MASH 2-2 Modulators For 18bit ∑△ADC

An analog to digital converter is a circuit system that converts analog signals to digital signals. Analog to digital converter in dozens of years of development have different structure, in speed, precision, complex degree, each has its own advantages and disadvantages, is designed in this paper, the application of electrical energy measurement in the field of demand for high precision, low speed, so choose sigma-delta ADC witch using oversampling and noise shaping technique.In this thesis, the basic theory of sigma delta ADC, including noise shaping and over sampling technology is detailed, and on this basis, using MATLAB to sigma delta modulator for system modeling, with non-ideal factors of complete modulator and the noise cancellation circuit model is set up, effective digits over 19, modeling and simulation are found effective.In this thesis, we design the circuit principle diagram of the Sigma-delta modulator with CMOS0.18 μm technology, and the simulation results are analyzed, the signal to noise ratio is 111dB, the effective number of bits is 18. Among them to corresponding system level modeling integrator has gain coefficient and feedback coefficient proposed a improved fully differential switched capacitor integrator structure. This structure can respectively adjust the gain coefficient and feedback coefficient. With a three level of a quantizer design differential comparator and SRAM six tube unit and clock synchronization. Proposed a method for programmable gain amplifier, in the design of operational amplifier, using switched capacitor and reach a programmable gain amplifier with the same effect, can greatly reduce the design difficulty and gain control of the accuracy.