This paper presents a 2 GHz 4-bit asynchronous successive approximation register (SAR) quantizer to enable an ultra-wideband continuous-time (CT) sigma-delta modulator (SDM). Low latency is required for the stability of the SDM. The excess-loop-delay compensation (ELDC) is embedded in the SAR quantizer by adding an extra switched-capacitor DAC segment with two separate reference voltages. To achieve high speed, a g_m-boosted StrongARM latch and the monotonic switching scheme are used. This paper presents the transistor-level circuit implementation and the complete verification of the CT SDM. Simulation results show the power consumption of this SAR-based quantizer including ELDC is 0.98 mW, leading to a very competitive Figure-of-Merit of 30.6 fJ/conv.-step.

This paper proposes an architecture design approach for a wideband continuous-time (CT) ΣΔ modulator with ultra-low oversampling ratio (OSR). The ultra-low OSR is beneficial in terms of power consumption for both the clock distribution network and the subsequent decimation filter. In this work, three signal feedforward paths and an additional feedback path are used to reduce the power consumption. Extensive system-level simulations demonstrate the effectiveness of the proposed solutions. Furthermore, this work verifies the proposed methods by transistor-level design and simulations of a 2 GHz 4^th-order CT ΣΔ modulator achieving an SNDR of 46 dB in a signal band of 250 MHz while consuming only 1.91 mW of power in 40 nm CMOS. The proposed solutions enable CT ΣΔ modulators for low power ultra-wideband (UWB) applications.

The state of the land surface and the water cycle over the South and East Asia can be determined by space observation. New or significantly improved algorithms have been developed and evaluated against ground measurements. Variables retrieved include land surface properties, i.e. NDVI, LAI, FPAR, albedo, soil moisture, glacier and lake levels. Based on these biophysical parameters derived from microwave and optical remote sensing observations, a hybrid remotely sensed evapotranspiration (ET) estimation model named ETMonitor was developed and applied to estimate the daily actual ET of the Southeast Asia at a spatial resolution of 1 km. The changes in glaciers and lakes on the Tibetan Plateau, and the drainage links between glaciers and lakes are determined in this climate-sensitive region.