TDC7200: Delay lines and other strategies for avoiding deadtime.

Hello Mitch,

This is not possible with the TDC7200, but you can measure lower than 12ns with the TDC7201(dual channel version).   See the post below.

https://e2e.ti.com/support/sensors-group/sensors/f/sensors-forum/1275801/tdc7200-continuously-measure-the-time-difference-between-start-stop-event-and-clock-edge   

The datasheet for the TDC7201 says 12ns too.

But the question was how to insert a 12ns delay  into the input to the STOP pin.

Or, suggest an entirely different TDC that has no (0) dead time.

I have not seen any method for creating a 12ns delay  to the stop pin.  Typically, if you want to make measurements within the 12ns dead period, you can use the method described in the link above.  You are correct that the TDC7201 also has the 12ns requirement, which is why two channels must be used.  This is common for applications like lidar where shorter measurements are needed.

On quick perusal it s not clear how it fits my case.   There they are measuring the difference between a clock and an event,  and they still have to make sure that both occur after 12nsecs.

My case is more general, and the event will most often come within a few nsec of the start.

But let's say I can start the experiment with a clock from an MCU.   If I can do that, then I can run the clock signal to the start of the TDC, and continue it (with a "T")  through another 12nsec of cable to start the experiment.   I dont need two boards for that.

But let's say I am looking for quantum entanglement, I am counting two particles that fly off in opposite directions, and I want to tag the arrival times.   In that case it is two TDC boards, and I either arrange for 12nsec of flight or do the above with the start cable, run the start to the tdc's and run a longer length of cable to whatever the start is for the experiment.

So those are the easy solutions that are available when the start event is or can be synchronous. 

The problem remains, how do tag an event that occurs within a few nsec of an asynchronous start.

Thank you

Mitch,

I want to first be clear what my suggestion is.  Take a look at section 8.22 of the datasheet of TDC7201.  It is correct that you must have the "reference start" at least 12ns before sending the actual start pulse.  Is there a specific issue with using the device in this manner for your application? 

https://www.ti.com/lit/ds/symlink/tdc7201.pdf 

I am not aware of any such IC to delay the signal.  

If we can have the reference start 12nsec before the start pulse, then we don't need a 12nsec delay in the circuit.