An inductively Gm enhanced 34-GHz VCO with gain linearization and switched transformer tuning

This paper presents a G_m-enhanced low power high-frequency voltage-controlled oscillator (VCO). Transconductance enhancement by a factor of 3 is achieved by means of modified cross-coupled pair with coupled inductors. Low flicker noise corner is obtained using a varactor linearization technique. Furthermore, a switched-transformer method is used to extend the tuning range. Output loading is decoupled from the tank by tapping the output at the gate of cross-coupled pair, thus improving the phase noise performance and achieving a higher output power. A proof-of-concept prototype VCO is implemented in a 65-nm CMOS process. The chip occupies only 285 × 130 μm². The VCO draws 2.6 mA from a 1 V supply and achieves a linear tuning range of over 110 MHz centered at 34.55 GHz. The measured phase noise of the VCO over its tuning range is from -91 to -94.7 dBc/Hz (1 MHz offset) which results in a figure-of-merit (FoM) of -181 to -177 dBc/Hz.