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Frequency Domain Split-band Scrambler IC



  • Full Duplex Operation
  • High Recovered Audio Quality
  • Uses Split-Band Inversion
  • Fixed or Rolling Code Capabilities
  • Simple Serial Interface
  • Low Power Requirement with Standby Mode


  • Mobile Radio
  • Fixed Code Voice Scramblers
  • Rolling Code Voice Scramblers

Supply Requirement:

  • 3.0V power supply

The CMX264 is a frequency domain voice scrambler for use in analogue cellular phone systems, fixed and rolling code voice scrambler applications.

It contains separate Tx and Rx paths for full duplex operation and operates under µProcessor control via a simple serial interface.

In the Tx path, scrambling is achieved by splitting the audio band into two parts, or sub-bands, and frequency inverting each one.

The frequency at which the signal is split, the "split-point", can be either fixed or rolling between four possible settings resulting in a transmitted audio signal which is unintelligible to eavesdroppers.

Descrambling is achieved by a receive device set to the same split point as the remote transmitter.

Thus if the Tx and Rx devices are synchronously cycled through the same sequence of split points, a clear recovered signal will emerge at the output of the receiver

A 4.433619MHz crystal is used allowing up to four split points to be programmed. The device is designed to be compatible with existing mobile and cell phone circuitry.

Block Diagram


CMX264 Sound Samples

CMX264 Scrambler IC Demonstration
Please use the links below to hear this scramble/descramble voice demonstration.

To use the audio aspects of this demonstration, you will need a multi-media function on your computer. Please ensure that the volume function is activated.

Design Support Information

C-BUS Guides Guides to operation and interfacing
Variable Split-Band Scrambling How it works
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