Audio clocking in video applications
View Patent ↗A method of operating an electronic video device such as a DVD player, wherein video clock signals and audio clock signals are derived from a system clock signal using two phase-lock loops, and these video and audio clock signals are used to process encoded video data and encoded audio data, but digital-to-analog conversion of the audio data stream is controlled by the system clock signal rather than the audio clock signals. By using the system clock signal to control the audio digital-to-analog converter (DAC), the DAC avoids the poor performance issues that can arise from jitter introduced into the audio clock signals by the PLL. The system clock signal may be divided by an integer to generate the sampling clock for the audio DAC. In the illustrative embodiment, the system clock signal has a rate which is not an integer multiple of the sample rate of the audio data stream.
1. A method of operating an electronic video device, comprising:
generating a system clock signal;
deriving one or more video clock signals from the system clock signal;
deriving an audio converter clock signal from the system clock signal;
processing encoded video data to generate a video data stream sampled at a video sample rate;
processing encoded audio data to generate an audio data stream sampled at an audio sample rate;
converting the video data stream into video output using the one or more video clock signals; and
converting the audio data stream into audio output using the audio converter clock signal, wherein the frequency of the audio converter clock signal is a non-integer multiple of the audio sample rate.
2. The method of claim 1 wherein the audio converter clock signal has a frequency equal to the frequency of the system clock signal multiplied by N/M, where N and M are integers.
3. The method of claim 1 wherein said step of deriving the audio converter clock signal derives an audio master clock signal and an audio sample signal, the system clock signal having a rate which is not an integer multiple of a rate of the audio sample signal.
4. The method of claim 1 wherein the audio converter clock signal has a frequency equal to 27 MHz multiplied by N/M, where N and M are integers and M is less than or equal to 16.
5. The method of claim 1 wherein the audio converter clock signal has a frequency equal to 54 MHz multiplied by N/M, where N and M are integers and M is less than or equal to 32.
6. The method of claim 1 wherein the audio converter clock signal has a frequency equal to 108 MHz multiplied by N/M, where N and M are integers and M is less than or equal to 64.