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TDC7201: Dead time between multiple hits in the TDC7201

David Batlle
Prodigy 10 points
Part Number: TDC7201

TDC7201

I am interested in a LiDAR application for the TDC7201. The idea is to measure the time-of-flight of a laser pulse that is reflected first by the water surface and later by the bottom of the water tank to know the depth.

Usually TDC systems present a dead time after the first hit is received that can vary from few nanoseconds to less than 1ns. This is the main limitation for shallow water depths. For example if the dead time between multiple hits is 2 ns no waters shallower than aprox. 60 cm will be measured.

I was looking for some information about this dead time in the TDC7201

Many thanks in advance

David

  • 0
    TI__Mastermind 21685 points
    Hello David,
    TDC7201 has two builtin TDC channels with separate START/STOP inputs. Each TDC channel is capable of measuring upto 5 stops (or hits) and for a given TDC channel, START to STOP1 min is 12ns and the min time for STOPx to STOP(x+1) is 66ns (x=1 to 4). See page 4, Section 6.3 of the data sheet.

    Since there are two channels you can use them together to go around the 66ns min time. By connecting START1 and START2 together, you can have TDC1 measure START to STOP1 and use TDC2 measure START to STOP2. Then as long as START to STOP1 and START to STOP2 are greater than 12ns, you can measure STOP1 to STOP2 all the way down to 0.25ns.

    Thanks,
    Vishy