Wave transmission lines and networks – Coupling networks – Frequency domain filters utilizing only lumped parameters
Reexamination Certificate
2001-03-19
2003-04-15
Ham, Seungsook (Department: 2817)
Wave transmission lines and networks
Coupling networks
Frequency domain filters utilizing only lumped parameters
C334S056000
Reexamination Certificate
active
06549096
ABSTRACT:
TECHNICAL FIELD
The present invention relates, in general, to electronic components and circuits for selecting signals having specific frequencies and signals within frequency bands and, in particular, to a variable inductor and associated circuitry for frequency and frequency band selection.
BACKGROUND OF THE INVENTION
Many mixed signal and radio frequency applications require variable reactive elements (e.g., inductors or capacitors) to achieve tuning, band switching, phase locked loop functions, etc. Such reactive elements are used in some type of circuit where the reactive element is resonated with another reactive element. The desired result is a resonant circuit that has a response that can be tuned from one frequency to another dynamically.
Typically, this is accomplished using a varactor to provide a variable capacitance that is resonated with a fixed inductor. One problem with using a varactor that is integrated in a typical silicon process is that the tuning range is limited, particularly for “free” varactors that use the standard BiCMOS diodes or FETs as the variable capacitance element. The tuning range typically is less than 2:1.
Varactors implemented with special processing steps to optimize the tuning range and/or the quality factor Q will cause the overall processing cost and turn around time to increase. When a large change in frequency is desired for a varactor that does not have the desired tuning range, a bank of capacitors might be used that can be switched in and out of the circuit selectively to provide a range of discrete capacitance values. A varactor is placed in parallel with this “discrete variable” capacitor to provide a smooth variation of capacitance around the larger steps provided by the switched bank. This is shown in FIG.
1
.
Referring to
FIG. 1
, a varactor
10
is connected in parallel with a resonating inductor
12
. A bank of capacitors
14
and series connected switches
16
is connected in parallel with varactor
10
and resonating inductor
12
. Operation of switches
16
is controlled by a controller
18
from which control signals are supplied to selectively open and close the switches and thereby change the tuning of the circuit as capacitors
14
are switched into or out of the circuit. Controller
18
receives input signals along input lines
20
that define which of the capacitors
14
are to be switched into the circuit or switched out of the circuit.
A major disadvantage of a circuit, such as the one illustrated in
FIG. 1
, is that the effective “smooth” tuning range of the combined discrete capacitor/varactor structure is inversely proportional to the amount of fixed capacitance in parallel with the varactor. Therefore, if a large discrete capacitor is placed in parallel with a comparatively small varactor, the overall smooth tuning range of the combined structure will be significantly reduced. This means that more bits of resolution are required from the “discretely variable” capacitor bank to compensate for the lost smooth variation provided by the varactor that is placed in parallel. This increased resolution takes up valuable chip area resulting in increased cost.
Another disadvantage is that the capacitance of the discrete capacitor bank might have a strong dependence on process variation, causing a large statistical variation in the capacitance.
Finally, the quality factor Q of capacitors with sufficient capacitance per unit area to be used in a practical manner in a capacitor bank is usually lower than desired. These capacitors are typically MOS devices with severe limitations on the quality factor Q due to series resistance through the device well.
SUMMARY OF THE INVENTION
To overcome the shortcomings of prior art integrated inductors and prior art inductor/varactor tuning circuits, a new and improved integrated inductor and a new and improved inductor/varactor tuning circuit are provided by the present invention.
It is an objective of the present invention to provide a new and improved variable integrated inductor.
It is another objective of the present invention to provide a new and improved inductor/varactor tuning circuit.
A variable integrated inductor, constructed in accordance with the present invention, includes an inductor, a single loop winding positioned in proximity to the inductor and having an open circuit, and means for selectively closing the open circuit of the single loop winding to magnetically couple the single loop winding to the inductor and decrease the magnetic field of the inductor. A switched inductor/varactor tuning circuit, constructed in accordance with the present invention, includes this variable integrated inductor connected with a varactor.
It is to be understood that the foregoing general description of the present invention and the following detailed description of the present invention are exemplary, but are not restrictive of the invention.
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Groves Robert A.
Jadus Dale K.
Abate Joseph P.
Ham Seungsook
International Business Machines - Corporation
Ratner & Prestia
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