Design of Wide Tuning-Range CMOS VCOs Using Switched Coupled-Inductors

• Published in: IEEE journal of solid-state circuits Vol. 43; no. 5; pp. 1156 - 1163
• Main Authors: Demirkan, M., Bruss, S.P., Spencer, R.R.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: New York, NY IEEE 01.05.2008; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Applied sciences; Circuit properties; Circuits; CMOS; CMOS process; Design. Technologies. Operation analysis. Testing; Digital; Electric, optical and optoelectronic circuits; Electronic circuits; Electronics; Exact sciences and technology; Frequency measurement; Inductors; Integrated circuits; Integrated transformers; Magnetic devices; Mutual coupling; Noise; Noise measurement; Oscillators, resonators, synthetizers; Phase measurement; Phase noise; radio-frequency (RF) CMOS; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Simulation; Studies; switched coupled inductor; Testing; Testing, measurement, noise and reliability; Tuning; tuning range; voltage-controlled oscillator (VCO); Voltage-controlled oscillators; Phase noise; Electric transformer; Mutual coupling; Die; Voltage controlled oscillator; tuning range; Radiofrequency; Inductor; Integrated transformers; radio-frequency (RF) CMOS; Switching; Operating rate; Complementary MOS technology; switched coupled inductor; Testing equipment; Radiofrequency integrated circuits; CMOS integrated circuits; voltage-controlled oscillator (VCO); Figure of merit
• ISSN: 0018-9200; 1558-173X
• DOI: 10.1109/JSSC.2008.920346

Two designs of voltage-controlled oscillators (VCOs) with mutually coupled and switched inductors are presented in this paper to demonstrate that the tuning range of an LC VCO can be improved with only a small increase in phase noise and die area in a standard digital CMOS process. Particular attention is given to the layout of the inductors to maintain Q across the tuning range. In addition, different capacitive coarse-tuning methods are compared based on simulated and measured data obtained from test structures. Implemented in a 90 nm digital CMOS process, a VCO with two extra coupled inductors achieves a 61.9% tuning range with an 11.75 GHz center frequency while dissipating 7.7 mW from a 1.2 V supply. This VCO has a measured phase noise of -106 dBc/Hz at 1 MHz offset from the center frequency resulting in a higher figure-of-merit than other recently published VCOs with similar operating frequencies. In addition, the area overhead is only 30% compared to a conventional LC VCO with a single inductor.