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I am using two TDC(time to digital converter ) controller to record  time stamps of events/signals.I am applying exactly same signal to both the TDC.I am getting  diffrent timestamps in both TDC,since both controllers are running with its own clock ,the time stamps are not same.I want  same time stamps in both TDC(as I am applying same signal to them).To synch both TDC controller  I applied  reference clock from 1 controller to other controller.but again I  am getting different time stamps.how do I check that both controller are synchronised .how to ensure synchronisation between any two controller/FPGA/devices.


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@Clyde makes a good point. No one has any idea what your TDC is or how it works.

On a system level let's treat your TDCs as black boxes. You say that each has its own clock and presumably, source synchronous data output. This presents a system problem to address if the data changes every clock period. Time sources like GPS are one thing. There are extremely high resolution ( sub-ps ) differential time measurement devices and that is a totally different thing.

Two critical pieces of information to start with are what is the format and resolution of the TDC? What is the largest difference between the two TDCs ?

It's hard to get good answers to detailed and well framed questions. Your question doesn't provide enough information to expect a good answer.

Edited by zygot
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Thankyou Clyde and  zygot for reply.

TDC is FPGA based controller which counts the pulses and gives timestamps of pulses.(if i am applying 1Mhz signal to it,it will give time stamps like 1us,2us,....etc.).resolution of TDC is 400ps.I am using 2 TDC and controllng them by 2 computer.I tried to synch both TDC.(I applied ref clock  out of one TDC to ref clock In, of other, i mean first one is master and 2nd one is slave.)I am applying same input signal to Both TDC.I am expecting same time stamps in both TDC(obviously there should be some delay because of cable and all),but that should be constant (ie if I am applying 1 Mhz signal to both TDC,then if time stamps in first one are 1us,2us,3us.......then 2nd TDC should have time stamps like 1us+_ delay, 2us+_delay,  3us+_delay.....so on.)Now in my case this delay is varying with time. some time it is 7ns,50ns, or 700ns so on.It is random.is it mean that they are not synchronise?.if it so then how to ensure their synchronisation.

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6 hours ago, pooja said:

It is random.is it mean that they are not synchronise?.if it so then how to ensure their synchronisation.

Well, there are a lot of things that I still don't know. Understand that resolution and accuracy are not the same things. What is the guaranteed accuracy of the TDCs?

There's a difference between differential timestamps and absolute timestamps. You are likely going to get better accuracy from comparing the difference between events as opposed to trying to measure the time between an event and some absolute point in time. And that's one variable that I don't understand. How is the value of 0 time set?

I don't have a manual for your TDCs but it would seem that linking them as you do should to a common reference might be fine... again I don't have the manufacturer's reference material.

To answer you question. The units are certainly not synchronized to the degree that you expect them to be but without knowing how accurate them are it's hard to tell if they not providing expected results. You can get an idea of the accuracy by using a very precise and stable repeated pulse signal, like a 10 pps reference out of a rubidium clock reference or some such device. I'd start with figuring out what I have with 1 device before trying to compare tow of them.

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