The Research Of Key Technology Of VCO-sigma-delta A/D Converter

The semiconductor manufacturing process expands the applications of ?? ADCs,which originally are used in low speed occasions,into fields that need ADCs with high speed and wide band.Thus,the research of CT ?? ADCs are becoming hotspots.The application of VCO can increase the order of ?? ADCs and reduce the quantization noise,so the VCO quantizer is used in CT ?? ADCs widely.Therefore,a new 1 GHz 4th-order VCO-CT-?? modulator with 10 MHz bandwidth,which is suitable for high-speed field,is proposed in this thesis.This thesis offers detailed comparison between DT ?? ADCs and CT ?? ADCs and analyzes the influence of non-ideal effects on the overall performance.DT ?? ADCs are not suitable for high-speed applications because the requirement for amplifier is too difficult to be satisfied.To solve the problem of nonlinearity of the VCO quantizer which is controlled by voltage directly the VCO quantizer in this architecture is consist of a V-I converter and a Current-controlled-Oscillator(CCO).In this scheme,the voltage signal is converted into current signal firstly.Then,the current signal is used to control the frequency of oscillator.In this way,the linearity of VCO quantizer is improved greatly and the even harmonics of the frequency spectrum of the modulator output are suppressed.Multi-bit DAC can lead to deterioration of linearity at the same time.So the DEM digital calibration algorithm is adopted.The error introduced by DAC is randomized into white noise,so the error of DAC does not deteriorate the performance very much.Excess loop delay compensation technique is also introduced into VCO-CT-?? modulator.It can reduce sensitivity of modulator to the delay caused by VCO quantizer and digital circuits and improve the stability of the modulator.Half period of delay does not influence the performance of the modulator.In this modulator,self-coupling integrator is utilized to reduce the number of amplifiers and inverter-based amplifiers are used to decrease the total power consumption.So this new VCO-CT-?? modulator can achieve high performance with low power consumption.The system level modeling of this new VCO-CT-?? modulator is simulated by the Matlab,and the influence of non-ideal effects on the modulator is determined quantitatively.DEM digital calibration algorithm and excess loop delay compensation technique are verified by Matlab that they can improve the stability and performance at the same time.And requirements for every part of the modulator are determined.The schematic and layout of this circuit are simulated by Cadence Spectre.The new 1GHz VCO-CT-?? modulator achieves 83.6d B SNR,80.7d B SNDR,13.11 bit ENOB and 91.3d B SFDR in 10 MHz bandwidth.It is suitable for high-speed applications.