Modi?¬?ed Miller encoding has a
low pulse at the beginning of the bit window to encode a 0 or the low pulse is delayed by
half a period to encode a 1. However, if a 0 is preceded by a 1 the 0 is encoded with no low
pulse at all. This is shown in Figure 3.10.
To represent this in our text, we introduce the new ?¬?eld Vprev which corresponds the
previously encoded value. In the example from Figure 3.11, the modi?¬?ed Miller encoding is
??™0??™: if Lprev????™0??™ then Sig????™1??™ after 0 us & ??™0??™ after 18 us;
if Lprev????™1??™ then Sig????™0??™ after 0 us & ??™1??™ after 18 us;
T??36 us; A??12.5%;
??™1??™: if Lprev????™0??™ then Sig????™0??™ after 0 us & ??™1??™ after 18 us;
if Lprev????™1??™ then Sig????™1??™ after 0 us & ??™0??™ after 18 us;
T??36 us; A??12.5%;
FIGURE 3.6
Textual description of differential Manchester encoding.
Pulse0
Pulse1
PW
PW
Bit 0
Bit 0
Bit 1
Bit 1
T0
1.5 T0 < T1 < 2.0 T0
T = {6.25, 3.9, 3.1, 1.5} ?µs
50%
50%
or
or
00 or
01 or
10
11
or
or
(b) FM0 encoding (a) PIE encoding
FIGURE 3.7
Continuous waveform for bits 0 and 1 of PIE and FM0 encodings.
Design Automation for RFID Tags and Systems 41
shown for a period of 9.4 ms. To encode a 0 we either see a pulse at the beginning of the
window if the current bit was preceded by a 0 or no pulse if preceded by a 1. The encoding
1 does not specify a Vprev value.
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