• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 30 subscribers
  • Views 235 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TDC7201: Question about PWstart and PWstop pulse width minimum value.

Kazuya Nakai59
Guru 21585 points
Part Number: TDC7201

 Hello guys,

 One of my customers is considering using TDC7201 for their new sensor (LIDAR) unit.

 They have a few questions about PWstart and PWstop parameter (Start and Stop signal pule width) as the follows.

 Could you please give me your reply?

 Q1. PWstart and PWstop minimum value is 10ns. But the value is longer than their achievable pulse width by the customer.

        Can the minimum pulse width be reduced a little bit? For example, Is it difficult to use TDC7201 with 5ns pulse width of Start/Stop signal?

 Q2. What limits this pulse width? Is it the internal ring oscillator frequency?

       Or the ring oscillator clock is not used for those pulse reading and is the minimum pulse width determined

       from the time which can reaches the internal circuit surely in all (Voltage, temperature and manufacturing variation) conditions?

 Your reply would be much appreciated.

 Best regards,

 Kazuya.

  • 0
    TI__Mastermind 23045 points

    Hello Kazuya,

    Thank you for the question, it seems to be a popular question today.

    I just submitted a reply for the first question which you can take a look at here: https://e2e.ti.com/support/sensors-group/sensors/f/sensors-forum/1002168/tdc7201-start-and-stop-signal

    For the second question, the START and STOP pulse widths are limited by the Schmitt Triggered Comparators which is the first stage they encounter after they are input into the system, the clock used for this comparator is not the ring oscillator but the external reference clock used for calibration. I hope this answers your question!

    Best,

    Isaac

  • 0 in reply to Isaac Lara
    Guru 21585 points

     Hello Isaac,

     Thank you very much for your reply.

     Could I ask you an additional question as the follow?

     We can see the start/stop pulses width is about 5ns at Figure 8 on page 9 of TI application Report "Short Time Measurement Using TDC7201".

     https://www.tij.co.jp/jp/lit/an/snaa292/snaa292.pdf

      So it seems that the 5ns pulse width is OK for start/stop signal to control TDC7201.

      Is the 5ns not OK to control TDC7201 correctly?

     Could you please give me your reply?

     Thank you again and best regards,

     Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 23045 points

    Hello Kazuya,

    It seems like the 5ns pulse width works fine for the application report linked, but I would just like to highlight that application report does not reflect all the validation that is performed by the team before a part is released in order to develop these specifications. While it may work in the test conditions shown in the application report the 5 ns might not work in other test conditions (such as temperature).

    What I recommend is, if your customer is considering on using a smaller pulse width then the system should be tested thoroughly just to ensure that it is performing the way the device is behaving as expected. If the sensor or device being used to develop the STOP and START pulses is the issue maybe it might be possible to look into workarounds that would increase the pulse width to the necessary amount.

    I am unable to test at a pulse width lower than 15 ns so I cannot validate proper functionality at a lower pulse width, but like I mentioned in the post linked above I cannot guarantee how the digital state machine would behave or if the Schmitt Triggered Comparators in a smaller pulse width scenario.

    Best,

    Isaac