Research And Design On Low-voltage And Low-power ?? Modulator

With the development of IOT technology,the energy efficiency integrated circuits and systems are highly demanded.Low supply voltage technique is an attractive way to improve the power performance of integrated circuits,and has been adopted by lots of designes.Analog-to-digital converters(ADCs)are the bridge between analog signal domain and digital signal domain,which is unavoidable in modern integrated systems.The amplitude of the analog signal is decreasing with low supply voltage,which limits the resolution of converter.This is the main challenge for low voltage electronic system design.?? Modulator(Delta-Sigma Modulator)guarantee the high-accuracy analog to digital conversion by the system architecture with oversampling and noise shaping technology,which relax the requiremnts of low voltage circuits.Low-voltage and lowpower.?-? modulator has a broad application prospect in the high efficient sensor nodes,low power SOCs,mobile IoT devices,wearable biosignal acquisition system,energy havesting system,and is worth further research.Firstly,this paper analyzes the basic structure of ?? modulator and many limitations of non-ideal factors,especially for limited signal swing under low voltage and the nonlinearity of low voltage circuits design.The analysis and summarize of previous research works provide an important reference for the designs in this paper.Secondly,for the challenge of low voltage continuous time ?? modulator design,this paper porpose two low votlage moudulators,which are based on Active RC integrator and Gm-C PI integrator respectively.The main contribution of the two research worksinclude:(1)A new inverter based two-stage OTA(Operational Transconductor Amplifier)with feedforward compensation is proposed in Active-RC integrators.(2)A low signal swing system for low voltage ?? modulator is proposed.(3)A proposed FIR feedback DAC of modulator,based on the Gm-C PI integrators,effectively reduce the input signal swing of the first transcondcutor.Its nonlinear problem under open loop operation is solved.(4)In the design of Gm-C PI integrator,the bias circuit based on feedback control is proposed to realize a stable transconductance,gain and bandwidth of low voltge transconductor based on Nauta-Gm.This also guarantee the stability of noise shaping.Based on the above design works,innovation points in this thesis are verified by testing two chips which are fabricated by 130 nm and 90 nm CMOS respectively.The modulator based on Active-RC integrator works under 0.3V power supply and 64 times oversampling ratio.It could achieve 68.7dB SNDR,82.6dB SFDR and 50 KHz bandwidth.The power consumption is 26.3 ?W,Thus,the FoMs of this modulator is 120.9 fJ/step.The other modulator based on the Gm-C PI integrator could opearate under 0.4V power supply and 104 times oversampling ratio.the performance could achieve 74.4dB SNDR,85.2dB SFDR and 50 KHz bandwidth.Meanwhile the power consumption is 26.4 ?W,Thus,its FoMw is 61.5 fJ/step.With the comparison with other low voltage modulator designs,the two modulators in this thesis could achiveve a high level performance among them.Meanwhile,it is the first time for low voltage continuous ?? modulator to reach below 0.5 V supply.