Applications of Polyphase Filters for Bandpass Sigma-delta Analog-to-digital Conversion
نویسندگان
چکیده
The traditional lowpass Sigma-Delta (Σ∆) based Analog-to-Digital (A/D) conversion principle has been recently extended to bandpass for direct IF conversion. Such converter offers high Signal-to-Noise (SNR) ratios for narrowband signals relative to the sampling frequency, at significantly lower oversampling ratios in comparison to the conventional lowpass Σ∆ converters. In this paper a sixth-order modulator sampled at 1.82MHz coupled with a multistage polyphase decimation filter is reported for the conversion of bandpass signals centred at 455kHz with 14kHz bandwidth. The decimation filter is using a small number of short-wordlength filter coefficients. The simulations undertaken demonstrated that this setup realises 124.3dB SNR with less than 4μdB passband ripples for a half/full-scale composite 20-sinewave input signal potential of up to 20-bit performance. The resultant converter can directly accomplish demodulation of narrow-band AM signals.
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