PMR Signalling Processor
CMX881
1.4.2
Modulator Outputs
The combination of CMX881 and the modulator output components, R3/C3 and R4/C4, achieve roll-off
rates better than –60dB/decade. If required this can be increased to better than –100dB/decade by
replacing R3/C3 and R4/C4 with the active filter circuit shown in Figure 4.
C17/C19
MOD_1 & 2
+
R11/R13
R12/R14
C16/C18
VSS(A)
Modulator 1 & 2
-
Figure 4 Modulator output components to achieve -100dB/decade roll-off
R11 120kΩ
R12 120kΩ
R13 120kΩ
R14 120kΩ
C16 220pF
C17 440pF
C18 220pF
C19 440pF
(2 x C16)
(2 x C18)
Resistors ±5%, capacitors and inductors ±20% unless otherwise stated.
Notes:
8. The external op-amp must be chosen to ensure that the required signal output level can be driven
within acceptable distortion limits.
2004 CML Microsystems Plc
12
D/881/7
CMLMICRO [ CML MICROCIRCUITS ]
