Abstract: A noise filter 10 of the present invention includes an inductor 71 and a resistor 11 connected in parallel with each other. A power supply frequency current bypasses the resistor 11 but passes through the inductor 71. A high frequency noise current including a resonance frequency current, on the other hand, bypasses the inductor 71 but is dissipated at the resistor 11. Therefore, the noise filter 10 does not accumulate noise power and so does not suffer from a problem due to power releasing. The resonance frequency current caused by combination of inductance of the inductance and earth capacitance in the noise filter 10 is also dissipated at the resistor 11, thus giving rise to no problem of its own.

Abstract: A tunable electrical filter constructed pursuant to the teachings of the present invention includes: (a) a plurality of resonator units coupled between an input locus and an output locus; and (b) a plurality of tunable dielectric varactor units; respective individual varactor units of the plurality of varactor units being coupled between respective pairs of the plurality of resonator units, coupled between the plurality of resonator units and the input locus, and coupled between the plurality of resonator units and the output locus.

Abstract: A control system for the characteristic parameters of an active filter includes: a system for the determination of the technological distribution of the components that provides the information related to said technological distribution of the components; an elaboration system for said information related to said technological distribution of the components; an active filter including at least two programmable passive circuital elements receiving said information related to said technological distribution of the components; said elaboration system, being aware of the topology for said active filter, comprises means for determining the value for said at least two programmable passive circuital elements; means for correcting the value for said at least two programmable passive circuital elements according to the value of the information related to said technological distribution of the components; means for determining the programming values for said at least two programmable passive circuital elements.

Abstract: A device and method for tuning a planar filter through a wide range of center frequencies are disclosed. The tuning assembly includes a superconductive tuning tip and an actuator configured and adapted to move the tuning tip through a sufficient range of distances from a resonator or a portion thereof to vary the resonant frequency of the resonator by at least about 10% of the untuned frequency in at least one increment of 0.01% or smaller. An actuator and a position-sensor can be employed in a closed loop feedback system to control the position of the tuning tips. The present invention also provides a method of tuning a filter that includes moving a tuning tip through a sufficient range of distances from a resonator to vary the resonant frequency of the resonator by at least about 10% in at least one increment of 0.01% or smaller.

Abstract: There is disclosed a variable capacitance circuit which comprises: first to Nth variable capacitance elements C1-CN (N is an odd number) sequentially connected in series between an input terminal I and an output terminal O, whose capacitances change depending on voltage applied thereto; an ith bias line on the input terminal side provided between an input terminal portion of the first variable capacitance element and a connection point between a 2ith variable capacitance element and a (2i+1)th variable capacitance element; and an ith bias line on the output terminal side provided between an output terminal portion of the Nth variable capacitance element and a connection point between a (2i−1)th variable capacitance element and the 2ith variable capacitance element, where N and i are integers satisfying N=2n+1, n≧1, 1≦i≦n.

Abstract: An apparatus and method for tuning a filter (11) with oscillator alignment for applications where the filter tuning signal (19, 27) is generated independently of the local oscillator tuning signal and the tuning range is large, for example such as terrestrial and cable TV broadcasting (40 to 860 MHz). The filter being adapted to a filter tuning modulation signal (25) having a first frequency (F1) and a second frequency (F2). Values of the output signal (28) are measured, a first value (S1) at the first frequency, and a second value (S2) at the second frequency, and a comparison signal (26) is generated in comparing the first value and the second value to adjust filter with the tuning control signal in response to the comparison signal, modulation signal and an approximate filter tuning signal to provide a desired signal at the output signal.

Abstract: A method for damping an LC filter coupled to a converter and generating a filter signal. The method comprises sensing the filter signal and processing the filter signal to generate a corresponding feedback signal. The feedback signal is subtracted from a controller signal to generate a difference signal. The difference signal is used for damping the LC filter.

Abstract: A novel system and method for a frequency tunable filter is described. The inventive system and method may be used, for example, in multi-band cellular phones and/or transceivers in wireless networks. The inventive system and method avoids the creation of undesired spurs thus minimizing design difficulties and obviating the need for complex multiple frequency conversions and the associated deleterious effects on performance. The inventive system and method provides at an output terminal an output signal at one of a plurality of predetermined frequencies.

Abstract: A continuously variable filter (110) that includes at least one filter element (146). The filter also includes a fluidic dielectric (108) having a permittivity and a permeability, a composition processor (101) adapted for dynamically changing a composition of the fluidic dielectric (108), and a controller (136) for controlling the composition processor (101) to selectively vary the permittivity and/or the permeability in response to a filter control signal (137). The filter element (146) is at least partially coupled to the fluidic dielectric (108). A second fluidic dielectric having a different composition than the first fluidic dielectric can be provided and a second filter element (148) can be partially coupled to the second fluidic dielectric. The controller (136) and composition processor (101) also can be adapted for varying the permittivity and/or permeabiliity of the fluidic dielectric (108).

Abstract: A receiver, such as a television receiver, tunes an inductive (“L”) and capacitive (“C”) filter based on a desired frequency. The LC filter includes a plurality of inductors, configured in at least one inductive (“L”) bank, and a plurality of capacitors configured in at least one capacitive (“C”) bank. The inductors are selectively enabled for the LC filter by an N code, and the capacitors are selectively enabled for the LC filter by an M code. The receiver uses a functional comparator to compare offset, capacitive, inductive and frequency values to tune the LC filter. Techniques for tuning the LC filter for operation in the VHF and UHF bands are disclosed.

Abstract: The present invention tunes a coupled resonator filter to a given tuning specification using a reference filter that was previously tuned to the specification. A method of tuning a subject filter comprises determining a frequency change for each resonator of the subject filter and applying each determined change to the respective resonator, such that the subject filter is tuned to the specification. The frequency changes are determined from frequency-pushing interactions between combinations of resonators in either the reference or subject filter. A system for tuning the subject filter comprises a measurement system, a tuning program stored in a system memory, and a controller that controls the measurement system and executes the tuning program. The tuning program comprises instructions that preferably implement the tuning method. A tuned coupled resonator filter comprises a plurality of resonators that are adjusted in accordance with the method or using the tuning system.

Abstract: By using ICs with combined inputs for the VHF-high bandpass circuit and the UHF bandpass circuit, undesirable resonances occur which are caused by one of the tuned circuits. The problem is solved by providing a switching means for decoupling the UHF bandpass circuit from the combined inputs when a VHF-high band signal is received by the VHF-high bandpass circuit. The switching means comprises a switch coupled between the UHF bandpass circuit and the common inputs.

Abstract: An integrated tunable resonator for radio includes an RF resonator having a micromechanical tunable capacitor with high Q- (quality factor) value. A first conducting layer (4) forms the first capacitor electrode (8), and/or the electrodes (9) to create the electrostatic force on a movable micromechanical structure (2), and the interconnecting wire (10) between the inductor coil (1) and the capacitor electrode. This arrangement with the use of a dielectric insulating layer provides a substantial improvement to the linearity, power consumption, occupation space and reliability of RF resonator circuits.

Abstract: A first operational amplifier receives a reference voltage at one input terminal, a first transistor is connected between a first power source line and the first operational amplifier, a second transistor is connected between the first power source line and the first operational amplifier, a resistor is connected between the first transistor and a second power source line, a first switch is connected to the second transistor, a variable capacitor connected between the first switch and the second power source line, a second switch is connected the variable capacitor and the second power source line, a second operational amplifier is connected to the variable capacitor and the reference voltage, a third switch is connected to the second transistor, a load is connected between the third switch and the second power source line, and a control circuit is connected to the first to third switches.

Abstract: A radio-frequency input stage is specified and has a radio-frequency coupling element which couples an air interface to the inputs of parallel-connected radio-frequency resonant circuits. In order to allow a circuit configuration which has no switches and is of simple construction, only one capacitance, which forms a low-pass filter, is provided in the coupling element, and splits an antenna signal between the various bands, in the process suppressing influences from bands other than that which has been selected. The radio-frequency input stage can be used, for example, in three-band TV tuners.

Abstract: A ferro-electric filter and method of tuning same. The filter includes a switch for switching between quarter wave resonator and half wave resonator modes. The filter also includes a ferro-electric component for tuning the resonant frequency. The method includes applying a switching control signal to the switch for switching between resonant frequencies and applying a tuning control signal for tuning the resonant frequency.

Abstract: A filter switching circuit includes first and second amplifiers, relays, and bandpass filters in which a bandpass filter having a higher frequency passband is selected by a smaller number of relays and the selected bandpass filter is connected in a decreased distance. A first relay is disposed near the input or output end of the first or second amplifier, respectively, and the other relays are positioned to correspond to the filters. The other relays are provided in opposite sides of a line connecting the output and input end, and the switching terminals of each pair of relays on the same side of the line are sequentially connected to one fixed terminal of each of the relays so that the other relays are sequentially connected to first and second fixed terminals of the first relay and each relay is connected to each second fixed terminal of each of the other relays.

Abstract: A sharp-cutoff VHF elliptic filter includes a folded signal path and internally coupled feedback in a conductive enclosure. Sized for the power requirements of commercial television broadcast transmission, the filter implements the elliptic filter equation through use of cavities, resonators, and couplers. The negative feedback required by the elliptic filter equation is implemented by folding the RF signal path and coupling the feedback energy through a gap in an internal septum to sum negatively with the signal in the main signal path. The elliptic filter can have an interdigital configuration, which puts successive resonators on opposite walls of the enclosure and couples the signal at half-wavelength spacing. The elliptic filter can alternatively have a comb line configuration, which places all resonators on one wall and employs full-wavelength spacing.

Abstract: A method for damping an LC filter coupled to a converter and generating a filter signal. The method comprises sensing the filter signal and processing the filter signal to generate a corresponding feedback signal. The feedback signal is subtracted from a controller signal to generate a difference signal. The difference signal is used for damping the LC filter.

Abstract: A radio frequency electronic filter includes an input, an output, and first and second resonators coupled to the input and the output, with the first resonator including a first voltage tunable dielectric varactor and the second resonator including a second voltage tunable dielectric varactor. The resonators can include a lumped element resonator, a ceramic resonator, or a microstrip resonator. Additional voltage tunable dielectric varactors can be connected between the input and the first resonator and between the second resonator and the output. Voltage tunable dielectric varactors can also be connected between the first and second resonators.

Abstract: A voltage tunable dielectric varactor includes a substrate having a low dielectric constant and having generally planar surface, a tunable ferroelectric layer positioned on the generally planar surface of the substrate, and first and second electrodes positioned on a surface of the tunable ferroelectric layer opposite the generally planar surface of the substrate. The first and second electrodes are separated to form a gap therebetween. The varactor includes an input for receiving a radio frequency signal and an output for delivering the radio frequency signal. A bias voltage applied to the electrodes changes the capacitance of the varactor between the input and output thereof. Phase shifters and filters that include the varactor are also described.

Abstract: The invention relates to trimming of analogue filters (201) in integrated circuits by means of an automatic adjusting circuit. A local oscillator (202) in the automatic adjusting circuit provides a periodic reference signal (R) to an adjustable phase shifter (203), which on basis thereof, produces a periodic phase shifted signal (R*). A phase detector (204) receives both the periodic reference signal (R) and the phase shifted period signal (R*) and produces a test signal (T) in response to a phase difference between the periodic reference signal (R) and the periodic phase shifted signal (R8). A lowpass filter (205) receives the test signal (T) and generates a level signal (TDC) relative a reference level, e.g. representing a zero voltage. A digital signal processor (207) produces a primary control signal (CS), having a serial format, on basis of the observation signal (M). A serial-to-parallel converter (208) converts the primary control signal (CS) into a control signal (CP) having a parallel signal format.

Abstract: A filtering device for filtering out a supply voltage interference of a voltage source that delivers a supply voltage for an electrical load, in which the filtering device includes a capacitor that establishes a connection between the voltage source and the load to a reference potential, and in which a diode is connected between the voltage source and the capacitor, to which a variable resistor is connected in parallel.

Abstract: A phase shifter for changing the phase of a signal fed thereto. The phase shifter includes an inductive reactance element and a capacitive reactance element having one electrode connected to either the input or the output port and a pair of switching elements. A first switching element thereof switches between a conducting state and a non-conductive state when the control signal changes from a first logic state to a second logic state while a second switching element thereof switches between a non-conducting state and a conductive state when the control signal changes from the first logic state to the second logic state.

Abstract: An inductive (“L”)-capacitive (“C”) filter bank has application for use in a television receiver. The LC filter includes inductors configured in at least one inductive (“L”) bank, and capacitors configured in at least one capacitive (“C”) bank. The inductors and capacitors are selectively enabled so as to configure an LC filter with at least one inductor from the L bank and at least one capacitor from the C bank. A combination of inductors and capacitors are selected through the semiconductor switches so as to maximize a Q factor for the LC filter.

Abstract: A receiver, such as a television receiver, tunes an inductive (“L”) and capacitive (“C”) filter based on a desired frequency. The LC filter includes a plurality of inductors, configured in at least one inductive (“L”) bank, and a plurality of capacitors configured in at least one capacitive (“C”) bank. The inductors are selectively enabled for the LC filter by an N code, and the capacitors are selectively enabled for the LC filter by an M code. The receiver uses a functional comparator to compare offset, capacitive, inductive and frequency values to tune the LC filter. Techniques for tuning the LC filter for operation in the VHF and UHF bands are disclosed.

Abstract: A tunable filter having a fixed substrate, a first and second plate comprising a high-temperature superconductor material on the fixed substrate, a movable substrate, a mechanical driver attached to the fixed substrate and the movable substrate, a floating plate comprising a high-temperature superconductor material on the fixed substrate wherein the floating plate, the first plate, and the second plate define a gap, and wherein the gap is varied by length changes in the mechanical driver is provided.

Abstract: A method for tuning a filter to a desired frequency using successive approximation. Elements of the filter are selected according to a control code used to vary the filter's oscillation frequency. The control code is set to the middle of the control code range and resulting oscillation frequency is compared to the desired frequency. If the control code needs to be increased, the control code is set to ¾ of the control code range. If the control code needs to be decreased, the control code is set to ¼ of the control code range. The method continues using successive approximation to determine the value of each bit of the control code. Thus, successive approximation is used to converge on the value of the control code that produces an oscillation frequency of the filter that is closest to the desired frequency (with a maximum error of 1 least significant bit).

Abstract: A duplexer is provided that includes a first tunable bandpass filter, a second tunable bandpass filter and means for coupling the first bandpass filter and the second bandpass filter to an antenna. The duplexer is operated by tuning the first tunable bandpass filter to provide a passband corresponding to an assigned transmit frequency, and tuning the second tunable bandpass filter to provide a passband offset from an assigned receive frequency, when the duplexer is operated in a transmit mode. When the duplexer is operated in a receive mode, the first tunable bandpass filter is tuned to provide a passband offset from an assigned transmit frequency and the second tunable bandpass filter is tuned to provide a passband corresponding to the assigned receive frequency.

Abstract: A voltage-controlled tunable filter includes at least two cavity resonators electrically coupled to each other. A voltage tunable dielectric capacitor is positioned within each of the resonators. Connections are provided for applying a control voltage to the voltage tunable dielectric capacitors. An input is coupled to the one of the resonators, and an output is coupled to the other resonator.

Abstract: A new type of frequency-tunable active notch filter achieves frequency selectivity through interaction among input derived signal components that are passed through parallel signal channels in a forward-only direction. The notch filter differs from earlier channelized notch filters by using multiple, instead of just one, bandpass channels that maintain required forward signal flow in the main, passband-determining signal path without signal distortion at passband frequencies. The new approach has been experimentally verified with a hybrid-integrated three-channel filter whose 40-dB-deep band-reject notch can be continuously tuned, with the help of voltage-controlled variable-capacitance elements, from 9.5 to 10.5 GHz. A single-pole bandpass filter tunes in frequency with the help of only one variable capacitance element, yet still maintains constant passband width across the tuning span.

Abstract: An apparatus and method for tuning a filter (11) with oscillator alignment for applications where the filter tuning signal (19,27) is generated independently of the local oscillator tuning signal and the tuning range is large, for example such as terrestrial and cable TV broadcasting (40 to 860 MHz). The filter being adapted to a filter tuning modulation signal (25) having a first frequency (F1) and a second frequency (F2). Values of the output signal (28) are measured, a first value (S1) at the first frequency, and a second value (S2) at the second frequency, and a comparison signal (26) is generated in comparing the first value and the second value to adjust filter with the tuning control signal in response to the comparison signal, modulation signal and an approximate filter tuning signal to provide a desired signal at the output signal.

Abstract: A system and method for filter tuning are presented. The system comprises means for adjusting the components of a filter by coarse adjustments such that the filter is set with an initial cutoff frequency of adequate accuracy to satisfy the requirements of the filter application, and means for adjusting the components of the filter by fine adjustments such that the filter is set to maintain the accuracy of the initial cutoff frequency in response to cutoff frequency drift. The method comprises the steps of adjusting the components of a filter by coarse adjustments such that the filter is set with an initial cutoff frequency of adequate accuracy to satisfy the requirements of the filter application, and adjusting the components of the filter by fine adjustments such that the filter is set to maintain the accuracy of the initial cutoff frequency in response to cutoff frequency drift.

Abstract: Disclosed is a radio frequency filter used for a mobile communication apparatus such as a mobile phone, having an inductor component, a capacitor component, and a resistor component formed of a conductor pattern. The filter includes the conductor pattern formed on the surface of dielectric layer, and an adjusting layer for adjusting the frequency characteristic of the filter formed so as to cover at least a part of the conductor pattern. In the radio frequency filter, the conductor pattern is formed and sintered, followed by adjusting the frequency characteristic of the filter. Accordingly, in the radio frequency filter, the yield of the manufacture is improved. Further, the electrode layer can be single-layered by using extra-thin lines for the conductor pattern and interdigital electrodes for the capacitor. As a result, it is possible to make the filter smaller and thinner by using intaglio-printing technique and thin-film forming technique.

Abstract: A resistor tuning network for an RC filter has a first, fixed resistor and a second, variable resistance connected in parallel with the fixed resistor. The variable resistance is an R-2R ladder circuit having an input and first and second output terminals, with a first line having a plurality of first arms connected in series with the input and first output terminal and nodes between each pair of arms, each arm having an identical resistor R. A series of shunt arms are selectively connected between the respective nodes and the first or second output terminal. Each shunt arm has a 2R resistor and a switch in series, and each switch has a first, closed position connecting the shunt arm to the first output terminal and a second, open position connecting the shunt arm to the second output terminal, such that the resistance of the ladder network is varied dependent on the switch positions and is at a maximum value when all switches are closed and a minimum value when all switches are open.

Abstract: A phase shifter for changing the phase of a signal fed thereto. The phase shifter includes a first inductive reactance element and a first capacitive reactance element having one electrode connected to either the input or the output port. The phase shifter includes a first pair of switching elements. A first switching element thereof switches between a conducting state and a non-conductive state when the control signal changes from a first logic state to a second logic state while a second switching element thereof switches between a non-conducting state and a conductive state when the control signal changes from the first logic state to the second logic state. Also provided is a second pair of switching elements.

Abstract: The magnetic field of an inductor is decreased by the presence of one or more single loop windings positioned in proximity to the inductor. The single loop windings have open circuits that are selectively closed to magnetically couple the single loop windings to the inductor. A switched inductor/varactor tuning circuit is formed by connecting a varactor to the inductor.

Abstract: An elementary electrical resonator which includes a ribbon conductor forming a flat loop with at least one turn, the conductor having ends which form two parallel segments. The resonator further includes a conducting bridge which forms an arch straddling the two parallel segments of the ribbon conductor wherein opposing surfaces of the arch and the parallel segments form a capacitor. A part of the bridge is capable of being displaced with respect to the parallel segments under the action of a control signal so as to cause the capacitance of the capacitor and therefore the tuning frequency of the resonator to vary.

Abstract: Filters and methods for eliminating a DC component from an electronic signal provide for circuitry having a zero corresponding to a cut-off frequency, and circuitry for shifting the zero by an amount corresponding to the absolute value of that cut-off frequency. The filters and methods, which include integration and operation of gyrators, are particularly well-suited for incorporation in integrated circuits by virtue of reducing the physical size of the required capacitors. A further advantage is the reduction of time-dependent inertia. Applications of the filters and methods include, but are not limited to, radiotelephony.

Abstract: A multilayered LC composite component in which a fine adjustment to a desired frequency can be performed, includes multilayered body sheets on which internal electrodes including capacitor electrodes and inductor electrodes are stacked via dielectric layers. On surfaces of the multilayered body sheets, there are disposed a ground internal electrode and input/output extraction electrodes. A trimming electrode is arranged on the multilayered body such that the trimming electrode is opposed to some of the internal electrodes and is electrically connected to the ground internal electrode. In order to make a rough frequency adjustment, insular electrodes are isolated from the trimming electrode by trimming grooves. Then, a coating material is filled in each of the trimming grooves to make a fine adjustment.

Abstract: A tuning circuit, as for a television receiver or video recorder, employs switchable tuning circuits including micro-electronic electro-mechanical switches for selecting the ones of an array of capacitors and/or inductors as is useful in tunable circuits. The array of capacitors and/or inductors and micro-electro-mechanical switches of the switched tuning matrix is formed on an integrated circuit or an electronic circuit substrate along with amplifiers and other electronic elements of the tuning circuit for which the switched tuning matrix is employed. The switchable capacitance and inductance matrices are well suited for use in the resonators employed in the pre-selector filters, post-selector filters and oscillators of electronic tuners, such as those employed in television receivers and video recorders.

Abstract: The bandpass filter has a comparatively large pass bandwidth, with, at the same time, comparatively steep edges up to the stop band and low attenuation in the passband. The bandpass filter contains three parallel LC elements, one of which is connected between the bandpass filter input and the bandpass filter output. The other two parallel LC elements each have one of their connections coupled to a fixed reference-ground potential.

Abstract: A frequency variable filter in which both the frequency of an attenuation pole and the attenuation bandwidth can be varied. In the frequency variable filter, two serial resonance sections composed of resonators and resonance capacitors are electrically connected to each other via a capacitor. The respective resonator in each of the serial resonance sections is electrically connected in parallel with a corresponding serial circuit composed of a frequency shifting capacitor and a PIN diode. A coupling capacitor electrically connects the junctions defined respectively between the frequency shifting capacitor and the PIN diode in each of the serial circuits.

Abstract: The filter is composed of a series of cells (E1-E4) Coupled to each other by coupling capacitors (Cc12, Cc23 and Cc34), each cell forming a resonant circuit composed of at least one inductor (Ip1-Ip4) connected in parallel with at least one variable capacitor (Cp1-Cp4). The coupling capacitors (Cc12, Cc23 and Cc34) are variable capacitors. The filter is substantially symmetrical between its signal input (FI) and its signal output (FO). It finds applications notably for the transmission of channels in the UHF band, where it provides frequency agility.

Abstract: An integral dual frequency by-pass and transient suppressor device has at least two ceramic semiconductor layers, the upper surfaces of which are formed with electrodes of generally U-shaped configuration. The base portions of the electrodes are exposed at opposite surfaces of the semiconductor layers, the leg portions of the U-shaped electrodes extending toward the base portions of electrodes of opposite polarity. The overlap or registration area of one pair of legs differs from the overlap area of the other leg pair with the result that two capacitors of different values are formed, the capacitors being in parallel and accordingly defining a low impedance path at two discrete frequencies. By varying the conductive paths as a function of the length of the electrode and/or the base of the U, a desired internal inductance is developed.

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.

Abstract: This invention provides a voltage tunable filter comprising an input connection point, an output connection point, and at least one circuit branch electrically coupled to the input connection point and the output connection point and including a voltage tunable dielectric varactor electrically connected to an inductor. The voltage tunable filter can be one of a low-pass, high-pass, band-pass, or band-stop filter. The varactor can include built-in DC blocking capacitors.

Abstract: A method is provided for operating a duplexer including a first tunable bandpass filter, a second tunable bandpass filter and means for coupling the first bandpass filter and the second bandpass filter to an antenna. The method comprises the steps of tuning the first tunable bandpass filter to provide a passband corresponding to an assigned transmit frequency, and tuning the second tunable bandpass filter to provide a passband offset from an assigned receive frequency, when the duplexer is operated in a transmit mode. When the duplexer is operated in a receive mode, the first tunable bandpass filter is tuned to provide a passband offset from an assigned transmit frequency and the second tunable bandpass filter is tuned to provide a passband corresponding to the assigned receive frequency.

Abstract: A tunable filter (300) includes first (302) and second (304) “bridged-T” resonators. The first (302) and second (304) resonators are capacitively coupled together via bandwidth control/coupling section (306). A biasing section (314) provides the proper biasing and decoupling for the filter (300). Filter (300) provides for low-side injection mode operation, and provides for a very deep zero on the lower side of the passband resulting in excellent selectivity. Filter (300) provides for excellent selectivity while reducing the number of inductors and varactors needed in the filter circuit. A high side injection mode filter (500) similar to filter (300) is also described in the disclosure.

Abstract: The magnetic field of an inductor is decreased by the presence of one or more single loop windings positioned in proximity to the inductor. The single loop windings have open circuits that are selectively closed to magnetically couple the single loop windings to the inductor. A switched inductor/varactor tuning circuit is formed by connecting a varactor to the inductor.