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A sixth-order bandpass (BP) delta-sigma modulator (ΔΣM) that uses subsampling relative to the radio frequency (RF) or intermediate frequency (IF) of a receiver, while oversampling the signal bandwidth is described in this paper. The continuous-time (CT) filter that works at RF/IF frequency together with the discrete-time (DT) filter operating at lower frequency provide both noise shaping to quantization noise and subsampling noise. The transfer function derivation with finite Q-factor bandpass filter is analyzed. A pulse-shaped DAC is used to reduce the DAC clock jitter and realize the frequency translation. Because the sampling frequency is much lower than the RF/IF frequency, the complexity and power consumption of the subsequent digital signal processing stage is greatly reduced.
Date of Conference: 23-26 May 2005