Research On Design Method And Implementation Technology Of High Precision Sigma-Delta Modulator

The Sigma-delta A/D converter has the advantages of high precision,low noise,high signal to noise ratio and so on.Therefore,the Sigma-delta A/D converter is the focus of the research in the field of A/D converter.The Sigma-delta modulator uses noise shaping and over sampling,reducing the complexity of analog circuits,shifting the emphasis of circuit processing to the digital part,and achieving higher signal noise ratio.In this paper,the reverse analysis method is used to analyze a sigma-delta A/D converter chip.Then analyze and redesign the modulator.The sigma-delta modulator in this paper uses a 2-1 structure,the front stage is a 2 order feed forward modulator,the rear stage is the 1 order modulator,and use the error elimination structure.The modulator in this paper has an instrument amplifier with variable gain,low noise,and low offset voltage.In order to improve the load capacity,the instrument amplifier contains the buffer.In this paper,the internal band gap reference source is used in the modulator.The modulator can also use the external bandgap reference.If the user has higher requirements for bandgap reference,the external bandgap reference can also be used as needed.In addition,the modulator has an internal oscillator,and the oscillator can also use an external clock.With external clock,the clock will passes through two frequency division.This paper proves the feasibility of the circuit from the theory and the simulation.This paper designs and simulates by BCD350 GE process.The offset voltage of the instrument amplifier is analyzed by Monte Carlo method in the whole process angle.The offset voltage is less than 1.8mV,and the equivalent input noise is less than 224nV/sqrt(Hz).The temperature coefficient of the internal band gap reference is 16.2ppm.The accuracy of the internal oscillator is kept within 4.3%.The output of the modulator is extracted and filtered by a digital filter to verify the modulator function.The simulation results show that the sigma-delta modulator can achieve the basic function of modulator by reverse analysis.