CMX138 Audio Scrambler and Sub-Audio Signalling Processor

General Description:
The CMX138 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 CMX138 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 CMX138 includes a crystal clock generator, with buffered output, to provide a common system clock if required. A block diagram of the CMX138 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:
Single microphone input with input amplifier and programmable gain adjustment
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 23/24bit DCS encoder
Programmable In-band Tone generator
Programmable audio tone generator (for custom audio tones)

Rx functions:
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
23/24bit DCS decoder
In-band Tone decoder

Auxiliary functions:
Programmable system clock output
Auxiliary ADC
Auxiliary DAC, with built-in programmable RAMDAC
Selectable default Xtal options, 6.144MHz or 3.6864MHz

Interface:
C-BUS: 4 wire high speed synchronous serial command / data bus
Open drain IRQ to host
Two Output Enable pins