Envelope-dependent order-varying filter control

A method for controlling a digital interpolation filter having an adjustable filter order, the method comprising:

• receiving a digital signal;
• detecting an envelope signal of a digital signal using a digital peak detector, the envelope signal having an envelope bandwidth less than a bandwidth of the digital signal;
• determining an envelope signal magnitude;
• and
• adjusting a filter order of a digital interpolation filter at least in part in response to information indicative of the envelope signal magnitude.

A sigma-delta over-sampling digital-to-analog conversion circuit, comprising:

• a digital signal input;
• a digital interpolation filter having an adjustable filter order;
• an envelope detector circuit coupled to the digital signal input, the envelope detector circuit configured to provide information indicative of an envelope signal of a digital signal received from the digital signal input, the envelope signal having an envelope bandwidth less than a bandwidth of the digital signal;
• and
• an interpolation filter control circuit configured to adjust a filter order of the digital interpolation filter at least in part in response to information indicative of an envelope signal magnitude;
• a digital sigma-delta modulator coupled to an output of the digital interpolation filter;
• and
• a current-mode digital-to-analog conversion (DAC) circuit coupled to the output of the digital sigma-delta modulator, the current-mode DAC configured to provide an analog output signal representative of the digital input signal.