CMX649 Wireless Voice Link Design Guide
©
2004 CML Microcircuits
Page 5 of 42
MSP430F1232 disassembles the frames and passes the resulting bit stream to the
CMX649 for reconstruction of the voice signal. The CMX649 ADM decoder converts
the bit stream into the original analog voice signal, which is then passed to a power
amplifier for delivery to a headset speaker.
Tx Frame:
Master to Slave
Tx Frame:
Slave to Master
TDD Latency
= 2ms
Time
Figure 3, TDD Latency
In addition to providing the time-division duplexing scheme, the microcontroller
firmware also accomplishes a ‘pairing’ procedure that causes the master and slave
units to communicate together while ignoring signals from other sources.
4 Hardware
Description
4.1 Voice Coding – CMX649
The CMX649 is ideal for this design because of its robust voice coding, low power
consumption, and highly integrated feature set. Some of the many features of this
innovative chip are:
•
Full duplex ADM, CVSD, Linear PCM,
µ
-law PCM, and A-law PCM
•
Ability to transcode between coding schemes
•
Low power consumption (2.5mA @ Vdd=3.0V typical)
•
Data clock recovery
•
Flexible clock generation capabilities
•
Programmable ‘voice activity detector’ (VAD)
•
Programmable digital scrambler
•
Flexible microcontroller interfaces
•
Programmable filters, including anti-alias and anti-image filters
•
Programmable gain stages
•
‘Sidetone’ generation
•
On-chip microphone amplifier
The CMX649 operates from a 3.3V supply and uses an 8MHz clock source in this
design. The CMX649’s extensive power control settings are adjusted in software to
provide the lowest possible power consumption.
