INTERPOLATIVE BANDPASS-A/D-CONVERSION

Interpolative A/D-converters need only few quantizing levels at the A/D-interface. Oversampling combined with noise shaping allow efficient fine quantization by the use of digital interpolation. Because of the high oversampling rate needed, the known approach of interpolative A/D-conversion is restricted to narrowband lowpass-signals. In this paper an interpolative A/D-converter allowing the processing of bandpass-signals will be derived. This is done by modification of the feedback loop of known interpolative structures. The proper noise shaping within the feedback loop is achieved by bandpass-integration. The resolution of the A/D-converter depends on the order of its feedback loop and the oversampling ratio related to the bandwidth. When, e.g., the oversampling ratio is 128, a dynamic range of 44 dB can be achieved in case of the first order and 83 dB in case of the second order A/D-converter. Moreover, it is shown that the resolution can be improved by 9 dB (first order) and 15 dB (second order) for each doubling of the oversampling ratio.