CMX882 View Datasheet(PDF) - CML Microcircuits
Part Name
Description
MFG CO.
'CMX882' PDF : 70 Pages View PDF
FRS Signalling Processor
CMX882
1.5.4.1 Processing Voice Signals for Transmission over Analogue Channels
The microphone input(s), with programmable gain, can be selected as the voice input source. Pre-
emphasis is selectable with either version of the 2 analogue Tx audio filters (for 12.5kHz and 25kHz
channel spacing). These are designed for use in ETS-300-086 and/or TIA/EIA-603 compliant
applications. Both filters attenuate sub-audio frequencies below 250Hz by more than 33dB wrt the signal
level at 1kHz. These filters together with a built in limiter help ensure compliance with ETS-300-086
(25kHz and 12.5kHz channel spacing) when levels and gain settings are set up correctly in the target
system.
10
reference 0dB at 1kHz
0
+0.5dB/-2dB wrt ref.
3kHz
-10
-20
-30
-33dB
-40
-14dB/octave
-50
-60
10
100
1000
10000
Frequency (Hz)
Figure 8 25kHz Channel Audio Filter Response Template
100000
The filter characteristics of the 12.5kHz channel filter fits the filter template shown in Figure 9 (solid
outline). This filter also facilitates implementation of systems compliant with TIA/EIA-603 ‘A’ and ‘B’
bands. To achieve attenuation above 3kHz of better than −100dB/decade for TIA/EIA-603 ‘C’ bands
(dashed outline), additional external circuitry is required, such as suggested in section 1.4.2.
10
+0.5dB/-2dB wrt ref.
reference 0dB at 1kHz
0
3kHz
-10
-20
-30
-40
-50
-60
-70
-80
-90
10
-33dB
100
1000
Frequency (Hz)
-60dB/decade wrt ref.
(-50dB)
20kHz
-100dB/decade
(-82.5dB)
20kHz
10000
100000
Figure 9 12.5kHz Channel Audio Filter Response Template
2004 CML Microsystems Plc
26
D/882/7
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