Audio Scrambler and Sub-Audio Signalling Processor
CMX138A
6
General Description
The CMX138A is intended for use in half duplex analogue two way mobile radio or family radio equipment
and is particularly suited to enhanced MURS/GMRS/FRS designs. The CMX138A provides a user
programmable frequency inversion audio scrambler integrated with signal processing functions, CTCSS,
DCS and in-band tones, permitting sophisticated levels of tone control and voice processing. A flexible
power control facility allows the device to be placed in its optimum powersave mode when not actively
processing signals.
The CMX138A includes a crystal clock generator, with buffered output, to provide a common system
clock if required. A block diagram of the CMX138A is shown in Figure 1.
The signal processing blocks are assigned to particular inputs/outputs. A facility to completely bypass the
device is provided (with programmable gain).
Tx functions:
o
o
o
o
o
o
o
o
o
o
o
o
o
Single microphone input with input amplifier, programmable gain adjust and AGC
Filtering selectable for 12.5kHz and 25kHz channels
Selectable pre-emphasis
Selectable compression
Selectable frequency inversion voice scrambling
Programmable scrambler inversion frequency
Selectable audio processing order
Single-point modulation outputs with programmable level adjustment
Pre-programmed 51-tone CTCSS encoder
180 degree CTCSS phase shift generation
Programmable 23/24-bit DCS encoder
Programmable In-band Tone generator
Programmable audio tone generator (for custom audio tones)
Rx functions:
o
o
o
o
o
o
o
o
o
o
o
Demodulator input with input amplifier and programmable gain adjustment
Audio-band and sub-audio rejection filtering
Selectable de-emphasis
Selectable expansion
Selectable frequency inversion voice de-scrambling
Programmable scrambler inversion frequency
Selectable audio processing order
Software volume control
1 from 51 CTCSS decoder + Tone Clone™ mode
23/24-bit DCS decoder
In-band Tone decoder
Auxiliary functions:
o
o
o
o
Programmable system clock output
Auxiliary ADC
Auxiliary DAC, with built-in programmable RAMDAC
Selectable default Xtal options, 6.144MHz or 3.6864MHz
Interface:
o
o
o
C-BUS: 4-wire high speed synchronous serial command/data bus
Open drain IRQ to host
Two Output Enable pins
© 2010 CML Microsystems Plc
Page 12
D/138A/2
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