THS788 Datasheet, PDF (27/43 Pages) Texas Instruments – QUAD-CHANNEL TIME MEASUREMENT UNIT (TMU)

THS788
www.ti.com
SLOS616B – MARCH 2010 – REVISED JUNE 2011
The overtemperature alarm initiates an automatic power down to prevent overheating of the device. The digital
blocks remain functional when in automatic power down. Following a power down, the user is required to reset
OT_ALM using the serial interface. A register bit (RST_OT_ALM) is used for this purpose.
The temperature-monitoring function and its associated overtemperarture alarm circuit may be disabled by the
user, using a register bit (OT_EN). The default for the temperature-monitoring function is enabled.
OT_EN = 1: Temperature-monitoring function is enabled.
OT_EN = 0: Temperature-monitoring function is disabled.
Counter Range
The course counter has three supported ranges: 18, 27 and 34 bits. The course counter applies to the 1.2-GHz
clock.
COUNTER RANGE
Reserved
18 bit
27 bit
34 bit
Table 22. Counter Range
MAX TIME RANGE
X
218.45 µs
111.84 ms
14.31 s
CNT_RNG1
0
0
1
1
CNT_RNG0
0
1
0
1
APPLICATION INFORMATION
BASIC THEORY OF OPERATION
The THS788 is a high-speed, high-resolution time-measurement unit that measures the difference in time
between a signal applied to an event channel and the signal applied to the sync channel. This difference is then
transmitted to a result interface in the form of a digital word. Figure 8 shows an example of three time
measurements.
SYNC
EVENT
T1
T2
T3
T1 - 0000 1100
T2 - 0011 1010
T3 - 1110 0010
T0429-01
Figure 8. Time-Measurement Example– With 8-Bit Words Triggered by Rising Edges
The previous time difference is calculated by an internal ALU that subtracts the time stamps created by the Event
signal and the SYNC signal stored in a FIFO. These time stamps are performed by the TDC that is composed by
the following: an interpolator, a synchronizer, a programmable (18-, 27-, 34-bit) counter, and a 1.2-GHz clock. It
is important to note that the event and sync channels share the same TDC. When a valid edge is applied to the
event channel, the TDC uses the value in the counter and stores it in the FIFO. Then the ALU uses the value of
the event and the value of the sync, stored in the FIFO already, and subtracts them. After the operation is done,
the final value is shifted out to the result interface for retrieval.
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