Research Of Pipelined SAR ADC Based Zero Crossing Detector

With the rapid development of the semiconductor industry, mobile electronic products are becoming more and more common in our daily life. The development of electronic terminals such as wearable electronic products and smart phone imposed higher requirements on analog-to-digital converter(ADC). High speed, high accuracy and low power consumption is the main development trend of ADC. Mainly used in the field of high speed and high accuracy, Pipeline ADC have greater advantages, However, the traditional MDAC module of Pipeline ADC needs high bandwidth and high gain operational amplifier to realize, which possesses higher design difficulty, bigger power consumptionand and larger area. Nevertheless, SAR ADC has become the research hotspot of ADC gradually since the semiconductor technology is developing, the feature size is decreasing, the supply voltage is reducing. SAR ADC has advantage of area and power consumption, but it is difficult to achieve a higher level in speed and accuracy. Successive approximation-pipeline ADC(pipelined SAR ADC),a new hybrid structure of ADC absorbing the advantages of pipeline ADC and SAR ADC, has a good tradeoff in speed, accuracy, area and power consumption, has become a research hotspot nowadays. An important module of the pipelined ADC- the traditional MDAC circuit consists of an operational amplifier, which the design difficulty is high, the power consumption is big and area is large. According to the traditional structure, the article proposed MDAC circuit using zero crossing detector, which has the advantages of simple structure, low power consumption and small area, is a new implementation method of MDAC circuit.The basic principle and structure of SAR ADC and Pipeline ADC is introduced in the thesis, and a new type of Pipelined SAR ADC based on the advantages and disadvantages of these two kinds of ADC is proposed. At first, the structure and principle of Pipelined SAR ADC is analyzed, and the redundancy calibration algorithm is researched. Then the MDAC circuit is introduced. Starting from the MDAC circuit based on op-amp, according to the raditional structure, comparator based and zero crossing detector based structure are used to implement the MDAC circuit. The non ideal factors of Pipelined SAR ADC based on zero crossing detector are studied, and put forward the improvement method. Then the whole system of ADC is further optimized. In the thesis, the SMIC 1.8V 0.18 ?m CMOS process technology is used to design a 12 bits 50MS/s Pipelined SAR ADC based on zero crossing detector. The two level structure of 6+7 is used, and the redundancy calibration technique is adopted to obtain 12 bits. Use zero crossing detector instead of the traditional op-amp structure to achieve the MDAC circuit, effectively reducing the power consumption and area. In the MDAC charge transfer phase, the two-stage charge transfer technology is applied, it can effectively shorten the building time and improves the accuracy of the MDAC. A novel design method of high speed, high accuracy and low power consumption is created by combining Pipelined SAR ADC with MDAC based on zero crossing detector.The layout design of the whole Pipelined SAR ADC is given. On condition of the supply voltage is 1.8V and the sampling rate is 50MS/s, the SNDR is 66.53 d B, the SFDR is 78.95 d B, the ENOB is 10.76 bits and the power consumption is 5m W.