4.02-5.48 GHz wideband VCO with coupling reduction and small Kvco variation. Issue 11 (1st November 2020) - Zou, Wei
ABSTRACT: A wideband voltage-controlled oscillator (VCO) with coupling reduction and small VCO gain ( K v c o ) variation has been fabricated for multi-standard RF transceivers. A high-quality factor 8-shaped inductor is adopted to reduce the magnetic coupling between inductors and optimise the phase noise of the VCO. Electromagnetic simulations of magnetic coupling are carried out between an octagonal inductor and an 8-shaped inductor, and as high as 36 dB reduction in magnetic coupling is achieved by using 8-shaped inductors. A novel varactor group is proposed to realise a constant K v c o in the fine-tuning process, in which the scheme adopts an inversion-mode MOS varactor to revise the capacitance variation of an accumulation-mode MOS varactor. Meanwhile, an extra 3-bit varactor array is employed to reduce K v c o variation in the coarse tuning process. Based on a conventional TSMC 0.18-μm CMOS process, a nearly constant K v c o of 58 MHz/V is obtained for a wide frequency range of 4.02 to 5.48 GHz. The proposed VCO achieves a phase noise of less than −119.8 dBc/Hz at 1 MHz offset. The current consumption is 4.3–8.8 mA under a source voltage of 1.8 V.