THS789 Datasheet, PDF (24/34 Pages) Texas Instruments – THS789 Quad-Channel Time Measurement Unit (TMU)

THS789
SLOS776A – SEPTEMBER 2012 – REVISED DECEMBER 2015
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8.2.2 Detailed Design Procedures
8.2.2.1 Time Measurement
Time measurements in the THS789 device follow the timing of Figure 8. This diagram illustrates that time
measurements are valid as long as events do not happen at speeds higher than 200 MHz. If an event happens
at less than 5 ns from the previous one, then this event is ignored. The same applies to the SYNC signal. Even
though the minimum period is 5 ns, the pulse duration of both Event and SYNC signals can be as low as 200 ps.
SYNC
Max Freq.
200 MHz
200 ps Min PW
EVENT
T1
T2
T3
T0430-01
Figure 8. Time-Measurement Example at Maximum Retrigger Rate and Minimum Pulse Duration
The TH788 is capable of making time measurements using any combination of rising-falling edge between Event
and SYNC. The example in Figure 8 uses rising edges only to trigger the time measurement. Table 16 describes
what registers bits must be programmed to achieve the desired combination. Registers to be programmed are
00h, 20h, 40h, and 60h for event channels and 80h for the sync channel. The examples in Figure 9 illustrate the
other three combinations. All of the channels can be programmed individually with respect to the sync channel.
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