Apparatus and resonant circuit employing a varactor diode in parallel with a transmission line and method thereof
AssigneeFreescale Semiconductor, Inc.
InventorsKong S. Luen, Philip Huang, Robert Masucci
Life of this patent
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Abstract
A resonant circuit includes a transmission line in parallel with a varactor diode. The varactor diode has a capacitance that is variable in response to an applied voltage, which allows for real time impedance matching, attenuation control, and/or compensation for tolerances of other components. The resonant circuit is used with a quarter wavelength transmission line to provide impedance transformation and matching between multiple ports. A high frequency switch provides low current consumption, improved impedance matching, relatively low insertion losses, and excellent isolation between ports.
Claims22
An apparatus comprising:
- a plurality of ports;
- a first quarter-wavelength transmission line comprising a first end electrically coupled to a first port of said plurality of ports and a second end electrically coupled to a second port of said plurality of ports;
- a first resonant circuit electrically coupled from said first port to ground, said first resonant circuit comprising:
- a first varactor diode having a capacitance variable in response to an applied voltage;
- and
- a first transmission line in parallel with said first varactor diode.
A resonant circuit comprising:
- a varactor diode having a capacitance variable in response to an applied voltage;
- and
- a transmission line in parallel with said varactor diode.
A method comprising:
- applying a first voltage to a first varactor diode in parallel with a first transmission line, wherein:
- the first varactor diode and the first transmission line form a first resonant circuit having a first resonant frequency;
- the first resonant circuit is electrically coupled in parallel with a first port having an impedance;
- and wherein
- the first resonant frequency is such that the first resonant circuit presents a high impedance to a signal at the first port having a desired resonant frequency;
- matching the impedance of the first port to the impedance of a second port using a first quarter-wavelength transmission line electrically coupled from the first port to the second port;
- applying a second voltage to a second varactor diode in parallel with a second transmission line, wherein:
- the second varactor diode and the second transmission line form a second resonant circuit having a second resonant frequency;
- the second resonant circuit is electrically coupled in parallel with a third port having a characteristic impedance;
- and wherein
- the second resonant frequency is such that a signal at the third port having the desired resonant frequency is presented with a low impedance;
- and
- transforming the low impedance at the third port to a high impedance at the second port using a second quarter-wave transmission line electrically coupled from the second port to the third port.
A method comprising the steps of:
- applying a voltage to a varactor diode in parallel with a transmission line, wherein:
- the varactor diode and the transmission line form a resonant circuit tuned to a first frequency;
- the first resonant circuit is electrically coupled in parallel with a first port having an impedance;
- the first frequency is such that the first resonant circuit presents an intermediate impedance to a signal at the first port having a desired resonant frequency;
- and
- attenuating a signal traveling from the first port to the second port using a quarter-wavelength transmission line electrically coupled from the first port to the second port, wherein the amount of attenuation is determined by the first frequency.
Dependencies are inferred from the claim text.