Abstract: The disclosed amplifier comprises a high-frequency power output stage for current amplification of the high-frequency signals and a separate low-frequency power output stage for current amplification of the low-frequency signals. Reactive coupling means, including either inductors or a capacitor or both, together with resistors, coact with the two output stages to provide a novel crossover circuit to transmit high-frequency signal to the amplifier output terminal and low-frequency signals to the inputs of the low-frequency output stage to drive the latter. Each output stage is disclosed as having its own power supply. Each output stage may thus be implemented with devices optimized for its respective frequency range, intermodulation distortion is substantially reduced, and similar benefits accrue in the design of the separate power supplies.

Abstract: A high speed switching circuit is disclosed in which two cascode circuits are coupled and operated in push-pull operation. The cascode circuits are clamped to avoid slowing down of the transistors due to saturation.

Abstract: To obtain a constant quiescent current, high dynamics and high stability of a class AB output stage of low-frequency amplifiers, comprising an input transistor; a driving circuit comprising a current source, a first pair of driving transistors connected in series between the current source and the input transistor, a second pair of driving transistors mutually connected in series and driven by the first pair of driving transistors; as well as a pair of output transistors driven by the second pair of driving transistors, the driving circuit comprises a first resistor connected between the current source and the base of one of the first pair of driving transistors, a second resistor connected between the bases of the transistors of the first pair and a resistive network inserted in series between the transistors of the second driving pair.

Abstract: An audio amplifier and power supply having a power transformer with power supply and control means to provide pulses of electrical energy at a substantially constant supply voltage, with the duration of the pulses being dependent upon a value that is related to the demands of the amplifier. The transformer charges a power capacitor to a substantially constant voltage to supply power for the amplifier. The frequency range of the pulses is between about 400 to 2,000 cycles per second, with a frequency being at about 1,100 cycles per second in a preferred embodiment.

Abstract: Two cascode amplifiers are connected in parallel and include RC bypass circuits across their emitter and collector load resistors. The amplifiers are biased so that positive going transitions of an input video signal drive one amplifier into conduction and negative going excursions drive the other amplifier into conduction. The RC bypass circuits make the amplifier wide band and low power dissipation is obtained because the collector load resistors can be made large.

Abstract: A linear high power amplifier suitable for low voltage operation comprising a push-pull output stage (Q1, Q2) arranged to control the voltage supplied to a load (Z.sub.L) in dependence on an input signal (V.sub.IN) applied to the amplifier. Means (L.sub.S, S) is provided for separately supplying to said load (.sub.Z L) a current (I.sub.S) which changes at a rate faster than the maximum rate of change of current (I.sub.L) in the load (Z.sub.L) required by the input signal (V.sub.IN) thereby to produce a corresponding change in the current (I.sub.A) required to be supplied by the output stage (Q1, Q2) to the load (Z.sub.L) in order to maintain the voltage across the load (Z.sub.L) at the value required by said input signal (V.sub.IN). Switching means (Q3, Q4, C) operated in dependence on the value of the current (I.sub.A) supplied to the load (Z.sub.L) by the output stage (Q1, Q2) causes the sense in which said changing current (I.sub.S) changes to reverse when said current (I.sub.

Abstract: The positive and negative outputs of an operational amplifier are employed to drive two oppositely phased current mirror circuits, which in turn drive oppositely phased power amplifier stages which drive the load directly without the use of an output transformer. Negative feedback is provided from the output to the operational amplifier to enhance flat response over the frequency range of interest. The oppositely phased power output stages are supplied by a power source which provides positive and negative supply voltages with reference to reference "ground". A plurality of capacitors are selectively connected as need be between the positive and negative voltage busses and ground to bypass spurious high frequency oscillations. A relatively high voltage output is achieved from the amplifier without exceeding the breakdown voltages of the transistors by employing a plurality of cascaded "Darlington" type circuits in the power amplifier.

Abstract: Unity gain buffer amplifier circuits having a reduced input-to-output offset voltage characteristic are described. Compensation for the effects of base-to-emitter voltage variations and early voltage is employed.

Abstract: A driver-sensor circuit for a circuit-testing device has a sensor amplifier (Q1, Q2, Q3, and Q4) for sensing the voltage on a device under test connected to its input-output terminal (12). The driver-sensor circuit also includes a driver amplifier (Q5, Q6, Q7, and Q8) for driving the same terminal (12). The driver amplifier (Q5, Q6, Q7, and Q8) can be switched on and off, and a limiting amplifier (Q9, Q10, Q11, and Q12) applies the sensor-amplifier output voltage to the input terminal (20) of the driver circuit (Q5, Q6, Q7, and Q8) to keep the reverse bias on the driver-amplifier transistors (Q5, Q6, Q7, and Q8) to a minimum. To eliminate offset bias current at the input terminal 12 of the sense amplifier (Q1, Q2, Q3, and Q4), compensation transistors (Q15, Q16 ) matching the input-stage transistors (Q1, Q2) of the driver amplifier have their bases tied together to force their base currents to cancel.

Abstract: An operational amplifier is provided with at least one output supplementary stage and current mirror amplifiers for coupling amplified signal current variations to drive supplementary output stage source and sink transistors. Those transistors have their internal collector-emitter paths directly connected between supply rails and perform further amplification of the signals. A current source circuit is employed for so limiting those signal current variations that, after the further amplification, circuit devices will not be damaged.

Abstract: The output stage for power amplifiers, in particular of the minimum drop, low tension type, is intended for use with apparatus which do not require a high output current, which output stage can operate at a lower minimum voltage supply than comparable known stages. The output stage comprises upper and lower sections interposed between a power supply line and a ground line, each section including transistors across which voltage drops (V.sub.CE sat, V.sub.BE) appear and forming current sources for each section, diodes, and at least one current mirror circuit of the multiplying type adapted to determine as a first approximation the current gain of each section. The minimum voltage drop between the power supply line and ground line, as computed for any electric line connecting the power supply line and ground line, never exceeds the value of V.sub.BE +2V.sub.CE sat.

Abstract: The input voltage signals to a comparison circuit may vary between levels substantial equal to the first and second supply voltages (e.g. typically 5 volts and ground). A first transistor circuit is coupled to a current mirror circuit and to an output node for supplying a mirrorable current to the current mirror circuit which in turn reduces the voltage at the output node when the first input voltage approaches the upper supply voltage, and supplies a current to the output to increase the voltage thereat when the second input approaches the upper supply voltage. A second transistor circuit is also coupled to the current mirror and to the output for supplying a mirrorable current to the current mirror means so as to reduce the voltage at the output when the second input voltage approaches ground, and supplies current to the output to increase the voltage thereat when the first input voltage approaches ground.

Abstract: An amplifier for bidirectionally driving a motor includes circuitry for enabling the amplifier to operate with a bipolar input signal while employing a single power supply. The amplifier includes an input section which receives the bipolar input signal and provides a unipolar output voltage. The operational amplifier drives a bridge drive network to provide a drive current to output bridge transistor in one of two directions. The bridge network includes control circuitry for causing all of the transistors of the drive bridge to be operated in their active regions, thereby improving the power dissipation characteristics of the network. The output bridge transistors are also controlled to operate in their active regions. In addition, circuitry is included for providing negative feedback for the amplifier despite the fact that the output current is always a positive current.

Abstract: A power amplifier, suitable for use as an audio amplifier, having an improved power supply circuit in which distortion caused by switching between power supply levels is substantially eliminated. Transistors of a push-pull amplifier stage are selectively couplable to either first or second supplies, with the output voltages of the second supplies exceeding those of the first supplies. In ordinary operation, switching of the output transistors between the first and second supplies is done in accordance with an absolute magnitude of the output signal from the amplifier. However, when the magnitude of high frequency components in the output signal exceeds a certain level, the output transistors of the push-pull stage are supplied power only from the first supplies.

Abstract: Disclosed is an amplifier wherein, in order to prevent the mixing of hum and other noise from the ground potential of the amplifier, the driving power supply circuit of the amplifier is separated from the ground potential into a floating state. In addition, the overall capacity of the power supply is reduced.

Abstract: In a combination of an amplifier (2,5,6) and a signal-dependent voltage supply source (16-23) coupled thereto, a portion of the signal from a signal source (1) is applied by an amplifier (9) to a comparator (16), the output signal of which controls a limiter (20-21). A portion of the output signal thereof is applied as a feedback signal to a second input of the comparator (16) by means of a low-pass filter (22) and a feedback network (23) in series. The feedback loop thus formed is arranged so that it oscillates at a comparatively high frequency. A signal-dependent modulation of the pulse width and/or the pulse density then occurs at the limiter output. A supply voltage for the amplifier is derived from the output of the filter (22). Owing to the high feedback factor of the feedback loop at the signal frequencies the supply voltage can adequately follow the output signal of the amplifier independently of component tolerances and any load variations.

Abstract: A final bridge stage for a receiver audio amplifier, which can be monolithically integrated, consists of two pairs of complementary bipolar transistors. The collectors of the transistors of each of the transistor pairs are connected together to form two terminals to which a transducer is connected. The transistor emitters of NPN type and PNP type transistors are respectively connected to the negative pole and, through a constant current generator, to the positive pole of a supply voltage generator. The constant current generator consists of a small resistor to which a constant voltage is applied by means of a suitable circuit. The bases of the bridge transistors are connected to the signal source by means of suitable circuits. The signal source controls similar transistors in phase opposition, while at the same time controlling the complementary transistors in phase opposition.

Abstract: A power amplifier with power supply switching is arranged so that large positive and negative power supply voltages are supplied to collectors of second and fourth transistors via first and third transistors, respectively. Small positive and negative power supply voltages are supplied to collectors of the second and fourth transistors, respectively, and an input signal of the amplifier is amplified by the second and fourth transistors to supply an output of the amplifier to a load, wherein to a base of the first transistor is selectively applied either a divided voltage between a positive constant voltage greater than the small positive power supply voltage and the voltage of the input signal or a voltage which is a sum of the voltage of the input signal and a positive constant voltage.

Abstract: A class BC power amplifier having a symmetrical push-pull preamplifier and a pair of symmetrical branches coupled, respectively, to the outputs of said push-pull preamplifier. Each of said branches includes a first power stage, operating in class B, coupled to the output of said branch, a control stage coupled to the respective output of said push-pull preamplifier for controlling said first power stage, a second power stage, operating in class C, coupled to said first power stage, and a first comparative stage coupled between said control stage and said branch output for controlling said second power stage. Each branch of said power amplifier further comprises a third power stage, operating in class C, also coupled to said first power stage, and a second comparative stage coupled between said control stage and said branch output for controlling said third power stage.

Abstract: The invention provides a class BC power amplifier which permits control by a circuit with a transistor, which circuit, besides its control functions, effects also a protection of the end stage from transient processes caused by the inductive character of the load. The efficiency of the amplifier is not lowered, but it remains sufficiently high and corresponds to the class BC. The use of an output transformer is not obligatory.

Abstract: A power amplifier in which a DC power supply is coupled to a load through a switching element, a smoothing circuit, and an output amplifying element. The output amplifying element receives an input signal voltage to be amplified. A voltage detecting circuit is provided which compares a feedback voltage proportional to an output volgage of the smoothing circuit with the input signal voltage to switch the switching element, thereby varying both the power supply voltage of output amplifying element and the load output voltage in accordance with the input signal voltage. As the output voltage of the smoothing circuit is compared with the input signal voltage, the delay of the change of the power supply voltage of the output amplifying element relative to the load output voltage can be reduced, and the generation of distortion and the lowering of efficiency can be suppressed.

Abstract: The disclosed operational amplifier comprises a first pair of complementary type transistors (Q5, Q6) (of high current carrying capacity) that have their emitter-collector paths connected in series across a source of reference potential. The emitters of the transistors are connected together and to an output terminal (17). A second pair of complementary type transistors (Q3, Q4) are coupled across said reference potential, each transistor of said second pair being coupled across the similar conductivity type transistor of said first pair. A first pair of resistances (R1, R2) of predetermined value are respectively connected between the bases of the similar conductivity type transistors of said first and second pair. A second pair of resistances (R3, R4) respectively connect the emitters of the transistors of said second pair to said output terminal.

Abstract: A circuit, for providing a periodic signal of programmably controllable amplitude, includes an oscillator having a substantially constant amplitude signal of desired frequency and waveform at an output thereof connected to the input of a first programmable voltage divider having its output connected to one input of an operational amplifier. The remaining operational amplifier input is connected to the output thereof via a second programmable voltage divider used as a programmably controllable feedback network. The operational amplifier output signal amplitude may be controlled by external data signals to values less than, equal to, and greater than, the substantially constant oscillator waveform amplitude. Both computer and hard-wired circuitry for controlling the output signal are disclosed. An isolation-and-rectification network may be used to recover a D.C. voltage of programmably controlled amplitude.

Abstract: A power amplifier circuit includes an output complementary emitter-coupled transistor pair driven by a second pair of complementary transistors having a parallel resistor diode combination serially connected between their emitters to establish idling currents. Base drive for the output transistors flows through the resistor of the resistor-diode combination until the potential thereacross exceeds the diode forward breakdown potential after which all increases in drive current pass through the diode. The use of the diode limits the bucking potential in the base current drive circuit thereby enhancing available output power.

Abstract: An single-ended push-pull amplifier comprises first and second complementary single-ended push-pull circuits connected in parallel across a power source. Each push-pull circuit has paired complementary transistors and an output connected together to drive a common load such as a loudspeaker. Inputs of the first and second push-pull circuits are connected with a bias circuit connected to receive an audio signal to be amplified. The first to fourth transistors are so controlled that the first and second transistors are operated Class A at small signal levels, and the first and fourth complementary transistor pair and the second and third complementary transistor pair are operated Class B at large signal levels, thus producing a low distortion factor and a high power efficiency.

Abstract: An output amplifier comprises an output transistor and a biasing transistor whose emitter is connected to the emitter of the output transistor. The polarity of the biasing transistor is the same as that of the output transistor. Resistors of small resistance are connected to the collector and base of the biasing transistor, respectively. The other ends of these resistors are connected to the base of the output transistor. When an input signal in the positive cycle is applied to the base of the output transistor, the circuit comprising the biasing transistor and the resistors operates as a resistance circuit. On the other hand, when no signal is applied to the base of the output transistor, or when a signal in the negative cycle is applied to the base of the output transistor, the circuit operates as a current mirror circuit. Therefore, when the output transistor is cut off, the biasing transistor is simultaneously cut off.

Abstract: An electronic gain control circuit comprising a logarithmic circuit portion and an antilogarithmic circuit portion which is coupled to a current mirror circuit producing an output signal which is linearly related to an input signal applied to the logarithmic circuit portion thereof having a magnitude which is varied in response to a gain-control signal applied to the circuit. The logarithmic circuit portion of the gain control circuit provides a logarithmic voltage drive signal which drives the antilogarithmic circuit portion to supply an input current at the input of the current mirror having no fundamental signal components of the applied input signal. The output of the antilogarithmic circuit portion is coupled at an interconnect node with the output of the current mirror such that direct current components as well as second harmonic signal components of the applied input signal are cancelled and do not appear in the output of the electronic gain control circuit.

Abstract: A tone generator for a telecommunication--especially telephone--system operating in the PAM/TDM mode comprises two complementary transistors with interconnected emitters joined to a "hot" conductor of a two-wire transmission path forming part of a trunk line between two groups of subscribers, the collectors of these transistors being connected through respective series resistors to a positive and a negative terminal of a DC source. These collectors are further coupled via respective shunt condensers to the "cold" conductor of the transmission path which is grounded through a low-ohmic further resistor.

Abstract: A balanced preamplifier is disclosed for impedance-coupling an audio signal source, such as a microphone, to a differential amplifier. In one embodiment, the preamplifier comprises a first stage wherein a pair of complementary bipolar transistors are connected in a common-base configuration and coupled to a low-impedance microphone so that the microphone signal is appied to the respective emitters of the transistors and transformed to an appropriately higher impedance level at the respective collectors thereof with common-mode passage of external and internal noise. A second stage including a complementary pair of bipolar transistors in a common-emitter configuration is coupled to the first stage for greater power and voltage amplification requirements.

Abstract: A protection device for a power output circuit, designed such that the device protects the power output circuit from damage due to output overloads and simultaneously eliminates the power dissipation of the protected device, thereby conserving power and eliminating unnecessary heating of both the protected device and adjacent components. The protection device includes a comparator for comparing the voltage at the input to the power output circuit with the voltage at the output of the power output circuit. If the power output circuit has a unity voltage gain, its voltage output equals its voltage input under normal operating conditions but its voltage output becomes lower than its voltage input under overload conditions. The comparator is arranged to inhibit the power operation of the power output circuit and reduce its power dissipation to zero when the input voltage of the power output circuit exceeds the output voltage thereof by a specified value, that is, under overload conditions.

Abstract: A complementary differential amplifier comprises a first differential amplifier circuit having first conductivity type differential transistors and a second differential amplifier circuit having second conductivity type differential transistors. To improve a dynamic range and a slew rate of the complementary differential amplifier and, to prevent of the generation of TIM distortion with a simple construction, a constant voltage circuit is connected between commonly connected electrodes of differential transistors of the first differential amplifier circuit and commonly connected electrodes of differential transistors of the second differential amplifier circuit. To improve a slew rate in a high frequency range and to prevent the generation of TIM distortion, a capacitor may be connected between the commonly connected electrodes of the differential transistors of the first differential amplifier and the commonly connected electrodes of the differential transistors of the second differential amplifier.

Abstract: A power amplifying circuit detects the crest factor of an electric signal, especially an audio signal, requiring amplification. In case this crest factor is great, the level of supply voltage for power amplifying elements of the power amplifying circuit is raised, and conversely in case the crest factor is small, the supply voltage level is lowered, thereby minimizing the development of distortions in the power amplifying elements as well as minimizing thermal loss thereof.

Abstract: A Class "B" amplifier circuit in which Class "B" conversion takes place in a converter portion of the circuit in combination with a differential amplifier input circuit, rather than in the output stage. The converter modulates the DC bias current supplied to the differential amplifier input circuit as a function of the input signal, in order to achieve Class "B" operation. The output amplifier portion of the circuit includes a pair of complementary, series-connected transistors, each of which is connected in a common-emitter configuration. The disclosed circuit provides a high input impedance and excellent dynamic range.

Abstract: The video amplifier circuit comprises a complementary symmetrical arrangement of a first and second solid state transistor element with the video input source coupled through a level shifting circuit to the first element and through a DC level shifting circuit to the second element and with means provided for operating each element in a clamped mode approaching saturation. Additional circuit modifications include means for modulating the video input signal with a high frequency signal to cause continuous gray scale variation.

Abstract: A switching circuit having two complementary transistors of collector coupling type, a drive transistor, a current backflow-preventing diode and a level-shifting power source. When the drive transistor is on, one complementary transistor is turned off by the level-shifting power source. When the drive transistor is off, the other complementary transistor is turned off by the current backflow-preventing diode. It is sufficient that the drive transistor can switch a current which corresponds to the sum of the base currents of the complementary transistors.

Abstract: A bias adjusting circuit for a push-pull amplifier is disclosed, which automatically increases or decreases the bias in the amplifier circuit so that the desired bias level is maintained. The bias adjusting circuit measures the current consumption of both halves of the push-pull amplifier, determines the point at which output current zero crossings have occurred, and at these times makes any necessary changes to the bias current to conform to a desired level. The circuit has an insignificant effect on the amplifier's power efficiency, and offers a degree of bias stability unattainable with conventional techniques.

Abstract: A vertical deflection amplifier includes a driver amplifier stage having a source of sawtooth deflection signals at the vertical rate and direct current feedback from the vertical deflection winding as inputs. The driver amplifier stage drives a pair of voltage translation stages each of which drives a transistor in a complementary-symmetry output stage. The voltage translation stages are independent of each other and are biased to operate as constant current sources with no signal present for controlling the quiescent current of the output stage. The improved vertical amplifier can thus be utilized to pass a horizontal rate signal combined with the vertical rate signal to effect image rotation when the deflection amplifier is used with an image pickup tube.

Abstract: A power transformer connected to an amplifier, said transformer being adapted to operate at maximum power output at a relatively high frequency, in the order of 20 KHz. There is a control circuit which produces control pulses at a frequency of 20 KHz. The voltage level at the output of the transformer is compared to the amplitude of the audio signal to be amplified to produce a control signal related to the difference between the two. This control signal acts through a modulator to pass portions of each control pulse, with the duration of the pulse portions that are passed being generally proportional to the magnitude of the control signal. These pulse portions in turn open and close a switch connected to the primary winding of the transformer to control the duration of current pulses which flow through the transformer at a 20 KHz frequency.

Abstract: Circuitry for protecting the output transistors in a double power source, single ended, push-pull amplifier when a reactive load is employed, the load is short circuited, the transistors are overdriven, etc. Various embodiments are described for effecting the foregoing.

Abstract: A power amplifier comprises: a complementary symmetry push-pull circuit formed with two complementary transistors mutually coupled at their emitters and having an operating point for Class-A mode operation; a floating power supply having a neutral terminal serving as the output terminal of the power amplifier, a positive and a negative terminal connected respectively to the collectors of the respective transistors; a bootstrapping circuit for driving the mutually coupled emitters in proportion to the potential at the output terminal; and a circuit for negative feedback of signal from the output terminal to the bases of the transistors.

Abstract: A transistorized power amplifier includes a differential pair coupled to a push-pull driver. The latter provides an amplified signal to an output stage through a compound driver, which comprises a pair of complementary transistors. The collector of the input transistor of the compound driver is connected to the base of the other transistor in the compound driver.

Abstract: A transistor amplifier comprises an input stage circuit and an output stage circuit direct-coupled to the input stage circuit: the input stage including complimentary paired transistors having bases commonly connected to an input terminal and emitters AC-wise grounded and further connected to constant current sources, respectively; the output stage being a single-ended push-pull amplifier circuit including complimentary paired transistors having bases connected to collectors of the input stage transistors, respectively, and emitters commonly connected to an output terminal. This transistor amplifier has advantages that it is simple in arrangement and that both its DC and AC operations are highly stabilized against variations in the ambient temperature and in the voltages of operating power supplies.

Abstract: In a push-pull power amplifier which amplifies an audio-frequency signal supplied thereto and supplies its output signal to a load, a pair of output transistors constituting the push-pull circuit are alternately turned on and off according to the polarity of the input signal. In the power amplifier, current flowing through the current path leading from a DC power source to each of the output transistors includes many harmonic components besides its fundamental wave component. These harmonic components of current are introduced through a stray magnetic field into the signal path in the power amplifier thereby producing distortion of the signal supplied to the load.

Abstract: A high fidelity audio amplifier having a pair of cooperating active amplifying devices includes two diodes, each of which is connected in a distinct signal pathway directly associated with an active amplifying device so that the amplifier achieves true Class A operation over the full range of normal input signals. The amplifier can achieve true Class A operation using bipolar transistors, field effect transistors, or vacuum tubes as the active amplifying devices.

Abstract: The present invention comprises a circuit for addition to a non-linear amplifier wherein the non-linearity is of the first degree. The circuit essentially adds a signal (or signal variable impedance path) to that already existing to remove non-linearity in operating characteristics over a given range of voltage.

Abstract: An amplifier circuit is provided with a first transistor receiving at the base an input signal and a second transistor related to its first transistor in complementary fashion. A first load resistor is provided between the base and the collector of the second transistor. A second load resistor is provided between the junction of the collector of the first transistor and the emitter of the second transistor and a power source. An output signal is taken out from the junction.

Abstract: In order to eliminate distortion a power amplifier is biased to Class-A or Class-B operation and in order to minimize the power loss the supply voltage of a power source is decreased as much as possible and the power source is driven by another highly efficient power amplifier so as to follow an output voltage.

Abstract: An amplifier circuit suitable for use as a video amplifier in a color television circuit for driving the variable impedance load provided by a color television picture tube, in which the load impedance of the amplifier element of the circuit is also made variable. This is achieved, in one embodiment by using as the output stage of the amplifier two transistors with a complementary symmetrical configuration so that one is always substantially cut-off while the other conducts. In another embodiment a transistor in common collector configuration acts as the amplifier element and its emitter from which the output of the amplifier is taken is connected by a diode to the collector of a transistor which feeds the base of the common collector transistor.

Abstract: A bias circuit comprises first and second cascade-connected transistors of the same conductivity type; series-connected diode means adapted to be forward biased by part of a drive current toward the first and second transistors; and means for applying a voltage across a series circuit of the diode means between the bases of the first and second transistors, emitter voltages of the first and second transistors being applied to a next stage class B push-pull circuit.

Abstract: An audio frequency power amplifier wherein an input signal is applied to respective input electrodes of a pair of transistors of the same conductivity type to produce an output signal at an output electrode of one of the pair of transistors. A common electrode of the one transistor is connected with an output electrode of the other transistor and a power from a first D.C. power supply is supplied to the junction thereof through a diode while a power is supplied to a common electrode of the other transistor from a second D.C. power supply having a higher voltage than that of the first D.C. power supply. The other transistor and the diode are alternately rendered conductive and non-conductive in response to the signal level of the input signal, a capacitor is connected to the input electrode of the other transistor, which capacitor is charged during the turn-off of the other transistor whereby the charge is supplied to the other transistor upon turning on of the other transistor to shorten the rise time.