Multiple Coupled Quadrature Oscillator with Desirable Phase Shift to improve phase noise

In this paper, a Multiple Coupled CMOS LC Quadrature Oscillator (MC-QO) in order to generate quadrature signals with a favorable phase noise and low power consumption is presented. In this work, the core of oscillator is coupled by the different passive and active coupling techniques in each stage. The active dynamic current-clipping technique is applied in the active coupling network, which can provides phase shift alone and results into the phase error and phase noise corrections of output signal. However, the passive coupling technique is also used in order to increase the corrections further. The passive coupling network consists of one RLC filter that besides the inherent reduction of noise, it provides compensating phase for reducing the resonator phase shift (RPS) in order to improve phase noise, which is proven by the analysis results. Using two coupling paths has a big contribution for increasing the coupling factor’s value, which leads to the improvement of output’s phase accuracy. Meanwhile, the passive coupling network does not dissipate additional power.  Moreover, the applied tail current-shaping technique in the source of tail current causes the improvement of circuit’s performance. To confirm the validity of the proposed quadrature oscillator’s performance and the presented analysis, the MC-QO is simulated in TSMC 0.18RF-CMOS technology at 3.38 GHz fundamental frequency. The power consumption is 4.6 mW from 1.8 V power supply, the phase noise is -128.2 (dBc/Hz) @ 1MHz and -138.5 (dBc/Hz) @ 3 MHz offset frequencies with the quality factor (Q10.8). Eventually, the excellent Figure of Merit (FOM) of -192.25 (dBc/HZ) at 1 MHz offset frequency is achieved.