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Serial-Port 16-Bit SoundPort Stereo Codec

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The AD1847 SoundPort ® Stereo Codec integrates key audio data conversion and control functions into a single integrated circuit. The AD1847 is intended to provide a complete, low cost, single-chip solution for business, game audio and multimedia applications requiring operation from a single +5V supply. It provides a serial interface for implementation on a computer motherboard, add-in or PCMCIA card. See Figure 1 for an example system diagram.

External circuit requirements are limited to a minimal number of low cost support components. Anti-imaging DAC output filters are incorporated on-chip. Dynamic range exceeds 70 dB over the 20 kHz audio band. Sample rates from 5.5 kHz to 48 kHz are supported from external crystals.

The Codec includes a stereo pair of Sigma Delta analog-to-digital converters (ADCs) and a stereo pair of Sigma Delta digital-to-analog converters (DACs). Inputs to the ADC can be selected from four stereo pairs of analog signals: line 1, line 2, auxiliary ("aux") line #1, and post-mixed DAC output. A software-controlled programmable gain stage allows independent gain for each channel going into the ADC. The ADCs' output can be digitally mixed with the DACs' input.

The pair of 16-bit outputs from the ADCs is available over a serial interface that also supports 16-bit digital input to the DACs and control/status information. The AD1847 can accept and generate 16-bit twos-complement PCM linear digital data, 8-bit unsigned magnitude PCM linear data, and 8-bit µ-law or A-law companded digital data.

The Sigma Delta DACs are procceded by a digital interpolation filter. An attenuator provides independent user volume control over each DAC channel. Nyquist images are removed fom the DACs' analog stero output by on-chip switched-capacitor and continuous-time filters. Two stero pairs of auxiliary line-level inputs can also be mixed in the analog domain with the DAC output.

The AD1847 serial data interface uses a Time Division Multiplex (TDM) scheme that is compatible with DSP serial ports configured in Multi-Channel Mode with 32 16-bit time slots (i.e., SPORT0 on the ADSP-2101, ADSP-2101, ADSP-2115, ext.).



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