Loral Microwave-FSI (Chelmsford, MA) has issued an application note on frequency-linear tuning varactors (FLTVARs), or varactor diodes. FLTVARs' Q is optimised via a restriction on the epitaxial-region thickness. The capacitance will cease varying as a function of voltage at the punchthrough voltage. Q and tuning range are thus in a design trade-off. GaAs diodes are affected by upconversion of surface noise because of the lack of GaAs passivation. Thermal-oxide-passivated silicon is thus better for wideband or high-power VCOs if FM noise is a worry. Article discusses FLTVARs in further detail.