Power-scalable multi-mode reconfigurable continuous-time lowpass/quadrature bandpass sigma-delta modulator for zero/low-IF receivers

Abstract

A multi-mode reconfigurable wideband continuous-time lowpass/quadrature bandpass sigma-delta (CT LP/QBP ΣΔ) modulator employing power scaling technique (PST) for LTE-advanced/industry-specialized zero/low-IF receivers is presented. The proposed modulator consists of a loop filter with active-RC integrator configured as 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> -order lowpass or 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> -order complex bandpass architecture and 4-bit internal quantizer operating at 80MHz, 160MHz and 320MHz, respectively. A programmable differential current-steering DAC unit is adopted for high linearity. In LP mode, the excess loop delay is set to half the sampling period of the quantizer and an additional feedback DAC is used to maintain stability, which is not used in QBP mode. The modulator employs flexible high gain and high bandwidth amplifiers with PST to optimize power consumption among various modes. Implemented in 65nm CMOS, the modulator achieves 84.8/85.8/84.5dB SNDR, 94.9/94.1/94.6dB SFDR over 2.5/5/10-MHz signal bands in LP modes and 83.8/ 84.6dB SNDR, 94.3/96dB SFDR across 2.5/5-MHz bandwidth with programmable center frequencies of 2/4-MHz in QBP modes, respectively. Powered by a 1.2-V supply, the modulator consumes 1.8 to 4.2mW, which results in simulated FOMs of 15.5 to 27.8fJ/conversion.