Abstract: Switched transistors (T1 . . . through T4 . . .) are arranged in a bridge circuit such that a plurality of transistors (T1 . . . through T4 . . .) are connected in parallel in every bridge branch. These transistors are secured on a thermally and electrically conductive ring (R, R'), are symmetrically distributed over this ring (R1, R1'), and have a respective terminal electrically connected thereto. The connection to further terminals of the transistors (T1 . . . through T4 . . .) occurs essentially in rotationally-symmetrical fashion via large-area printed circuit boards (LE1 through LE6). Short connecting paths with low values of inductance are achieved with this arrangement. Furthermore, the waste heat from all transistors (T1 . . . through T4 . . .) is uniformly carried off via the rings (R1, R1'), so that all transistors (T1 . . . through T4 . . .) work at the same temperature. A uniform current division onto all transistors (T1 . . . through T4 . . .

Abstract: A power amplifier for a plate load of an AM, RF transmitter includes plural switching stages each powered by a DC source. Each stage is switched from non-sourced to saturation in response to the amplitude of an analog source exceeding a threshold amplitude for the stage; each stage has a different threshold. The thresholds and analog source are arranged so that responses derived between output terminals of the stages change between zero and predetermined amplitudes as the source amplitude changes relative to the thresholds of the different stages. The responses of the different stages are summed. A triangular wave having a small constant maximum amplitude relative to the analog source maximum value effectively changes the threshold of each stage.

Abstract: A minimum pulse width switching power amplifier utilizes digital logic for generating a control pulse having a pulse width at least as large as a fixed minimum period of time when a base control pulse generated by a comparator has a pulse width at least as large as a given value. A high power switching output stage is switched between different voltage levels under control of the control signal generated by the digital logic so that an average actual output of the amplifier is equal to the desired output.

Abstract: A closed-loop control system for a Class-D power amplifier circuit, having a variable output resonant circuit impedance, maintains high-efficiency operation by using the phase angle between the resonant load voltage and current to control tuning of the resonant circuit. The resonant load circuit voltage and current are supplied to a phase detector for detecting the phase angle therebetween and for generating a voltage proportional thereto. The output voltage from the phase detector is compared to a reference voltage by an error amplifier. The resulting error voltage is employed as the input signal to control circuitry for tuning the output resonant circuit. Such a control system is suitable for maintaining high-efficiency operation of an electrodeless high intensity discharge lamp system.

Abstract: A driver circuit for a voltage-switching, high frequency Class-D power amplifier provides an input sinewave power signal and controls the transition time between switching the two active devices thereof, resulting in substantially lossless switching. The transition time is optimized by controlling the amplitude of the voltage signals at the inputs of the two active devices, depending on the output capacitance of the switching devices, the threshold voltage of the switching devices, the power output requirement, and the impedance of the resonant load network of the Class-D power amplifier.

Abstract: A class SM amplifier is provided having a threshold circuit with a plurality of threshold levels for generating a plurality of threshold signals. In response to an input signal passing a particular threshold level, the threshold circuit generates as an output a particular threshold signal. A voltage supply is provided having a plurality of voltage levels. The class SM amplifier includes a plurality of transistors coupled to a load and the threshold circuit, and the plurality of voltage levels from the voltage supply. The transistors switch a particular voltage level across the load in response to a particular threshold signal from the threshold circuit. The plurality of voltage levels are adjusted to approximate the input signal.

Abstract: A class SM amplifier is provided having a threshold circuit with a plurality of threshold levels for generating a plurality of threshold signals. In response to an input signal passing a particular threshold level, the threshold circuit generates as an output a particular threshold signal. A voltage supply is provided having a plurality of voltage levels. The class SM amplifier includes a plurality of transistors coupled to a power combiner and the threshold circuit, and the plurality of voltage levels from the voltage supply. The transistors switch voltage levels across the power combiner in response to a particular threshold signal from the threshold circuit. The power combiner is coupled to a load, and outputs the combination of the voltages from the transistors across the load. The plurality of voltage levels are adjusted to approximate the input signal.

Abstract: An r.f. power amplifier, typically a high efficiency, class E amplifier in which a reactive load circuit (18) is connected to a semiconductor switching device (10), the load circuit being designed to have the required input load angle and loaded Q so that the voltage across the device (10) goes to zero with zero slope before it switches on and passes current, is provided with a step recovery diode (32) connected to the device (10) to limit the voltage swing across the device (10) with no significant loss of efficiency. This allows the voltage-handling capability required of the device to be reduced or the amplifier output power to be increased by increasing the supply voltage.

Abstract: A pulse width modulation technique regulates the output power of each cycle of a radio frequency surgical signal of an electrosurgical generator. The delivered power of the surgical signal is determined by multiplying the sensed current and the sensed voltage of the surgical signal. An error signal is established by the difference of the actual delivered power with respect to a selected desired output power. The error signal is operatively utilized to modulate the pulse width of each driving pulse which creates the cycles of the surgical signal. Limits on the sensed voltage and sensed current signals are established to limit the output characteristics of the surgical signal. A minimum current limit signal is utilized to limit the maximum output voltage into relatively high impedances. A minimum voltage limit signal is utilized to limit the maximum output current into relatively low impedances.

Abstract: A digital power amplifier system includes means providing a signal having predetermined characteristics is digitally synthesized and applied as input signals to a digital symmetrical pulse width modulator. The digital pulse width modulated signals are amplified in a digital or switching power amplifier. The resulting signals are then passed through a tuning or filter circuit to produce an analog signal having the desired frequency and wave shape characteristics which is then applied to a suitable load device. In the thus provided amplification system all of the amplification is accomplished through digital circuitry with no analog influence until the amplified circuits are applied to the tuning or filter elements.

Abstract: A digital power amplifier system features an analog signal which is converted to a corresponding digital signal and is, in turn, applied as input signals in a digital binary format to a digital pulse width modulator. The digital pulse width modulated signals are amplified in a digital or switching power amplifier. The resulting signals are then passed through a tuning or filter circuit to produce an analog signal having a desired frequency and wave shape characteristics. The analog signal is then applied to a suitable load device. In the thus provided amplification system, all of the signal processing and amplification is accomplished through digital or power switching circuitry with no analog influence until the amplified signals are applied to the tuning or filter elements.

Abstract: A MOSFET isolation amplifier apparatus to allow stable high frequency linear operation of MOSFET power stages and to provide precise regulation of a load current through a magnetic yoke load. Variations of transfer characteristics and input parameters in the MOSFET power stages are corrected by use of a feedback signal which is generated in a current sense resistor by the load current. Such a power stage allows the implementation of isolation amplifiers which can provide high power high frequency linear regulation at elevated voltages and currents.

Abstract: A high efficiency MOSFET sine wave generator is provided using the class D pulse width modulation principle. A triangle wave at f.sub.0 is compared to a variable amplitude sinusoid at about 1/10 f.sub.0 to provide a pulse width modulated signal for driving a pair of power MOSFETS connected for switching a B+ and a B- power supply. The power switch output is LC filtered and fedback for regulating the amplitude of the modulating sinusoid.

Abstract: An efficient power amplifier for high-capacitive device C2 in load string 10. The load string 10 includes a reference capacitor C3, a resistor R1, and an inductor L1. A large capacitor C1 is connected to load string 10 through high voltage power bridge 28. A current sensing feedback 30 is utilized to produce a triangular waveform of current in load string 10 for causing charge to be alternatively removed from capacitor C1 and delivered to device C2 through inductor L1 and then returned to capacitor C1 with any losses replenished by the dc power source. A voltage sensing feedback 14 is used to modulate the triangular current waveform. The power amplifier behaves as a stable linear dc coupled operational amplifier delivering a large reactive current with only slight losses.

Abstract: The invention comprises an isolation amplifier including an input circuit and an output circuit coupled through an isolation transformer. A switching type balanced modulator modulates a square wave carrier with an analog signal input and delivers the resulting signal to the input of the isolation transformer. A demodulator in the output circuit inverts alternate points of the modulated square wave carrier to essentially reproduce the analog input. A sample and hold capacitor circuit connected to the output of the demodulator fills the gap between the trailing and leading edges of successive pulses.

Abstract: A digital amplifier having a modulator for transforming the analog audio input signal into two complimentary trains of pulse width modulated signals for driving the power switches, which modulator utilizes a precision triangular waveform to control the transformation. The modulator employs all differential processing without saturated transistors to achieve a minimal distortion modulation system. Upon the occurrence of over-modulation, pulses from the width modulated pulse train produced by the modulator are dropped, and the resulting loss of pulses is detected and fed back to a variable gain amplifier stage of the system. The distortion detection system for detecting the missing pulses utilizes a timing network to establish the missing pulse period necessary to begin input attenuation of the audio signal by the variable gain amplifier stage.

Abstract: An apparatus amplifies a signal in two different modes. The apparatus amplifies the signal in a linear mode when the voltage of the signal is much less than the voltage of the power source, and in a switching mode when the signal is at other voltages.

Abstract: This dual operating mode switching power driving circuit arrangement comprises an amplifying circuit of conventional form which is operated substantially as a Class A feedback amplifier in a servosystem "following" mode and is switched to operate as a Class D amplifier in the "seeking" mode under program control calling for the latter mode and reswitched to the "following" mode only at the succeeding transition of the Class D waveform whereby transients are avoided. For operating in Class D mode, the Class A feedback loop is opened and the amplifier circuit is arranged so that the input wave now overdrives the input circuit and drives the output circuit between .+-. values of the energy potential, whereby the efficiency is very high.

Abstract: An arrangement for improving the performance of Class D pulse width modulated amplifiers which comprises circuitry for short circuiting turns on the output transformer during intervals between pulses and thus enabling extended linear control of the power output of said amplifier and protecting the amplifier against transients fed back from a load connected thereto.

Abstract: A power amplifier connection comprises a switching amplifier and a proportional amplifier. The output signal from the switching amplifier and the output signal from the proportional amplifier are supplied to a summation member which, by addition of the two output signals, forms the resultant output signal of the amplifier connection. The switching amplifier is adapted to be controlled in dependence on the input signal of the amplifier connection in such a way that its output signal endeavours to follow the input signal. The proportional amplifier is adapted to be controlled in dependence on the deviation between the input signal and output signal of the amplifier connection.

Abstract: An audio power amplifier with class-D push pull output stage is disclosed using a "mixture" of pulse-width modulation and pulse-amplitude modulation and driving the class-D push pull output stage with the resulting combination signal. To do this, the digital output signal of the analog-to-digital converter in the input stage is split up in such a way that only its high-order bits control the pulse-width modulator, while the other low-order bitsare changed into the aforementioned pulse-amplitude-modulated signal by means of an analog-to-digital converter.

Abstract: In an electrodeless discharge lamp of the type including an ionizable medium within a sealed envelope capable of emitting radiant energy when subjected to a radio frequency field, an oscillator for generating an output signal at a given radio frequency of 13.56 MHz, an RF amplifier responsive to the oscillator output signal, and an induction coil and a capacitor connected in series and responsive to the output of the amplifier, the coil being positioned in close physical proximity to the medium in the envelope for coupling to the medium an electric field having a magnitude sufficient to initiate ionization of the medium and a magnetic field for maintaining ionization, there is disclosed an improvement wherein a Class D amplifier drives the series connected coil and capacitor without a separate load circuit connected in the output circuit of the amplifier. A specially selected filter and matching network coupled between the Class D amplifier and the series connected coil and capacitor reduces CV.sup.

Abstract: A compact and inexpensive LF power amplifier is disclosed. A plurality of pulse trains which are phase shifted relative to each other are width-modulated by an input LF signal. The modulated pulse trains are individually amplified, preferably by means of a plurality of respective power transformers and switch elements. The switch elements include any suitable combination of electron tubes and semiconductor switches. The keying ratio of the amplifier is improved by associating the pulse trains in pairs, the two members of each pair being phase shifted 180.degree. relative to each other. The amplified pulse trains are superimposed to form a single combined amplified pulse train.

Abstract: A pulse width modulated signal amplifier includes a first DC voltage source having first and second terminals, first and second switching transistors each having a control electrode, the main current path of which is connected in series between the first and second terminals of the first DC voltage source, the connection point of which is connected to an output terminal, a signal input circuit for supplying a pulse width modulated signal to the control electrodes of the first and second switching transistors, a low pass filter having an input connected to the output terminal and an output to be connected to a load, a second DC voltage source having first and second terminals, the output voltages of which are lower than those of the first and second terminals of the first DC voltage source, a first circuit including a first diode and connected between the first terminal of the second DC voltage source and the output terminal, and a second circuit including a second diode connected between the second terminal o

Abstract: An AM broadcast transmitter uses a PWM modulator that requires a pulse width filter. It has been found that the filter load varies over the modulation cycle resulting in distortion. To overcome this problem, a varying voltage is applied to an RF driver stage during portions of the modulation cycle.

Abstract: There is disclosed a high power and/or high voltage switching operational amplifier arrangement having a comparator with a first input for a low frequency AC signal. The output of the comparator is connected with the data input of a bistable element. The bistable element is triggered by a clock pulse signal with a rate substantially higher than the frequency of the AC input signal. An amplifying stage arranged between both poles of a high power and/or high voltage source is composed of a pair of alternately operating switch means, each arranged between a respective pole of the voltage source and a common amplifier stage output. Each of the switch means is coupled by a control input to at least one of the outputs of the bistable element. A low pass filter network coupled to the amplifier stage output forms the output stage of the operational amplifier arrangement. Means for providing feedback are arranged between the filter network and a second input of the comparator.

Abstract: A pulse width modulated switching amplifier is provided for amplifying an analog signal. Means is provided for producing positive and negative signals representative of positive and negative excursions of the analog signal, respectively. The positive and negative signals are applied to level shifters which produce positive and negative replica signals having the same waveshapes as the positive and negative signals, respectively, but which vary about a predetermined reference level. The level shifted replica signals are then applied to first and second comparators, respectively, which continuously sum the instantaneous magnitude thereof with the instantaneous magnitude of a triangular modulation signal also varying about the reference level. Each comparator produces a logical ONE output signal when the sum is positive and a logical ZERO output signal when the sum is negative.

Abstract: A pulse width modulated signal amplifier includes first and second switching transistors and a diode which are connected in series across a DC power source and in the forward direction with respect to the polarity of the DC power source, the diode being connected between the first and second transistors. The first transistor has its base connected to a corresponding terminal of the DC power source and the second transistor has its base supplied with a pulse width modulated signal to be amplified. A connection point of the first transistor and a diode is connected to a lowpass filter which provides a demodulated audio signal to a load. A coil is connected between the diode and the second transistor and the connection point of the coil and the second transistor is connected to the base of first transistor.

Abstract: In a Class D amplifier system comprising a pulse width modulator for pulse width modulating with an audio signal a carrier signal having a frequency higher than that of the audio signal, an output switching amplifier connected to the modulator, and a lowpass filter connected to the output amplifier to supply a demodulated audio signal to a load in which a trap circuit resonant at a carrier signal frequency is provided in the lowpass filter to permit part of an output signal from the trap circuit which is free from a carrier signal component to be negative-fed back to the pulse width modulator.

Abstract: An overload detecting circuit for a PWM amplifier includes an output current detecting circuit and an output voltage detecting circuit. The output of the output voltage detecting circuit is supplied to a rectifying circuit having a discharge time constant determined by the cut-off frequency of a low pass filter as a demodulator of the PWM amplifier. A comparison circuit is provided to produce an overload indicative signal in response to the comparison result between the outputs of the rectifying circuit and of the output current detecting circuit.

Abstract: A pulse width modulated signal amplifier comprises a DC power supply for rectifying an AC input voltage to produce a pair of DC voltages of opposite polarity, a pulse width modulated signal amplifying circuit supplied with a pulse width modulated signal to produce a demodulated signal through a low pass filter, and a detecting circuit responsive to an abnormal level of the DC voltages to produce a detecting signal when a smoothing condenser of the DC power supply is overcharged by a current flowing through the low pass filter in one direction. Such detecting signal is desirably employed to prevent the appearance of the output signal from the pulse width modulated amplifying circuit.

Abstract: A system wherein input signals are pulse duration modulated to provide a plurality of pulse trains having a predetermined phase relation therebetween. The plurality of pulse trains control the operation of separate switching elements. The output of the switching elements are summed and filtered to provide a composite amplified signal. The number of switching elements and the number of pulse trains are determined by the desired fidelity of operation and the frequency response of the switching elements. The system is particularly useful as a power audio amplifier for use in modulating stages of RF transmitters.

Abstract: This invention relates to an amplifier system comprising two or more Class D amplifiers the outputs of which are associated with a common system output in a known manner. To avoid the appearance of spurious sidebands in the system output which are associated with the switching process of the amplifiers, separate clock pulse trains are applied to the Class D amplifiers, the separate clock pulse trains being interlaced to obtain cancellation of switching frequency ripple at the common system output.

Abstract: A modulation amplifier having an output amplifier element which contains an accumulation choke, a switching tube and a low-pass filter connected in series, with a commutation diode connected to the switching tube is disclosed. The switching tube is controlled by pulse duration-modulated pulses and a semiconductor switch is connected between the switching tube and the pulse duration-modulated pulses. The semiconductor switch comprises two branches, each of which are connected to a different electric potential and each including a controlled semiconductor which acts as a switch, one of the branches being controlled into a conducting state and the other of the branches being controlled into a non-conducting state upon a potential jump in the pulse time-modulated pulses in either the increasing or decreasing directions.

Abstract: A negative feedback operation of a PWM-type amplifier is stabilized by the use of a resistor. The input signal is voltage-compared with the triangular wave of a higher frequency than the input signal to form a PWM-signal, which is, in turn, power amplified and is provided to a load after demodulated by a low-pass-filter. A part of the output voltage is fed back from a common connection point of an inductor and a capacitor of an LC-filter forming the low-pass filter. A resistor is connected in series with the capacitor, and the negative feedback operation is, thereby, stabilized.

Abstract: An isolation circuit with duty cycle feedback is disclosed which includes an operational amplifier with capacitive coupled negative feedback such that its output voltage varies to maintain its input terminals at the same potential, and which output is connected to the control terminal of a voltage controlled oscillator which generates a square wave voltage in which the ratio of ON time to the total period is directly related to the voltage from the operational amplifier. The output pulses of the voltage controlled oscillator are fed through a resistor to the negative input terminal of the operational amplifier. The output pulses from the oscillator are also fed through a driver transistor to control the input of an opto-coupler. The output from the opto-coupler passes through an amplifier to produce a square wave voltage with the same ON time ratio as the voltage controlled oscillator.

Abstract: A system providing linear amplification of a signal including a pulse duration modulation of the signal upon a carrier signal, the system further including a plurality of amplifying units which are sequentially activated by the modulated carrier. The amplifying units are arranged in the form of a bridge circuit, the nodes of which are coupled to a load, the amplifying units including transistors which are driven alternately in states of conduction and nonconduction for maximizing power coupled to the load while minimizing power dissipated in the transistors. A filter connected between the amplifying units and the load attenuates signals at the frequency of the carrier so that the waveform of the signal applied to the load duplicates the waveform of the signal at the input of the system.

Abstract: A pulse width modulation circuit which comprises a mixer for combining an input audio signal with a feedback signal and for developing a difference signal to feed to an integration circuit. The integration circuit is coupled to a pulse width modulator which has a sawtooth carrier input for modulating the input audio signal. The resulting pulse modulated signal is then fed to a pulse amplifier and a low-pass filter and finally to a load. The output of the low-pass filter is coupled back to the mixer.

Abstract: A low level class D amplifier is disclosed. High effeciency is assured by operating the active devices in the switching or class D mode and recovering substantial portions of the power contained in the harmonics generated. The amplifier includes a switching circuit or class D active circuit, a harmonic impedance circuit and an RF circuit serially connected across a power supply for supplying DC power to the amplifier. During the conducting state of the class D active circuit, the harmonic impedance circuit limits the harmonic currents and stores energy as a magnetic field. Substantially all of the stored energy is recovered during the non-conducting portion of the active circuit and returned to the DC power supply. Limiting harmonic currents reduces the dissipation of the active devices. Recovering the stored energy substantially improves the efficiency of the amplifier.

Abstract: A protective coupling circuit is located between the D.C. supply voltage the amplifier components of a push-pull switching amplifier to suppress transients created during switching. The coupling circuit comprises a power supply filter with an inductor coil and capacitor, and circuitry for limiting the voltage on the individual switching elements and the output coil. Excess voltages caused by transients are fed to the power supply filter. In an alternative embodiment the power supply filter inductor coil is actually an auxiliary winding on the amplifier output transformer rather than a separate coil. This allows for use of some smaller capacity circuit elements.

Abstract: An A.C. powered amplifier for converting low power information input signals to corresponding signals of a substantially increased power level without requiring a power transformer. A signal processor having a low power information signal input and a feedback signal input controls the state of a controllable switch. The switch power input is coupled to a source of relatively high A.C. voltage via a rectifier circuit and a first low pass filter circuit, and the switch output is coupled to the amplifier output terminal via a second low pass filter circuit. A feedback path is provided from either the switch output or the amplifier output terminal to the feedback signal input of the signal processor. The signal processor may comprise a pulse width, or pulse frequency modulation circuit.The amplifier provides high efficiency, low power loss, and has a band width limited only by the maximum switching frequency of the controllable switch.

Abstract: A direct coupled linear transistorized amplifier in which transistors function as switches rather than as semilinear amplifying devices; this is effected by comparing a negative feedback signal with the input signal and utilizing the sense of the resultant error signal to apply power-supply voltage to the load in the direction which tends to minimize this error signal. In the most preferred embodiment, the output switching is performed in push-pull manner.

Abstract: A circuit arrangement for the ungrounded transmission of signals through testing points in communication systems with the aid of high-frequency oscillations. The high-frequency oscillations are controlled on the one side of the testing point and are rectified on the other side of the testing point. The rectified signals are utilized to reproduce the signals again. A resonant circuit is adjusted to the high-frequency oscillations and is galvanically separately coupled to a high-frequency generator. The resonant circuit is also connected to a modulation circuit and to the input of the testing point. The resonant circuit is coupled inductively to a demodulation circuit which forms the output of the testing point.

Abstract: A drive circuit responsive to the phase of the amplifier output current eres that the non-conducting amplifier element remains off while the other amplifier element conducts. The output current phase can be detected either from the individual amplifier element outputs or from their combined outputs. Adjustments are made to compensate for any phase shift which occurs between the input to the amplifier and the point in the output at which the phase is detected.

Abstract: An amplifier having ready application as an amplifier for pulse width modulated signals, is comprised of first and second field effect transistor devices which exhibit triode-type dynamic characteristics. These field effect transistor devices are connected in push-pull amplifying relation for receiving a signal to be amplified and for supplying an amplified signal to a load. A low-pass filter device connects the load to the push-pull field effect transistor devices. The output terminals of the field effect transistor devices are connected in series across a voltage supply which is used to supply the energizing voltages to the transistor devices.

Abstract: A switching amplifier includes a pulse width modulator for converting a bipolar input signal, which may be a speech signal, into a train of unipolar pulses having durations which vary with the instantaneous absolute amplitude of the input signal. The pulses control the energizing of a series switch which supplies current to a switching bridge circuit. The switching arms of the bridge circuit are controlled by the polarity of the input signal. Another switch and several diodes are used to provide a path for output current when the series switch is open. The output current is filtered to remove fluctuations at the switching rate, and applied to a load. The amplified output voltage signal accurately follows the input signal, and the efficiency of conversion of DC power to AC output power can approach 100 percent, limited only by switching and filtering losses. A single polarity DC supply, such as a battery, is used to provide bipolar output current to an ungrounded load.

Abstract: A pulse width modulated signal amplifier system includes a signal input circuit, an amplifier for receiving an input signal from the signal input circuit, a pulse width modulator for receiving an output signal from the amplifier and producing a pulse width modulated signal, and a phase splitter for receiving the pulse width modulated signal and producing a pair of corresponding pulse width modulated signals having different polarities to each other.

Abstract: A pulse width modulated signal amplifier includes a pair of transistors, each having a base, an emitter, and a collector. The bases are supplied with a pulse width modulated signal to be amplified, and the emitters are connected to each other and to an output terminal. A low pass filter connects the output terminal to a load. The collectors are connected to first and second terminals of a DC power source through first and second DC voltage sources, respectively, and first and second diodes are connected between the connection point of the emitters and corresponding terminals of the DC power source, respectively. First and second voltage limiting circuits are provided between the bases of the first and second transistors and corresponding terminals of the DC power source so as not to produce a longitudinal amplitude distortion in response to the switching operation of the first and second transistors.

Abstract: A protective circuit for a pulse width modulated signal amplifier includes a signal input circuit, a carrier signal generator, a pulse width modulator for receiving both the output signals of the signal input circuit and the carrier signal generator and for producing a pulse width modulated signal, an amplifier for receiving the pulse width modulated signal and for amplifying it to drive a load through a low pass filter, a detecting circuit for detecting whether the pulse width modulated signal is present or not, or detecting DC voltage of undesirable duration produced at the output of the amplifier and for producing a control signal, and a protective circuit activated by the control signal for cutting off the operation of the amplifier.

Abstract: A digital amplifier having a modulator for transforming the analog audio input signal into two complimentary trains of pulse width modulated signals for driving the power switches, which modulator utilizes a precision triangular waveform to control the transformation. The modulator employs all differential processing without saturated transistors to achieve a minimal distortion modulation system. Upon the occurrence of overmodulation, pulses from the width modulated pulse train produced by the modulator are dropped, and the resulting loss of pulses is detected and fed back to a variable gain amplifier stage of the system. The distortion detection system for detecting the missing pulses utilizes a timing network to establish the missing pulse period necessary to begin input attenuation of the audio signal by the variable gain amplifier stage.