Analysis of phase noise in CMOS injection-coupled LC quadrature oscillator (IC-QO) using LTV model

Nowadays, many researches and studies have been performed to improve the performances of wireless communication systems. The phase noise is very important aspect of oscillator design. It is defined as phase noise spectral density due to voltage or current spectrum at an offset from center frequency of an oscillator related to the total power of oscillators. On the other hand, the performance of wireless communication system depends on the phase noise of a quadrature oscillator. This paper presents the study of phase noise of source injection coupled quadrature oscillators (IC-QOs) in the perspective of the LTV model and proposes analysis base on the Impulse Sensitivity Function (ISF), superposition integration which is linked to the IC-QO’s system as linearity and also phase modulation and not time invariance. Based on the represented equations, the output of IC-QO is a function of injection current and the current of source equivalent capacitor and also bias current. The derived equations show that phase noise with considering the certain portion of frequency spectrum like 1/f3 region can be improved by the adjusting tail current and controlling the drain currents of switching pairs which go through the LC tanks. To evaluate the study of proposed idea, an IC-QO with 5 GHz oscillation frequency using TSMC 0.18μm CMOS technology was implemented. A parametric sweep for considered current has been done and the results show the improvement in phase noise performance by controlling this current. All the presented simulations confirm the theoretical concepts.