A 10-b Fourth-Order Quadrature Bandpass Continuous-Time $\Sigma \Delta $ Modulator With 33-MHz Bandwidth for a Dual-Channel GNSS Receiver

Abstract

A 4 th -order quadrature bandpass (QBP) continuous -time (CT) sigma-delta (ΣΔ) modulator for a dual-channel global navigation satellite system (GNSS) receiver is presented. With a bandwidth of 33 MHz, the modulator is able to digitalize the down-converted GNSS signals in two adjacent signal bands simultaneously, realizing dual-channel GNSS reception with one receiver channel instead of two independent receiver channels. To maintain the loop-stability of the high-order architecture, any extra loop phase shifting should be minimized. In the system architecture, a feedback and feedforward hybrid architecture is used to implement the 4 th -order loop-filter, and a return-to-zero (RZ) feedback after the discrete-time differential operation is introduced into the input of the final integrator to realize the excess loop delay (ELD) compensation, saving a spare summing amplifier. In the circuit implementation, power-efficient amplifiers with high-frequency active feedforward and antipole-splitting techniques are employed in the active RC integrators, and self-calibrated comparators are used to implement the low-power 3-bit quantizers. These power saving techniques help achieve superior figure of merit (FoM) for the presented modulator. With a sampling rate of 460 MHz, currentsteering digital-analog converters (DACs) are chosen to guarantee high conversion speed. Implemented in only 180 nm CMOS, the modulator achieves 62.1 dB peak Signal to Noise and Distortion Ratio (SNDR), 64 dB dynamic range (DR) and 59.3 dB image rejection ratio (IRR), with a bandwidth of 33 MHz, and consumes 54.4 mW from a 1.8 V power supply.

A 20‐MHz bandwidth, 75‐dB dynamic range, continuous‐time delta‐sigma modulator with reduced nonidealities

“…Performance comparison of CT-DSMsPaperKim et al17 Loeda et al13 Ho et al18 Jo et al19 Sabouhi et al20 Zhang et al21 Liu et al22 This Study…”

Design and implementation of quadrature bandpass sigma-delta modulator used in low-IF RF receiver

“…Quadrature band-pass sigma-delta analog to digital converters (ADC), by using a complex filter in the loop, com-bine the complex filtering idea and the real bandpass sigma-delta ADC. The effective signal bandwidth is cut in half which doubles the over-sampling-ratio (OSR) giving ideal SNR improvement [4][5][6][7][8] . Also, it is possible to choose the locations of the zeros of the noise-transfer function (NTF) to minimize errors due to quantization effects, and, finally, the following digital bandpass filter can filter out images from an imperfect preceding image-reject mixer.…”