Baseband Processor For Mixed Mode Land Mobile Radio
CMX880
10
0
250Hz
-10
-20
Filter response
-30
-40
-50
-60
Template
300Hz
3kHz
10Hz
100Hz
1000Hz
Frequency (Hz)
10000Hz
100000Hz
Figure 5 Analogue Channel, RX Audio Filter Frequency Response
The FM Discriminator path through the Delta-Sigma ADC has a programmable gain stage. Whilst in receive
mode this should be set to full (the default) gain. This gain adjustment facility can be used, under host mC
software control, to provide vogad capability when transmitting voice band from either of the microphone inputs,
but is not intended for use whilst in receive mode.
De-emphasis at -6dB per octave from 300Hz to 3000Hz (shown in Figure 6) can be selected to facilitate
compliance with TIA/EIA-603.
16
12
8
4
0dB/octave
0
-6dB/octave
dB
+1dB
-4
0dB
-8
-3dB
-12
-16
-18dB/octave
-20
100
1000
10000
Frequency (Hz)
Figure 6 De-emphasis Curve for TIA/EIA-603 Compliance
Associated Control and Status
·
·
Digitised voice data word.
‘Data word present’ flag and (interrupt) mask. Flag set if data is present and interrupt issued if appropriate
mask bit is set.
·
·
·
·
Audio output gain.
Enable/ Mute/Power-save audio output.
Enable De-emphasis.
Data destination - to an external processor (µC/DSP) or direct to speaker output.
ã 2001 Consumer Microcircuits Limited
14
D/880/1
CMLMICRO [ CML MICROCIRCUITS ]
