Utilization of Multi-Resonant Defected Ground Structure Resonators in the Oscillator Feedback for Phase Noise Reduction of K-Band VCOs in 0.18-$\mu$ m CMOS Technology
Nusrat Jahan, Baichuan Chen, Adel Barakat, Ramesh K. Pokharel
Abstract
This work proposes a new theory to reduce the phase noise of K-band Voltage-Controlled Oscillators (VCOs) in Complementary Metal Oxide Semiconductor (CMOS) process by introducing one or more transmission poles around the parallel resonance of an LC-tank circuit. Introduction of transmission poles beside the parallel resonance of the LC-tank circuit sharpens the skirt characteristics of the Scattering (|S|) parameters of the resonators. In return, sharp |S|-parameters slope enhances the resonator loaded quality (Q) factor without compromising the unloaded Q-factor. In addition, the transmission pole can be realized near the second harmonic of the oscillation. This allocation of the transmission pole leads to the cancellation of this second harmonic and a further reduction of the phase noise. The proposed theory is verified by three different designs based on defected ground structure (DGS) resonators. These designs realized a low-band transmission pole before the parallel resonance, a high-band transmission pole after the parallel resonance, and dual-band transmission poles around the parallel resonance. First, each design is verified and compared to the others using circuit and electromagnetic simulations to establish the Q-factor improvement. Then, each of the resonators is utilized in a differential VCO topology and the phase noise reduction in post-layout simulations is confirmed. Finally, two chips are fabricated in 0.18-μm CMOS technology and measured. The measurement results are in good agreement with the simulations, which confirm our claim about the proposed theory.