Texas Instruments TIRIS SCBU025, Справочное руководство

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Shorter Charge-Up (TX) Pulses for Speed Applications
Table 5-1 shows the antenna voltage multiplication factor for different charge-up times and the resulting
charge-up voltage in the transponder (V
cl
). You can calculate the maximum allowed antenna voltage by
first finding out from Table 2-1 what the antenna voltage level is for 50 ms, then multiplying it by the
multiplication factor given in Table 5-1 for the TX time selected (or calculate it using Equation 5-2 ).
Table 5-1. Charge-Up Times, Multiplication Factors,
and Transponder Charge-Up Levels
Multiplication Factor for
TX V
cl
Antenna Voltage
90 ms 0.91 5.58
50 ms 1 5
30 ms 1.167 4.39
15 ms 1.547 3.5
10 ms 1.862 3
5 ms 2.6 2.24
Example: Using Antenna G01C in France:
The antenna voltage (for 50 ms) allowed is = 688
If TX = 90 ms then 688
×
0.91 = 626 V
ant
For short TX pulses (and antenna voltage adjustment) the transponder is not charged-up enough at the
same distance from the antenna as in the case of a 5 V charge-up in 50 ms. You can see from
Table 5-1
that in some cases V
cl
is lower than 3 V, which means that the transponder voltage is too low to transmit
back any ID code. This means that you have to look for a different charge-up voltage for example: 7 V at
50 ms (move the transponder closer to the antenna). Then you get:
7/5
×
2.24 = 3.1 V at 5 ms (enough to transmit back)
For CISPR countries, it is not possible to give such a calculation.
SCBU025 – November 1996 Speed Applications (Detecting Moving Transponders) 25
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