Abstract: A low IF receiver frequency translates an input signal in quadrature related mixers, filters in respective low pass channel filters, and derotates to produce a wanted signal and its image. At switch-on, the receiver is operated as a zero IF receiver in order to determine which of the adjacent channels to the wanted channel has the smaller interferer, and the local oscillator frequency supplied to the mixers is then adjusted to bring that interferer into the channel bandwidth of the low pass channel filters.

Abstract: A RF receiver for modulated RF signals based on a N-port junction (1) providing LO/RF isolation is proposed. N thereby is an integer larger than two, such that the N-port junction (1) can be preferably a three port, four port, five port and six port junction. The N-port junction (1) supplied with a first RF signal at a first input (2) and with a second RF signal originating from a local oscillator (2) at a second input (3). An isolation block (13) comprising an active circuitry (22) is comprised in the N-port junction for isolating the second input (3) from the first input (1). Thereby can be ensured that the LO signals are significantly attenuated at the RF port (2).

Abstract: A radio transmitter and/or receiver comprising: an oscillator tuning circuit comprising an adjustable capacitor whose capacitance is adjustable by means of a first tuning signal; a filter tuning circuit comprising an adjustable capacitor whose capacitance is adjustable by means of a second tuning signal; an oscillator whose operational frequency is dependant on the reactance of the oscillator tuning circuit; a filter for filtering signals in the course of transmission and/or reception, and whose response is dependant on the reactance of the filter tuning circuit; and a tuning unit for generating the first and second tuning signals; wherein at least a part of the filter tuning circuit is a replica of at least a part of the oscillator tuning circuit and the tuning circuit is capable of generating one of the first and second tuning signals in dependence on the other of the tuning signals.

Abstract: The present invention provides a square wave local oscillator (LO) technique, applicable to devices or systems using Improved Harmonic Boosting Technique (IHBT), for achieving a DC-offset free Zero-IF signal in direct conversion receiver (DCR). A down converter using anti-parallel diode pair (APDP) cell or a modified Gilbert cell circuit mixes a received radio frequency (RF) signal with a LO signal having a square wave shape. A LO signal with a square wave-forming network provides the square wave forming circuit. A voltage control oscillator (VCO) generates a lower even order base frequency of the received RF signal.

Abstract: The present invention describes an Improved Harmonic Boosting Technique (IHBT) for achieving zero DC-offset in a direct conversion receiver (DCR). The technique may be applied to devices such as down converter, combiner, synthesizer, and voltage control oscillator.

Abstract: Methods and devices relating to radio applications. An input signal with an input frequency is fed into a double quadrature mixer circuit along with a local oscillator signal with a local oscillator frequency. These two signals are multiplied by the mixer circuit and produces an output signal with a frequency substantially equal to either a sum of the local oscillator frequency and the input frequency or a difference of the local oscillator frequency and the input frequency. By using the quadrature mixer, the output signal consists mainly of only one sideband of the multiplication process. The carrier is mainly suppressed along with the other sideband. The output signal is particularly useful as a small frequency offset for a synthesized signal.

Abstract: A data-pattern feedback mechanism is introduced into the peak detection process of an automatic frequency compensation system in a Gaussian Frequency Shift Keying (GFSK) modulated system, providing fast and accurate fine-stage automatic frequency compensation (AFC). Maximum positive and negative peak registers are updated with new values as necessary based on detection during a sequence of identical binary bit values (e.g., during a “00” for detection of maximum negative peak frequency, or during a “11” for detection of maximum positive peak frequency), in a particular data frame. As soon as an initial value is determined for both the maximum positive and negative peak frequencies (e.g., after the first occurrence of a “11” and a “00”, in any order), fine-stage automatic frequency compensation can be initiated. Subsequent adjustments to the VCO of the local oscillator will further refine the frequency offset towards the ideal of zero.

Abstract: A receiver for a wireless communication device is disclosed. The receiver comprises a plurality of frequency tines coupled to receive an intermediate frequency signal, each frequency tine of the plurality of frequency tines having a pair of NCOs; a comb filter coupled to the center frequency tine of the plurality of frequency tines; and a comparator circuit coupled to said plurality of frequency tines, the comparator circuit comparing two outputs of the plurality of frequency tines. A method of determining an intermediate frequency in a wireless communication device is also disclosed. The method comprises the steps of providing a plurality of frequency tines for receiving signals at a plurality of different intermediate frequencies; determining an approximate magnitude of a frequency offset from a center frequency; and determining the sign of the frequency offset.

Abstract: A frequency synthesizer provides first and second frequency output signals based on first and second control signals, respectively. The first control signal determines the frequency of the first output signal produced by a main frequency synthesizer. The second control signal determines the frequency of a variable offset frequency signal produced by a programmable offset frequency synthesizer. A mixer combines this variable offset frequency signal with the first output signal to produce the second output signal. As such, the second output signal has a programmable variable offset frequency relationship with first output signal. First and second control signals are independently controllable. A mobile terminal may advantageously use the frequency synthesizer to generate a receiver injection signal and a transmitter carrier generation signal having a variable frequency offset relationship.

Abstract: In one embodiment, this disclosure describes a frequency synthesizer for use in a wireless communication device, or similar device that requires precision frequency synthesis but small amounts of noise. In particular, the frequency synthesizer may include a phase locked loop (PLL) and an integrated voltage controlled oscillator (VCO). The frequency synthesizer may implement one or more calibration techniques to quickly and precisely calibrate the VCO. In this manner, the analog gain of the VCO can be significantly reduced, which may improve performance of the wireless communication device. Also, the initial state of the PLL may be improved to reduce lock time of the PLL, which may enhance performance of the wireless communication device.

Abstract: A differential RF input signal drives the plus and minus terminals of a center tapped primary winding, which couples the differential RF input signal to the plus and minus terminals of a center tapped secondary winding. From the secondary winding, the coupled, differential RF signal drives a double-balanced mixer core operating in response to a differential local oscillator signal. The output of the mixer core is a differential IF signal representative of the differential RF input signal down-converted at the local oscillator frequency. A step reduction in gain associated with the RF input signal may be implemented using bypass circuitry coupled across the primary of the transformer, wherein a relatively small resistance or impedance is coupled across the primary to effectively reduce the load of the differential amplifiers driving the primary.

Abstract: If a local oscillation wave of a frequency approximately half the received signal frequency is input to a low noise amplifier 2, a dc offset voltage caused by the nonlinearity of the amplifier is produced, thus degrading reception sensitivity. This problem is resolved by disposing before the low noise amplifier 2 a filter means, such as a bandpass filter 12, band-elimination filter 13, or high pass filter 14, with characteristics for passing the received wave and suppressing a frequency band at approximately half the received wave frequency, thus preventing a radiation wave at substantially the same frequency as the local oscillation wave from being input to the low noise amplifier 2. A filter circuit 15 is also provided in the low noise amplifier 2 as a means for eliminating a radiation wave input to the low noise amplifier 2.

Abstract: The invention provides an up/down converter with low phase noise. Signals from a first local oscillator are fed through a power splitter to first and second mixers. Signals from a second local oscillator and signals from the power splitter are mixed by the second mixer. The frequency component of the difference between the two signals is removed by a first bandpass filter and passed to a third mixer. Input signals are mixed with signals from the power splitter by the first mixer, and the lower frequency component of the output signals from the first mixer is removed by a second bandpass filter and is passed to the third mixer. Signals from the first and second bandpass filters are mixed by the third mixer. The higher frequency component of the output signals is removed by a low pass filter and is output.

Abstract: The receiver for various frequency bands has only one oscillator (OSZ), which is followed downstream by a frequency divider having a settable real divisor value. For generating the real divisor value, this frequency divider in turn has a multiplier with a settable integral multiplier value (M1) and a divider, downstream of the multiplier, with a settable integral divisor value (N1).

Abstract: The present invention relates to a local oscillator balun using an inverting circuit. The local oscillator balun using an inverting circuit comprises a complementary output converting circuit for amplifying a weak signal as a single signal from a local oscillator to produce two signals; a differential amplification circuit for producing two signals having a given amplitude from the two signals of said complementary output converting circuit; and an inverting circuit for inverting the two signals of the differential amplification circuit. Thus, a complementary signal having the maximum amplification and small phase difference can be produced. Therefore, the present invention can implement the maximum gain and small local oscillating leakage of the frequency mixer in a Gilbert type high frequency double balance frequency mixer.

Abstract: A mixer circuit (21) includes first (31) and second (32) transconductance amplifiers, a switching circuit (34), and an oscillator processing stage (36). The transconductance amplifiers (31,32) generate differential current signals in response to modulated signals having different carrier frequencies. The oscillator processing stage (36) generates a local oscillator signal from a reference oscillator signal. The switching circuit (34) switches the differential current signals at the frequency of local oscillator signal to generate an intermediate frequency output signal.

Abstract: In a quadrature mixer circuit for receiving a radio frequency signal to generate first and second quadrature output signals, a first three-input mixer receives the radio frequency signal, a first local signal having a first frequency and a second local signal having a second frequency to generate the first quadrature output signal, and a second three-input mixer receives the radio frequency signal, the first local signal and the second local signal to generate the second quadrature output signal. The second local signal received by the first three-input mixer and the second local signal received by the second three-input mixer being out of phase by &pgr;/2 from each other.

Abstract: A local oscillator signal for direct downconversion is generated using an upper frequency oscillator signal and a lower frequency oscillator signal, both of which have frequencies different from a frequency of an RF input signal. The local oscillator signal thus generated has a frequency that is either the sum or the difference of the frequencies of the upper and lower frequency oscillator signals. As a result, the risk of local oscillator signals re-radiating and coupling the RF signal input is significantly reduced. In addition, in QPSK systems, a quadrature local oscillator signal can be generated with accurate phasing relative to an in-phase local oscillator signal.

Abstract: An apparatus for centering the frequency of an injection locked oscillator (ILO) measures the difference of the phase (or a parameter related to the phase) between ILO output signals in response to alternate high level and low level RF drive signals, and can tune the center frequency of the ILO in accordance with the measurements to minimize the phase difference.

Abstract: Methods in intermediate frequency and direct conversion receivers for reducing pre-selection filter leakage and harmonic coupling to a programmable voltage controlled oscillator by mixing a receive signal at a mixer having a mixer injection frequency outside a pre-selection filter passband. In some applications, the mixer injection frequency is conditionally moved outside the pre-selection filter passband. In other applications, signal gain is increased to compensate for any loss resulting from shifting the mixer injection frequency outside the pre-selection passband.

Abstract: A two transistor mixer for mixing radio frequency signals in a communications device. A mixer core section comprised of a pair of matched semiconductor devices having their drain ports connected to a first common node through matched load resistors and their source ports connected to a second common node end. A local oscillator (LO) signal input connected to the first and second nodes, wherein the connection to the second node is through a current source. A radio frequency (RF) signal input connected to the gate ports of said pair of semiconductor devices and an intermediate frequency (IF) output obtained from the drain ports of said pair of semiconductor devices.

Abstract: A local oscillator apparatus is disclosed for use in radio frequency communication systems. The local oscillator apparatus comprises at least one mixer coupled to an oscillator input signal and to a feedback signal such that a local oscillator signal may be produced by fractional multiplication of the oscillator input signal. In an embodiment of the invention, the local oscillator apparatus includes a regenerative modulator comprising a pair of frequency dividers and a single side band mixer.

Abstract: An LO generation circuit generates an LO signal by doubling and quadrupling the frequency of a VCO signal. The frequency doubling and quadrupling provides high VCO-RF isolation as well as suppression of spurious noise signals in the LO output. The frequency doubler takes a quadrature signal input and utilizes mixer cores having double balanced transistor pairs to provide an output signal having doubled frequency but maintaining the phase balance of the input signal.

Abstract: A mixer circuit including a mixer (MIX) for mixing the RF signal supplied to the mixer (MIX) and reinforced in a preamplifier (LNA) with an LO signal supplied to the mixer (MIX). A line (L1) common to the RF signal and the LO signal is connected with the input of the preamplifier (LNA). In addition, there is another line (L2) which the RF signal and the LO signal have in common, and which connects the output of the preamplifier (LNA) with the input of the mixer (MIX), the level of the LO signal being below the compression point of the preamplifier (LNA).

Abstract: An analog multiplier or mixer that mixes a signal fc with a square wave local oscillator improves heterodyning operation of a circuit. In various square wave analog multiplier or mixer embodiments, heterodyning performance is improved in noise reduction, saturation performance, linearity, and other measures by adding a DC current path in parallel to a signal current path of the multiplier or mixer. The parasitic capacitances, noise, and nonlinearity problems in a heterodyning circuit are solved by adding a path to a square wave mixer for carrying the signal current and the DC current on different paths. An apparatus includes a circuit coupled between a first voltage reference and a second voltage reference. The circuit includes a first square wave oscillator branch and a second square wave oscillator branch. The first square wave oscillator branch is driven by a square wave oscillator signal and the second square wave oscillator branch is driven by an inverse of the square wave oscillator signal.

Abstract: A receiver of a mobile communication terminal comprising a down-converter for down-converting a signal received to the receiver into an intermediate frequency signal, a first received signal path for providing the received signal to the down-converter, the first received signal path including a low-noise amplifier for low-noise amplifying the received signal, and a band pass filter for band pass filtering an output signal from the low-noise amplifier to pass only signal components within a reception band of the mobile communication terminal, a second received signal path for providing the received signal directly to the down-converter, and a controller for providing the received signal to the down-converter through one of the first received signal path and second received signal path on the basis of first and second received signal power threshold values. The first and second threshold values are set in consideration of losses of the low-noise amplifier and band pass filter.

Abstract: Angle-modulated signals are transmitted in a communications system, in which coding information has been inserted into the transmitted data at regular intervals. The coding information is phase-modulated together with the transmitted data. This coding is used for pulse shaping, so that the receiver can recover the digital transmitted data with less implementation complexity and without carrier phase control by using appropriate signal processing.

Abstract: Whenever the oscillator frequency is a fraction or a multiple of the received frequency, another received frequency could in turn be there, which would then work as a kind of received disturbance frequency, and thus oscillator pulling occurs, which then severely impairs evaluation of the received signal. The method according to the invention for driving a receiver stage having a selection means, having a control unit and an oscillator is distinguished by the fact that the selection means is driven such that whenever the oscillator frequency is a fraction or a multiple of a received disturbance frequency, this received disturbance frequency is attenuated by the selection means.

Abstract: A down-converting circuit for a multiple-band wireless communications device needs only one voltage-controlled (VCO) with a relatively narrow tuning range, and down-converts multiple different received RF signals to produce intermediate frequency (IF) signals having a common frequency. The VCO output signal serves as a first LO signal. The circuit also has up to two frequency translators, the first of which (e.g., a divide-by-2 translator) receives the VCO output signal and produces a second LO signal. The second frequency translator (e.g., a divide-by-1.5 frequency translator) also receives the VCO output signal and produces a third LO signal. The received RF signals are down-converted using the LO signals and mixers. One of the received RF signal types is a GPS signal, which is down-converted using an LO produced at the output of a divide-by-1.5 frequency translator.

Abstract: A mixer comprises an LO (Local Oscillator) switching circuit for switching in response to an LO signal, a driver amplifier driven in response to an RF signal, an IF generator for generating an IF signal by detecting a difference between the LO signal and the RF signal, a filter for detecting a nonlinear low frequency intermodulation component of the RF signal, a low frequency amplifier for amplifying the low frequency intermodulation component and inverting a phase of the low frequency intermodulation component and an intermodulation component feed-forwarding circuit for feed-forwarding the amplified low frequency intermodulation component to output terminals of the driver amplifier or the LO switching circuit whereby the low frequency intermodulation component can be removed. The mixer removes an intermodulation component of an input RF signal generated due to the nonlinear characteristic of an RF amplifier, thereby to improve the linearity of the mixer.

Abstract: A microwave frequency converting receiver of an RF unit should be generally used in wireless/mobile communications systems such as cellular, PCS, WLL and IMT2000 systems and also have low power consumption, low-noise characteristic, high gain and small size.

Abstract: A frequency conversion circuit includes a first mixer for performing frequency conversion of a received signal having components disposed at first frequency intervals into a first intermediate frequency signal which has a frequency lower than that of the received signal and which has components disposed at predetermined frequency intervals, two second mixers for performing frequency conversion of the first intermediate frequency signal into a second intermediate frequency signal having a frequency lower than that of the first intermediate frequency signal. A first local oscillation signal changing at second frequency intervals different from the first frequency intervals is supplied to the firs mixer, and a second local oscillation signal having a frequency which is the reciprocal of an integer of the frequency of the first local oscillation signal is supplied to the second mixers.

Abstract: A frequency translating device (FTD) includes at least one mixer diode connected to down-convert a radio frequency (RF) to an intermediate frequency (IF) and to up-convert an IF to an RF and a source of direct current (DC) bias that is connected to the mixer diode. The source of DC bias provides DC bias to the mixer diode that moves the voltage applied to the mixer diode closer to the threshold voltage of the mixer diode. The mixer diode is turned on in response to the DC bias and a local oscillator (LO) drive. Because DC bias is applied to the mixer diode, the peak to peak voltage range of the LO drive can be reduced, thereby reducing the voltage-dependent capacitance of the mixer diode, causing the FTD to exhibit improved reciprocity. The FTD can be used in a three-pair measurement system to determine the conversion response of another FTD.

Abstract: A system for amplifying a transmitted signal is provided. The system includes a receiver that receives the transmitted signal and generates a conducted signal from the transmitted signal. A non-linear oscillator, such as a synchronous oscillator that is operating in a borderline stable condition, is connected to the receiver. The non-linear oscillator receives the transmitted signal from the receiver and amplifies the transmitted signal without modifying the frequency of the transmitted signal, or its relative phase. The amplification by a non-linear oscillator causes the signal to be amplified relative to the noise, thus improving the signal-to-noise ratio.

Abstract: An integrated circuit includes at least an inductive element and an active region which may include resistive, capacitive and semiconductor elements. The inductive element and part of the active region are superimposed. The integrated circuit has a screen for insulating the active region with respect to an electromagnetic field that the inductive element develops. The screen allows the implementation of inductive elements having high quality factors in integrated circuits of reduced size and in which the electromagnetic interactions between the inductive elements and the other elements are reduced.

Abstract: A direct conversion receiver which amplifies a high-frequency reception signal from an antenna by using an amplifier and converts the signal into a baseband signal by using a mixer comprises an attenuator provided on the input stage of the mixer, and a control device for comparing an antenna reception power with a first threshold and controlling the attenuation amount of the attenuator on the basis of an comparison result. The control device comprises a switching control section for comparing the antenna reception power with the first threshold and controlling switching between a route through the attenuator and the route through the amplifier on the basis of the comparison result.

Abstract: A tuner comprises a frequency changer which converts an input signal to a predetermined fixed intermediate frequency. The frequency changer is followed by an IF filter having a filter parameter, such as center frequency, which is electronically adjustable. A controller adjusts the adjustable filter characteristic so as to achieve a predetermined desired filtering performance, such as ensuring that the filter center frequency corresponds to the desired intermediate frequency. The controller comprises a local oscillator having the same type of tuned circuit as the IF filter. A phase locked loop compares the local oscillator frequency with a reference frequency and controls the tuned circuits of the IF filter and the local oscillator.

Abstract: The present invention proposes a direct receiver technique based on one power measurement and time multiplexing of input signals. The proposed technique allows I/Q demodulation. The proposed technique bases on the passive linear three-port high frequency circuitry (1) having two RF signal input (2, 5) and one output port (3) attached to a power sensor (4). The signals output from the power sensor (4) is low pass filtered (17) and supplied to a DC interface. The proposed linear three-port circuitry (1) contains at least one RF switch and at least one passive circuit having at least one phase shifter functionality.

Abstract: An antenna receiver includes a plurality of mixers for frequency-converting signals received by a plurality of antennas into intermediate-frequency signals; a plurality of local oscillators, which correspond to the plurality of mixers and which supply local oscillation signals having the same frequency to the mixers; a plurality of PLL circuits, which correspond to the plurality of local oscillators and which set the frequency of the local oscillation signals; and an adder for adding the intermediate-frequency signals output from the mixers. The phases of reference signals supplied to the PLL circuits can be changed independently from each other.

Abstract: A voltage control oscillation circuit is provided on the respective layers of a ceramic multilayer substrate, and an unbalanced transmission line and a balanced transmission line are provided to sandwich a predetermined ceramic layer, whereby an unbalance-balance conversion circuit is defined due to the mutual induction coupling between the transmission lines.

Abstract: An active balun circuit is provided for single-ended to differential RF signal conversion with enhanced common-mode rejection which suppresses common mode signal and which achieves phase and amplitude balance without sophisticated tuning or compensation methods. The circuit has a single-ended input and balanced output with phase and amplitude balance error less than 2° and 1.2 dB, respectively, measured from 1.5 GHz to 1.8 GHz at 5V supply. When supply voltage drops down to 1.5V, its phase and amplitude balance error remains within 5° and 2 dB, respectively. The circuit achieves a balanced output via an output network which behaves as an impedance matching network for differential mode signal and is grounded for common mode signal. As a result, common mode signal is suppressed and 180-degree phase balance at output is achieved. The circuit has high-linearity (P1 dBin=5 dBm, IIP3=16.

Abstract: An analog tuning circuit, a phase locked loop and a controller form a semiconductor integrated tuning device, and the analog tuning circuit has a variable band pass filter between a mixer and an amplifier so as to match an intermediate frequency signal to a telecasting facility standard, wherein the controller supplies control signals produced on the basis of an external instruction to the variable band pass filter so that the semiconductor integrated tuning device is shareable between the products exported to difference countries.

Abstract: A method and apparatus for defining and generating a digital waveform such as used for the local oscillator for a down converter in a receiver is disclosed. The method and apparatus is particularly useful where the digital waveform is not an integer submultiple of a reference signal. A plurality of different digital waveforms meeting the timing criteria but having different combinations of segments needed to meet the timing criteria are generated. Each of the digital waveforms so generated are tested in, for instance, a receiver to enable the selection of the best combination of segments.

Abstract: A communications interface adapter facilitates both wired and wireless communications between crew members of a vehicle having a wired intercom and has an intercom communications circuit having an input/output port for providing electrical communication between the interface adapter and the wired intercom and also has a fixed radio transceiver. The fixed radio transceiver comprises a receive circuit for receiving radio communications and for communicating the received radio communications via the intercom communications circuit to the wired intercom of the vehicle and a transmit circuit for transmitting communications received via the intercom communication circuit from the wired intercom of the vehicle.

Abstract: The present invention use the properties of a TDD-transmission on a general mixer in such a manner that in the transmit mode a first RF signal is amplified in the mixer with an amplification factor greater than, or equal to, or less than one, and in the receive mode the received RF signal is mixed with a second RF signal.

Abstract: A frequency converter includes a multiplying circuit, a load circuit, and an output buffer circuit. The multiplying circuit is arranged to multiply an RF signal and an LO signal and output a difference frequency signal with a frequency, which is the difference between the frequencies of the two signals, from its output terminal. The load circuit is arranged to connect the output terminal of the multiplying circuit to a power supply. The output buffer circuit is arranged to have an input terminal connected to the output terminal of the multiplying circuit, and an output terminal for outputting a signal to the next stage. A notch circuit for removing an undesired signal frequency component is combined in the load circuit. The notch circuit has an impedance characteristic in which the impedance is abruptly reduced to provide a valley point at the undesired signal frequency.

Abstract: A receiver is operable even if including a local oscillator generating a signal at high frequencies but not in a wide frequency range. The receiver includes: a first frequency converter for mixing a received signal with a first local oscillation signal to convert the received signal into respective signals of plural first intermediate frequencies corresponding to a frequency of the received signal; and a second frequency converter for converting the signals of the first intermediate frequencies into a signal of a second intermediate frequency.

Abstract: An image rejection mixer (IRM) for rejecting signals having image frequency and, more particularly, a mixer for rejecting signals of image frequency by using mismatch compensation is provided.

Abstract: A voltage controlled oscillation device includes a voltage controlled oscillator, fixed-frequency oscillator, frequency mixer, and frequency selector. The voltage controlled oscillator changes the output signal frequency in the microwave band in accordance with the input voltage of a frequency control signal. The fixed-frequency oscillator has a fixed oscillation frequency higher than that of the voltage controlled oscillator. The frequency mixer mixes the output signal from the fixed-frequency oscillator and the output signal from the voltage controlled oscillator and outputs the sum frequency and difference frequency between the two signals. The frequency selector selects and outputs one of the sum frequency and difference frequency contained in the output signal from the frequency mixer.

Abstract: A compact frequency multiplier can perform high-degree frequency multiplication and can be incorporated in a wireless device. The frequency multiplier includes an input terminal for inputting an input signal, a first resonant circuit resonating with the frequency &ohgr; of the input signal, a second resonant circuit and an idler circuit, which resonate with the frequency n·&ohgr; that is, n times the frequency of the input signal, a variable reactor such as a varactor diode, coupling-adjusting capacitors, a bias resistor, and an output terminal for outputting multiplied output signals. In one embodiment, the frequency multiplier is a current-excitation type. The first resonant circuit and the second resonant circuit, each of which is constituted of an LC series resonant circuit, are connected in series between the input terminal and the output terminal.