Quality Factor

The quality factor is now defined by $$\bbox[10px,border:1px solid grey]{Q_p = {R \over X_{L_{p}}} \appro { R_s || Q^2_l R_l \over X_L}}$$ Quite obviously, therefore, $R_s$ does have an impact on the quality factor of the network and the shape of the resonant curves.
If an ideal current source ($R_s = \infty Ω$) is employed, or if $R_s >> R_p$, $$Q_p \appro { R_s || Q^2_l R_l \over X_L} = {Q^2_l R_l \over X_L} = {Q^2_l \over X_L / R_l} = {Q^2_l \over Q_l}$$ and $$\bbox[10px,border:1px solid grey]{Q_p \appro Q_l} \,\, (Q_l \geq 10, Rs >> R_p)$$