The HC-55564 is a half duplex modulator/demodulator CMOS intergrated circuit used to convert voice signals into serial NRZ digital data and to reconvert that data into voice. The conversion
is by delta-modulation, using the Continuously Variable Slope (CVSD) method of modulation/demodulation.
While the signals are compatible with other CVSD circuits, the internal design is unique. The analog loop filters have been replaced by very low power digital filters which require no external timing components. This approach allows inclusion of many desirable features which would be difficult to implement using other approaches.
The fundamental advantages of delta-modulation, along with its simplicity and serial data format, provide an efficient (low data rate/low memory requirements) method for voice digitization.
The HC-55564 is usable from 9kbits/s to above 64kbps. See the Harris Military databook for a MIL-STD-883C compliant CVSD. Application Note 607.

*All Digital
*Requires Few External Parts
*Low Power Drain: 1.5mW Typical From Single 4.5V To 6V Supply
*Time Constants Determined by Clock Frequency; No Calibration or Drift Problems: Automatic Offset Adjustment
*Half Duplex Operation Under Digital Control
*Filter Reset Under Digital Control
*Automatic Overload Recovery
*Automatic “Quiet” Pattern Generation
*AGC Control Signal Available

*Voice Transmission Over Data Channels (Modems)
*Voice/Data Multiplexing (Pair Gain)
*Voice Encryption/Scrambling
*Audio Manipulations: Delay Lines, Time Compression, Echo Generation/Suppression, Special Effects, etc.
*Data Acquisition Systems
*Voice I/O for Digital Systems and Speech Synthesis Requiring Small Size, Low Weight, and Ease of Reprogrammability
*Related Literature
- AN607, Delta Modulation for Voice Transmission

HC1-55564-2, HC1-55564-5, HC1-55564-9, HC3-55564-5, HC9P55564-5

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