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Clock Recovery Algorithm Using a PCM Data Stream to Detect the Presence or Absence of an External System Clock

IP.com Disclosure Number: IPCOM000131787D
Publication Date: 2005-Nov-18
Document File: 2 page(s) / 28K

Publishing Venue

The IP.com Prior Art Database

Abstract

This invention applies generally to the field of digital electronics and specifically to the field of data communications.

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Title

Clock Recovery Algorithm Using a PCM Data Stream to Detect the Presence or Absence of an External System Clock

Abstract

This invention applies generally to the field of digital electronics and specifically to the field of data communications.

We have a DSP/codec connected to a Bluetooth radio chip. The DSP can generate its own clock internally, but this is too slow and the clock needs to be synchronized to the Bluetooth radio’s clock. Accordingly, the DSP/codec uses the Bluetooth radio’s clock, which is much faster, as the system clock to improve the MIPS available for DSP and to ensure that the audio data communicated between the DSP and the radio is always synchronized.

However, if the radio does not have an active link open to another Bluetooth radio device, such as a cell phone handset, then the radio goes into a condition known as “deep sleep” which disables the main high-speed clock. When the radio’s clock is disabled, the DSP stops and cannot be revived until the clock restarts. This would be fine except that when the clock does restart, the clock waveform grows gradually, rather than provide a clean start. This gradual clock start behavior can be misread by the DSP and cause some parts of the DSP to malfunction.

One solution is to not permit the radio to enter the deep sleep mode, which means the clock will never stop. This has a significant negative impact on talk time.

Another solution is to always reset the DSP when the clock restarts. The time to finish the power-up reset initialization procedure is normally too long for most applications....