Varactors for Integrated RF Circuits in a 130 nm BiCMOS Technology

This paper addresses the optimization of accumulation-mode MOS-type (A-MOS) varactors in a 130 nm BiCMOS technology for applications in voltage-controlled oscillators (VCOs). By optimizing the varactor well doping profile, the tuning gain of the varactor decreased from ~ 3 fF/V•μm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> to less than 2 fF/V•μm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, while the linear voltage range of the C-V curve increased from 0.8 V to 1.8 V maintaining an overall tuning range larger than 3. The impact of the varactor optimization on VCO performance was studied through circuit simulations, demonstrating a reduction of the phase noise at 32.8 GHz carrier frequency and 1 MHz offset by 4 dB/Hz.