Comparative Analysis of Ring Oscillators Based on Different Feedback Paths

By analyzing the interpolation linearity and accuracy of the output phase and phase interpolation clock data recovery circuit of the VCO, this paper aims to design a ring oscillator that can provide 12 Phase clock signal for Phase Select/ phase Interpolator-Clock and Data Recovery circuit (PS/PI-CDR), the frequency range of 50MHz ~ 4GHz. The parameters of two different feedback paths were compared and analyzed at 28nm process, and the phase noise of the two structures was analyzed using the pulse sensitivity function of the Hajimiri model, and a better topology was finally selected. In addition, in the delay unit, the starting vibration auxiliary device is added, which can make the oscillator be used with the start, and greatly reduce the starting vibration time. The simulation results show that the frequency adjustment range of the feedback ring oscillator is 0.05GHz ~4.29GHz, and the phase noise is -82.97dBc/GHz(@1MHz) when the frequency is 2.5GHz. At the same frequency and power budget, it is about 3dB lower than the feedforward ring oscillator.