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The Care and Feeding of,
"They Love a -Can--Tube of Green Worms" Click-blocks-for-details
Paramount to using any piece of equipment effectively, is having some understanding of what is going on inside; this is especially true for the Oscilloscope. 
The Oscilloscope has evolved from the basic Analog Oscilloscope to the Digital Storage Oscilloscope (DSO), and now the latest, the Digital Phosphor Oscilloscope (DPO), which is the best of both the Analog scope and the DSO. See the Evolution of the Oscope.

Since even the latest and most sophisticated Oscilloscope is still bound to the original Analog concept, this tutorial will focus on the Analog Oscilloscope.

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Scope Front Panel
 -Click image to Enlarge
 
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"OK, I give up. Where the Hell is the 'Trigger Level' on this one?"
Don't be intimidated by the myriad of different Oscilloscope layouts. 
When I approached an unfamiliar oscilloscope, I felt as though I was at the blackboard, in the third grade, doing a math problem, with the rest of the class looking on and snickering...
If automobiles were designed the way Oscilloscopes are, you might hear the following: "Oh John, look at this model, it has the Steering Wheel in the glove compartment." "Well, take a look at this one Marsha, this one has it in the trunk."
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Overview
-As seen in the Animation, the Oscilloscope is comprised of two main sections:
1) The Vertical Amplifiers receive the signal voltages and amplify these signals sufficient to deflect the CRT's beam vertically.
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2) And, the Horizontal Scanning or Sweep Circuits, that "spread out" and synchronize the display of events on the CRT.
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Also, there are very important subsections that interface these two main sections. The ability to cause the beam to start at some event is crucial: to this end, the vertical input amplifier furnishes an amplified version of the input signal voltage to a "sync detector" which tells the horizontal sweep generator to sweep, or spread out the signal, when the signal transitions through some preset voltage or trigger level preset by the user. In other words: "when the little green wiggly garter snake raises his little green head above or below some pretend crayon mark on the screen, he's kicked in his little snake butt, and flies across the screen, leaving an 'ooey-gooey' green slime trail."
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As important as knowing what is going on inside, is knowing how to make effective measurements using an integral part of the oscilloscope: the Scope Probes. The probe and how it is used, can make or break the usefulness of the oscilloscope. To skimp on the quality of the probe, is like buying a big expensive television set for a couple thousand dollars, and then connecting it to fifteen dollar rabbit-ears.
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Scope Probes
-Probe Inputs, "Channels A & B"----------------
A Probing Question
Once you have the right scope, the correct probes, and some understanding of what you're doing: you still need to know how to use the probes correctly. I once knew a professor--who should have known better--who would never use the probe's ground clip lead; he would leave it off the circuit he was measuring, or remove it completely from the probe. He relied, instead, on the scope's being grounded to the computer through the AC power mains. Needless to say, he got some pretty strange results. This is not what you want to do.
MORE Scope Probes

 
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A "Check-List" for Measurements is as Follows:

1.. Always use "10 X" probes: they load the DUT (device-under-test) ~ 10 Meg ohms @ ~ 10 pfd. A "1 X" probe offers 1 Meg ohm @ ~ 50 pfd. The designation "10 X" refers to the attenuation of the signal by the probe (not gain). In order to attain such light loading by the scope--while maintaining bandwidth--this tradeoff is required.

2.. Make sure the probes are compensated (adjust trimmer at connector housing) if attaching them to a different scope. This ensures maximum fidelity and bandwidth of the signals being eyeballed.

3.. Use the shortest ground lead or clip-lead possible: the shorter the better! Excessive ground lead length introduces unnecessary inductance and can alter the displayed signal, as well as reducing the scope's effective bandwidth (acts like a lowpass filter).

4.. When Measuring very high frequencies--especially in tight spaces--consider using a RF probe (see figure). Also, there are--so-called--FET or active probes, which are non-loading (almost) wideband probes with built-in amplifiers.

5.. When buying probes for your oscilloscope, make sure the probe is of sufficient bandwidth for your particular scope: the probe is the first-order bandwidth determinant of any scope.

Some scopes have such a wide bandwidth, that no passive probe is able to do it justice, and the only way to use the maximum bandwidth of this type of scope is to drive the scope from a 50 ohm source through a 50 ohm coax, terminated into 50 ohms at the scope's input. In fact, some high performance scopes have a 1Meg ohm/50 ohm termination switch for just such occasions.
 

 
 
--Input Amplifier
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Input Amplifier
Basic Differential Amplifier Stage
Showing Differential Input
Showing Common Mode Input
 Simplified Differential Amplifier Stage
showing single ended input, differential output W/Pos Control
Vertical Positioning: Centered
Vertical Positioning: Bottom
Vertical Positioning: Top

 
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Input Multiplexer
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Channel A
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Alternate
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Chop
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A-B
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Channel B
Input Multiplexer
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Vertical Amplifier, Phase Inverter

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Simplified Schematics
Input Stage---see above
Gain Stage
Phase Inverter
-Vertical Deflection Amplifier
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Vertical Deflection Amplifier 
High Voltage Deflection Plate Drive
   
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-Delay Lines
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A Delay in Discussing a Loose End

Something that cheap scopes are guilty of, is the fact that you never see the leading edge of the event that triggered the sweep. That is to say, the sweep is triggered by the leading edge of a pulse, and by the time the beam starts across the screen it is now displaying the signal ~ 100 nsec after the event. To solve this little "hand-is-quicker-than-the-eye" problem, the Keebler Elves added wideband analog delay lines between the vertical amplifier and the CRT's deflection plates. So, by the time the beam has started its short trip across Mr. CRT's face, the signal that triggered the sweep is finally dribbling out of that long delay line.


The red trace is the triggering event; the green trace is the delayed view of the event.
Delay Lines driving Vertical Deflection Plates
Note: Sync Signal picked off before delay
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Vertical Deflection Plates
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Vertical Deflection Plates
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-Triggered Sweep / Timebase Generator

Triggered Sweep / Timebase Generator
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On the Level
Oscilloscopes have several sync modes: internal sync; external sync; line sync and delayed sync. The selection of any of these sync sources sends the signal to the "sync detector." For example: if the internal sync is selected, it sends the input signal, picked-off from the vertical input amplifier, to the "sync detector" which is a fast analog comparator that gets its other comparison input from a front panel mounted control, called the "LEVEL" control. This allows the user to preset the exact voltage level and polarity, at which the scope "triggers" the sweep generator to sweep the beam across the screen once. Every time the signal goes above this preset voltage (except during an active sweep time), a new sweep is started: this is called "Triggered Sweep."

 
 
 
 

Trigger Pick-off from Vertical Amplifier

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Trigger Level & Trigger Polarity
Oh, By The Way...

There is a sweep begun whenever the signal reaches the trigger level, regardless of whether it is a rising or falling voltage. This means that--in the case of a sine wave--the scope is just as apt to start the display at zero degree phase, as 180 degree phase. To solve this little oversight, a switch is used to tell the sweep generator which excursion--rising or falling--to trigger on: this is called the "SLOPE." (+) SLOPE (-)

The figure above show several combinations of settings.

Sweep Voltage: Horizontal Scan
Gated Integrator
SawTooth Sweep Wave Form
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Horizontal Deflection Amplifier
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Horizontal Deflection Amplifier
High Voltage Deflection Plate Drive
   
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Horizontal Deflection Plates
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Horizontal Deflection Plates
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CRT, Cathode Ray Tube
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Photo of typical Electrostatic Oscilloscope CRT, 
including mu metal shielding material for protection against stray electromagnetic fields
 
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Z-Axis
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Z Axis Intensity Modulation
ZAxis, or Intensity, has a limited function on general oscilloscopes. Blanking during retrace; Blanking during Hold off in Delayed Time base operation; Intensify for markers; delineation of traces as in, "A" intensified by "B," etc.

On hybrid Analog & Digital Oscopes, it also aids in the implementation of alphanumeric and simple graphics display. 

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Delayed Sweep Timebase
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"Delayed Sweep"
Another feature of most good scopes is "Delayed Sweep." Delayed Sweep, allows the user (that could be you, if you behave and eat your vegetables) to trigger on an event and observe the signal after some predetermined time interval. For example: if you wanted to observe one single scan line--out of 525--in a television signal, you would trigger off of the beginning of each television field time (16.67 msec) but holdoff displaying that particular scan line (HD = 63.5 usec) until the correct amount of time has passed. In essence the Delayed Sweep is just a fancy "One-Shot" multivibrator with a ten-turn pot, triggered from the scope's normal sweep circuit; and holds off the sweep across the screen until some time interval--determined by our old friends Ms. R & Mr. C--has passed, after which time the scope sweeps for the interval of one TV scan line.
Numbers Don't Lie... People Do:

Let's say I wanted to eyeball the 188th horizontal scan line, and I had dialled in both the "Delay" and the "Sweep" intervals: as soon as the field sync pulse (VD) occurs the delay sweep starts to time out for 11,885 usec (187 x 63.5), at which point it triggers the scope's sweep generator. The sweep runs for ~ 65 usec--displaying one complete horizontal scan line (the 188th).

Other features of the oscilloscope that are available, are left for the user to discover in the user's manual: you know, that thing you read when "all-else-fails!"

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----Appendix-A----

Scope Probe Characteristics
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Scope Probe Voltage Derating

 

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Evolution of the Oscilloscope

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--USEFUL--LINKS:

---- www.tektronix.com/Scopes/
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---- www.fluke.com/Scopes/

---- www.agilent.com/--Formally HP
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