Abstract: The invention relates to a device identifying traffic on a cable. The different types of traffic are characterized by different levels and frequency ranges. The device includes a limiter connected to the paired cable and delivering an output signal having substantially constant amplitude And a frequency corresponding to the strongest frequency component of the input signal. The limiter may be constructed of inverters coupled as an amplifier or of an amplifier having a Schmitt trigger. The limiter is connected to a frequency indicator indicating what frequency ranges within which the strongest frequency component lies. The frequency indicator may consist of monostables or counters and decoders. The decoder interprets the output signal of the counter and may be constructed of a fixed gate network or of a programmable memory. The output signal of the frequency indicator is connected to an indicator indicating the frequency range in question, e.g. by means of flashing light-emitting diodes.

Abstract: There is disclosed a rectangular filter which has a simple configuration and is capable of producing an improved rectangular wave. An input step wave is differentiated by a differentiator circuit and amplified by a first amplifier. The output from the amplifier is inverted by an inverting amplifier having a gain of -1. The output from the first amplifier is integrated by an integrator circuit having a time constant equal to the time constant of the differentiator circuit. The output from the inverting amplifier and the output from the integrator circuit are summed up by an adding circuit. The input signal is faithfully reproduced at the output of the adding circuit. After a given time passes since the input signal has been applied, the capacitor of the integrator circuit is shorted out. In this way, a rectangular wave is obtained. There is also disclosed a filter amplifier comprising this rectangular filter and a gated integrator for integrating the output from the rectangular filter for a predetermined time.

Abstract: A method and apparatus for increasing the bandwidth of an operational amplifier and including a capacitor being connected across the inverting and non-inverting inputs of the operational amplifier and further including a feedback circuit connected from the output to one of the inputs, the inverting input, and wherein the value of the capacitance is selected such that the time constant of an RC network including the capacitance and the feedback circuit impedance is proportional to the inverse of the product of the closed loop gain and a factor .beta. which equates the absolute value of the gain at two different frequencies.

Abstract: An active bandpass filter offers freely settable values of quality factor Q and peak gain. The active bandpass filter has a first transistor, the base of which is connected to an input terminal of the filter via a first capacitance element, the collector of which is connected to a first constant voltage source, and the emitter of which is connected to a first constant current source or a resistance element. The active bandpass filter also has a second transistor, the base of which is connected both to a second constant voltage source via a first resistance element and to the emitter of the first transistor via a second capacitance element, the collector of which is connected both to an output terminal of the filter and, via a second resistance element, to the first constant voltage source, and the emitter of which is connected both to the base of the first transistor via a third resistance element, and also to a second constant current source or a resistance element.

Abstract: A balanced current amplifier mirrors either a fully differential or single ended input signal into common output circuits in a manner to generate a fully differential output signal without any d.c. bias. Input signal nodes are maintained at a desired voltage by circuit elements other than those of the current mirror circuits, thus freeing the current mirroring elements from having to be sized for this purpose. The sizes of the output transistors are adjustable in order to set the gain of the circuit. In addition to amplifier circuits, a full-wave rectifier, a comparator, and a filter, all operating with current signals, are described. A single circuit module may include all of these circuits with a user provided the capability to program the module to perform any one or more of these functions.

Abstract: A circuit for an intermediate frequency filter combines a variable bandwidth series resonant filter circuit and a parallel resonant filter circuit. A variable output impedance drives the filter and a variable input impedance amplifier buffers the output of the filter. The output impedance of the driver is made to track the input impedance of the output buffer. Changes in the gain of the filter with respect to bandwidth are relatively small. The noise figure of the filter remains low. The circuit is not operated in the non-linear region of the crystal because relatively low drive currents are needed at narrow bandwidths so that the crystal is not overdriven. The LC filter tunes out the stray capacitance from the load of the crystal filter.

Abstract: A cellular receiver range extender has an input terminal connectable to an antenna and an output terminal to which may be connected a microwave radio receiver for cellular communication signals. The input terminal directs RF signals to a bandpass preselector covering a frequency spectrum of 825 MHz to 890 MHz leading to a low-noise preamplifier for amplifying the preselected RF signals. A divider coupled to the preamplifier feeds signals from the preamplifier at equal power levels into first and second RF paths. The first path includes a band pass filter covering the reverse cellular communication channel RF signal band from 825 MHz to 845 MHz, and the second path includes a band pass filter covering the forward cellular communication channel RF signal band from 870 MHz to 890 MHz. In the first path reverse channel signals are amplified by a low-noise amplifier while in the second path forward channel signals are attenuated.

Abstract: A vital railway signal link for passing DC signals between a first terminal location and a second terminal location. A transmitter at the first terminal location receives a DC input signal and responsively produces a light signal modulated at a preselected frequency. The light signal is conducted through an optical fiber to the second terminal location. There, a receiver detects the light signal and produces a DC output signal. The receiver contains discriminator circuitry preferably including a bandpass filter to prevent light signals other than those modulated at the preselected frequency from giving an output signal.

Abstract: A high-frequency band amplifier system which is capable of containing the amount of ripple produced in the band passed by an SAW filter, and which is also capable of avoiding an increase in the noise factor. Such an amplifier system is constructed of a surface acoustic wave filter and a common-base connected transistor amplifier for amplifying the output from the surface acoustic wave filter.

Abstract: An integrated biquadratic, continuous-time filter section includes a plurality of operational transconductance amplifiers (OTAs). Simutaneously changing a transconductance (GM) of each of the OTAs is provided by adjusting a differential voltage applied to a plurality of differential transistor pairs of each OTA. Each of the OTAs include a plurality of current sources and a common mode feedback circuit for controlling a common mode output voltage level. Changing the transconductance of the OTA is independent of the common mode voltage level control.

Abstract: A broadband amplifier includes an amplifier device and input and output networks formed of microstrips. The impedance of the output microstrip is chosen by taking the geometric mean of the real parts of one of the scattering parameters of the amplifier device, at the lower and upper limits of the frequency range of interest, and by taking the geometric mean of the system impedance with the result obtained previously. The final result of these calculations is the impedance of the output network. The impedance of the input network is made to be at least twice, and preferably twice, the impedance of the output network. The amplifier is also provided with a slope compensation circuit. It has been discovered that an amplifier designed in this manner exhibits remarkable flatness over a five-octave range. The amplifier circuit is therefore suitable for use in cable television and other broadband telecommunications applications, where the frequency range of interest may be 30 MHz to 1000 MHz.

Abstract: A low noise linear amplifier and a microwave voltage controlled oscillator constructed from such amplifier. Each amplifier within the VCO utilizes a ratioed transistor configuration to generate a linear output over a wide range of inputs. Output current from the amplifier is split into a main output current and components of in-phase and 180.degree. out-of-phase current. A logarithmic tuning control combines the components of in-phase and 180.degree. out-of-phase currents in inverse ratio to provide a constant d.c. feedback current.

Abstract: A current-mode amplification system including a first gain section and at least one second gain section chained together to form a chain of gain sections. The first gain section containing a first amplifier and a first low-pass filter. Each second gain section contains: a second amplifier having (1) a first input receiving the amplified and filtered output current from the preceding gain section in the chain, and (2) a second input receiving an input current of the amplification system, and delivering an amplified output current; an activator/deactivator for activating/deactivating the second input; and a second low-pass filter, the low-pass filter of each of the chained-together gain sections having a high cut-off frequency, the high cut-off frequencies of the various gain sections increasing from the input to the output of the amplification system.

Abstract: There is disclosed a system for linearizing an RF amplifier by the application of suitable load impedances to its 2nd, 3rd, and higher order output signals, thereby reducing output distortion products and improving performance. Intermodulation Distortion (IMD) reduction results from controlled termination of harmonic tuned filters produced by impedance selection and/or filter detuning. Preferably the apparatus comprises parallel band-pass filters including a filter passing the fundamental signals only; a filter passing 2nd harmonics; and a filter passing the 3rd harmonics. These, and optionally higher order filters, are employed for suppressing harmonic frequencies and reducing IMD. Preferably all filters have sufficient isolation to prevent serious interaction between filters. Therefore a selected mismatch provided at each of the harmonic output ports linearizes the amplifier's output.

Abstract: A microwave amplifier includes a field effect transistor having its source grounded. The drain of the transistor is connected through a first inductor of gold wires to an output-side matching circuit, while the gate of the transistor is connected through a second inductor of gold wires to an input-side matching circuit. A series circuit including a capacitor and a third inductor is disposed near the input-side matching circuit and is connected between the junction of the input-side matching circuit and the second inductor and a reference potential.

Abstract: The method and apparatus for improving linearization of a radio frequency power amplifier which includes extracting a small portion of the output signal of the power amplifier and utilizing this extracted signal as a feedback signal. The feedback signal is then adjusted in phase, attenuated, and combined with the input signal of the power amplifier and then filtered prior to being transmitted to the power amplifier.

Abstract: The input impedance of a high-frequency monolithic integrated-circuit amplifier is modified to increase the maximum output power capability of the amplifier. This modification compensates for a reduction in output resistance at high frequencies caused by feedback capacitance coupling the output and input of the amplifier.

Abstract: In an intermediate frequency amplifier circuit having a crystal filter and a transistor amplifier, a tuning circuit including a coil and a capacitor is provided therebetween, and a current feedback resistor and a voltage feedback resistor are connected to the amplifying transistor. The resistance component of impedance is matched between the crystal filter and the amplifier by suitably selecting values of the resistors. Further, the reactance component of the impedance is matched therebetween by suitably selecting values of the coil and the capacitor. Thus, it is possible to obtain impedance matching between the crystal filter and the amplifier without degradation of NF and hence S/N ratio due the thermal noise caused by resistance elements in a conventional resistive attenuator which is conventionally used for impedance matching.

Abstract: A broad-band power amplifier circuit having a transistor with a base terminal, an emitter terminal, and a collector terminal connected between a positive power source terminal and a negative power source terminal. A bias circuit is connected to the base terminal of the transistor, a capacitor is connected between the collector and emitter terminals of the transistor, and an inductor is connected between the emitter terminal of the transistor and the negative power source terminal. A decoupling choke is connected between the collector terminal of the transistor and the positive power source terminal, a first decoupling capacitor is connected to the collector terminal of the transistor, and a second decoupling capacitor is connected to the base terminal of the transistor.

Abstract: A frequency translated filter adapted for integration into a conventional monolithic integrated circuit arrangement. The filter includes an RF amplifier having a gain determining port; a one port, AF (audio frequency), frequency selective, gain determining immittance network; a forced-commutated bridge of bilateral switching elements interconnecting the immittance network and the gain affecting port of the amplifier, and an RF local oscillator for providing a commutating drive signal to the bridge. The action of the RF commutating bridge is to convert the voltage and current appearing at the gain affecting port of the RF amplifier to a low frequency at the terminals of the AF immittance network, and to reflect the immittance of the AF network back through the RF commutating bridge, translating it up again in frequency. The effect is to permit the use of AF frequency selective elements to render an amplifier frequency selective at radio frequencies.

Abstract: In a high efficiency F-class amplifier, output current may be reduced to cause distortion of the current, or deterioration of high efficiency operation of the amplifier, when an instantaneous output voltage of an amplifying transistor becomes lower than a saturation voltage. To prevent this, the peak value of the high freqency instantaneous output voltage is restricted by a peak value restricting circuit provided in parallel to a load. Thus, an ideal high efficiency amplifier can be provided by avoiding distortion of the output current.

Abstract: An audio amplifier having a volume-dependent tone control which is inexpensive and hardly distorts the audio signal. A filter in the signal path of the audio amplifier determines the tone control at low volumes. The bass tones and possibly treble tones are then amplified to a greater extent than the mid-range tones. With an increasing volume, a continuously controllable amplifier stage increasingly compensates this tone control. To this end a linear feedback path is arranged across this amplifier stage, with a pole in or near the frequency range of the bass and mid-range tones.

Abstract: The present invention comprises a fully differential non-op-amp based BJT biquad filter. The biquad filter comprises an unity gain follower receiving a positive and a negative differential input signals for generating a positive and a negative differential output signals. The biquad filter further includes a first positive feedback line connecting the positive output signal to the positive input signal and a second positive feedback line connecting the negative output signal to the negative input signal. The first positive feedback line includes a first capacitor connected in series therein and the second positive feedback line includes a second capacitor connected in series therein wherein the first and the second capacitors are of substantially equal capacitance. The unity gain follower further comprises a plurality of bipolar NPN devices and resistors connected between a common higher DC voltage and a common lower DC voltage through a constant DC current emitter.

Abstract: The present invention relates to an optical signal input-type amplifier circuit. The object of the invention is to provide an optical signal input-type amplifier circuit which includes a photoelectric converting element with a small light receiving surface, whereby the hf component attenuation in the amplifier can be suppressed and the drive voltage and power consumption can be reduced.

Abstract: A microwave amplifier circuit has input and output coupling circuits (21 and 22) designed on quite different matching principles to obtain a circuit compactness similar to a reactively-matched amplifier and cascadable electrical characteristics similar to a distributed amplifier. The input coupling circuit (21) is formed as a bandpass filter network (7a, 7b, 7c, 17a, 17b, 9) supporting a travelling wave to which the amplifying device (3) is capactively connected. This input network (21) terminates in a resistor (9) in which the travelling wave is dissipated. The output coupling circuit (22) is a reactively matched circuit (8a, 8b, 18a, 18b) which also has a bandpass characteristic. By making the input network (21) bandpass (instead of low pass) a large amplifying device (3) can be used, without reducing line impedance and gain.

Abstract: A filter (62) receives an input current signal and provides a filtered output signal in response. The filter (62) presents an extremely low-impedance input node (72) to the source of the input current signal, such as a current digital-to-analog converter (DAC) (62), thus avoiding modulating the input current signal. The filter (62) includes a virtual ground circuit (70) connected to the input node (72) followed by a filter (80) such as a biquad filter. The virtual ground circuit (70) has a high-gain cascoded loop to provide an intermediate current at a high-impedance output terminal (82), which is connected to an input terminal of the filter (80). The virtual ground circuit (70) is implemented without operational amplifiers and resistors, thus providing high linearity without a large amount of integrated circuit area.

Abstract: A high frequency amplifier has a distributed amplifier having a sufficiently wide band and formed on a microwave integrated circuit, and at least one bandpass filter directly connected to the distributed amplifier and formed of a microstrip line having a desired frequency band having a desired center frequency.

Abstract: A simple and effective "RF snubber" circuit resolves the problems associated with transient spectral noise caused by radio transmitter activation in nearby channels. By connecting an RF snubber circuit in parallel with the RF amplifier output, the rise time or turn-on characteristic of the RF signal generated by the transmitter is controlled. As a result, adjacent channel interference is substantially eliminated.

Abstract: A low noise narrow band amplifier with low power consumption for amplifying radio frequency and microwave signals. The amplifier includes a high frequency transistor that has a cut-off frequency greater than the center frequency of the input signal. The amplifier includes an emitter inductor for low noise and better input match. The amplifier is stabilized for out-of-band high frequency oscillations by a collector inductor and a base inductor. The amplifier is further stabilized unconditionally for out-of-band high frequency oscillations by a stabilizing circuit coupled between the output and ground, including a stabilizing capacitor in series with a stabilizing resistor.

Abstract: A gyrator based resonator comprises first and second differential amplifiers cross coupled to form a quadrature phase voltage controlled oscillator. The differential amplifier circuits include matched transistor pairs and associated transconductance adjusting components to control the resonant frequency of the resonator. Transconductance delay and admittance loss elements are also provided and these elements serve to control the loop gain of the resonator. A loop gain greater than unity results in the resonator oscillating while a loop gain less than unity produces a bandpass filter. A resonator having gain less than unity may be slaved to a similar resonator having gain adjusted to be greater than unity thus creating a low noise oscillator and tracking filter.

Abstract: An integrated circuit is disclosed that includes a biquadratic filter in which the poles and zeroes are independently adjustable. The transfer function of the filter has a pair of zeroes in the numerator and a pair of complex conjugate poles in the denominator. The integrated circuit includes a first circuit for constructing the complex conjugate poles of the filter transfer function. The first circuit has an input port for receiving an input signal and an output port at which an output current representative of a filtered output signal is presented. The integrated circuit includes a second circuit for constructing, independently of the poles, the zeroes of the filter transfer function. The second circuit has an input port coupled to the input port of the first circuit for receiving the input signal. The second circuit includes a differentiator for differentiating the input signal to produce a differentiated input signal.

Abstract: A distributed amplifier produced from monolithic microwave integrated circuit (MMIC) processes employs a bandpass filter structure as opposed to a low-pass filter network to enhance gain, efficiency and output power over wideband operation of 6 GHz to 18 GHz. Derivation of the preferred embodiment is shown from a three port circuit employing bandpass filter image-parameter half-sections.

Abstract: Power amplifier operating at a fixed frequency or a narrow bandwidth and based upon a non-linear gain element. The power amplifier includes a resonant circuit operably connected to the non-linear gain element, the circuit being resonant at a harmonic of substantially the band center frequency of the non-linear gain element and being arranged to dissipate energy resulting from harmonic generation by the non-linear gain element during signal amplification. In a particular aspect of the power amplifier, resonant circuits comprising inductor-capacitor harmonic trap circuits tuned to different harmonics are placed at both the input and the output of a gallium arsenide heterojunction bipolar transistor HBT providing the non-linear gain element.

Abstract: A power amplifier apparatus having an operational amplifier which works as a PWM (pulse width modulation) amplifier as well as an analog amplifier according to an input signal level to miniaturize the size of the apparatus and to maintain amplifying function thereof at the changeover of the function, which allows gain and frequency characteristic of the operational amplifier to have continuity before and after the changeover.

Abstract: An X-band (8-12.5 GHz) amplifier comprises a bipolar junction transistor (BJT) arranged for receiving an X-band signal, amplifying the signal and providing the amplified signal to further circuitry. Input and output matching networks are advantageously provided for the BJT. Each network may have a first end for connection to a BJT and a second end for connection to a terminal, and may comprise a series connection of a first inductor, a first capacitor and a second inductor extending from the first end to the second end in that order; a third inductor connected between ground and the connection point of the first capacitor and the second inductor; and a second capacitor connected between ground and the second end. The various reactance components may be implemented on a dielectric board, for example by microstriplines and/or shaped cladding portions. An X-band oscillator may comprise the X-band amplifier described above, and a feedback circuit interconnecting an output and an input of the amplifier.

Abstract: A control network operates a GaAs FET with a quiescent current closer to the maximum output current, I.sub.max, than to zero current. An output network couples the FET to the load and is characterized as having a low impedance at a fundamental frequency and a high impedance lower than an open circuit impedance at at least the second harmonic frequency. As a result, the peak voltage on the output terminal is greater than two times the supply voltage. A preamplifier raises the level of the input signal so that it has a positive voltage peak when biased by the control network and applied to the input terminal. This overdrives the FET and produces an output current that is at the maximum output current level for a longer time during each cycle than the output current is at a minimum level. This enhances the effect of the output network to produce an output voltage spike on the FET that is several times the DC voltage.

Abstract: An active filter circuit includes a first and second differential pairs each having a pair of transistors. A capacitor is connected to a collector of one transistor from each of the first and second differential pairs. A first and second negative feed-back paths are connected, respectively, between the collector and a base of one transistor of the first differential pair and between the collector of one transistor of the second differential pair and a base of the other transistor of the first differential pair. By applying suitable voltages to respective inputs of the differential pairs, the active filter circuit functions as a band-pass filter, lowpass filter, high-pass filter, band elimination filter or phase-shifting filter with the same circuit configuration. A current mirror circuit correlatively changes current amounts of the first and second differential pairs in response to a control voltage, whereby a filter characteristic can be changed.

Abstract: An RF power FET amplifier is designed using parasitic resonant matching to reduce low intermodulation distortion. An input inductor is connected in parallel with the capacitance of the common-source input capacitance, an output inductor is connected in parallel with the common-source output capacitance. Feedback provided by the common-source capacitance between gate and drain is utilized to improve linearization and stability. The field effect transistor is designed so that the feedback signal resulting from the feedback capacitance is 180.degree. with respect to the forward gain.

Abstract: Generally, and in one form of the invention, a method is disclosed for terminating third harmonic frequency of a transistor amplifier comprising: determining the magnitude of the susceptance at the third harmonic frequency of initial circuitry, 41, 43, and 45, attached to the output of a transistor 39, wherein the initial circuitry has no third harmonic termination; determining whether the susceptance of the circuitry presented to the output of the transistor 39 is capacitive or inductive at the third harmonic frequency; and adding a compensating parallel susceptance 60 to the output of the transistor 39 that is substantially equal in magnitude to the susceptance of the circuitry attached to the output of the transistor 39, but capacitive if the susceptance of the circuitry presented to the output of the transistor 39 is inductive, or inductive if the susceptance presented to the output of the transistor 39 is capacitive, whereby the imaginary part of the susceptance of the total circuitry attached to the out

Abstract: A device and method is provided for filtering frequency components of an electrical signal above a selectable low pass cutoff frequency which is changeable within a designated range. An input filter having a fixed low pass cutoff frequency provides aliasing protection for a first of at least three clock driven filter stages respectively having variable low pass cutoff frequencies proportional to a clock rate of a received clock signal. The overall selectable low pass filter is determined at an intermediate stage of the clock driven filter stages. Clock rates of respective clock signals applied to clock driven stages proceeding the intermediate stage having the selectable cutoff frequency are adjusted so that each provides aliasing protection for the next. Similarly, the low pass cutoff frequencies of clock driven filter stage succeeding the intermediate stage having the selectable cutoff frequency are adjusted to eliminate staircasing distortion in the output signal.

Abstract: An operational amplifier circuit is composed of a differential amplifier circuit for delivering a signal which is obtained by amplifying a difference between voltage levels of two signals; a level shift circuit for shifting and delivering the voltage level of the signal delivered from the differential amplifier circuit; a first amplifier circuit for amplifying and delivering the signal from the level shift circuit; and a second amplifier circuit for amplifying and delivering the voltage level of the signal delivered from the differential amplifier circuit, and a CMOS output circuit whose conductive state is controlled in accordance with voltage levels of the signals delivered from the first and second amplifier circuits.

Abstract: A simple and effective "RF snubber" circuit resolves the problems associated with transient spectral noise caused by radio transmitter activation in nearby channels. By connecting an RF snubber circuit in parallel with the RF amplifier output, the rise time or turn-on characteristic of the RF signal generated by the transmitter is controlled. As a result, adjacent channel interference is substantially eliminated.

Abstract: A high-frequency power amplifier comprises a pair of FETs, a divider which supplies opposite-phase versions of a signal to be amplified to the FETs, distributed-parameter transmission lines connected respectively at one ends thereof to output electrodes of the FETs, and a combiner which combines signals appearing at another ends of the transmission lines into a signal of a common phase. Stubs which short-circuit for even harmonics included in output signals of the FETs are connected respectively to the transmission lines at positions distant from the output electrodes of the FETs by a multiple of a quarter wavelength of the fundamental wave included in the output signals of the FETs.

Abstract: The frequency response of an RF power amplifier in a Cellular Phone Base station is improved by providing a shunt capacitor with the choke coil which interconnects a DC power source to the active device of the amplifier. The cutoff frequency of the bias network can be adjusted so that sum and difference frequencies of multiple-input signals are not attenuated by the feed network thereby permitting the sum and difference frequency signals to be shunted to ground. The linearity and bandwidth of the power amplifier is thus improved.

Abstract: An impedance matching and bias feed network for interfacing to a low noise amplifier of a receiver section of an electrically steered phased array antenna. The impedance matching and bias feed network includes an inductor and capacitor network for impedance transformation while providing in shunt with a 50 ohm input side of the network a gate bias path via the inductor to the low noise amplifier thereby substantially reducing the receiver noise figure.

Abstract: A limiter amplifier includes amplifiers connected in cascade each having differential outputs and differential inputs, and a lowpass filter connected between adjacent amplifiers. The filter includes resistors having different values connected between the differential outputs and the differential inputs of adjacent amplifiers, and a capacitor connected between the differential inputs of one of the adjacent amplifiers, the filter thereby limiting a high frequency characteristic of the limiter amplifier.

Abstract: An all-pass filter includes an adder which comprises a variable conductance amplifier and a capacitor connected to the output terminal thereof. The adder is being arranged to add the output of a band pass filter and an input signal together.

Abstract: A transimpedance pre-amplifier circuit is arranged to have a complex pole response resulting from the interaction of the open-loop pole with the pole associated with a circuit feedback. The pre-amplifier circuit includes a transistor with a load capacitor connected in the transistor output circuit to determine the open-loop pole. The feedback includes a resistive element. The first stage of the pre-amplifier comprising the transistor may be followed by one or more further amplifying stages. The feedback to the input of the first stage may be from the output of one of the further stages. A receiver incorporating the pre-amplifier circuit includes only post-amplifiers connected to receive the output of the pre-amplifier. The response of the pre-amplifier makes it unnecessary to include a dedicated passive filter in the receiver and the post-amplifiers can have smaller bandwidths than in conventional receivers.

Abstract: An equivalent inductance circuit includes a feedback type integration circuit and a differential amplifying circuit. An input signal applied to an input terminal is integrated by the feed-back type integration circuit and, a signal according to a difference component between an integrated output signal and the input signal is outputted by the differential amplifying circuit. By feeding the difference signal back to the input terminal, an input impedance equivalently represents an inductance characteristic. Such equivalent inductance can be changed by a current from a variable current source which supplies the current to the differential amplifying circuit and, a change of the equivalent inductance shows an inverse proportional manner.

Abstract: A power line communication amplifier circuit for providing a signal transmission across a power line medium when operating in a transmit mode, and for providing a relatively high input impedance to the power line when in a receive mode includes a unity gain buffer integrally coupled with a filter. The filter operates upon an input signal provided by a digital driver means. A control means is coupled to the digital driver means and to the buffer such that when said amplifier is switched to a receive mode, both the driver means and buffer provide a high input impedance.