Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – Utilizing two electrode solid-state device
Reexamination Certificate
1999-09-16
2001-05-01
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
Utilizing two electrode solid-state device
C327S308000
Reexamination Certificate
active
06225861
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an improvement of the circuit construction of a variable capacitance circuit suitable for use in an antenna input circuit of a radio receiver for reducing cross modulation and mutual modulation, a frequency modulator having low high harmonic wave distortion, or a variable phase shifter.
DESCRIPTION OF THE PRIOR ART
A continuous variable attenuator comprising PIN diodes and etc. as a conventional variable attenuator is developed. This utilizes that its input resistance varies greatly but since it is utilized therein that its input resistance varies exponentially, the inner resistance depends on a voltage or a current and is non-linear with respect to an input signal. Accordingly, an applicable amplitude of an input signal to that attenuator is limited to very small range.
So, the inventor provided a variable attenuator including a variable capacitance diode to which an input signal having more large amplitude is applicable in Japanese Patent Application No. 10-253297. Since said diode is used with backward bias polarity in this variable attenuator, applicable amplitude of the input signal to it can be made more large. However, in this case, its capacitance depends on a voltage and thus said attenuator only utilizes characteristic of said element (diode) as it is.
SUMMARY OF THE INVENTION
In view of such present situation, an object of the invention is to provide a variable capacitance circuit comprising variable capacitance diodes applicable to a variable attenuator and etc. so constructed that characteristic of the variable capacitance diode in the vicinity of an operating point can be corrected.
In order to attain the object, a first variable capacitance circuit according to the invention is characterized by employment of at least two variable capacitance diodes, means for applying an input signal to each of said diodes with backward polarity and means for applying a capacitance control voltage to each of said diodes with same polarity.
Further a second capacitance circuit according to the invention is characterized by employment of a first variable capacitance circuit comprising at least two variable capacitance diodes, a second variable capacitance circuit comprising at least two variable capacitance diodes and connected in parallel with an out of the first variable capacitance circuit, means for applying an input signal to each of the variable capacitance diodes of said first variable capacitance diode with backward polarity and means for applying a capacitance control voltage to each of the variable capacitance diodes of said first and second variable capacitance circuits with same polarity.
As previously described, a conventional variable attenuator is constructed so as to make use of characteristic of a variable capacitance diode as it is. However, dependability of capacitance on an applied input voltage can be greatly improved by using two variable capacitance diodes as attenuating elements with backward A.C. polarity because their operating points on exponential characteristics are the same with each other and an input high frequency signal is applied to them with backward polarity.
This improved situation will be explained by referring to
FIGS. 1 and 2
.
FIG. 1
shows an example of capacitance variation characteristic of a variable capacitance diode. FIG.
2
(
a
) shows an example of capacitance variation characteristic of two variable diodes connected with backward A.C. polarity to which a capacitance control voltage of 2 volts is applied. In this case, since an input signal is applied to said diodes with backward polarity with each other, the capacitance variation characteristic shown in the dotted line becomes addition of two characteristics corresponding to each of said diodes as shown in the solid lines.
FIG.
2
(
b
) shows the capacitance variation characteristic wherein the capacitance control voltage is 6 volts.
These figures show that the composed capacitance variation characteristic of said two diodes shown in the dotted line in
FIG. 2
has almost never voltage dependability. Accordingly, an input signal having large amplitude can be applied to said two variable capacitance diodes to control capacitance thereof effectively.
REFERENCES:
patent: 3391347 (1968-07-01), Bosse et al.
patent: 4021740 (1977-05-01), Horna
patent: 4195274 (1980-03-01), Suganuma
patent: 4701714 (1987-10-01), Agoston
patent: 5327017 (1994-07-01), Fischer et al.
patent: 5378937 (1995-01-01), Heidemann et al.
patent: 5378939 (1995-01-01), Marsland et al.
patent: 5990761 (1999-11-01), Hamparian et al.
patent: 6011432 (2000-01-01), Fratti et al.
Cunningham Terry D.
Flynn ,Thiel, Boutell & Tanis, P.C.
General Resaerch of Electronics, Inc.
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