10
Continuous waveform for bits ??™0??™ and ??™1??™ of modi?¬?ed Miller encoding.
??™0??™: if Vprev????™0??™ then Sig????™0??™ after 0 us & ??™1??™ after 4 us;
if Vprev????™1??™ then Sig????™1??™ after 0 us;
T??9.4 us; A??5%;
??™1??™: Sig????™1??™ after 0 us & ??™0??™ after 4.7 us & ??™1??™ after 4 us;
T??9.4 us; A??5%
FIGURE 3.11
Textual description of modi?¬?ed Miller encoding.
Design Automation for RFID Tags and Systems 43
Waveform variables are parameters that are converted from the waveform description
?¬?le. These parameters describe the physical layer characteristics of an encoding mechanism
in a way that the hardware blocks used to detect the waveform can understand. Thus, the
synthesis process translates the textual description into the parameters for the feature
library.
A bit window period is a simple example of a waveform characteristic. A bit window
can contain a transition at a particular time during the period. Similarly, the direction of
this transition is another characteristic. From Figure 3.4a, the Manchester encoding requires
a 50% duty cycle waveform with a period of 36 ms where the direction determines the
value. A 1 has identical features with a 0 except that it is composed of a rising edge at the
middle of a bit window as opposed to a falling edge. Because the waveform is a continuous
wave, a transition may also occur at the edge of two adjacent bits depending on the values
of these windows.
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