EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: Sankha on January 21, 2022, 10:50:21 am
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Hi,
Im Sankha from university of Colombo, Sri Lanka. To measure nanosecond scale [1 to 5 ns] pulse width we need to make a time to amplitude convertor (TAC). Can anyone help me to find a circuit diagram of such a device or any alternative solution to this problem is highly appreciated..!
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I'm not sure if you are looking for help with an assignment, or rather working in a lab and needing a circuit to assist you with the research you are working on.
In the case of it being an assignment, I'll give you something to help you on your way. I think you'll learn a lot more from it than just finding a circuit. So think about this: what happens to the voltage on a capacitor when a constant current flows into it? And how could that principle be used to make what you are looking for?
If the latter, I'm sure others will tune in with something that will get you to what you need.
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I guess you would want to measure the voltage afterwards, to get a digital value proportional to the pulse?
If yes, then there is an integrated solution called "Time to Digital Converter" TDC from TI https://www.ti.com/product/TDC7200 (https://www.ti.com/product/TDC7200)
This has been used in an open source project: https://github.com/TAPR/TICC/tree/master/TICC (https://github.com/TAPR/TICC/tree/master/TICC)
You can also buy this: https://tapr.org/product/tapr-ticc/ (https://tapr.org/product/tapr-ticc/)
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Other than just using a (fast) scope, the only way I can think of that doesn't require complex RF design is to use a FPGA with a fast SERDES block.
That TI chip, while quite interesting, can only go down to 12ns.
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Other than just using a (fast) scope, the only way I can think of that doesn't require complex RF design is to use a FPGA with a fast SERDES block.
That TI chip, while quite interesting, can only go down to 12ns.
I am not sure where you get this from, the datasheet says under application information "measurement range of 0.25ns to 8ms and accuracy of 28ps" and "single shot resolution of 55ps"
Edit: Scrolling down I see now :palm:, they manage the shorter pulse width but with a pre-trigger you have to generate yourself....
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Thank you very much for that information. Im currently working in a project to measure phase difference of two pulses which has a pulse separation of few nanoseconds.
Hope your idea of using a TDA will work for me. If you have a better idea, please let me know.
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I am not sure where you get this from, the datasheet says under application information "measurement range of 0.25ns to 8ms and accuracy of 28ps" and "single shot resolution of 55ps"
Mode 1: 12 ns to 500 ns
Mode 2: 250 ns to 8 ms
You can use mode 1. Leading edge of 1. signal triggers "START". Leading edge of 2. signal has to be delayed by 100 ns (10 MHz clock) to trigger "STOP". So results are from 100 ns to 200 ns. All you need are three D-FFs.
Another TDC is AS6500/6501 which works from 0 ns phase difference directly.
To realize a time-to-voltage-converter you need some analog stuff or one fast XOR gate and an integrating circuit.
I wouldn't do so.