A fourth-order bandpass Δ-Σ modulator using second-order bandpass noise-shaping dynamic element matching

This paper describes a multibit bandpass ΔΣ modulator (DSM) for a frequency-interleaved analog-to-digital (A/D) converter (ADC). A frequency-interleaved ADC using low oversampling ratio (OSR) DSMs is an attractive approach for broadband and high resolution A/D conversion. A multibit DSM is suitable for low-oversampling operation; however, the overall resolution of a multibit DSM is restricted by the accuracy of the internal D/A converter (DAC). Some methods have been reported for improving the internal DAC accuracy of a low-pass DSM, but no bandpass-shaping technique applicable to a bandpass DSM has been implemented, although some methods have been proposed by using simulation. This paper proposes a multibit bandpass DSM with bandpass noise-shaping dynamic element matching (BPNSDEM), which enables bandpass shaping to mismatch error of the internal DAC, and presents its implementation. The modulator was implemented in a 0.25-μm CMOS technology. It operates at a 2.5-V power supply and achieves a signal-to-noise ratio of 77.4 dB over a 250-kHz bandwidth centered at 566 kHz