GMSK Packet Data Modem
CMX909B
AQLEV Sequence
AQBC Sequence
SFH or SFS is set up to 28 bits after AQLEV;
Frame Sync is being searched for:
1 bit of clamp.
Lossy Peak detect until Frame Sync is detected.
Residual setting.
SFH or SFS is set up to 14 bits after AQBC;
Frame Sync is being searched for:
‘Wide’ setting until Frame Sync detected.
30 bits of ‘Medium’ setting.
Residual setting.
SFH or SFS is not set; Frame Sync is not being
searched for:
SFH or SFS is not set; Frame Sync is not being
searched for:
1 bit of clamp.
30 bits of Lossy Peak Detect.
Residual setting.
16 bits of ‘Wide’ setting.
30 bits of ‘Medium’ setting.
Residual setting.
Figure 16 Bit Clock and Level Acquisition Example
1.6.4
AC Coupling
For a practical circuit, ac coupling from the modem’s transmit output to the Frequency Modulator
and between the receiver’s Frequency Discriminator and the receive input of the modem may be
desired. There are, however, two problems.
Firstly, ac coupling of the signal degrades the Bit Error Rate performance of the modem.
See Figure 17.
ã 2001 Consumer Microcircuits Limited
40
D/909B/1
CMLMICRO [ CML MICROCIRCUITS ]
