Baseband Processor For Mixed Mode Land Mobile Radio
CMX880
Modulator Outputs
The combination of CMX880 and the modulator output components, R3/C3 and R4/C4, achieve roll-off rates
better than –60dB/decade. 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.
C16/C18
MOD_1/2
+
R11/R13
R12/R14
C15/C17
VSS(A)
Modulator reference/control
-
Figure 4 Modulator output components to achieve -100dB/decade roll-off
R11 120kW
C15 220pF
C16 440pF (2 x C15)
C17 220pF
R12 120kW
R13 120kW
R14 120kW
C18 440pF (2 x C17)
Resistors ±5%, capacitors ±20% unless otherwise stated.
The op amp must be chosen to ensure that the maximum possible signal output level can be driven without
unacceptable distortion.
<further notes tbd>
ã 2001 Consumer Microcircuits Limited
9
D/880/1
CMLMICRO [ CML MICROCIRCUITS ]
