Measuring if signals and waveforms are in sync

[PrescottDan]

When measuring if the signals and waveforms are in sync with a Timer, a clock, a oscillator, a crystal, or PLL circuit

How does a tech know if the signals/waveforms are sync to a timer, a clock , a oscillator, a crystal or PLL circuit?

When looking at a schematic , how does a tech know which signals/waveforms are sync to a timer, a clock, a oscillator, a crystal, or PLL circuit?

Sometimes they buss lines for the clock and multiple TTL or CMOS chips are tied to it

But Timers are not on a buss line mostly
Also Oscillators aren't on a buss line either

A crystal i have seen goes to microcontrollers or to a flip flips clock input , crystals don't have a buss line

A Analog Oscope has a Ramp Generator, the vertical beam circuit and horizontal beam circuit is synced to the Ramp Generator

To measure if the vertical beam circuit and horizontal beam circuit are sync to the Ramp Generator

Oscope channel#1 or Ext Trigger input: Probe output of Ramp Generator

Oscope channel#2: on output of horizontal beam circuit
Oscope channel#3: on output of vertical beam circuit

Set the Oscope to Normal mode or single sweep to check the sync? because auto mode is not good to measure the syncing of multiple waveforms?

 

[Audioguru]

Why are you obsessed with "syncing"?
If your Oscope trace is an unsync'd blur then read its operating instructions.

 

[PrescottDan]

Because I don't know how to measure if a circuits signals or waveforms are in sync and what the signals or waveforms are in sync with

How do you check to make sure the signals/waveforms are in sync with the sync circuit of any circuit?

can a timer be a sync circuit?
can a PLL be a sync circuit?
can a crystal be a sync circuit? cause i only seen a crystal to a microprocessor

- - - Updated - - -

When checking the sync of any waveforms/signals or multiple waveforms/signals

Do you use the Oscope external trigger?
set the Oscope to normal mode or single sweep mode?
Do you have to use a Storage scope when checking the sync of any circuits?

 

[D.A.(Tony)Stewart]

Anyone who knows how to use a scope ought to know if a lower frequency is derived or synchronized to a higher f, uses the lower f to trigger the scope and test the waveform phase stability of the higher f on the scope.

 

[PrescottDan]

So when measuring video signals you always set the Oscope's trigger to TV?
the video signals can be RGB, composite, component , etc. color signals , you always set the Oscope trigger to TV mode?

 

[betwixt]

TV is a rather special case because there is already voltage or data based sync signal present. The name "composite" means composed of video and sync so your scope reference is derived by extracting the sync part of the signal in the same way a TV would.

As for other signals, for the most part, the 'sync' used by a scope is any repeating part of the signal it is measuring. The trigger level control sets the amplitude used to start the sweep, the X timebase sets the duration of the sweep and the 'hold off' (if it has one) is to prevent re-triggering for a while.

With the exception of PLL based systems where phase locking is essential, you would normally use a schematic to see if signals were supposed to be synchronous, not an oscilloscope. In all cases, synchronous signals will be derived from a single timing source.

Brian.

 

[PrescottDan]

Can you please give some examples of when you or a tech would want to measure the synchronous of signals?

When have you measured signals that were sync to something? for what kind of circuits or applications

Just to get a basic knowledge, basic circuits about sync and measuring sync

I know when using a logic analyzer, a tech will have multiple logic waveforms to check if they are all in sync and aligned.

For what kind of circuits or applications would a tech be doing this?

 

[Audioguru]

Why would a tech need to "measure" a video signal? A video signal is almost always changing unless it is produced by a video signal generator.
If the tech is repairing a defective video product then its symptoms on its screen and the tech's knowledge of the signals show what is section probably wrong then its schematic shows exactly which part has failed. A quick measurement with a multimeter confirms it.

Today most failed video products are not repaired, they are simply thrown away then replaced. A video tech is doomed.

 

[betwixt]

Can you please give some examples of when you or a tech would want to measure the synchronous of signals?

I already told you, in a PLL. There are very few, if any, other cases where you would measure for synchronism. Things are either synchronized or not, there are no in between states. I think you are looking for a solution to a problem that doesn't exist.

If by design there are signals which are supposed to happen simultaneously and due to a fault they are not, you would backtrack from the fault position until you found the place where they diverge but you almost certainly wouldn't measure phase difference to find it.

Brian.

 

[PrescottDan]

here are very few, if any, other cases where you would measure for synchronism.

So a Test Technician never measures or checks if the signals/waveforms are synchronized with a clock, a timer, an oscillator or CPU microcontroller?

When using a Logic Analyzer a tech can view display multiple channels of logic signals to see if they are in sync with each other or in sync with the sync circuit, a clock, a timer , a oscillator or microcontroller

This is what I thought test techs did when using a Logic analyzer is this true? or they don't check or measure the sync?

 

[betwixt]

Well, you could use a logic analyzer for that purpose but why would you?

Consider why signals might by synchronized and why they might not. It would be incredibly rare for one part of a circuit to continue to function with a correct but randomly phased clock of it's own creation. Synchronous circuits are driven from a master frequency source, typically the system clock. It might be divided down, multiplied up or gated on and off but it would always maintain the same speed and phase relationship because itself and whatever controlled it are driven by the same timing source.

The more usual use for a logic analyzer is to look at 'cause and effect' scenarios, for example whether something is responding to incoming data properly or whether the correct data is present on a bus given the correct stimulus. Think of them as oscilloscopes with many channels but only two trace elevations for each of them. Yes, they can see the timing relationship between channels but their purpose isn't to test for or measure sync.

Brian.

 

[PrescottDan]

Yes, they can see the timing relationship between channels but their purpose isn't to test for or measure sync.

I thought when a tech using a logic analyzer was testing for the timing relationships and to measure the sync for each waveform

The Timing relationships is relative to the sync circuit right?

The Timing relationships changed depending on the clock buss, a timer, or what else?

A Tech is checking the timing relationships for pulse width,duty cycle, phase offset, time duration, mark & space ratio, rise time/fall time, phase shift. what else?

The more usual use for a logic analyzer is to look at 'cause and effect' scenarios, for example whether something is responding to incoming data properly or whether the correct data is present on a bus given the correct stimulus.

True, it's testing if the input combinations will give u the correct output combinations

ATE computer or test fixture will do all the testing of the input combinations and output combinations for you

Which is the cause and effect tests

 

[Audioguru]

You "synchronize" one oscillator to another completely separate oscillator. Logic usually has only one oscillator (the master clock signal) so nothing is sync'd or out-of-sync.

But an FM stereo decoder has a 38kHz oscillator that MUST be sync'd to the 38kHz oscillator used in the encoder. But the transmission does not have the 38kHz carrier, instead it has a pilot tone at 19kHz which is the 38kHz carrier divided by two. You cannot simply divide the 19kHz to get 38kHz.

An old analog color TV has a 3.58MHz oscillator that MUST be sync'd to the 3.58MHz oscillator used in the encoder. But the received signal does not have a continuous 3.58MHz signal, it has only a few cycles of 3.58MHz called the color burst. The TV's oscillator sync's on the burst cycles each horizontal line time (about 15,734 times per second). A TV also has a vertical oscillator and a horizontal oscillator that MUST be sync'd to the original oscillators.

A power inverter that feeds power to the mains MUST be sync'd to the 60Hz of the mains.

 

[betwixt]

As you are talking logic circuits you need to understand there are two types:
1. Combinatorial - the output depends only on the instantaneous input states,
2. Sequential - the output depends upon previous states as well as present ones.

Synchronism isn't really a term you would use in a combinatorial design as by it's nature it could be static (no output change when there is no input change).

In a sequential system, the 'events' that change the states are called clock pulses and are normally derived from a central timing source and are therefore synchronized directly or indirectly with it.

A Tech is checking the timing relationships for pulse width,duty cycle, phase offset, time duration, mark & space ratio, rise time/fall time, phase shift. what else

I'm not sure what your question is asking. A Tech might be looking for all or any of those things but it would depend entirely on what the circuit was designed to do. For example, in a serial data link the concept of duty cycle, phase offset, time duration and phase shift have no meaning. The mark/space ratio of a composite TV signal has no meaning and the phase offset of an oscillator has no meaning.

If I can make an analogy, it's like you are saying a car steering wheel should be tested for exhaust emissions, battery voltage, tire tread depth and maximum speed, what else? Each term has it's own meaning in it's own context but not all together in the same test.

Brian.

 

[Audioguru]

It is called "make work" when a tech has nothing to work on.
The tech simply fools around doing anything with the test equipment.

 

[PrescottDan]

When you're using a Logic Analyzer with multiple waveforms/signals , what kinds of timing relationships would you be measuring? the timing relationships of what and compared to what?

Are you measuring the propagation delay of each IC chips input and output and the timing relationships of each IC chips switching times and propragation delays of the time of the input and output?

 

[Audioguru]

Why would the timing in a circuit change? Because somebody added a capacitor to ground to slow down the timing? I doubt it.
Why would the propagation time of an IC change? It will not change.
You are wasting time measuring timing and propagation times.

A logic IC fails to do logic. Maybe its output gets stuck high or low. A logic analyser will not find it unless you know what the output of the logic is supposed to do. The logic analyser does not know what the output of the logic is supposed to do.