Abstract: Disclosed are an apparatus and a method of tuning a microwave filter. An apparatus for tuning a microwave filter according to the present invention includes: a measurement device configured to measure a scattering (S) parameter curve of a microwave filter desired to be tuned; a control device configured to perform tuning so that a shape of the S parameter curve according to a movement of a preselected tuning screw is matched to a shape of a target S parameter curve, and then determine a quantity of transfer of the tuning screw based on feature points on the S parameter curve by using a least squares method in which a preset weight is reflected; and a tuning device configured to move the tuning screw based on the determined quantity of transfer of the tuning screw.

Abstract: A circuit converts a single-ended signal to differential signals that are balanced to have the same amplitudes and opposite phases relative to a reference point of the differential signals. The circuit includes a balance tunable balun, a detector, and a controller. The balance tunable balun has a primary winding, a secondary winding, a control input, and a switched resistor-capacitor (RC) network. The primary winding receives the single-ended signal and the secondary winding outputs the differential signals. The control input receives a control signal and the switched RC network controls the reference point of the differential signals responsive to this control signal. The detector detects the output imbalance and the controller generates the control signal to control the switched RC network to effectively adjust the reference point as needed to reduce that output imbalance. The circuit produces well balanced differential signals over a wide range of signal frequencies.

Abstract: A system for performing an ocular surgical procedure is provided. The system includes a multiple frequency signal source, a configurable tuned output filter connected to the multiple frequency signal source, and a multiple frequency ultrasonic handpiece. The multiple frequency signal source operates at a first frequency and is configured to drive the configurable filter and the multiple frequency ultrasonic handpiece at the first frequency. The multiple frequency signal source operates at a second frequency and is configured to drive the configurable filter and the multiple frequency ultrasonic handpiece at the second frequency, and the design addresses third harmonic frequency issues for the multiple frequency ultrasonic handpiece. Switchable passive components, such as inductors, resistors, and/or capacitors may be employed in the configurable tuned output circuit, or alternately multiple similar circuits may be employed. Alternately, a multi-tap transformer may be provided.

Abstract: Tunable resonator systems and methods for tuning resonator systems are disclosed. In one aspect, a resonator system includes an array of resonators disposed adjacent to a waveguide, at least one temperature sensor located adjacent to the array of resonators, and a resonator control electronically connected to the at least one temperature sensor. Each resonator has a resonance frequency in a resonator frequency comb and channels with frequencies in a channel frequency comb are transmitted in the waveguide. Resonance frequencies in the resonator frequency comb are to be adjusted in response to ambient temperature changes detected by the at least one temperature sensors to align the resonance frequency comb with the channel frequency comb.

Abstract: The average EMR emissions of an electronic device may be reduced by implementing an electrically-active modulated termination. For example, the impedance may be continuously varied at one or more termination locations between two metal substructures to cause a like variation in the amplitude of each component of the EMR. According to one approach, cyclically varying the electrical impedance with a period of less than the time interval over which the EMR is measured will result in a reduction in the average measured EMR.

Abstract: Calibrating a frequency filter includes applying a series of input electrical signals at different frequencies to a shock sensor, using circuitry to identify a particular one of the frequencies as a resonance frequency of the shock sensor based on responses of the shock sensor to the series of input signals, and setting a center frequency of the notch filter equal to the particular frequency identified as the resonance frequency of the shock sensor.

Abstract: Since known detection devices include detectors of the same number as that of samples, the system configuration is complicated. According to the present invention, therefore, a plurality of electromagnetic-wave-transmission lines with different propagation-delay times and a coupled-transmission line coupling the electromagnetic-wave-transmission lines with each other are provided, and an electromagnetic wave is detected by the same electromagnetic-wave-detection unit. Subsequently, a detection device including at least one electromagnetic-wave detector of a number smaller than that of samples can be provided, which decreases the system complexity.

Abstract: Embodiments of a capacitive tuning system implementing a tunable capacitive array are presented herein. The tunable capacitive array includes both scaled coarse capacitors and one or more fine capacitors. The one or more fine capacitors advantageously reduce a differential nonlinearity associated with the scaled coarse capacitors. The use of fine capacitors limits additional area requirements in an integrated circuit implementation, while improving the accuracy of the capacitive tuning system.

Abstract: A method to track and control the resonance frequency of a band-pass filter provides a solution for the sensitivity limitations against temperature and process variations. A phase sensing module obtains the phase difference between the input and output and a negative feed-back control architecture can be used to tune the filter's resonance over the input RF frequency.

Abstract: An electromagnet structure comprises a magnetic shell having a cavity, a magnetic pole located within the cavity and having a magnetic gap for focusing a magnetic field on a magnetically tunable filter, a conductive coil located within the cavity of the magnetic shell and forming multiple turns around the magnetic pole, and a heater located within the cavity of the magnetic shell and configured to maintain the conductive coil at a substantially constant temperature when the magnetically tunable filter is tuned to different frequencies.

Abstract: An automatic protection system for receiver circuitry includes a waveguide switch having a permanent magnet attached to a rotatable manifold and at least one electromagnet axially surrounding the rotatable manifold. An automatic actuation circuit is coupled to the waveguide switch. The automatic actuation circuit includes an RF power detector for detecting incident RF power around the rotatable manifold and generating a detection signal therefrom, a controller coupled to receive the detection signal and for generating at least a first control signal based on the detection signal, and a magnet current driver coupled to receive the first control signal and coupled to the electromagnet. The magnet current driver provides a first drive signal responsive to the first control signal that automatically rotates the rotatable manifold into a protected position that implements a protected path, such as when the incident RF power exceeds a predetermined RF power level.

Abstract: A method and apparatus for automatic compensation of insertion loss in video signals transmitted over conductors is presented. The present invention is particularly applicable to the transmission of video over long lengths of CAT-5 or similar twisted-pair cables. A reference signal having a known form and strength (e.g. a pulse signal) is provided to each pair of conductors carrying a component of a video signal from a transmitter to a receiver. The receiver includes adjustable gain amplifiers for each conductor pair over which a component of the video signal is transmitted. The gains of the amplifiers are initially set at an initial level (e.g., their maximum gain) to allow detection of the reference signal. Once the reference signal is detected in a conductor pair, the amplifier gains are adjusted such that the level of the reference signal is restored approximately to its original form and strength.

Abstract: Tunable notch filters and control loop systems and methods can include a tunable notch filter providing a stop band, a sensing circuit in communication with the tunable notch filter and adapted to determine a phase change between a reference signal and a signal reflected from the tunable notch filter, and a control loop in communication with the tunable notch filter and the sensing circuit, the control loop being operable to adjust the tunable notch filter to modify the phase change.

Abstract: An integrated circuit (IC) for compensating for a package inductance is disclosed. A first ground pad is directly connected to an on-chip ground node. A second IC ground pad is connected to the on-chip ground node via a tunable capacitor circuit, where the capacitance of the tunable capacitor circuit resonates with the package inductance at the operating frequency of the IC.

Abstract: Tunable resonator systems and methods for tuning resonator systems are disclosed. In one aspect, a resonator system includes an array of resonators disposed adjacent to a waveguide, at least one temperature sensor located adjacent to the array of resonators, and a resonator control electronically connected to the at least one temperature sensor. Each resonator has a resonance frequency in a resonator frequency comb and channels with frequencies in a channel frequency comb are transmitted in the waveguide. Resonance frequencies in the resonator frequency comb are to be adjusted in response to ambient temperature changes detected by the at least one temperature sensors to align the resonance frequency comb with the channel frequency comb.

Abstract: A frequency tunable filter is disclosed. The frequency tunable filter includes a filter unit that can tune a frequency band of a frequency signal being filtered, a communication module that receives a control signal for controlling the tuning of the frequency band, and a control unit that controls the tuning of the frequency band based on the control signals. The disclosed filter can control the tuning of the filter's frequency band wirelessly.

Abstract: In one embodiment, an integrated circuit antenna array includes: a substrate, a plurality of antennas adjacent the substrate; and an RF network adjacent the substrate, the RF feed network coupling to a distributed plurality of amplifiers integrated with the substrate, wherein the RF feed network and the distributed plurality of amplifiers are configured to form a resonant network such that if a timing signal is injected into an input port of the RF network, the resonant network oscillates to provide a globally synchronized RF signal to each of the antennas.

Abstract: A tuning method and circuit for an LC tank resonant circuit, including an inductor and a variable capacitor, are described. In a tuning mode, an RF input signal is applied to an input port of the circuit, and the RF output signal is monitored as a variable capacitor control input is varied. A peak output is detected, and the corresponding variable capacitor control input is stored, and applied to the variable capacitor in an operating mode. In one embodiment, the variable capacitor control input is adjusted for delay in the peak detection process. In one embodiment, the variable capacitor comprises a coarse capacitor and a fine capacitor; the tuning procedure is repeated for each capacitor; and both coarse and fine variable capacitor control inputs are stored and applied to the respective capacitors in operating mode.

Abstract: A digitally-tunable filter includes a tunable filter circuit (110) for generating an output signal by processing an input signal based at least on a plurality of filter control signals (114). The filter also includes an input power sampler (118) for sampling an input power of the input signal, an output power sampler (120) for sampling an output power of the output signal, and a tuning processor (112) for generating the plurality of filter control signals based on at least one channel control signal (116) associated with a current communications channel and a comparison of the input and the output powers. In the filter, the plurality of control signals configure the tunable filter circuit to attenuate at least a portion of the input signal if a difference between the input power and the output power is less than a threshold value.

Abstract: A vanadium dioxide front-end advanced shutter device. The electronic shutter device is designed to protect receiver front-ends and other sensitive circuits from HPM pulse events such as HPM weapons, directed energy weapons, or EMPs. The shutter incorporates a transition material such as thin-film vanadium oxide (VOX) materials that exhibit a dramatic change in resistivity as their temperature is varied over a narrow range near a known critical temperature. A high-energy pulse causes ohmic heating in the shutter device, resulting in a state change in the VOX material when the critical temperature is exceeded. During the state change the VOX material transitions from an insulating state (high resistance) to a reflective state (low resistance). In the insulating state, the shutter device transmits the majority of the signal. In the reflective state, most of the signal is reflected and prevented from passing into electronics on the output side of the shutter device.

Abstract: The present invention is a hybrid RF-digital signal processor-based filter for multiband radio architectures systems capable of spectrum re-farming and software defined radios. It performs low-loss frequency agile multiple notch filtering at RF where a large dynamic range exists at a filter input between signals in a stopband and passband. It is a frequency dependent signal attenuation apparatus having two paths connected together by directional couplers. The first path comprising a component such as a delay component or duplexer. The second path comprising a bandstop filter connected to a down converter, a digital filter, and an up converter. At the output of a power amplifier, the invention can be used to attenuate spurs, or noise within bands with strict emission constraints. At the input of a low noise amplifier, the invention can be used to attenuate blockers and transmitter noise outside of the receiver passband.

Abstract: The present invention is a hybrid RF-digital signal processor-based filter for multiband radio architectures, systems capable of spectrum re-farming and software defined radios It performs low-loss frequency agile multiple notch filtering at RF where a large dynamic range exists at a filter input between signals in a stopband and passband It is a frequency dependent signal attenuation apparatus having two paths connected together by directional couplers The first path comprising a component such as a delay component or duplexer The second path comprising, in series, a down converter, a digital filter, an up converter, and a bandstop filter At the output of a power amplifier, the invention can be used to attenuate spurs, or noise within bands with strict emission constraints At the input of a low noise amplifier, the invention can be used to attenuate blockers and transmitter noise outside of the receiver passband.

Abstract: An integrated circuit, a non-contact IC card, a reader/writer, a wireless communications method, and a computer program are provided to improve communication. The integrated circuit configured to execute wireless communication by means of magnetic field. The integrated circuit has a resonance circuit having resonance frequencies of a plurality of levels, a confirmation block configured to confirm whether a predetermined condition is satisfied, and a switching block configured to change the resonance frequencies if the predetermined condition is found satisfied as a result of the confirmation.

Abstract: Compensation of a signal using resonators as well as related methods and devices are described. Some embodiments include methods and devices for performing frequency compensation on a signal.

Abstract: Architectures and implementations of a transceiver system for wireless communications are presented, the system including one or more antennas supporting a single frequency band or multiple frequency bands, a transmit circuit, a receive circuit, and an isolation circuit that is coupled to the one or more antennas and the transmit and receive circuits and provides adequate isolation between the transmit circuit and the receive circuit.

Abstract: Tuning a programmable power line filter, the power line filter including a live line, a neutral line, and a ground line connected to input terminals of the filter on an input side of the filter, the live line and the neutral line connected through inductors in the filter to output terminals on an output side of the filter, X-capacitors selectably connected through tuning switches between the live line and the neutral line, Y-capacitors selectably connected through tuning switches between the live line and ground and/or between the neutral line and ground, and a tuning control circuit connected to the tuning switches and selectably connected through one or more programming switches to the load, including measuring by the tuning control circuit the input impedance of the load and programming by the tuning control circuit the tuning switches in dependence upon the input impedance of the load.

Abstract: An adaptive electromagnetic interference (EMI) detection and reduction device for multi-port applications is provided. The invention includes at least two physical devices (PHY), where the PHYs transmit data along wire pairs to a register jack (RJ). The transmissions create EMI along the wire pairs, where the transmissions have constructively interfering resonant frequencies having phases and amplitudes. An antenna is disposed proximal to each RJ, where the antennae detect each frequency. A resonating network determines a peak amplitude of each frequency, an envelope detector amplifies each peak amplitude from the resonating network. A discretization circuit converts the amplified peak to discrete amplitude values, where the discretization circuit transmits the discrete amplitude values to a controller.

Abstract: A lattice tunable filtering circuit includes a first input and a second input, and a first output and a second output. The circuit includes two series branches and two parallel branches. The first and second series branches include a Tunable Resonator Component (TRC) which presents a first series resonance frequency whereas the third and fourth parallel branches present a second series resonance frequency which has a value being lower than that of the first series resonance frequency. The first and second series resonance frequencies are tunable by one analog control quantity. The filtering circuit further includes a feedback control loop for the control of the analog quantity, which feedback is based on a criterion of equality between the modulus of impedances Zs and Zp.

Abstract: The electrically tunable inductive device includes an electromagnet including an electromagnet core and a bias or tuning coil cooperating therewith to define opposing magnetic poles for generating a quiescent magnetic field that may be varied. An inductor is tunable based upon the variable magnetic field and includes an inductor core having a toroidal shape and fixed at a position adjacent the opposing magnetic poles of the electromagnet, and an inductor or signal coil is around at least a portion of the inductor core. The electromagnet core may include a pair of opposing legs and a bight portion therebetween defining a horseshoe shape. The inductor core may be positioned between ends of the opposing legs of the electromagnet core, and the tuning coil may surround the bight portion of the electromagnet core. The electrically tunable inductive device may have the combination of fine precision, high speed and high power handling, useful for tunable RF filters.

Abstract: A digitally-tunable filter includes a tunable filter circuit (110) for generating an output signal by processing an input signal based at least on a plurality of filter control signals (114). The filter also includes an input power sampler (118) for sampling an input power of the input signal, an output power sampler (120) for sampling an output power of the output signal, and a tuning processor (112) for generating the plurality of filter control signals based on at least one channel control signal (116) associated with a current communications channel and a comparison of the input and the output powers. In the filter, the plurality of control signals configure the tunable filter circuit to attenuate at least a portion of the input signal if a difference between the input power and the output power is less than a threshold value.

Abstract: Methods, systems and apparatus for filter design, analysis and adjustment are provided. Various embodiments may include, for example, methods, systems and apparatus for electric signal filter tuning. Embodiments may also include design techniques for planar electric signal (e.g., RF signals) filter tuning. In at least an embodiment of the present invention a technique for filter tuning is provided which may include parameter extraction, optimization and tuning recipes techniques that may require only a single permanent filter tuning. In at least another embodiment a system and method of filter design, analysis and adjustment according to the present invention includes use of tuning that may be set using a mechanical scribing tool or a laser trimming device. In at least one other embodiment, a filter tuning technique may be provided and include providing trimming tabs on a resonator edge that may be disconnected or trimmed for filter tuning.

Abstract: A second operational amplifier (7) is arranged, as an interface circuit (6), between a first operational amplifier (5) outputting the control voltage (Vcd) of a dummy filter (2) and a main filter (1), and the reference voltage (Vr) of the second operational amplifier (7) is optimized such that the control voltage (Vcd) obtained by using the dummy filter (2) is converted through the interface circuit (6) into a control voltage (Vcm) most suitable for the main filter (1), thereby obtaining a control voltage (Vcm) most suitable for regulating the frequency characteristics of the main filter (1) to desired characteristics.

Abstract: A tuning method and circuit for an LC tank resonant circuit, including an inductor and a variable capacitor, are described. In a tuning mode, an RF input signal is applied to an input port of the circuit, and the RF output signal is monitored as a variable capacitor control input is varied. A peak output is detected, and the corresponding variable capacitor control input is stored, and applied to the variable capacitor in an operating mode. In one embodiment, the variable capacitor control input is adjusted for delay in the peak detection process. In one embodiment, the variable capacitor comprises a coarse capacitor and a fine capacitor; the tuning procedure is repeated for each capacitor; and both coarse and fine variable capacitor control inputs are stored and applied to the respective capacitors in operating mode.

Abstract: An embodiment pertains to a phase locked loop (PLL) circuit. The PLL includes a voltage controlled oscillator which outputs a signal at a desired frequency. A phase detector is coupled to an output from the voltage controlled oscillator. The phase detector compares the phase of a signal output from the voltage controlled oscillator (VCO) with the phase of a reference signal. A loop filter is coupled to the VCO and the phase detector. The loop filter has a locking mode of operation for locking the phase of the VCO signal to the phase of the reference signal. The loop filter can subsequently be placed in a tracking mode of operation which adjusts the phase of the VCO signal to track the phase of the reference signal.

Abstract: Programmable SAW filter module are provided to overcome undesirable drawbacks, limitations and shortcomings associated with “in-line” SAW filters, such as insertion loss, propagation loss and strong signal capture effects. The programmable SAW filter modules remove the SAW structure from the primary signal path, adding signal gain to drive the splitter and using the SAW portion of the circuit as a programmable impedance element. The programmable SAW filter module includes an amplifier, an impedance, a surface acoustic wave propagation element, a splitter, input and output IDT electrodes, input and output interdigitated transducers, means for gain control and a combiner to combine or sum the signals received from the output IDT electrodes and form an output signal. The input and output IDT's are fully integrated circuits comprising the power splitter and power combiner functions, the phase shift, and gain functions.

Abstract: The average EMR emissions of an electronic device may be reduced by implementing an electrically-active modulated termination. For example, the impedance may be continuously varied at one or more termination locations between two metal substructures to cause a like variation in the amplitude of each component of the EMR. According to one approach, cyclically varying the electrical impedance with a period of less than the time interval over which the EMR is measured will result in a reduction in the average measured EMR.

Abstract: A method to track and control the resonance frequency of a band-pass filter provides a solution for the sensitivity limitations against temperature and process variations. A phase sensing module obtains the phase difference between the input and output and a negative feed-back control architecture can be used to tune the filter's resonance over the input RF frequency.

Abstract: A radiofrequency identification device (RFID) featuring an antenna (10) connected to a chip designed to be affixed to an object to be identified by a remote reader transmitting to the identification device electromagnetic signals received by the antenna and containing the data allowing the identification as well as the supply voltage (VDC) of the device, the antenna transmitting in return to said reader signals provided by the chip by retromodulation by means of a switch (22) in the chip whose open or closed position defines the digital identification data transmitted by the device. The chip features a variable impedance (30) connected in series with the switch to the terminals of the antenna and a means for detecting (32) the supply voltage to adjust the impedance value so that this supply voltage is always greater than a predetermined value (Vthreshold) below which the device can no longer transmit digital identification data.

Abstract: An antenna device includes an antenna element, a high-frequency circuit connected to the antenna element, a first ground section connected to the high-frequency circuit, a reactance circuit connected to the first ground section, and a second ground section connected to the reactance circuit. Employing the structure above allows the antenna device to have a compact body and to easily control antenna characteristics, such as radiation characteristics and input impedance characteristics.

Abstract: Compensation of a signal using resonators as well as related methods and devices are described. Some embodiments include methods and devices for performing frequency compensation on a signal.

Abstract: The system for the automatically tuning of multicavity filters of high frequency signals, by means of screws sticking out from the lid of the plate incorporating said cavities, comprises a robotized movement imparting subsystem SUB-1A, a measuring subsystem SUB-2M for the extraction of the transfer characteristic, a subsystem SUB-3C to compare said measured values to reference parameters, a subsystem SUB-4G for the generation of said reference parameters, and a subsystem SUB-5CO enslaved to said SUB-4G and SUB-1.

Abstract: The invention relates to a variable capacitance circuit which achieves reduction in both of distortion and current consumption and furthermore achieves requirements of high power handling capability, cost reduction, and downsizing of the circuit.

Abstract: Methods, systems and apparatus for filter design, analysis and adjustment are provided. Various embodiments may include, for example, methods, systems and apparatus for electric signal filter tuning. Embodiments may also include design techniques for planar electric signal (e.g., RF signals) filter tuning. In at least an embodiment of the present invention a technique for filter tuning is provided which may include parameter extraction, optimization and tuning recipes techniques that may require only a single permanent filter tuning. In at least another embodiment a system and method of filter design, analysis and adjustment according to the present invention includes use of tuning that may be set using a mechanical scribing tool or a laser trimming device. In at least one other embodiment, a filter tuning technique may be provided and include providing trimming tabs on a resonator edge that may be disconnected or trimmed for filter tuning.

Abstract: An automatic tuning system for a magnetic field generating tuned circuit includes a processor configured to maintain the resonant frequency of a tuned circuit equal to a reference frequency. The tuned circuit is driven by a power amplifier whose output provides an amplified signal at the reference frequency. The tuned circuit includes a magnetic field generating inductor and a bank of individually switchable capacitors controlled by the processor capable of adding and removing the respective capacitances to and from the tuned circuit. The inductor includes a Faraday shield to shield the tuned circuit from the influence of electric fields. In an embodiment of the invention, the variable capacitor is in the form of a diode variable capacitor (varicap) in parallel circuit relationship with the tuned circuit capacitor and the inductor.

Abstract: Methods, systems and apparatus for filter design, analysis and adjustment are provided. Various embodiments may include, for example, methods, systems and apparatus for electric signal filter tuning. Embodiments may also include design techniques for planar electric signal (e.g., RF signals) filter tuning. In at least an embodiment of the present invention a technique for filter tuning is provided which may include parameter extraction, optimization and tuning recipes techniques that may require only a single permanent filter tuning. In at least another embodiment a system and method of filter design, analysis and adjustment according to the present invention includes use of tuning that may be set using a mechanical scribing tool or a laser trimming device. In at least one other embodiment, a filter tuning technique may be provided and include providing trimming tabs on a resonator edge that may be disconnected or trimmed for filter tuning.

Abstract: A programmable surface acoustic wave filter and methods thereof including a piezoelectric substrate, a ground electrode formed in a comb structure on the piezoelectric substrate, a plurality of output electrodes formed in comb structures on the piezoelectric substrate and alternately disposed together with the ground electrode, and a switching unit performing a switching operation so as to selectively transmit output signals output from the plurality of output electrodes to an output node. As a result, a filtering characteristic of the programmable surface acoustic wave filter can be programmed in a desired format.

Abstract: Embodiments of the invention provide an adaptive notch filter that employs a power detector as a feedback control mechanism to steer the notch filter. One such embodiment of the invention provides adaptive control of the notch filter capacitor to tune the notch filter frequency based upon a diode power detector. One embodiment of the invention provides a system including multiple cascaded adaptive notch filters each having a feedback control method from a power detector to separately control each filter. For one embodiment of the invention a method is disclosed for tuning an adaptive notch filter using a dithering process to determine a minimum power output at the power detector. One embodiment includes an adaptive notch filter implementing a device with a tunable resonance frequency.

Abstract: Channel equalization in a 1000BASE-T receiver is performed by a fixed mode analog filter 2 suitable for the longest possible cable length, by a FFE (3), and by a digital filter 4. The digital filter (4) has two sets of taps. One set is optimal for shorter cable lengths and so cancels adaptation for long cable lengths and assists operation of the analog filter. A decision block (5) selects an appropriate set of taps.

Abstract: A filter circuit including first and second real filters of a zero-IF scheme. The first and second real filters receive an I component and a Q component separated from a reception signal, respectively; and a switch section for producing a complex filter by switchably connecting the first and second real filters through interconnection elements. The switch section further receiving a switching signal for connecting the first and second real filters, thereby switching from the zero-IF scheme to a low-IF scheme.

Abstract: The invention provides a filter automatic adjustment apparatus and method, and a mobile telephone system, which realizes low power consumption while adjusting a characteristic frequency of a main filter having an adjustment function to a target frequency. The filter automatic adjustment apparatus includes: a phase difference detector 104 which outputs a signal having a duty ratio corresponding to a phase difference between an input signal and an output signal of a reference filter 103; a comparator 105 which converts the output signal of the phase difference detector into a rectangular wave; a counter 106 which consecutively counts a predetermined interval of the rectangular wave plural times; and a determination circuit 107 which selects a count value satisfying a predetermined criterion from the plural time count values, and the filter automatic adjustment apparatus adjusts the characteristic frequency of the main filter based on the selected count value.