Patent ID: 7345606

Claim:
A DA-converter system comprising: a digital sigma-delta modulator ( 1 ) for receiving a multi-bit digital input signal (v 1 ), for providing a reduced word-length digital output signal (v 2 ) and for noise shaping the quantization noise generated thereby to a frequency band outside the frequency band of the digital input signal, said DA-converter system further comprising, a digital to analog converting combiner ( 2 ) with first and second digital inputs (I 1 , I 2 ) and an analog output (O) and with the first digital input (I 1 ) connected to the output of the digital sigma-delta modulator, characterized by said sigma-delta modulator providing a reduced word-length multi-bit digital output signal and by a noise reduction arrangement for reducing the out-of-band quantization noise generated by the sigma-delta modulator, said noise reduction arrangement comprising means (M 2 ) connected to the sigma-delta modulator for isolating the quantization noise generated thereby, a second noise shaper ( 3 ) with substantially frequency independent signal transfer function receiving the isolated quantization noise and reducing the word-length of this quantization noise, and means to supply the reduced word-length quantization noise from the second noise shaper ( 3 ) to the second digital input (I 2 ) of the digital to analog converting combiner for generating an analog output signal with reduced out-of-band quantization noise at the combiner output (O).