GMSK Modem
CMX589A
3 External Components
Figure 3: Recommended External Components
Component
R1
R2
R3
R4
C1
C2
C3
Notes
1
1.0MΩ
2
3
1
4
4
Value
Tolerance
±5%
±10%
±10%
±10%
±10%
Component
C4
C5
C6
C7
C8
C9
X1
5
6
6
7
8
Notes
Value
0.1µF
1.0µF
Tolerance
±20%
±20%
±20%
Table 2: Recommended External Components
Recommended External Component Notes:
1. The RC network formed by R1 and C1 is required between the Tx Out pin and the input to the modulator.
This network, which can form part of any DC level shifting and gain adjustment circuitry, forms an
important part of the transmit signal filtering. The ground connection to the capacitor C1 should be
positioned to give maximum attenuation of high-frequency noise into the modulator.
The component values should be chosen so that the product of the resistance and the capacitance is:
For a BT of 0.3
For a BT of 0.5
R1.C1 = 0.34/bit rate (bps)
R1.C1 = 0.22/bit rate (bps)
©
2002 CML Microsystems Plc
6
D/589A/4
CMLMICRO [ CML MICROCIRCUITS ]
