Abstract: A switchable filter for passing one of a plurality of frequency bands has n bandpass filter sections coupled in parallel between a filter input terminal and a filter output terminal. Each of the n bandpass filter sections is arranged to pass a different frequency band. Each of n switches is coupled to a respective one of the n bandpass filter sections, and each of the n switches is operable in either an OFF state for activating a corresponding one of the n bandpass filter sections or an ON state for deactivating the corresponding one of the n bandpass filter sections. The n switches are arranged and controlled so that, when any one of then switches is operated to its off state, the remaining n−1 switches are operated to their ON states and form a series circuit for conducting a common current.

Abstract: An input trap circuit removes a predetermined frequency component included in an input signal and then outputs the input signal to a circuit at a later stage. The input trap circuit is provided with: a parallel oscillation circuit in which a pair of variable capacitance diodes are connected in series such that cathodes thereof are connected to each other at a junction portion and in which an inductance is connected in parallel to the variable capacitance diodes between anodes of the variable capacitance diodes at both ends thereof; a voltage applying device for applying a voltage to the junction portion so as to vary capacitance values of the variable capacitance diodes on the basis of reverse voltage characteristics of the variable capacitance diodes respectively; and a variable capacitor element connected between the junction portion and a ground.

Abstract: A filter unit comprises a wideband bandpass filter; at least one band-elimination filter having a stop band within the passband of the bandpass filter, so that the passband is divided into a plurality of pass bands by the stop band; and the wideband bandpass filter and the band-elimination filter being disposed in a single dielectric member. Since the passband of a wideband bandpass filter is divided into a plurality of pass bands by stop bands of one or more band-elimination filters, signals having frequencies corresponding to these divided pass bands are able to pass through the filter unit simultaneously.

Abstract: A tunable capacitor that introduces significantly less loss, if any, costs less and is smaller than previously available. A bias electrode is coupled to a FE material. The capacitor electrodes are electro-magnetically coupled to the FE material, such that the capacitor electrodes and the bias electrode are not touching. Only non-conductive material is in the gap defined by the capacitor electrodes. The bias electrode is used to apply a variable DC voltage to the FE material. A capacitor electrode serves as a DC ground for producing a variable DC field between the bias electrode and the capacitor electrodes.

Abstract: The invention relates to a resonator (200,300) with variable resonance frequency, intended for connection to an amplifier, thus forming an oscillator, said resonator comprising a resonator circuit (205,305) for deciding the resonance frequency of the resonator and the oscillator, said resonator circuit comprising an inductance (L), a variable capacitance (Cj), and means (Vtune) for varying the capacitance. The resonator also comprises connection means (C1, Ck; C1, Ck, C2) for connecting the resonator to an amplifier. The resonator is provided with means (Vtune) for varying the capacitance of the connection means in proportion to the variation of the capacitance (Cj) of the resonator circuit. Preferably, the means (Vtune) for varying the capacitance (Ck) of the connection means are arranged such that an essentially constant relationship (Ck/Cj) is maintained between the capacitance (Ck) of the connection means and the first capacitance (Cj) of the resonator across all resonance frequencies.

Abstract: A signal filter employs digital control signals to selectively establish and adjust analog impedance components of the filter. In the case of a first-order R-C filter, adjustable resistance and reactance assemblies are coupled in series. The resistance assembly has multiple parallel signal paths sharing a common input and output. Each signal path includes a prescribed electrical resistance and a digital switch to selectively enable and disable the resistance. Between the common input and output, the signal paths provide a collective resistance which varies depending upon which switches have been activated. The reactance assembly is similar to the resistance assembly, with capacitors or inductors instead of resistors. A digital controller selectively activates the switches to adjust the assemblies' respective resistance and reactance.

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: An input trap circuit removes a predetermined frequency component included in an input signal and then outputs the input signal to a circuit at a later stage. The input trap circuit is provided with: a parallel oscillation circuit in which a pair of variable capacitance diodes are connected in serial such that cathodes thereof are connected to each other at a junction portion and in which an inductance is connected in parallel to the variable capacitance diodes between anodes of the variable capacitance diodes at both ends thereof; a voltage applying device for applying a voltage to the junction portion so as to vary capacitance values of the variable capacitance diodes on the basis of reverse voltage characteristics of the variable capacitance diodes respectively; and a variable capacitor element connected between the junction portion and a ground.

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: A structure (110, 150) for enhancing the quality factor (Q) of a capacitive circuit (112, 152). The capacitive circuit (112, 152) includes a first resistance (122, 164), a capacitance (124, 166), and a second resistance (126, 168). The capacitance (124, 166) represents the net capacitance of the capacitive circuit (112, 152), and the first resistance (122, 164) and second resistance (126, 168) represent elements of the intrinsic resistance of the capacitive circuit (112, 152). In a one embodiment the structure (110) includes a first capacitor (128) which is connected in parallel with the capacitive circuit (112), and second capacitor (130) which is connected in series with the capacitive circuit (112).

Abstract: A reduced length filter including a housing having a female connector end and an opposed male connector end, and a circuit board positioned within the housing. The circuit board has first and second filter sections positioned on upper and lower surfaces thereof, and a ground plane positioned therebetween. The first filter section is in electrical communication with the second filter section. A first isolation shield is provided in electrical communication with the ground plane, and extends from the upper surface of the circuit board in a direction substantially perpendicular thereto and proximate one of first and second ends of the circuit board, and a second isolation shield is provided in electrical communication with the ground plane, and extends from the lower surface of the circuit board in a direction substantially perpendicular thereto and proximate the other one of the first and second ends of the circuit board.

Abstract: An integrated filter circuit and a method of fabrication are disclosed, wherein the integrated filter has an input and an output parasitic shunt impedance. Input and output electrical components are coupled to the input and output terminals, respectively, to reduce the input and output parasitic shunt impedances. The input and output electrical components each include one of a coil, a section of transmission line, a coil and tuneable capacitance connected in a series tuned circuit, or a coil and tuneable capacitance connected in a parallel tuned circuit.

Abstract: An impedance matching circuit (10) matches the impedance of a load (19) coupled to an RF amplifier (12) to that of the RF amplifier (12). The impedance matching circuit (10) samples a transmitted signal from the RF amplifier (12) and a reflected signal from the load (19). The amplitude and the phase of the sampled reflected signal are compared with those of the sampled transmitted signal to calculate the impedance mismatch. A control logic circuit (80) adjusts the capacitance and inductance values of variable capacitance (23; 27) and inductance (35) elements in the impedance matching circuit (10), thereby matching the impedance of the load (19) to that of the RF amplifier (12).

Abstract: An apparatus (Z) having controllable impedance is inserted from output (22) to ground (23) of an audio-signal amplifier (20). Typically, the apparatus comprises a switch-chain (50) having multiple switches (52, 53, and so on); the first switch (52) is connected to one terminal (62) of the apparatus. A capacitor (82, 84, and so on) is connected from each switch to a second terminal (61). The network formed by the switch-chain (50) and the capacitor network (80) is called a matrix (60C). To bypass audio frequencies away from the chopping effect of the switches, an inductor (31) parallels the matrix. To prevent shorting of audio signals to ground, a larger capacitor (30) is in series with the inductor. An unstable voltage at output will see increasing capacitance as more switches are closed. The changing of capacitive impedance in relation to the amplitude of the unstable voltage is designed such that the unstable voltage cannot grow too large. More complex matrices further reduce voltage fluctuations.

Abstract: A filter circuit comprising a balanced filter system, a non-balanced filter system, and two switching units. The balanced filter system includes balanced filter-matching circuits, each composed of parallel elements. The non-balanced filter system is connected to a voltage neutral point defined by dividing the parallel elements of each of the balanced filter-matching circuits to halves. The switching units are provided at the input and output of the balanced filter system, respectively, and switch the input and output of the balanced filter system, each from a balanced state to a non-balanced state, and vice versa.

Abstract: The invention relates to a bandpass filter that follows the frequency of an input signal especially for reducing the noise on the receive band of mobile communications devices. More specifically the invention relates to a method and arrangement for tuning a resonator (100), where an input signal feeds the resonator in such a manner that the resonator oscillates at, the frequency of the input signal, and where the center frequency of the pass band of the resonator is set substantially to the frequency of the input, signal. In accordance with the invention, there is generated (200) a difference signal (Vc, Ve) proportional to the phase difference (&Dgr;&phgr;) between the input signal voltage (Vi) and resonator voltage (Vo) and the resonance frequency of the resonator is changed using the difference signal in such a manner that said phase difference becomes smaller.

Abstract: Elementary electrical resonator (1), characterized in that it comprises:

Abstract: A tunable electronic filter circuit is provided including an input terminal and an output terminal connected to the input terminal with a node therebetween. An inductor, a variable capacitor, and a variable resistor are connected between the node and ground. Coupled to the variable capacitor and the variable resistor is a feedback control circuit. The feedback control circuit is operable to tune the variable capacitor in order to set a predetermined frequency, or center frequency, of the electronic filter circuit. The feedback control circuit is further operable to tune the variable resistor in order to calibrate a quality factor of the electronic filter circuit. In use when an input signal is applied to the input terminal, the electronic filter circuit passes an output signal to the output terminal. Such output signal includes components of the input signal within a predetermined frequency bandwidth set by the predetermined frequency and filters out other components of the input signal.

Abstract: A method and system for tuning a tunable bandpass filter includes a bandpass filter having a passband which is dependant on the value of a tuning signal. A data signal having a dominant frequency component is applied to the filter and the power of the signal passed by the filter is determined. The tuning signal is adjusted until the passed power is maximized, indicating that the filter is tuned to the dominant frequency. The tuning signal can then be applied to other tunable circuits, including an oscillator having an output used as a clock signal to extract data from the data signal applied to the filter.

Abstract: A resonator circuit capable of resonating at a predetermined frequency is provided. The resonator circuit comprises a fixed position coil inductor (62) having a longitudinal axis (92) and a capacitor (88, 82) electrically connected in parallel with each other to form a resonator (60), so that respective first and second ends of the inductor and the capacitor are electrically coupled together at a high-voltage end (64) and a low-voltage end (66) of the resonator (60). A radio frequency (RF) input coupling (70) is coupled directly to the inductor (62) at the low-voltage end (66) of the resonator. A high-voltage electrode (72) is coupled to the high-voltage end (64) of the resonator. A first resonator tuning mechanism is provided for varying the inductance of the inductor, comprising a plunger (90) movable within the coil of the inductor (62) along the longitudinal axis (92). A second resonator tuning mechanism is provided for varying the capacitance of the capacitor (88, 82).

Abstract: An electronic system 8 is disclosed herein. The system includes circuitry 10 for processing a signal and a plurality of antennas 12a-12b. A plurality of switches 22a-22b are also included. Each of the switches 22a-22b is coupled between the processing circuitry 10 and a corresponding one of the antennas 12a-12b. Each of the switches 22a-22b includes first and second power MOSFETs where the source of the first MOSFET is coupled to the source of the second MOSFET. The system further includes circuitry 28 for selecting of one of the plurality of switches 22a-22b to be on.

Abstract: A programmable high frequency (HF) bandpass filter is disclosed. The programmable filter has a tunable bandwidth and center frequency over a large range of the radio frequency (RF) and intermediate frequency (IF) spectrum. The programmable filter incorporates micro-electro-mechanical switches (MEMS), Acoustic Charge Transport (ACT) devices, or a combination thereof, to provide tunability of the bandpass filter response characteristics.

Abstract: An inexpensive to produce and small profile programmable filter bank with a high quality factor that applies an adjustable frequency response to an input signal to produce a filtered output signal. In a preferred embodiment, the programmable filter bank includes an input for receiving the input signal, an output for transmitting the filtered output signal and a set of interconnected individually selectable filter elements, where each filter element provides a predefined fixed frequency response. A control unit, such as a digital state machine or a microprocessor is connected to the filter elements and enables a user to select one or more filter elements in order to generate a desired overall frequency response, for application to the input signal, that is formed of the combination of the frequency responses of the selected filter element(s).

Abstract: A filter 10 (30) includes a laminate body 11 (31), PIN diodes PD1 and PD2 of switching elements and choke coils CC1-CC2 are mounted on a top surface or a principal face of the laminate body 11, and six external electrodes Ta-Tf extend on a side surface from the top surface to the bottom surface of the laminate body 11 (31). Three external electrodes Ta-Tc among the external electrodes Ta-Tf are formed on one side surface of the laminate body 11 (31), and three other external electrodes Td-Tf are formed on the opposing side surface of the laminate body laminate body 11 (31). The external electrode Ta is an input terminal, the external electrodes Tb and Te are control terminals for controlling a voltage supplied to the PIN diode PD, the external electrode Tc is an output terminal, and the external electrodes Td and Tf are ground terminals.

Abstract: An article comprising a micro-machined, passively self-assembling inductor is disclosed. The inductor is fabricated using MEMS technology and advantageously utilizes materials compatible with CMOS such that inductor is monolithically integrable with a CMOS chip. The inductor includes passive self-assembly means by which the inductor loop is moved away from an underlying substrate, typically silicon, in the final steps of inductor assembly. Such passive self-assembly does not require separate actuation or monitoring steps.

Abstract: A tunable filter (400) provides dual injection mode operation over a continuously tunable frequency range (500). A combination of mirrored series resonant circuits (432, 446) tuned through varactors (434, 448) allows the frequency response to shift. The use of a series capacitor and shunted inductor (430, 428), (444, 442) mirrored onto each series resonator (432, 446) provides both high-side and low-side injection protection.

Abstract: An absorbent amplitude filter for HF signals employs a reflective filter and an absorption circuit comprising a load resistor. The absorption circuit inventively comprises another .lambda./4 line upstream of the filter, which comprises, at the input side, a series connection consisting of another diode and the load resistor. This series connection is connected with the reference potential, whereby an HF block is connected in parallel to the load resistor.

Abstract: A filter comprises an inductor, a first variable capacitance diode, a second variable capacitance diode having nearly identical characteristic as the first variable capacitance diode, a control terminal for applying voltage to the first and the second variable capacitance diodes, an input terminal, an output terminal and a signal line between the input terminal and the output terminal. A cutoff frequency is controllable with the voltage applied to the control terminal. The variable frequency filter which can receive a large signal has reduced size due to a structure in which the first and the second variable capacitance diodes having nearly identical characteristics are connected either in series or in parallel with their polarities reversed against each other.

Abstract: A variable bandwidth filter that includes either a parallel or series combination of a fixed impedance, such as a capacitor, and a variable impedance, such as a variable capacitor. The series and parallel combinations enable the ideal capacitance values for the filter coupling to be approximated thereby enabling a single control voltage to control the filter bandwidth without effecting the filter's upper frequency.

Abstract: The present invention relates to a laminated chip bead element demonstrating noise absorption characteristics over a broad range in a high frequency range of GHz or higher. An insulating body is constituted of a material achieved by mixing ferrite powder and an insulating resin. At least one signal conductor is embedded in the insulating body. It is desirable that the insulating body includes a plurality of composite members.

Abstract: An inductance/capacitance (LC) composite module with a built-in variable capacitor and coil is disclosed which includes a dielectric substrate having one principal surface on which a stator-side electrode is formed. Also formed thereon are a first terminal electrode connected to the stator-side electrode and a second terminal electrode independent of the first terminal electrode. The variable capacitor has a rotor of a chosen solid-state dielectric material in contact with the stator-side electrode. This rotor has thereon a rotor-side electrode which opposes the stator-side electrode with at least part of the rotor laid therebetween, thus forming an electrostatic capacitance. A rotatable support member is mounted so that it may rotate about the axis line at right angles to the substrate surface. The support member transmits its rotation to the rotor allowing the rotor to rotate with the support member.

Abstract: A radio frequency (RF) coupler transfers RF power between a first circuit on a rotary shaft and a second circuit relative to which the shaft can rotate. The coupler comprises a first RF transmission line arranged to rotate with the rotary shaft about the rotation axis of the rotary shaft for connection to the first circuit and a second RF transmission line relative to which the first RF transmission line can rotate for connection to the second circuit. The first and second RF transmission lines comprise first and second electrically conductive tracks arranged coaxially around the rotation axis in mutually overlapping relationship to provide RF coupling between the first and second RF transmission lines. Each track has a gap defining a pair of ports. One of the ports of each track is connectable to a respective circuit and another port in the track is connected to a RF reflecting termination. A notch filter tunable to a desired frequency within a predetermined RF band is also described.

Abstract: An antenna tuning circuit of a tuner with a band switching device, which can eliminate an image disturbance and a disturbance due to a UHF band frequency at reception of a high band and further eliminate a disturbance at a frequency higher than the image frequency at reception of a low band. At the reception of a high band, a coil 32 is provided to be connected between an input terminal 2 and a first high-band coil 9, and a first trap circuit 34 including a first capacitor 14 and the coil 32 is established between the input terminal 2 and an output terminal 4, and further a second trap circuit 35 including a second capacitor 15 and a second high-band coil 11 is formed therebetween.

Abstract: A high Q bandpass filter (102) is tuned by applying a transient (204) to the filter to cause it to ring. The ringing of the filter produces an output damped oscillatory waveform (206) whose zero crossings (208) are converted to a pulse train (210) and counted in a digital counter (112) to a predetermined number n. The output (214) of the counter is compared to an accurate timing signal (216) which has a time duration equal to the time of n pulses when the filter is accurately tuned. The output of the comparator (118) is applied to an integrator (122) to generate a control signal V.sub.c to tune the filter. The high frequency tuning problem is thus converted to a low frequency, time domain problem which is readily implemented.

Abstract: A filter network adapted to be placed in parallel with a power supply which acts like a short circuit at a specified frequency range above 80 kHz. The filter network comprises a plurality of parallel circuits, each of which comprise a capacitor, an inductor and a resistor in series with a second resistor coupled in parallel with the inductor.

Abstract: A phase shifter in which the change in phase changes with changes in temperature. The phase shifter includes a plurality of capacitors and inductors connected in series relation to form a filter network. Each of the capacitors has a dielectric material with a temperature coefficient so that the capacitance of the capacitor varies with temperature. Each of the inductors has a ferrite material which has a temperature coefficient so that the inductance of the inductor varies with temperature. The temperature coefficients of the dielectric material of the capacitors and the ferrite material of the inductors have the same sign, i.e, either negative or positive, and preferably are of the same value.

Abstract: In an RF filter having an input terminal, an output terminal, a plurality of resonator elements, and a plurality of coupling reactances for coupling one resonator element to another resonator element, for coupling the input terminal to a resonator element, and for coupling the output terminal to a resonator element, techniques are disclosed for providing an RF filter having an electronically tunable center frequency and an electronically tunable bandwidth. According to a specific embodiment disclosed herein, a first shunt reactance is provided from the input terminal to ground, and a second shunt reactance is provided from the output terminal to ground. The values of the coupling reactances remain constant, while the values of the resonator elements, the first shunt reactance, and the second shunt reactance are tuned to provide a specified filter bandwidth and/or a specified center frequency.

Abstract: The present invention aims to provide a CATV converter which can receive both of analog and digital signals. The CATV converter comprises a second mixer (10) coupled with a first filter (13) which attenuates approximately equal frequency to an audio carrier of an upper adjacent channel and approximately equal frequency to a video carrier of a lower adjacent channel, a first amplifier (14) coupled with an output terminal of the first filter (13), and a second filter (15) coupled with the output terminal of the first amplifier (14). The second filter (15) attenuates a video carrier of the upper adjacent channel and an audio carrier of the lower adjacent channel. When an input signal is within a predetermined frequency range, the input signal fed to the input terminal (1) can short-circuit the input and output terminals of the second filter with a high frequency of the input signal.

Abstract: In a filter unit having a first and a second bandpass filter (21 and 22) and an input terminal (101) supplied with a unit input signal, the first bandpass filter has a first filtering bandwidth with a first center frequency while a second bandpass filter having a second filtering bandwidth with a second center frequency. Only when the unit input signal has a bandwidth similar to the first filtering bandwidth, a first impedance-adjusting arrangement (11 and 31) matches a first impedance of a combination of the first bandpass filter and the first impedance-adjusting arrangement with an output impedance of an input side component. Only when the unit input signal has a bandwidth similar to the second filtering bandwidth, a second impedance-adjusting arrangement (12 and 32) matches a second impedance of a combination of the second bandpass filter and the second impedance-adjusting arrangement with the output impedance of the input side component.

Abstract: A radio-frequency tuning circuit includes an input tuning transformer, and an output tuning transformer. The input tuning transformer comprises a primary coil adapted to serve as input coil, and a secondary coil to which a pair of variable-capacitance diodes having cathodes thereof connected together are connected in parallel therewith to form a first tuning circuit. The output tuning transformer comprises a primary coil to which a variable-capacitance element is connected to form a second tuning circuit, and a secondary coil adapted to serve as output coil. The input and output tuning transformers are connected in such a manner as to form a double-tuning circuit. Q-factor of the output tuning transformer is made to be twice as high as that of the input tuning transformer, and resonant impedance of the first tuning circuit and that of the second tuning circuit are made to be substantially equal to each other.

Abstract: A resonator for a high frequency electric oscillator is disclosed. The resonator is and integrated capacitor and inductor. The capacitance and inductance of the resonator are continuously and simultaneously adjustable. The resonator includes a coaxial portion and a conductor portion. The coaxial portion has an inner dielectric with a longitudinal aperture and an outer conductive sheath or outer conductor. The conductor portion has a straight section slidable in the aperture and a V shaped bent or oblique section.

Abstract: A method and apparatus which realize an RF bandpass filter having a tunable bandwidth and center frequency over a large range of the radio frequency spectrum. The filter is comprised of a cascade of filter elements. Each element is comprised of a signal splitter which simultaneously feeds a signal to a delay line and a phase shifter in a parallel path. The delayed and phase shifted signals are summed. Each filter element exhibits periodic passbands and alternating transmission zeroes. Each successive filter element has a decreased delay by an incremental factor (e.g., typically 1.2), and exhibits an increase in the frequency intervals between stopband zeroes. The bandwidth is controlled by selecting a number of "activated" ones of the successive elements. A center frequency tuning is performed by adjusting a phase shift coefficient of at least one filter element.

Abstract: A device and a method for adjusting a bandpass filter, especially a combiner filter. The method includes deriving an RF sample signal proportional to the power of a modulated RF signal which is one of: passing forward to the bandpass filter, reflected from the input of the bandpass filter and passed through the bandpass filter; down-converting the sample signal by another RF signal; detecting the signal strength of the mixing result; adjusting the center frequency of the passband of the bandpass filter on the basis of the detected signal strength. There is an essential frequency or modulation difference between the signals to be mixed, and so the mixing result is an AC signal of a lower frequency. No accurate adjustment of the phase relation of the signals to be mixed is required. Preferably, the frequency or phase difference between the signals to be mixed is accomplished by utilizing the phase modulation contained in the transmission when one of the signals is unmodulated.

Abstract: A selective RF circuit for a double conversion tuner includes three sections: low and mid band double tuned bandpass sections and a high band double tuned bandpass section. Each section includes tuning varactors and one or more coupling varactors. The varactors are operated in a first tuning mode for exhibiting a variable capacitance and in a second mode for presenting a substantial low impedance across their terminals. A microprocessor controlled circuit arrangement applies DC potentials to the tuning and coupling varactors and to two pairs of switching diodes simultaneously for selecting and tuning the desired bandpass section. The varactors in each bandpass section are complemented with fixed capacitors selected so that the product of the loaded Q and the coupling factor of any active double tuned bandpass filter is maintained substantially equal to unity over the entire tuning range.

Abstract: An active filter apparatus makes it possible for a filter adjusting circuit to require a small number of elements when the filter adjusting circuit is contained in an integrated circuit, to be not easily affected by variations in the characteristics of the elements which form the circuit, and to be capable of easily adjusting the frequency characteristics of the filter to be adjusted. A characteristics conversion device converts, on the basis of an input signal and an output signal of the filter, to a characteristics conversion signal whose amplitude when the adjustment is completed is considerably larger than that of the output signal. As a result, the amplification factor of the characteristics conversion device, necessary to detect a maximum or minimum value of a characteristics conversion signal, is considerably small. Therefore, it is possible to considerably decrease an offset error of the characteristics conversion device.

Abstract: A bandpass filter network having a first two pole filter and a second two pole filter provided in parallel to the first two pole filter. The first filter is optimally coupled while the second filter is extremely overcoupled. Moreover, the first filter and second filter are shifted 180.degree. out of phase with one another. This phase shift is preferably accomplished by a balun transformer. Alternatively, the 180.degree. phase shift may be accomplished by having the first and second filters utilizing different forms of coupling (i.e., one inductively coupled, the other capacitively coupled).

Abstract: Tuning a combiner filter, which includes two separate tuning modes: coarse adjustment applied when the combiner is taken into use by utilizing a measuring branch for forward power and a coarse measuring branch for reflected power; and fine adjustment applied in continuous operation by utilizing the measuring branch for forward power and a fine measuring branch for reflected power. The two-stage adjustment decreases the mutual interference of the filters during tuning. The correct tuning frequency of the combiner filter is obtained as the average point of the reversing points obtained in the adjustment process, the filter being driven to the average position. This so-called positional average tuning has two advantages: the effect of noise present in the power measuring line is reduced, and the tuning error caused by the termination of the dynamics of the A/D converter positioned after the detector at low power levels and good combiner filter settings is diminished.

Abstract: An advantageous embodiment of the invention is the filter of the receiver branch of the duplex filter in a multi-channel radio transmitter/receiver having reception and transmission bands composed of plural radio-frequency channels. In the first state of the filter, when the radio transmitter/receiver is only receiving radio signals, the width of the pass band of the filter corresponds to said reception band. In the second state, in which the radio transmitter/receiver additionally transmits radio signals, the pass band of the filter is switched by current control to cover only part of the reception band. By constructing the filter in the manner proposed it is possible to use current control in the first resonator in the filter of the receiver branch. Because of its power consumption current control is otherwise unsuitable for use in e.g. the duplex filter of a portable radio-telephone.

Abstract: A monolithically integrated AC coupling circuit is presented for DC uncoupling and AC coupling (typically in telephone applications) to an input signal. The AC coupler includes a high-pass filter having a first pole at a frequency well below a frequency of interest and a zero at zero frequency. The AC coupler also includes a pole/zero doublet between the frequency of the first pole and the frequency of interest. The frequency of the first pole for a specified error is increased by addition of the doublet. Because the frequency of the first pole is increased, the size of the required capacitors is decreased, enabling integration. An implementation of the circuit using switched capacitor techniques is described. An alternative circuit employing a unit gain interface is presented. The alternative circuit reduces the dynamic range and driving voltage requirements of its field-effect transistors.

Abstract: A band-pass filter system comprises a band-pass filter, and a frequency band controller for controlling a frequency band of the band-pass filter by generating a corresponding up pulse voltage and a down pulse voltage according to a pre-controlled center frequency obtained from an output frequency of the band-pass filter to produce a control frequency for obtaining a desired center frequency of the band-pass filter.