Research Of High Speed And Low Power Comparator

With the development of electronic and communication technology, today’s mixed signals integrated circuit design has mainly concentrated in the direction of the system on chip (SoC). Mixed signal SoC, which has been applied widely in the wireless communications, digital communication and mobile chips, is mainly including analog circuit modules, digital circuit modules and memory, etc. In the mixed signals SoC, some circuit modules are processing analog signals; at the same time, there are also some modules are dealing with some digital signals. Therefore, ADC is the key circuit of SoC to convert the analog data into digital data. Recently, ADC has become the focus design of SoC.According to different conversion period, ADC can be divided into high speed ADC, middle speed and low speed ADC. In fact, there are a lot of different structures of ADC, such as Flash ADC, Pipeline ADC and SAR ADC, etc. Comparator is the necessary module in any ADC. In addition, in the design of ADC, comparator is the most important module whose performance parameters directly affect the ADC. The main performance parameters are speed, precision, power dissipation, offset voltage and operating voltage, etc. What’s more, the requirements and index of comparator are different in different kinds of ADC. For example, the characteristic of comparator in SAR ADC is high precision, not high speed; Flash ADC requires its comparator with high speed, low power consumption, etc.This paper is mainly aimed at the high speed and low power consumption comparator in Flash ADC. The main modules of comparator are preamplifier, latch comparator and output stage. To meet the design requirements, this paper puts forward two comparator design methods. And it shows that the simulation results of schematic and layout to verify the design.Based on TSMC0.18um process, this work has completed the design of comparator which can be used in high speed Flash ADC. In the process of comparator design, the key modules of comparator are analyzed and optimized to realize the requirements. The simulation results of comparator show that it can work for1GHZ clock and its power dissipation is only1mW with1.8V power supply voltage. What’s more, the transmission delay of the comparator is only85.5ps and the offset voltage is about1.8mV, which has met the design index.