Study On VCO Based Continuous-time Sigma-Delta Analog To Digital Converter

The rapid development of digital signal processing requires high speed, highresolution, low power dissipation analog to digital converter, additionally, deepsub-micron semiconductor fabrication technology presents great challenge for highperformance analog circuit design. This paper is focused on this problem, and a dualring VCO based continuous time sigma delta ADC is proposed and designed fortransistor circuits. The detailed contents include the following items.First, we study the principal of the VCO based ADC and analysis the advantageof this circuit such as fitting for digital CMOS process, additionally, we talk about thenon ideal characteristic, which may be the bottleneck for application. Then a dual VCObased CT ΣΔ ADC is proposed, which can reduce the non-linearity of the VCO andincrease the ENOB of the ADC.Second, behavioral models of circuits are built, and behavioral simulation is doneusing CPPsim. The simulation results show that the proposed ADC structure can reduceeven harmonics of the VCO output spectrum, which help increase SNDR. At last,specifications are made for the circuits of the ADC.Based on the GSMC0.18μm CMOS process, circuit modules such as amplifier,VCO quantizer, NRZ DAC and RZ DAC are designed. The simulation results show thatall the modules satisfy the specification and the system has76.9dB SNR,76dB SNDRand88dB SFDR, which prove the feasibility of the proposed ADC structure.Finally, we finish the layout design and talk about some problems existing in thedesign. The final design is under tape-out process...