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

Abstract

A wireless telephone ( ) is disclosed, in which audio input/output circuitry ( ) includes a digital-to-analog conversion function ( ) for producing an analog output signal (s(t)) based upon a digital baseband signal (S) from a digital signal processor ( ). The digital-to-analog conversion function ( ) includes first and second &Sgr;&Dgr; modulators ( ), each of which are controlled by a sampling clock generated by a dual frequency divider ( ) controlled by the first &Sgr;&Dgr; modulator ( ). A sampling latch ( ) samples the digital baseband signal synchronously with the sampling clock. The second &Sgr;&Dgr; modulator ( ) selects an oversampling multiple that is applied to a digit filter ( ) along with the sampled signal from the sampling latch ( ). The digital filter ( ) reconstructs a digital signal from the sampled value and the oversampling multiple that is the equivalent of that reconstructed by the decimation of an over sampled signal. The reconstructed signal is converted to analog by a digital-to-analog converter ( ). However, the digital filter ( ) and DAC ( ) can operate at a much lower frequency than in conventional circuits, thus providing excellent noise performance without requiring high frequency clocking.