Oscillators – Plural oscillators
Reexamination Certificate
2002-12-02
2003-11-18
Callahan, Timothy P. (Department: 2816)
Oscillators
Plural oscillators
C331S11700R, C331S143000, C331S057000
Reexamination Certificate
active
06650188
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to control of phase shift for a voltage controlled oscillator.
BACKGROUND OF THE INVENTION
A conventional approach of an LC-based ring oscillator uses three LC stages, with a phase shift sum for the three stages being 180°, as required to support an oscillation. Use of three stages is necessary with a conventional approach, because any stage provides a phase shift of less than 90°, except at certain extreme or unrealistic choices of parameter values. In the simplest three-stage oscillator, each stage provides 60° of phase shift. This arrangement is not suitable for applications that require in-phase and quadrature clock signals that are spaced 90° apart.
Some workers have attempted to handle this problem by providing two couplers and two identical LC-based voltage controlled oscillators (VCOs) to form a coupling loop. The couplers modulate the phases of the LC tank circuits and force the two clock signals to run in quadrature, with a relative phase shift of 90°. However, this arrangement operates at a frequency that is relatively far from the peak LC tank impedance so that the oscillator is less efficient than desired. This arrangement becomes less attractive as the clock frequency increases, because the couplers increase the capacitive load of the oscillator. This lowers the central frequency and/or reduces the frequency tuning range.
What is needed is a configuration that improves the efficiency of the, oscillator and increases the center frequency and/or frequency tuning range.
SUMMARY OF THE INVENTION
The invention meets these needs by incorporating a selected signal buffer in each stage of the coupling loop so that the buffer and an associated VCO maintain 90° phase shift within each stage. The additional phase shift introduced by each buffer, helps move the operating point of the oscillator toward the peak impedance point of the LC tank circuit, thus improving the efficiency of the oscillator. The capacitive loading of each oscillator stage is reduced, because the coupler in each stage is only required to drive a signal buffer, not a combination of buffer and in-path coupler. This provides an increase in center frequency or frequency tuning range.
REFERENCES:
patent: 5357217 (1994-10-01), Marchesi et al.
patent: 5418497 (1995-05-01), Martin
patent: 5561399 (1996-10-01), Haartsen
patent: 5592126 (1997-01-01), Boudewijns et al.
patent: 5789986 (1998-08-01), Drost et al.
patent: 5850163 (1998-12-01), Drost et al.
patent: 6218908 (2001-04-01), Oberhammer
patent: 6232844 (2001-05-01), Talaga, Jr.
patent: 6317008 (2001-11-01), Gabara
patent: 6323737 (2001-11-01), Broekaert
patent: 6417740 (2002-07-01), Anh et al.
Ting-Ping Liu, “A 6.5GHz Monolithic CMOS Voltage-Controlled Oscillator”, IEEE International Solid-State Circuits Conference, ISSCC99/Session 23/Paper WP 23.7, pp. 404-405.
Jafar Savoj, et al., “A 10Gb/s CMOS Clock and Data Recovery Circuit with Frequency Detection”, 2001 IEEE International Solid-State Circuits Conference, ISSCC 2001, Session 5/Gigabit Optical Communications I/5.3, pp. 78-79.
Chan Edwin
Qu Ming
Zhao Ji
Callahan Timothy P.
Cox Cassandra
Lattice Semiconductor Corporation
LandOfFree
Coupling for LC-based VCO does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Coupling for LC-based VCO, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Coupling for LC-based VCO will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3167598