Optimal nonrecursive noise shaping filters for oversampling data converters .I. Theory

Properties of nonrecursive filters appropriate for noise shaping coders and oversampling data converters are presented. When the noise shaping filter has optimal minimum phase, the number of quantizer levels required for loop stability is also minimized. Just as with infinite impulse response (IIR) noise shapers, the channel tones can appear in the baseband. These tones are diminished if at least one passband zero is reflected outside the unit circle. However, the filter is no longer minimum phase. This substantially increases the number of quantization levels required for stability. A better alternative is to use proper dithering in conjunction with a minimum phase filter. A stability test is derived which takes the dithering into account