Oscillators – Amplitude control or stabilization – Automatic
Reexamination Certificate
2003-04-22
2004-11-02
Mis, David (Department: 2817)
Oscillators
Amplitude control or stabilization
Automatic
C331S109000, C331S1170FE, C331S173000
Reexamination Certificate
active
06812802
ABSTRACT:
FIELD OF THE INVENTION
This invention relates in general to wireless communication systems and equipment, and more specifically to a method and apparatus for controlling a voltage controlled oscillator for use therein.
BACKGROUND OF THE INVENTION
It is desirable for a voltage controlled oscillator (VCO) used in a portable communication device to meet various conflicting requirements. Such requirements include, for example, low phase noise in order to satisfy sideband noise requirements, and fast start-up of the VCO when leaving a battery-saving mode as well as when switching to a different frequency band, in order to avoid delaying the start of a communication. In prior-art VCOs operating in open loop, guaranteeing startup has implied using a high gain in the VCO amplifier. This high gain in the VCO amplifier in turn has produced a large output swing. Although a large output swing may satisfy the phase noise specifications, it results in wasted power, which is unacceptable for portable communications equipment. A low-gain in the VCO amplifier implies better spectral purity (and fewer harmonics) since the VCO amplifier does not saturate or “clip” the output signal. However, with low gain, start-up may not be guaranteed. Thus, a trade-off or compromise has had to be made between the start-up requirement and the phase noise (or output amplitude). Some prior-art VCOs have used a “medium” gain, e.g., a small-signal total loop gain of two or three, as a compromise. Unfortunately, the compromise has not produced very satisfactory results in terms of either start-up speed or phase noise.
Thus, what is needed is a method and apparatus for controlling a VCO that decouples the relationship between guaranteed start-up and phase noise, and achieves reduced phase noise and a fast start-up, independently. The method and apparatus preferably will lend itself to fabrication as a low-power CMOS integrated circuit.
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Mihai A. Margarit, Joo Leong (Julian) Tham, Robert G. Meyer, and M. Jamal Deen, “A Low-Noise, Low-Power VCO with Automatic Amplitude Control for Wireless Application”, IEEE Journal of Solid-State Circuits, vol. 34 No. 6, Jun. 1999; pp. 761-771.
Godambe Nihal
Kehler Walt
Bethards Charles W.
Freescale Semiconductor Inc.
Mis David
Posz & Bethards, PLC
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