Flexible sample rate converter for multimedia digital-to-analog conversion in a wireless telephone

A method of converting an input digital datastream, having a bandwidth, to an analog signal, comprising the steps of:

• controlling a dual frequency divider to divide a system clock signal by a divisor selected from an adjacent pair of integers, to produce a sampling clock having an average frequency divided from the frequency of the system clock by a value between the pair of integers;
• sampling the input digital datastream responsive to the sampling clock;
• generating a sequence of digital words corresponding to oversampling multiples selected from an adjacent pair of integers;
• reconstructing a digital datastream from the sampled input digital datastream and the sequence of oversampling multiples;
• and
• converting the reconstructed digital datastream to an analog signal.

A wireless telephone, comprising:

• an RF transceiver, for receiving and transmitting RF signals from and to a wireless network;
• digital signal processing circuitry, coupled to the RF transceiver, for performing digital signal processing operations upon signals to be transmitted and received signals;
• a speaker;
• and
• audio input/output circuitry, coupled to the digital signal processing circuitry, for driving the speaker with an analog audio signal corresponding to digital baseband audio signals produced by the digital signal processing circuitry, the audio input/output circuitry including a digital-to-analog conversion function that comprises:
• a dual frequency divider, for dividing a system clock signal by a divisor selected from a pair of adjacent integers, to produce a sampling clock;
• a first sigma-delta modulator, for selecting the divisor for the dual frequency divider;
• a second sigma-delta modulator, for selecting an oversampling multiple from a pair of adjacent integers;
• a sampling latch, for sampling an input digital baseband datastream synchronously with the sampling clock;
• a digital filter, having an input receiving the sampled input digital baseband datastream and an input receiving the selected oversampling multiple in the form of a digital word, for generating a reconstructed datastream corresponding to the input digital baseband datastream;
• and
• digital-to-analog converter circuitry for producing an analog signal from the reconstructed datastream.