Common anode varactor tuned LC circuit
First Claim
1. A varactor tuning circuit comprising a pair of first and second varactor diodes having a common anode connection connected at a common node which is grounded for direct current (DC) and a shifting capacitor effectively connected to the cathodes of the first and second varactor diodes, wherein the resonant frequency of the tuning circuit is altered by the shifting capacitor and wherein the diodes change their capacitances or reactances in response to an applied voltage thereby effecting the functioning of a connected active circuit and wherein the diodes are effectively connected in parallel to the applied voltage.
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Accused Products
Abstract
A voltage controlled oscillator circuit in which the principal frequency determining circuit or tuning circuit comprises a pair of common anode varactor diodes. The circuit functions as a variable frequency oscillator controlled by an external DC control voltage, when utilized in conjunction with a parallel connected inductor and bypass or coupling capacitors to an oscillator circuit. This circuit has applicability as a basic building block or subcircuit for use in frequency synthesizer circuits, filter circuits, or the like, and which operate in baseband, I/F or R/F. The oscillator is a type which can be used in cellular or handheld telephones, both digital and analog, and in radio or communication equipment in general. The tuning circuit is symmetrical in form, and can isolate direct current (DC) paths of the tuning circuit from the alternating current (AC) or I/F or R/F current paths of the connected active circuit or drive circuit.
81 Citations
34 Claims
- 1. A varactor tuning circuit comprising a pair of first and second varactor diodes having a common anode connection connected at a common node which is grounded for direct current (DC) and a shifting capacitor effectively connected to the cathodes of the first and second varactor diodes, wherein the resonant frequency of the tuning circuit is altered by the shifting capacitor and wherein the diodes change their capacitances or reactances in response to an applied voltage thereby effecting the functioning of a connected active circuit and wherein the diodes are effectively connected in parallel to the applied voltage.
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19. A varactor tuning circuit including:
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a first varactor diode and second varactor diode having a common anode connection, the common anode connection connected to a direct current ground node;
a first input resistor connected to the cathode of the first varactor diode and a control voltage node;
a second input resistor connected to the cathode of the second varactor diode and the control voltage node;
a shifting capacitor effectively connected to the cathodes of the diodes;
a first coupling capacitor connected to the cathode of the first varactor diode; and
,a second coupling capacitor connected to the cathode of the second varactor diode. - View Dependent Claims (20)
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- 21. A varactor tuning circuit comprising two hyperabrupt varactor diodes connected in a common anode configuration and two coupling capacitors, each capacitor connected to a cathode of one of the varactor diodes and the active circuit, thereby direct current isolating the active circuit from the tuning circuit, and, wherein the small signal loading of the tuning circuit with respect to a ground node is approximately equal at each of the nodes connecting the active circuit to one of the two coupling capacitors.
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26. A oscillator drive circuit as claimed in clam 25, wherein the tuning circuit operates to provide an oscillating output signal in a frequency range in one or more of the baseband, I/F, or R/F, frequency ranges.
Specification