A 9.8 GHz back-gate tuned VCO in 0.35 μ CMOS

A fully-integrated voltage controlled oscillator (VCO) has been one of the focal points of CMOS RF design activities in recent years. As potential applications extend to higher frequencies, CMOS VCO designs have pushed from ultra-high frequency (UHF) into super-high frequency (SHF). The requirement for fully-integrated VCOs to operate with low voltage, low power and low phase noise usually leads to the use of relatively large transistors in a process where the quality factor (Q) of the resonant tank is low. As the operating frequency further increases, the designs become more difficult due to the large parasitic capacitance and poor high-frequency performance of the transistors. This circuit demonstrates a technique which makes a transistor parasitic capacitance tunable through the use of its back-gate thereby reducing or eliminating the need for a varactor. In other words, the functionalities of transconductance (gm) and variable capacitance (Î"C) are realized in the MOS transistors at the same time by utilizing (where it is possible) all the four terminals of the transistors