TDC7200: We are trying to use TDC7200 for some time of flight measurement

Hello Ray,

Thank you for your question.

Is it possible to obtain a scope-shot displaying the start and stop pulses that correlate with the TOF measurements you obtained?

Additionally, can you post the values used in the configuration registers? I want to verify everything Is set up properly.

Finally, is the TDC72000 being used with an EVM, or is it on a separate board?

All of these questions will help me understand how the device is configured, and possibly why a constant offset in time may appear.

Please let me know if you have any questions.

Thank you,

Jacob

Hi Jacob,

Good Day. Please see below the response of our customer to your reply. Thank you very much.

I attached the screenshot for the start and stop pulses. Trace 1 (yellow) is the signal from the function generator. Trace 2 (blue) is the stop signal for the TDC 7200. Trace 4 (green) is the start signal for TDC 7200.

In the txt files, I saved the measured tof values and the register values. In the measured values, you can see there are time offsets (about 14.14us) in all the tests.

We used Arduino DUE development board and a self developed circuit board for TDC 7200 to measure the tof.

Please help check if we set the registers correctly.

sn_customerservice_case_6cdac7941baeb8d0fd3b2022b24bcb81_attachments.zip

Best Regards,

Ray Vincent

Hello Ray, 

I am still in the process of debugging the offset in time. I replicated the attached register settings, however I am not experiencing any offset using my device with similar test conditions.  

Is this offset common among multiple devices, or is this isolated to one device? it may be worth while to test with another device to better understand where to continue looking for potential errors.

Please let me know if you have any questions.

Thank you,

Jacob

Hi Jacob,

Good Day. Please see below the response of our customer to your reply. Thank you very much.

The clock frequency used in our circuit is 16MHz. The file name is the actual delay time set by the function generator and the contents in the file are the calculated tof from the two timers and the register values. For example, do you get about 40us tof when using the register values in the Delay 40us.txt? I used Matlab to calculate the tof using the equation in TDC7200 datasheet page 18 and got the same results in the txt files, which is about 14.14us offset to 40us.

We only used 1 TDC7200 chip to calculate the tof values. Did we set the configuration registers correctly?

Best Regards,

Ray Vincent

Hello Ray,

Thank you for the information on the configuration. All registers looked to be configured properly.

I was also able to obtain the offset time through manual calculation (54.44 us for the 40us test).

The delay being constant through varied TOF measurements implies the delay could be related to the start or stop pulse. It is unlikely the stop pulses are to be the problem since the TDC measurements are longer than the real duration of start and stop pulses. It is however possible that the measurement start is being triggered early and adding the constant 14 us to the measurement. The TDC7200 will not restart a measurement if multiple start pulses appear, it will maintain counting in reference to the first start pulse. Is it possible to obtain a scope-shot that includes another 20 us before the green start pulse? It seems unlikely, but few things can contribute to a constant offset in time.

Additionally, I noticed the stop pulse exceeds the maximum input voltage specification for the TDC7200. Is it possible to reduce this value to be within specification of the device? Exceeding the input range of the device can cause permanent damage to the device.

Please let me know if you have any questions,

Thank you,

Jacob