Abstract: A microwave group delay equalizer in microstrip form comprises a dielectric substrate having a ground plane on one surface and on the other surface two conductive strips oriented end to end and spaced apart by a narrow gap and connected together by a relatively narrow inductive conductive strip of substantially greater length than the gap between the first two strips. A dielectric layer overlies the adjacent ends of the first two conductor strips. A fourth conductor strip is disposed over the dielectric layer to provide capacitive coupling between the first and second conductors. The fourth conductor is connected to a grounded capacitor by a fifth relatively narrow inductive conductive strip.

Abstract: An equalizer cavity apparatus which is directionally coupled to a rectangular waveguide utilizes a circular waveguide with an adjustable RF absorber therein to lower the quality factor, Q, of the equalizer cavity.

Abstract: A low cost automatic equalizer is provided for reducing the amplitude and phase distortion produced by close-in echos. The color subcarrier burst, or some other portion of the video signal having predetermined amplitude and phase characteristic prior to transmission, is gated into detection circuitry. A regenerated color subcarrier, phase shifted to be in phase with the subcarrier burst, is used to detect the in-phase and quadrature components of the subcarrier burst, which are indicative of amplitude and phase distortion. The signals indicative of amplitude and phase distortion are applied to a three tap delay line equalizer, where the amplitude and polarity of the first and third tapped signals are controlled in unison to reduce amplitude distortion, and where the amplitude of the first and third tapped signals is controlled in unison, but the polarity of the first and third tapped signals is controlled oppositely to reduce phase distortion.

Abstract: An electronic hybrid voice frequency repeater having a pair of term sets interconnected by a four-wire circuit for separating the two directions of signal transmission and amplifying each direction separately. Each term set couples the repeater's four-wire circuit to a two-wire line and has a differential current driver for driving the two-wire line and a differential amplifier connected in a feedback loop for sensing the differential signal voltage across the two-wire line, to drive the current driver and to feed an incoming differential signal on the two-wire line to the repeater's four-wire circuit while nulling signals arriving at the term set from the four-wire circuit to prevent them from returning to the four-wire circuit. Other features disclosed include a low frequency clamping circuit, an adjustable-gain amplifier, and an equalizer for non-loaded cable.

Abstract: An equalizer circuit for communication signals is constructed as an active Bode equalizer employing an amplifier having anti-phase outputs and a bridge circuit connected to the outputs. The susceptibility of the equalizer to manufacturing tolerances is reduced insofar as possible and the transfer function of a passive Bode equalizer is retained, as far as possible, even at frequencies which lie far above 10 MHz.

Abstract: The dispersive effects of frequency selective fading in a digital, FM, or AM radio system are reduced by means of an adaptive equalizer (11) comprising a cascade of feed-forward stages (1,2, . . . N), each of which includes: a first parallel wavepath (1-1, 1-2, . . . 1-N) including a first adjustable attenuator (20-1, 20-2, . . . 20-N); a second parallel wavepath (2-1, 2-2, . . . 2-N) including a second adjustable attenuator (21-1, 21-2, . . . 21-N) and delay means (22-1, 22-2, . . . 22-N); and means (23-1, 23-2, . . . 23-N) for combining the signals in said wavepaths and for coupling said combined signal to the next stage. By a suitable selection of parameters, according to two unique relationships, a transfer function can be realized which can compensate for amplitude and delay distortions caused by minimum and nonminimum phase fades.

Abstract: There is disclosed an automatic line buildout circuit which includes in its signal path two variable filters, each implemented by a transconductance operational amplifier circuit. Each filter exhibits a transfer function pole with a frequency which is directly related to a control current applied to that filter. At a point in the signal path after the two variable filters, there is a peak detector which provides an output level proportional to the peak amplitude of the signal in the path, and therefore proportional to the cable length. From the peak detector output level, there is derived for each of the variable filters a control current, related to the output level by a preselected function. For each variable filter, the associated function expresses the relation between cable length and the filter cutoff frequency which is required for proper equalization.

Abstract: A bandpass filter circuit includes first and second resistors connected in series between input and output terminals thereof, an amplifier having a gain of three and its output connected to the output terminal, and an RC circuit network connected between the connection point of the first and second resistors and the input of the amplifier and having bandpass characteristics. The RC circuit network comprises a series combination of a third resistor and a first capacitor connected between the connection point of the first and second resistors and the input of the amplifier, and a parallel combination of a fourth resistor and a second capacitor connected between the input of the amplifier and a common terminal of the filter circuit. The third and fourth resistors have an equal resistance value and the first and second capacitors have an equal capacitance value.

Abstract: An equalizer amplifier in which non-linear distortion is substantially eliminated. An input signal is applied to the base of a first transistor the output of which is applied to the base of a second transistor of the opposite conductivity type to the first transistor. Currents are supplied to the first and second transistors in a constant ration. The output from the circuit is provided in response to current flowing in one of the first and second transistors. At least one of the amplifier gain determining elements has a reactance component which varies depending on frequency.

Abstract: A split phase delay equalizer is provided which reduces loss without resorting to high values of load impedance. The equalizer has a pair of parallel circuit branches, one of which is through the base and collector of a transistor, and the other through a reactance network connected between the collector and base of the transistor.

Abstract: An amplitude equalizer, suitable for use on telephone lines, is disclosed. The circuit includes an adjustable-gain amplifier, and an adjustable-slope equalizer section. A mixer section serves to combine the input signal with a filtered version thereof, in a manner which enables the installer to bring the line of response to specification level at a first predetermined frequency, and then to bring the line to specification level at a second frequency, without disturbing the previously achieved gain at the first frequency.

Abstract: A split phase delay equalizer is constructed using a single transformer. An adjustment for Q loss is provided by a flat loss shift in the amplitude response of the equalizer down to a level at or below the lowest Q loss dip level.

Abstract: Stray reactance compensation is provided in a split phase delay equalizer by inserting an auxiliary compensating small reactance in the substantially real arm circuit branch which provides a third order response equal and opposite to the deviation from second to third order in the amplitude response curve caused by stray reactance deviated phase reversal from the ideal.

Abstract: A self-correcting audio equalizer is disclosed for use in a high fidelity sound reproduction system. The equalizer (46) responds to the audio signal to provide an equalized audio signal to a sound reproducing device (28) for generating a corresponding acoustic signal. The equalizer includes circuitry (48- 58) for dynamically measuring the differences between the frequency versus amplitude characteristics of the audio and acoustic signals. Another circuit (60- 68) automatically adjusts the frequency versus amplitude characteristics of the equalized audio signal so that the measured differences are reduced. The adjustment of the equalizer thus takes place automatically and substantially continuously during normal operation of the system.

Abstract: A transversal filter having an overall impulse response of the form ##EQU1## and producing, from an applied input x(t) an output ##EQU2## where y(t) is obtained by lowpass filtering of a waveform z(t) in use generated in the filter, where z(t) takes the form: ##EQU3## where h.sub.i represents a set of stored coefficients,f(.tau.) is an impulse response accounting for fixed linear filtering at the input and output, independent of the settings h.sub.i, and.delta.(.tau.-.tau..sub.i) is the Dirac delta function defined as a function of time interval .tau. and of a set of time delays .tau..sub.i, where .tau..sub.i is not equal to iT.

Abstract: In a frequency characteristic adjusting circuit having an arrangement of at least one adder, a filter circuit and feedback and/or feed forward means the transfer factors of which and the peak or dip of the filter circuit are freely selectable. Adjustment of the center frequency and Q are independent.

Abstract: An amplitude equalizer is provided for equalizing amplitude distorted signals within a predetermined frequency band. The amplitude equalizer comprises first means for splitting signals into first and second split signals. A first delay device receives one of the two split signals, and a second signal splitter splits the output of the first delay device into third and fourth split signals, the third split signal being applied to a second delay device having a delay equal to the delay of the first delay device. The output of the second delay device is combined with the second output from the first signal splitter in a first signal combiner, the output of which is applied to a circuit for adjusting the polarity and gain of the signal applied thereto. The output of the polarity and gain adjusting circuit is applied to a second signal combiner which combines the adjusted signal with the fourth output from the second signal splitter to thereby provide equalized signals.

Abstract: The invention is used in a receiver for a communication system, which transmits periodically occurring digital signals over a pair of orthogonally related polarized waves. Horizontal signals from one of the orthogonal waves are applied to a first input terminal of an equalizer in the receiver. Vertical signals from the other of the orthogonal waves are applied to a second input terminal. An individually associated, cascaded plurality of delay circuits is coupled to each of the input terminals. The delay in each of the delay circuits is equal to the time spacing between the occurring signals. Therefore, a plurality of the recurring digital signals appear simultaneously at the outputs of each of the delay circuits. A variable attenuator, individually associated with the output of each delay circuit, is adjusted to pass an incremental signal responsive to each of the occurring signals appearing simultaneously at the outputs of the delay circuits.

Abstract: In a loudness control circuit, the output DC voltage of a first variable DC voltage source is applied to a first amplifier for increasing volume to vary the gain of the latter, and to first and second differential amplifiers, while the output DC voltages of second and third variable DC sources are applied to the first and second differential amplifiers to provide difference voltages, which the applied to second and third tone control amplifiers which amplify the low and high frequency ranges, respectively, to control the gains thereof, so that the components of the sound in the low and high frequency ranges are boosted, thus achieving the weighting.

Abstract: An equalizer circuit arrangement is provided for use without readjustment for a wide range of transmission line lengths. The circuit (10) is comprised of a resistor (20) and a capacitor (22) which introduce an additional time constant delay into the transmission system in order to reduce the percentage change of the transmission line response time for the shortest line used as compared to the longest line employed. This reduction permits one equalizer to be designed and used for the complete range of transmission line lengths involved.

Abstract: A system is disclosed for frequency compensation and amplitude compression of signals from a scene having targets which radiate infrared energy. The system uses at least two combinations, where each combination consists of an operational amplifier and a variable resistance element. These combinations are electrically coupled to each other. A circuit connected to one of the amplifiers provides high frequency compensation for radiated energy by small targets in the infrared scene. The system also utilizes a reference source which is coupled to the input of another of the amplifiers.

Abstract: In a sampling function type equalizer having a transversal filter with a plurality of potentiometers, the tap weights of the transversal filter are adjusted according to the desired values of the amplitude-frequency characteristics A.sub.p (n), and the delay-frequency characteristics .tau..sub.p (n). The first multiplication of A.sub.p (n) and the predetermined discrete function in addition to the second multiplication of said .tau..sub.p (n) and said predetermined discrete function, are performed. Also, the Bessel function is provided according to the product of the second multiplication. The first convolution integration is performed for the product of the first multiplication, the second convolution integration is performed for the output of the Bessel function, and the third convolution integration is performed between the results of said first and the second convolution integrations. The result of the third convolution integration provides the tap weights of the potentiometers of the transversal filter.

Abstract: Circuitry is disclosed for detecting signal amplitudes of a signal which is phase indicative of a digital logic level and providing a feedback signal for use in amplitude adjusting the signal to have a substantially zero slope over the relevant frequency bandwidth. The compensation is obtained by applying a voltage to variable impedance pin diodes which form part of a reactive load circuit.

Abstract: An automatic equalizer for digital transmission systems is disclosed including a variable gain amplifier in one branch of a two-branch admittance circuit. The branch including the amplifier includes two frequency-dependent admittances while the other branch is insensitive to frequency. Varying the gain of the amplifier provides a minimum phase network which can be automatically adjusted to compensate for varying lengths and gauges of telephone pairs. This configuration permits digital transmission in the subscriber loop plant at rates up to 200 kilobits per second.

Abstract: Programmable or fixed delay response shape bulk delay extender circuit for a line conditioner or equalizer system having a cascade set of all pass sections for processing signals in which said sections introduce for different frequencies a delay of said signals, and programming apparatus for selectively neutralizing such delay introduced therein by one or more of the all pass sections to produce various delay response shapes or to effect a complete bypass of the bulk delay extender.The programming apparatus is a multi-position rotary switch having both indication mechanism and controlling mechanism selectively neutralizing delay introduced by one or more of the all pass sections to produce various delay response shapes or effecting a complete bypass of the bulk delay extender.

Abstract: A resonant circuit phase equalizer includes two quarter-wavelength-long strip conductors extending in parallel from adjacent ends of respective input and output strip conductors of a microwave stripline transmission line. A fixed MIS direct-current-blocking and radio-frequency tuning capacitor is connected across the remote ends of the quarter-wave strip conductors. A variable varactor capacitor is connected across the near ends of the quarter-wave strip conductors. A variable direct-current bias voltage is applied through radio frequency choke conductors to the varactor to vary the capacitance thereof and the center frequency tuning of the equalizer.

Abstract: A signal amplitude equalizer circuit, having linear phase, for reforming high density magnetically recorded read-back signals to remove peak shift and the resulting errors caused thereby. The equalizer circuit employs series balanced differential amplifier circuits in connection with properly terminated delay lines across the amplifier output terminals to provide an adjustable transfer function that transforms the readhead signal, that follows an exponential frequency spectra curve, into a cosine power frequency spectra curve which, in the time domain, possesses a sufficiently narrow base to eliminate peak shift and its resulting amplitude decay.

Abstract: A variable equalizer for compensating for the frequency characteristics of transmission media, comprising a plurality of variable circuits which are connected in cascade to an input terminal and which have the same variation characteristics, coefficient circuits which receive input and output signals of the variable circuits as inputs thereof and which multiply the inputs by coefficients, a plurality of impedance circuits which receive as inputs thereof signals with outputs of the coefficient circuits selectively combined and which have frequency-dependencies, and an adder circuit which adds outputs of the impedance circuits to provide an equalized signal as its output. No feedback circuit is required in the construction, and the plurality of variable circuits are constructed of the same circuits. Therefore, a variable equalizer which is capable of high-speed operation, whose circuit arrangement is simple and whose compensation accuracy is high is realized.

Abstract: An amplitude equalizer includes a pair of serially connected unit amplitude equalizers, each having complementary delay distortion characteristics to flatten the overall delay distortion characteristic. The unit equalizers include amplifiers or attenuators, delay circuits, and/or phase shifters. The amplitude versus frequency characteristic of the overall equalizer can be varied by controlling one or more of the attenuator/amplifiers and phase shifters. The variation can be controlled by a feedback circuit.

Abstract: A variable resistance device in the form of a PIN diode is connected between one of a pair of input terminals and one of a pair of output terminals, and the other input and output terminals are connected to a common terminal.A distributed constant line is connected between the output terminal of the PIN diode and the common terminal, and variable capacitance diodes are connected between the opposite ends of the distributed constant line and the common terminal. By applying a control voltage applied to the PIN diode and the variable capacitance diodes, the steepness and the center frequency of the variable resistance device are varied.

Abstract: An equalizer introduces into the attenuation versus frequency curve of a signal carrier transmission system compensatory bumps of adjustable magnitude and of adjustable frequency location. When the bumps are in their initial frequency locations, they exhibit the following features: (a) The middle frequencies of the bumps are each shiftable with respect to frequency by an amount equal to at least one half the frequency interval to the respective neighboring bump. (b) Adjoining bumps of equal magnitude have facing flanks which overlap and intersect at a point which is at least 0.6 of the way up the height of the bump. (c) The middle frequencies of the individual bumps are distributed within the frequency range to be equalized in at least approximate correspondence to the detail density distribution function d*. The function d* is a novel function defined herein.

Abstract: An active variable equalizer is arranged to provide a Bode type variable equalizer characteristic without requiring an inductor. The equalization shape remains unchanged as the amount of equalization is varied. This equalizer uses a tandem arrangement of additive feedforward and negative feedback to achieve the mentioned equalization shape.A circuit interconnects with input and output terminals for combining input and output signals into an intermediate signal having a magnitude equal to a weighted sum of the input and output signals. A frequency dependent circuit responds to the intermediate signal for producing a frequency dependent signal that is combined with the input signal to generate the output signal.

Abstract: An amplitude equalizer circuit utilizing active components in which unidirectional functional tuning of the amplitude, bandwidth and center frequency, may each be adjusted by varying a single resistance for each parameter. This eliminates the need for ganged-potentiometers or altering a plurality of interacting components.

Abstract: A transmission arrangement provided with at least one adjustable network whose transfer characteristic between input and output as a function of the frequency .omega. within a prescribed frequency band is approximately equal to C exp [kf(.omega.)], where C is a constant and k a continuously variable parameter.A simple design as well as a large practically feasible adjustment range are obtained because the adjustable network comprises a plurality of channels between input and output and the transfer characteristic of a channel is approximately proportional to a term, different for each channel, from the series of terms of the development of exp [kf(.omega.)] to powers of kf(.omega.), the number of terms corresponding with the number of channels.

Abstract: An equalizing network for attenuation/frequency characteristic equalization. The equalizing network comprises a plurality of attenuation branches B.sub.1 to B.sub.8 which are operative in mutually different frequency sub-bands covering a wide frequency band. A negative feedback amplifier 10 has its negative feedback factor set for each frequency sub-band by means of a potentiometer P.sub.1 to P.sub.8 which is part of the relevant attenuation branch. Resistors 17, 18, 19 and 20 form the negative feedback circuit for the amplifier 10 and provide voltage-dividing, to alter the feedback factor and thus the gain of the amplifier 10, for the individual frequency sub-bands as determined by the potentiometer settings. Attenuation branches pertaining to non-adjacent frequency sub-bands are grouped together in two groups X and Y to obviate the need for separation amplifiers for each attenuation branch.

Abstract: An active variable equalizer is arranged to provide a Bode type variable equalizer characteristic without requiring an inductor. The equalization shape remains unchanged as the amount of equalization is varied. This equalizer uses a tandem arrangement of additive feedforward and negative feedback to achieve the mentioned equalization shape.

Abstract: An equalizer network that exhibits stability and may be cascaded with a transmission channel is disclosed. The network includes only two operational amplifiers, resistors and capacitors and provides a bump shaped amplitude characteristic at resonance frequency. The equalizer may be modified to exhibit selectively a `bump` or `dip` at resonance, and may be so constructed that trimming operations and the independent selection of parameters is facilitated.

Abstract: Attenuation equalizer for correcting within a frequency range the temperature and frequency-depending attenuation variation of cables, comprising a cascade arrangement of a fixed and a variable attenuation correction circuit, connected to a control circuit, the variable attenuation correction circuit comprising a bridge-T network having a series arrangement, of two identical series resistors bridged by a variable bridging impedance and a parallel impedance connected between these two series resistors, the fixed attenuation correction circuit having a lower attenuation for higher frequencies than for lower frequencies, the temperature dependency of the cable being eliminated in the variable attenuation correction circuit and the frequency dependence being eliminated mainly in the fixed attenuation correction circuit for which purpose the variable attenuation correction circuit comprises only two adjustable components.

Abstract: A variable equalizer whose frequency characteristic varies in a range of 1-1/Y(f).sup.2when the gain x of a variable amplifier varies from 0 (zero) to .infin. (infinity), and which reduces the number of shaping networks for the variable frequency characteristic.It is constructed of a forward pass circuit which consists of a variable amplifier and a frequency-dependent first circuit connected in the order mentioned between input and output terminals, a feedback pass circuit which is dependent upon the frequency and which feeds-back an output of the variable amplifier to an input thereof, and a feed forward pass circuit which is independent of the frequency and which feeds forward part of the input of the variable amplifier to an output of the first circuit.

Abstract: In a microwave delay equalizer for an input signal of a microwave frequency having an inevitable delay distortion, a directional coupler and a pair of resonators are placed, respectively, on a center area of a conductive base member and on those side areas thereof which lie on both sides of the center area. The coupler comprises a pair of distributed-constant elements electromagnetically coupled to each other either with an air space or a dielectric plate interposed therebetween and to the respective resonators to derive from the input signal supplied to one of the elements a delay equalized output signal in the other element. Each element has a length equal to an odd multiple of a quarter wavelength of the signal travelling therealong. Each resonator consists of at least one resonance piece.

Abstract: A variable equalizer is provided which, using a single variable resistor, can make compensations in both the directions of the gain side, and the loss side and can set a reference gain as desired.An input signal to be equalized is received as an antiphase input signal of a differential amplifier, an output signal which has been equalized is fed back to the antiphase input signal, and a difference signal between an in-phase input signal and the antiphase input signal is delivered as an output. A resistor is connected between an input terminal and ground, first and second impedance circuits and a variable resistor are connected between an intermediate point of the first-mentioned resistor and ground in the order mentioned, and a voltage at the junction point between the first and second impedance circuits is used as the in-phase input signal.

Abstract: An improved, more compact microwave equalizer is provided by utilizing a length of coaxial transmission line to which at least a pair of relatively small diameter, flexible, coaxial cable resonant stubs are coupled through film type impedance means. Each coaxial cable stub is disposed adjacent the outer conductor of the transmission line, for compactness, and the length of each stub is minimized by use of high dielectric constant material therein. By shortening the length of each resonant stub and by shunting a capacitor across each resonant stub, the frequencies of the upper and lower band edges of the equalizer's attenuation curve are spread apart, while simultaneously providing the desired operating frequency band. Slots and/or an annular recess provided in the relatively thick outer conductor of the transmission line receive the stubs and the retaining apparatus for the film type impedance means.

Abstract: In a delay equalizer having a plurality of quadratic all pass networks for equalizing the delay characteristics of a circuit, the automatic adjustment of the value of Q of each quadratic all pass network when calculated through the asymptotic formula ##EQU1## CAN PROVIDE PERFECT DELAY EQUALIZATION, WHERE Q.sub.i.sup.k is the value of Q of the i'th quadratic all pass network, and .alpha..sub.i is the step size parameter of i'th quadratic all pass network. Before applying said formula, the delay of the circuit to be equalized at the center frequency of each quadratic all pass network is measured, and said formula is calculated according to the result of the measurement.

Abstract: In a band division type equalizer having a plurality of equalizer sections, the adjustment of each of the equalizer sections is accomplished through measurement of characteristics of a transmission means to be equalized and calculation of the difference of the measured characteristics and the desired characteristics. Since all of the equalizer sections are adjusted at the same time according to the result of the calculation, the adjustment does not suffer from interaction among the sections. An adjustable variable, for instance, a variable resistor for each section is mounted in a single setting unit separable from the rest of the equalizer circuit. Thus, after completely adjusting the setting unit, the setting unit is connected to the rest of the equalizer sections, and then the desired delay characteristic can be obtained. The equalizer section is for instance a Moschytz type delay circuit.

Abstract: A compensation network for a passive filter which compensates for the variation of the loss attenuation of the filter dependent on ambient temperature variations consists of an L-section whose series arm is formed by a temperature dependent resistor and whose shunt arm is formed by another temperature dependent resistor in series with a resonant circuit. The resonance frequency value of the resonant circuit is chosen nearly equal to the band limit frequency of the filter.

Abstract: A Bessel function type automatic delay equalizer comprising a plurality of transversal filters each of which has an independent delay cosine equalization component having a predetermined period, and the superposition of those filters providing the desired characteristics, characterized in that, said equalizer further comprises a Bessel function generator for controlling the tap gain of said transversal filters.

Abstract: A non-recursive discrete filter for simultaneously realizing for example two band-pass filter characteristics starting from a given lowpass transfer characteristic, wherein one bandpass filter has an in-phase transfer characteristic and the other filter the quadrature transfer characteristic of this in-phase filter. The central frequency of these filters is f.sub.o and the output sampling frequency is f.sub.s = 8f.sub.o. This discrete filter comprises multiplying means in which input signal samples x(n) are modified by an associated filter coefficient a(i) for generating modified input signal samples z(n,i) = a(i)x(n-i). The coefficients a(i) are the same for both transfer characteristics and are given by: ##EQU1## WHEREIN H.sub.1 (I) REPRESENTS THE DISCRETE IMPULSE RESPONSE OF THE LOWPASS FILTER.To realize the in-phase transfer characteristic the samples z(n,i) are thereafter multiplied by a factor sgn[cos (.pi.i/4)] and the products thus obtained are accumulated.

Abstract: To form a simple and economical variable equalizer, the equalizer is constructed of a differential amplifier having two input terminals to which an input signal to be equalized and an equalized output signal derived from the output terminal are applied, a first impedance circuit connected between the differential amplifier and the output terminal, and a series circuit having a second impedance circuit and a variable resistor connected in series between the output terminal and a ground terminal.

Abstract: An automatic equalizer is described including a first transistor to the input of which a cable is coupled and which is branched in common emitter configuration and a second transistor branched in common collector configuration a collector of the first transistor being coupled to the base of the second transistor and the emitters of the transistors being intercoupled through a positive feedback circuit. In variation by small variation of a variable which is substantially independent from active parameters of the transistors results in a gain variation which is independent of the cable length in the lower frequency region and utilizes no coils.

Abstract: A variable equalizer wherein a series circuit which consists of a voltage source and an impedance circuit having an impedance Z.sub.x is connected in parallel with a circuit for changing an input voltage into a current, and an impedance circuit having an impedance Z.sub.y is also connected in parallel with this current source. The voltage value of the voltage source is made one which is obtained by multiplying the current by a value proportional to 1/Z.sub.y, and the impedance circuit having the impedance Z.sub.y is endowed with a frequency characteristic.