A miniature and low‐power 24 GHz CMOS VCO using tunable lc source‐degeneration and transformer feedback techniques for automotive radars

A 24 GHz voltage‐controlled oscillator (VCO) using tunable LC source‐degeneration and transformer‐feedback techniques for automotive radar systems is demonstrated in a standard 0.18 μm CMOS process. The tunable LC source‐degeneration is made by adding two tunable LC tanks, which use varactors as the needed capacitors, to the source terminals of the cross‐coupled transistor pair of the VCO. Compared with the traditional cross‐coupled transistor pair, the equivalent parallel capacitance (C EQ ) can be significantly decreased. This in turn results in the increase of both the operation frequency and the tuning range of the VCO. In addition, a differential‐to‐differential spiral‐transformer‐shaped layout is adopted to realize the needed four inductors, that is, the two drain inductors and the two source inductors. This in turn results in the layout area and the power consumption of the VCO is minimized. The VCO core draws 7.2 mA current from a 0.85 V power supply, that is, it only consumes 6.12 mW. The VCO achieves a wide tuning range of 3.03 GHz, from 22.32 to 25.35 GHz. In addition, the VCO achieves a phase noise of −103 dBc/Hz at 1 MHz offset from 24 GHz. The corresponding figure‐of‐merit is −182.7 dBc/Hz, one of the best results ever reported for a K‐band CMOS VCO. The core circuit occupies a chip area of only 0.36 × 0.56 mm 2 , that is, 0.202 mm 2 . © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2553–2558, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27143