CML - Digital Voice - CMX639

As a member of the CML DuraTALK® family of digital voice products, the CMX639 is a Continuously Variable Slope Delta modulation (CVSD) full duplex codec for use in consumer and commercial digital voice communication systems.
With its robust and selectable coding algorithms, low cost, very low power and small size, the CMX639 is ideal for use in a wide variety of consumer and business digital voice applications.

Its completely integrated CVSD Codec simplifies design and eliminates the costs, complexity and risk of external filters and software algorithms.
8kbps to 128kbps data/sampling clock rates are supported both via external clock signals or internally generated, programmable clocks.

Internal data/sampling clocks are derived from an on-chip reference oscillator that uses an external clock crystal. An internal data/sampling clock output signal is provided to synchronize external circuits, if desired. Multiplexer applications are also well supported by the encoder output’s three-state/high impedance enable feature.

Block Diagram


  • Single Chip Full Duplex CVSD Codec
  • On-Chip Input and Output Filters
  • Programmable Sampling Clocks
  • 3 or 4-Bit Compand algorithm
  • Robust Coding for Wireless Links
  • Encode and Decode Force-idle
  • Separate Rx and Tx Paths
  • Simple Control


  • Consumer and Business Handheld Equipment
  • Digital Voice Systems
  • Spread Spectrum Wireless
  • Cordless Phones
  • Voice recording and storage
  • Delay Lines
  • Time domain Scramblers
  • Multiplexers and Switches

Supply Requirement:

  • 3.0 to 5.5 V