Burr-Brown Corp has taken another step towards integrating audio decoding and digital-to-analog conversion onto a single chip with two new stereo audio digital-to-analog converters. The new PCM1723 converter combines audio and video decoding along with audio and video synchronization onto a single chip, making conversion cheaper because a separate phase-locked loop chip is not needed to synchronize the audio and video. The on-chip phase- locked loop works to keep the clock signals of the chips in phase to stop video going out of synch with audio. This means the converter is suited to applications which combine compressed audio and video data, such as Digital Video Disk players, DVD-ROM drives, set-top boxes for digital and cable satellite, and MPEG sound cards. The issue of synchronization has become a greater problem in the last couple of years because of the increase in the use of digital video, explained Mike Pawlik, vice-president of marketing. Up until then, digital audio on its own was more common and there was no need to worry about synchronizing the video. The next phase for the development of digital to analog converters is to integrate audio decoding into the converter’s function, making the process both faster and cheaper. Pawlik said the company’s next step is to take on this work and he anticipates that a decoding and converter chip set will be on the market within 18 months. And now for the technical bit: PCM1723’s phase-locked loop derives either 256fS or 384fS system clock from an external 27MHz reference frequency, and accepts 16, 20 or 24- bit input data in either normal or I2S formats. The PCM1723’s digital filter performs an 8-times interpolation function and includes selectable features such as soft mute, digital attenuation and digital de-emphasis. The other new converter, the PCM1725, is an economy converter for high performance, low cost CD-quality sound. It has an on-board 8-times oversampling digital filter and is aimed at consumer audio applications including video CD, television games and digital satellite set-top boxes.
