Technology Of Suppression For CMOS High-frequent Ring Oscillator

Oscillators has been used in analog circuit for various purposes,such as clockgenerator and voltage control oscillator, so there are different Structures desired foroscillator to meet different applications in actual circuit. as CMOS ring oscillator, LCresonator and crystal oscillator. for IC desire, we mostly select ring oscillator for itseasy controllability and high integration, but the most important reason is its low price.Compare with the other oscillators, the ring oscillator produce many harmonics for itstemperature characteristics of CMOS and process difference in production. we call itphase noise in oscillator,it means it’s quality factor is not very well.In digital circuits, phase noise is called clock jitters, it occurs at the edge of clocksignals, so it destroy the stability of the ring circuits. we can explain it in frequencydomain:except the desired frequency,there are oscillation at other frequencies, if theharmonics is too much, so the SNR of oscillation will drop, the rising edge and fallingedge of clock will be early or delay, the quality of phase modulation becomes worseand error rate could increases rapidly.Particularly for the communication circuit, it willmake the frequency spectrum of local oscillator becomes wider, the frequency domainof useful signals become wider after mixing with local oscillator.it may make thefrequency domain of noise and signal overlap, this results to the second mixing andmodulation, which cause serious consequences.In this paper, we explain the principle of ring oscillator and analysis the reason ofits phase noise, after that, we explain the phase noise in mathematic words, in order tofind the way to decrease the phase noise. According that, we can use the devices withlarger quality factor, or increase the signal power, reduce delay time of the bias PMOS,using coherent source and improve the structure of inverter to restrain the source ofphase noise in oscillator circuits. Then we the designed the actual circuits forsimulations, the results show that our designs of the ring oscillator can achieve thedesired aims: the phase noise of them are below-110dBc/Hz. And the frequency andpower parameters completely meet the practical goal.