Compact wideband LC VCO with active inductor harmonic filtering technique

This article presents an active inductor harmonic filtering technique that improves the phase noise of the wideband LC voltage controlled oscillator (VCO). A Wu folded active inductor structure was chosen to design a wideband filtering device that consists of a single NMOS transistor and a resistor. Using an active inductor can reduce chip area by 37.68% while performing wideband harmonic filtering compared to existing LC filtering techniques. The chip was fabricated in 130 nm CMOS technology. The measured phase noise of the VCO is -119.21 dBc/Hz at a 1 MHz offset frequency at the 4.28 GHz carrier. The VCO is activated by a 3-bit digitally controlled switched capacitor array to achieve a 39% wideband tuning range from 3.8 to 5.6 GHz. A current of 4.2 mA flows continuously for the whole frequency from a 1.2 V supply voltage.