontal
defection system provides single, dual or delayed sweeps from
0.5s to 50ns per division (delayed sweep, 50ms to 50ns per
division).

Triggering Capability

Both Analog and Digital oscilloscope allow you to trigger and
display non-periodic signals such as single pulses, as well as
periodic signals such as sine waves and square waves. The types
of trigger include: Trigger Modes (AUTO, NORM, TV), trigger
Source (CH1, CH2, LINE, EXT), Trigger Coupling (AC, DC, HFR,
LFR), Trigger ("+" or "-" polarity or TV sync polarity) and
Trigger Sensitivity. The trigger can also be delayed by the
predefined time interval. Analog Oscilloscopes only display the
signal after receiving the trigger and Digital Oscilloscopes, the
trigger tells the oscilloscope to save the present data in
memory.

The Handheld digital Oscilloscope comes with flexible
triggering capabilities that allow you to isolate and capture the
condition you want to characterize. The advanced triggering
includes edge, pulse width, pattern, and video functionality to
help you isolate the signal you want to see. The Autoscale
enables the instruments to quickly display any active signals,
and automatically adjust the vertical and horizontal settings
with trigger control for best-possible signal display.

Probe Requirement
To make measurements with an oscilloscope, you can use
oscilloscope probe to connect the circuit to be tested to the
channel 1 or 2 input of your oscilloscope, and you will get more
precise measurements.

There are three types of oscilloscope probes, first is 1X probe
and it supplies an input signal that is of the same amplitude as
the signal being measured. The second is 10X probe and it
provides and input signal that is attenuated by a factor of ten.
The third types of oscilloscope combines the first two types
and it has a small switch that allows you to switch between the
1X setting and the 10X setting

The U1604A comes with a blue (not red) and a black
oscilloscope probe, the unit’s BNC connectors are blue and red.
The color difference is in the safety ratings.

Blue represents 600 V CAT. III while black is 300 V CAT.III.
DMM Probes include insulated alligator clip attachments,
because the BNC connectors are recessed.
Connectivity

The 40MHz Handheld Digital Oscilloscope comes with USB 2.0
full-speed interface and the he waveform can be saved (as a
data file for further analysis or as an image file for
documentation), printed, annotate, manipulated and displayed
as a computer file. You can also use a USB flash drive as an
option to save and retrieve configuration setups or waveforms
to and from the USB flash drive.

Analysis Capability

The 100 MHz Analog and Handheld Digital oscilloscopes have
similar triggering capabilities and to store analog oscilloscope
waveform you have to photograph it. On the other hand, the
Handheld oscilloscope's capability with the PC Link application
software and you can control the instrument remotely from PC,
retrieve your waveform and print it using a connected printer.
The average battery life is 4 hours and the charging time is 5
hours.

Where to purchase oscilloscopes

Digital oscilloscopes are replacing analog oscilloscopes in the
marketplace. If you buy oscilloscopes from Farnell then you will
save money, the less money you will spend to purchase
oscilloscopes the more oscilloscopes you will get. The others
oscilloscopes that you do not want then you can sell it to your
mates or on eBay website. For example:




Qty Price      Description
               buy one oscilloscope for £159.20 and you will
1+   £159.20
               NOT save money
               buy three oscilloscopes for £153.60 and you will
3+   £153.60
               save £324
               buy five oscilloscopes for £150.40 and you will
5+   £150.40
               save £645.6
               buy ten oscilloscopes for £145.60 and you will
10+ £145.60
               save £1,446.4



      You can buy Mixed Signal Oscilloscopes and Mixed Signal
   Oscilloscopes have spectrum analyser, higher sampling rates
     and provides larger number of channels and about 16 logic
      channels so that it can display both the analog and digital
 operation of a mixed signal on its display. For example, on the
 right is a MSO4104 Mixed signal Oscilloscope 1GHz and it has
                  2 or 4 analog channels plus 16 digital channels

								
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