Title :
Improved switched tuning of differential CMOS VCOs
Author_Institution :
Dept. of Electroscience, Lund Univ., Sweden
fDate :
5/1/2002 12:00:00 AM
Abstract :
Varactors for continuous frequency tuning are typically used in LC-oscillators. However, they have some drawbacks for large tuning ranges, such as high tuning sensitivity causing high sensitivity to noise and disturbances on the control voltage. Furthermore, large metal-oxide-semiconductor (MOS) varactors have high conversion of harmless amplitude noise into harmful phase noise. To reduce these problems a small varactor can be used in combination with MOS-transistors that switch fixed capacitors in and out of the oscillator. The limitations due to the imperfect complementary metal-oxide-semiconductor (CMOS) switches are investigated, and an improved structure for use with the popular differential CMOS LC-oscillator is presented.
Keywords :
CMOS analogue integrated circuits; UHF integrated circuits; UHF oscillators; circuit tuning; integrated circuit layout; switched capacitor networks; varactors; voltage-controlled oscillators; MOS-transistors; RF CMOS; differential CMOS LC-oscillator; differential CMOS VCOs; fixed capacitor switching; frequency tuning; imperfect CMOS switches; improved switched tuning; layout aspects; small varactor; Capacitors; Circuit optimization; Frequency; Parasitic capacitance; Phase noise; Switches; Tuning; Varactors; Voltage control; Voltage-controlled oscillators;
Journal_Title :
Circuits and Systems II: Analog and Digital Signal Processing, IEEE Transactions on
DOI :
10.1109/TCSII.2002.801415
