CMX264
Frequency Domain
Split Band Scrambler
D/CMX264/1 August 1999
Advance Information
1.0 Features
• Ensures Privacy
• Full Duplex
• High Quality Recovered Audio
• Low Height, Surface Mount Package
• 3.0V, Low Power Operation
• Fixed or Rolling Code
• Standby Mode
• Uses Split Band Inversion
• Low Current, Low Voltage
• 4.433619MHz Operation
1.1 Brief Description
The CMX264 is a frequency domain scrambler for use in analogue cellular phone systems. 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 cellphone circuitry.
© 1999 Consumer Microcircuits Limited