Frequency detect circuit for determining sample speed mode of decoded audio input data streams

A data converter which receives a signal representing an analog signal that has been sampled at a certain rate, comprising:

• a divider which receives a clock signal associated with the digital audio stream and which divides the clock signal by a selectable division factor according to divider control signals and provides an internal clock signal at its output;
• a frequency detection circuit comprising a counter connected to the output of the divider and a fixed time reference circuit, whereby the frequency detection circuit is operable:
• to receive the internal clock signal from the divider at the counter;
• to compare the clock transitions of the signal received from the divider with a fixed-time reference transition signal from the fixed time reference circuit;
• and to generate the divider control signals to the divider to set the division factor in the divider such that the internal clock signal has a known relationship to the original sampling rate;
• and
• a digital processing circuit which receives the internal clock signal from the divider, and incoming data derived from the digital audio stream, and generates an output signal.

A method of converting a received digital audio stream received at a data converter, the digital audio stream representing an analog signal that has been sampled at a certain rate and generating an analog output signal, the method comprising:

• receiving the digital audio stream at an input to the data converter;
• receiving at a divider within the data converter, a clock signal associated with the digital audio stream;
• dividing the clock signal by a selectable division factor in the divider according to divider control signals;
• providing an internal clock signal as an output from the divider;
• receiving at a frequency detector circuit, the internal clock signal from the divider;
• detecting in the frequency detector circuit, the original sampling rate based upon intrinsic characteristics of the digital audio stream;
• and
• generating in the frequency detector circuit, the divider control signals to the divider to set the selectable division factor thereof such that the internal clock signal has a known relationship to the original sampling rate;
• receiving in a digital processing circuit, the internal clock signal from the divider, and incoming data derived from the digital audio stream;
• and
• generating an output signal from the digital processing circuit using the internal clock signal and the incoming data derived from the digital audio stream.

A analog-to-digital converter which receives an analog signal and a first and second clock signal:

• a divider which receives the first signal and which divides the first clock signal by a selectable division factor according to divider control signals, and which further provides an internal clock signal at its output;
• a frequency detection circuit comprising a counter connected to the output of the divider and a fixed time reference circuit, whereby the frequency detection circuit is operable:
• to receive the internal clock signal from the divider at the counter;
• to compare the clock transitions of the signal received from the divider with a fixed-time reference transition signal from the fixed time reference circuit;
• and to generate frequency mode detection signals;
• a rate detection circuit connected to the frequency detection circuit and further connected to receive the first and second clock signals, the rate detection circuit operable to generate divider control signals to the divider to set the division factor in the divider such that the internal clock signal has a known relationship to the original sampling rate;
• and
• a digital processing circuit which receives the internal clock signal from the divider and the analog signal and generates a digital signal which is derived from the analog signal based on the timing from the internal clock signal.