Research And Design Of Ring Oscillator With Process And Temperature Compensation

Since the day of its advent,oscillators have found extensive applications,and the scope has ever beenexpanding.With the progress of science and technology and changes in people's lifestyles,new applicationscall for ever higher performance out of oscillators.This pursuit led scholars and circuit designers all over the world to having never stopped putting their efforts into this research field-because if there are some advantages in an oscillator,there must be some problems with it,and it has proven difficult,if not impossible,to have all the advantages without any drawbacks.To be specific,an LC oscillator outputs relatively stable frequency,which is desirable in mostapplications,but it takes up considerable area in a chip and dissipates a lot of power(operation current up to dozens of Ampere,for example)at the same time;crystal oscillator could provide almost ideal frequency,but it cannot be integrated into the chip with standard CMOS technology.Therefore,it is usually set up out of chip,which inevitably increases area of the whole system.Even though,circuit designers have tried out and succeeded in putting crystal oscillators into chips with MEMS process technology,but owing to its manufacturing cost,this way of providing oscillation has not become the first choice for customers.Based on these very facts,a low cost,fully integrated oscillator that consumes low power and outputs stable frequency has always been the research direction and objective of many circuit designers.Based on the above considerations,this thesis attempts to design an oscillator with temperature andprocess compensation out of the simple cascaded CMOS inverters.In the design process,three key jobs has been done:(1)the frequency characteristic and voltage control characteristic of the ring oscillator has been studied.The frequency characteristic of the ring oscillator describes how the output frequency changes with temperature and how random process deviation affects it,and this frequency characteristic is obtained with the control voltage(that is,the power supply voltage of the ring oscillator)kept constant.On the other hand,voltage control characteristic means in what pattern the control voltage should change when output frequency remains unchanged,which is somewhat different with conventional definition.In the latter aspect,the ring oscillator is treated as a voltage-controlled oscillator.(2)The effects of temperature and process deviation on key parameters of MOS devices are analyzed,also discussed are those effects on BJT(bipolar junction transistor)emitter junction voltage under the condition of stable collector current.These effects constitute the groundwork of the bias circuit that generates compensation voltages;(3)Compensation voltages are linearly combined to form the control voltage of the ring oscillator,and the combination coefficients are calculated by least squares method.The control voltage formed in this way proves close to the voltage control characteristic defined in(2)to a great extent,thus,temperature and process compensation of the ring oscillator has finally been accomplished.The achievement of this thesis-a ring oscillator with temperature and process compensation,are schematic-and-layout designed based on SMIC 0.18?m mixed-signal CMOS technology library,and are simulated and verified by Cadence software.A maximum frequency deviation of 1.5%(pre-layout simulation result,related to center frequency of 315/32=9.84375MHz)and 1.7%(post-layout simulation result)is achieved across different process corners interweaved with the temperature range of-20? to 80?;and in the corner of tt(typical typical)particularly,the frequency deviation is merely 3 ‰.When it comes to power dissipation,this compensated ring oscillator operates at current of 520?A(at room temperature and tt corner).