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TDC7201: TDC7201 resolution

Eric Chen4
Expert 2370 points
Part Number: TDC7201
Other Parts Discussed in Thread: TDC1000

Hi,
I have two question as below.
1. If using 16MHz oscillator with TDC7201, will the resolution enhance?
2. If customer need start from 0ns at Combine mode, how can implement it? Does it need to use two pcs TDC7201 IC implement? The product design as below.


 
Regards,
Eric

  • 0
    TI__Mastermind 31655 points
    Hi Eric,

    The resolution is determined by the internal ring oscillator, and is not affected by the external clock. However, the external clock is used to provide the calibration that greatly impacts the standard deviation of the timing. 16Mhz is the recommended external clock input for maximum performance (lowest standard deviation).

    For the combined measurement mode, the minimum time measured is 250ps. An overview of how to implement this is described in the TDC7201 datasheet in section 8.2.2.1 "Measuring Time Periods Less Than 12 ns Using TDC7201". This only requires one TDC7201 device.

    Regards,
  • 0 in reply to Scott Cummins
    Expert 2370 points

    Hi Scott,

    If need to measure start from 0 cm, how can we do it as below block?

    Thanks your suggestion.

    Regards,

    Eric

  • 0 in reply to Eric Chen4
    TI__Mastermind 31655 points
    Hi Eric,

    If you are intending to use ultrasonic transducers it is impossible to measure something 0cm away from the transducer itself since the transducer will still be transmitting when you would expect to see the reflected response. In order to measure "0cm" you will need to set the transducer further back so that your 0cm reference is actually several centimeters or more away from the transducer.

    Can you please explain your diagram? Is this a single unit with separate transmit and receive on each side? Does the transmitter fire toward the top of the screen?

    regards,
  • 0 in reply to Scott Cummins
    Expert 2370 points

    Hi Scott,

    Now use GP-21 *2pcs to implement 0cm measurement so I need your confirm whether TDC7201 also need 2pcs to achieve 0cm measurement. Thanks your help & suggestion.

    The below is real product for your reference.

    Thanks.

     

    Regards,

    Eric

  • 0 in reply to Eric Chen4
    TI__Mastermind 31655 points
    Hi Eric,

    I think there is still some misunderstanding. Is this sensor ultrasonic, or is this light-based? Are you measuring distance, or flow?

    The minimum time measurement of a single TDC7201 in combined measurement mode is stated as 250ps, but this is because of accuracy limitations. The measured time can technically be arbitrarily small, but we do not claim this because it it will not necessarily be accurate to that degree. The resolution of the TDC7201 is comparable to the GP21, and you will only need one device.

    Also, to clarify, the TDC7201 is only a time measurement device. If you need an ultrasonic AFE, then a TDC1000 will be necessary to drive the transducers.

    Regards,
  • 0 in reply to Scott Cummins
    Expert 2370 points

    Hi Scott,

    This is light-base meter product application and customer already verify TDC7201 performance but find out can't measure distance start from 0cm.

    But GP21 can measure distance start from 0cm with using 2 unit to implement this function.

    So TDC7201 only start from 4cm, right? If have any other method then can meet the spec requirement?

    Thanks your suggestion & help.

    Regards,

    Eric

  • 0 in reply to Eric Chen4
    TI__Mastermind 31655 points
    Hi Eric,

    As noted above, since the measurement in combined mode on the TDC7201 is based on the difference between two separate measurements with a common reference start, the minimum time measurement can technically be arbitrarily small. However, because of physical limitations to the accuracy and precision (which the GP21 is also affected by) we cannot claim to be able to measure 0s or 0cm. If you compare the datasheets of the two devices, you will see that the resolution is very similar, however you only need one TDC7201 to measure the minimum time period.

    Regards,