Research And Implementation Of High Speed Sigma Delta Analog To Digital Converter

Today, with the development of wireless sensor network technology, the demand of communication systems for analog to digital converters (ADC) has been continuously increasing. ADCs with high bandwidth, high resolution and low power become an important development direction. Because of that, the continuous time Sigma Delta ADC has been developing rapidly in recent years due to its good compromise between resolution, bandwidth and power and the low requirement for the match of analog devices.Firstly, the thesis studies the latest development status of Sigma Delta Modulator at home and abroad, and introduces the advantages and disadvantages of discrete-time and continuous-time modulators and the conversion methods between each other. According to the requirement of performance index, a two stage Continuous Time Sigma Delta Modulator with 10-bits resolution is designed. Considering the low complexity in designing, the feedback structure is adopted in this design. The noise transfer function is synthesized with the SDtoolbox. With a widely used method, invariant-impulse-response (ⅡR), the structural parameters in discrete time are converted into continuous time domain. Then, the non-idealities of the modulator are simulated in continuous time domain in MATLAB. The circuits are designed after the whole system is well simulated and designed. Active RC integrator is applied in this design because of the high requirement for the integrator. A folded cascode gain-boost amplifier is used in the integrator, so that the DC gain and the bandwidth are good enough and will not affect the performance of the modulator. The results of the simulation show that the design satisfies the requiment and the system works well.The circuits and layout are designed in TSMC 0.18μm CMOS technology. The power supply is 1.8V, and the sampling rate is over 15MS/s. With a 4.8828125MHz,0.5V input signal, the simulation results show 58dB SNR. The power of the whole modulator is 48mW. The results satisfy the design specs well.