Analysis of phase accuracy in CMOS quadrature LC oscillators

Using an analytical approach, new estimation of phase error in LC-Tank quadrature oscillators is proposed. The mismatches between passive components of LC tanks are considered as the reasons of the phase error. Closed form equations relating LC mismatches to phase errors are presented. Decreasing quality factor (Q) and increasing coupling factor (k) causes phase error be less sensitive to mismatches in LC tanks. On the other hand phase noise is inversely proportional to quality factor (Q), and directly proportional to coupling factor (k), so there is a tradeoff between phase noise and phase error. To evaluate the analysis, a 5 GHz quadrature LC-Tank oscillator is simulated using TSMC 0.18 μm model technology. The results confirm the simplicity and high accuracy of the proposed analysis.

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