On the Effects of Mismatch on Quadrature Accuracy in Tapped-Capacitor Load Independent Quadrature LC-Oscillators

This paper presents a study of quadrature phase error due to various systematic mismatches and loading effects on the oscillation frequency in a tapped-capacitor parallel coupled LC-tank oscillator. Vector based analysis is carried out to evaluate the general oscillating condition. Closed-form expressions for oscillation frequency and quadrature accuracy in the presence of loading are derived for the case of weak coupling. It is shown with rigorous analysis, for the first time, that the tapped-capacitor LC-tank oscillator exhibits oscillation frequency that is independent of loading conditions. The analysis clearly demonstrates that the effects of mismatch in tapped-capacitors on quadrature accuracy can be minimized by proper choice of coupling factor and shows that the error due to these tapped-capacitors is independent of the quality factor of the tank. Results from Spectre simulations are used to validate the analytical results.