Oscillators – Solid state active element oscillator – Transistors
Reexamination Certificate
1998-11-20
2001-07-31
Pascal, Robert (Department: 2817)
Oscillators
Solid state active element oscillator
Transistors
C331S109000, C331S183000
Reexamination Certificate
active
06268777
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to radio frequency communication and more particularly, to voltage controlled oscillators (VCOs) used in radio frequency signal transmission systems.
2. Description of Related Art
Voltage controlled oscillators (VCOs) are a common component in most communications circuits. VCOs typically utilize a variable control voltage input to produce a frequency output. The control voltage input typically may be tuned so that the VCO produces a desired, operational frequency output. Examples of VCOs and the manners in which they are tuned may be found in U.S. Pat. Nos. 5,663,690 and 5,764,109. As these patents show, a typical inductor and capacitor tuned VCO generally requires a number of off-chip components including inductors, capacitors, resistors and varactors. Using off-chip components rather than an integrated circuit (IC) requires more space, increases the power requirements, and adds significantly to the cost of a radio frequency communication system. One problem with known VCOs is that there are few, if any, integrated circuit VCOs that can provide a desired differential output, which is necessary for high performance transceivers, and that can maintain a fixed frequency over all process and environmental variations. Further, there are few, if any, integrated circuit VCOs that can adjust the amplitude of the VCO to optimize power consumption and optimize spectral purity, features that are key to battery operated wireless communication devices.
As such, there is a need for a VCO that can be fabricated with CMOS technology to reduce the cost and space required for typical VCOs. Further, there is a need for an integrated circuit VCO that can provide a differential output, maintain a fixed frequency, and adjust the amplitude for optimum power and optimum spectral purity.
SUMMARY OF THE INVENTION
The needs described above are in large measure met by a voltage controlled oscillator (VCO) of the present invention. The VCO generally includes an energy storage circuit portion, an oscillator operably connected to the energy storage circuit portion, a varactor connected to the oscillator and energy storage circuit portion, and an amplitude controller that is operably connected to the energy storage circuit portion, oscillator, and varactor. The energy storage circuit portion includes an inductance and a capacitance. The oscillator provides an oscillating output signal having a frequency and an amplitude. The varactor has a varying capacitance and receives an input signal having a varying level. The capacitance of the varactor varies according to the level of the input signal. The amplitude controller sets the amplitude of the oscillating output signal. Meanwhile, the inductance of the energy storage portion, the capacitance of the energy storage portion, and the varying capacitance of the varactor are used to set the frequency of the oscillating output signal. The VCO of the present invention is preferably fabricated entirely on a single integrated circuit chip utilizing low-cost CMOS technology.
The present invention further comprises a method of adjusting the frequency and amplitude of an oscillating output signal. The steps of the method include: (1) receiving a varying input signal having a varying level; (2) varying a capacitance of a varactor according to the varying level of the input signal; (3) adjusting the operating frequency of an oscillator according to the capacitance of the varactor; (4) providing current conduction for amplitude control upon an energy storage portion reaching or exceeding a peak level; (5) continuing to provide current conduction to stabilize the amplitude of the oscillating output signal; and (6) adjusting the current to achieve a desired amplitude after the amplitude of the oscillating output signal has stabilized.
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S Burns, P Bond “ Principles of Electroninc circuits” 1987 pp. 710 and 711.
Applied Micro Circuits Corporation
Cary Gary
Glenn Kimberly E
Pascal Robert
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