Cascaded noise shaping circuits with low out-of-band noise and methods and systems using the same

A method of converting a digital data stream to an analog signal with reduced out-of-band noise comprising:

• quantizing with a quantization error a combination of first and second filtered data streams to generate a quantized data stream;
• filtering the quantized data stream to generate the first filtered data stream;
• quantizing a error data stream representing the quantization error;
• integrating the quantized error data stream to generate an integrated quantized error data stream;
• filtering the quantized error data stream to generate the second filtered data stream;
• and
• generating the analog signal from the first filtered data stream and the integrated quantized error data stream.

A delta-sigma modulator comprising:

• an input summer for summing an input signal with feedback;
• a first loop filter for filtering an output from the input summer;
• a first quantizer generating a quantized output signal from a first quantizer input signal and the feedback to the input summer;
• a second quantizer for quantizing a quantization error introduced by the first quantizer;
• a second loop filter for filtering the quantized quantization error;
• and
• a second summer for summing the filtered quantization error with an output of the input summer to generate the first quantizer input signal.

An audio system comprising:

• a source of digital audio data;
• and
• a digital to analog converter comprising:
• a first quantizer responsive to outputs of first and second loop filters, the first quantizer introducing a quantization error during quantization and the first loop filter responsive to an output of the first quantizer;
• a second quantizer for quantizing an error data stream representing the quantization error introduced by the first quantizer, the second loop filter including an integrator for integrating a quantized error data stream output from the second quantizer;
• and
• an analog output path responsive to the output of the first quantizer and an output of the integrator.

A digital to analog converter comprising:

• a cascaded noise shaper for receiving a digital to analog data stream and in response outputting first and second noise-shaped data streams;
• first and second digital to analog converter stages for respectively converting the first and second noise shaped data streams into first and second analog streams;
• and
• an output stage for combining the first and second analog streams wherein out-of-band noise in the first analog stream cancels out-of-band noise in the second analog stream.