Design and Noise Analysis of Coupled Ring Oscillators

Abstract

This dissertation analyzes the phase noise in standard differential ring oscillator due to various noise sources by using a simple physical model. Employing the open loop noise analysis, the oscillator’s output noise at the frequency around fundamental and odd harmonics of oscillation frequency contributes to PM induced phase noise while the output noise around DC and even order harmonics is attenuated by the shaping function but can produce frequency modulated noise through the switching nonlinearities. Through the proposed theory, a common source coupled differential ring oscillator is analyzed that improves the phase noise by increased output slew rate, reduced noise at tail current source and coupling with phase shift. The proposed architecture can generate more output phases while maintaining the same oscillation frequency compared to its single ring oscillator counterpart. A 1.1-GHz oscillator with the phase noise of -110 dBc/Hz at 1 MHz is demonstrated, dissipating 5 mW of power per ring. Further, the application of coupled ring oscillator is illustrated in details with an embodiment of injection-locking PLL.