MX93000

The MX93000 Special Codec integrates key functions of the analog-front-end of Digital Answering Machine (DAM) into a single integrated circuit.  The MX93000 is intended to provide a complete, low cost, and single chip solution for telephone applications requiring a single +5V power supply.

The MX93000 Special Codec is especially powerful when applied to some DAM models which are intended to meet different countries' specifications in the same system hardware.  User can achieve this goal by simply setting control firmware.  This benifit will help DAM system makers to save developing time and R/D resources.

The A/D D/A converters are implemented with 2nd- order sigma-Delta modulators.  The on-chip digital filters, which are carried out with 16-bit and 2's complement format, are used to get the required frequency response of a PCM Codec.  The Codec can support 8-bit u/A law and linear format.  For the latter, it is 16-bit format with 14-bit resolution .

Before the A/D digitizing the voice-band analog signal into digital format, the analog signal can be processed by a built-in Automatic Level Control (ALC) and pro- grammable Gain Amplifier (PGA).  The ALC circuit controls the input level of A/D converter to about 1.5 Volt, so as to get a better signal to noise ratio during a low-level input.  The PGA circuit is used to control the gain of different sources : microphone, aux or line input.

After the digital data is converted into analog signal by the D/A converter, a fully differential line driver is supported to drive the telephone line directly without the need of external amplifier.  On the other hand, the analog signal can be monitored by passing the analog signal to the on-chip volume control circuit, which can drive an external driver like LM386.

In addition, the MX93000 supports switches and control registers so that users can program the Special Codec to be under line operations and all other specific operations of DAM.  To enhance an easy read/write of control registers by microprocessors, the control data is clocked by the 8 kHz sampling clock and synchro- nized by SDEN\, where SDEN\ is coming from the output port of microprocessor by detecting one of the rising edge of 8 kHz clock.