GMSK Packet Data Modem
CMX909B
Suitable values being:
8000 bits/sec
4800 bits/sec
R4
100k
Ω
100k
Ω
C5
430pF
710pF
The signal at the TXOP pin is centred around V
BIAS
and is approx 0.2 x V
DD
pk-pk, going positive
for a logic ‘1’ and negative for a logic ‘0’, if the modem is not inverting the Tx data.
A capacitor may be fitted if ac coupling of the input to the frequency modulator is desired, see
section 1.6.4.
The ‘eye’ diagram of the transmitted signal (after the external R4/C5 network) is shown in
Figure 5.
Figure 4 Typical Tx Filter Frequency Response (after the external RC filter)
©
2001 Consumer Microcircuits Limited
9
D/909B/1
CMLMICRO [ CML MICROCIRCUITS ]
