Abstract: A plurality of low-voltage, series-connected input dc-dc converters provide the input to a low-frequency, high-voltage dc-ac output bridge converter suitable for driving a gradient coil in an MRI system. The relatively low-voltage, series-connected dc-dc converters, or choppers, control the gradient coil current, while the dc-ac converter bridge steers the current to the proper coil polarity. A binary weighting of the voltage ratings of the input choppers results in the lowest voltage unit doing most of the high-frequency switching. Such an amplifier configuration is modular and allows for different gradient coil requirements to be met with a common approach by applying a predetermined number of choppers and bridges.

Abstract: A low cost analog signal amplifying circuit suitable for manufacturing in the form of an integrated circuit having an external load, two DAC, two signal control elements and two switching circuit means to reverse the direction of current flowing through said load.

Abstract: In a method for generating respective drive signals for four switch elements of a power output stage, a start signal and a stop signal are generated depending on an on-duration value first and second changeover signals are generated for driving each of two switch elements depending on the start and stop signals; and the drive signals are generated depending on the first and second changeover signals. A drive device and a power output stage are operated according to this method.

Abstract: A power amplifier for delivering large currents as well as high voltages of the order of some hundreds of amperes and 1000 or more volts, notably for MRI. The amplifier is constructed as a multilevel inverter in order to comply with the requirement of high voltages while utilizing transistors capable of withstanding lower voltages only. The amplifier is arranged for soft switching, so that the switching losses at said large currents are limited.

Abstract: Class D amplifiers and methods dynamically modulate the transition zone of a square wave as a function of the input signal. Stated differently, the slew rate of the square wave is dynamically modulated as a function of the input signal. Stated in yet another way, at least one of the rise and fall times of the square wave is dynamically modulated as a function of the input signal. By dynamically modulating the transition zone of the square wave as a function of the input signal, a trapezoidal wave is produced, at least one of the rise and fall times of which are dynamically modulated as a function of the input signal. The trapezoidal wave need not have dead zones. This can reduce and preferably minimize switching losses. The slow rise and fall transition zone rates can also reduce and preferably minimize spurious switching noise at zero and low level modulation. Furthermore, damping network and diode losses may be reduced.

Abstract: In a flexible and uncomplicated method for generating control signals for a power amplifier, and in a power amplifier having at least two output stages connected in series at the output side, which are driven dependent on a setting value, the setting value is classified into one of several setting value classes, a respective operating mode for each output stage is determined at least dependent on the setting value class and on a time slice value and at least one control signal for each output stage is generated dependent on the operating mode and, if warranted, on the setting value.

Abstract: A class D modulator 100 is self oscillating. It includes an input stage 110, an operational amplifier 120, an integrator 130 and a pulse width modulator 140. A start-up generator 22 generates signals ENABLE and MUTE. The MUTE signal is connected to the input stage 110 to prevent any unwanted, initial sound. The ENABLE signal connects a start-up voltage source to the integrator 130 to set the initial voltage for integration. The ENABLE signal is coupled to a dead time control circuit 16 which controls the operation of the output power transistors 42, 44 to assure that the low side power transistor 44 is turned on before the high side transistor 42.

Abstract: A parallel, synchronously driven linear power amplifier (6) and class D power amplifier (2) form an equivalent active filter, minimizing the scale of the passive filter (3), and effectively suppressing high frequency noise. First to third muting circuits (17-19) are used when the power supply is turned on and off to interrupt signal supply from the signal input terminal, and control operation of the class D power amplifier (2) and linear voltage amplifier (15), thereby preventing extraneous irritating noises such as popping sounds from a loudspeaker.

Abstract: A method and apparatus for efficient power amplification of a wideband signal with a correspondingly wide modulation bandwidth includes an envelope detector (220), an adaptive split band modulator (270), and a power amplifier (260). The adaptive split band modulator (270) amplifies the low frequency components using a class S modulator (760), and amplifies the high frequency components using a class B amplifier (750). The power supply of the class B amplifier (750) is adaptively modified as a function of the amplitude of the signal that it amplifies. In this manner, the class B amplifier (750) operates at a higher efficiency.

Abstract: A method and circuitry for amplifying an input signal. First, second and third input signals are provided with the third input signal being the average of the first and second input signals. A ramp signal is provided using the third input signal as the ramp base signal and the first and second signals are compared with said ramp signal to provide an output responsive to only one of the first and second signals when the ramp signal and one of the first and second signals are equivalent. A load is driven in response to the output. In addition, an error signal can be provided by comparing the output with the first and second input signals and altering the first and second input signals as a result of comparing the output with the first and second input signals. The output is a function of the value of the ramp signal when the ramp signal and one of said first and second signals are equivalent.

Abstract: An electromagnetic, compatible, clocked amplifier for d.c./a.c., current amplification including, for a single phase, a transistor power amplifier having at least one first switching transistor and at least one second switching transistor, and two diodes connected in parallel with respective ones of the first and second transistors; a set value adjuster; an output filter connected with an output of the transistor power amplifier and having at least one current limiting resistor, one filter inductance and one charging capsitor, and two power thyristors polarized in accordance with respective voltage signs and connected in parallel with the current limiting resistor.

Abstract: A high performance pulse width modulation amplifier system employing an H-bridge amplifier connected to a carrier wave output filter produces a pulsed wave signal with high power transfer efficiency and low total harmonic distortion characteristics. A carrier wave output filter used with the pulse width modulation amplifier system produces little peak resonance at low frequencies.

Abstract: A circuit for receiving an input signal having a phase component and an amplitude component which carry information, and for producing an output driver signal containing the phase and amplitude component information for driving a non-linear amplifier for generating linear amplification. The circuit includes a voltage controlled oscillator for receiving the phase component and for outputting a phase modulated carrier signal having a duty cycle and a constant amplitude. A driver stage made from a plurality of invertors, each having a pair of MOSFET transistors, receives the carrier signal at the gate terminals of the transistors. The amplitude component is used to drive the invertors by applying the amplitude component to the backgate terminals of at least some of the transistors in the invertors to pulse width modulate the carrier signal.

Abstract: A device for amplifying signals comprising at least two amplifier circuits (20, 30, 40, 50) as well as means for precluding interference between the amplifier circuits (20, 30, 40, 50). The amplifier circuit (20, 30, 40, 50) is provided with at least first and second modules (109, 110, 112) which are arranged in cascade, each module (109, 110, 112) being provided with an earth point (i, c, p). The means for precluding interference comprise at least one global earth point (60) and a number of earth connections (70, 80, 90) between the earth points (i, c, p) of corresponding modules (109, 110, 112). The global earth point (60) is connected to the individual earth connections (70, 80, 90).

Abstract: Class D amplifiers are difficult to incorporate into audio amplifier systems because of the interference created by the amplifier and/or the surrounding circuits. The modulation frequencies f1 and f2 of two class D amplifiers in an audio amplifier system are adjusted so that the frequency f1-f2 of interference between the modulation frequencies is outside the reproducible frequency band B1 of speakers converting the class D amplifier output to audible sound. As a result, interference that may result from simultaneous use of two class D amplifiers for similar purposes is inaudible and not perceived as noise.

Abstract: A method and apparatus for efficient power amplification of a wideband signal with a correspondingly wide modulation bandwidth includes an envelope detector (220), an multi-stage class S modulator (270), and a power amplifier (260). The multi-stage class S modulator (270) includes multiple stages (480), where each stage includes a pair of switching transistors (430, 440) and a capacitor (450). The capacitor (450) supplies the inrush current requirements of the stage (480) so that filtering at the switching frequency is substantially provided within the stage (480). Multiple stages (480) are included on a single semiconductor substrate resulting in higher switching frequencies, higher modulation bandwidths, and lower external filtering requirements.

Abstract: A low cost analog signal amplifying circuit suitable for manufacturing in the form of an integrated circuit having an external load, an external signal control element and switching circuit means to reverse the direction of current flowing through said load.

Abstract: A novel circuit that generates direct audio from a power supply that uses no power amplifier and that can provide full isolation to any impedance load. It has no power amplifier output stage and has a zero signal-to-noise ratio when there is no signal input because the circuit is designed with MOSFETS that do not conduct unless there is a signal input.

Abstract: An improved class D power amplifier is disclosed. Instead of using prior art triangle waves, a ramp signal having a first state of about 90% or greater is used and a second state for the remainder of the cycle. Further, the amplifier includes flip-flops and amplifers with hysteresis to reduce switching noise. Also, level shifting circuitry is provided for shifting the level of the input signal in response to both DC and AC variations in the power supply and to provide power supply rejection. Still further, multiple channels may be used with all of the channels synchronized to the same timing source.

Abstract: A delta-modulated magnitude amplifier is used to amplify the magnitude component of an RF power amplifier that employs envelope elimination and restoration. The delta-modulated amplifier introduces a smaller amount of non-linearity than traditional approaches, which are based upon pulse-width modulation. The disclosed technique can be implemented using switched-capacitor circuits in a standard MOS technology with only two external components, i.e., an inductor and a capacitor. Thus, the disclosed technique allows the implementation of an efficient and yet linear RF power amplifier using low-cost MOS technology.

Abstract: The transition time of power switching devices ultimately limits the rate at which such devices can be switched. Because the occurrence of unacceptably narrow pulses is relatively rare in an oversampled, noise-shaping signal processor, the elimination of such narrow pulses is introduced through the use of circuitry in the modulator loop which constrains the time between transitions to be greater than or equal to some minimum time period which, in turn provides for a smooth interface to power switching devices. However, because of the delay introduced by this pulse qualification circuitry, the modulator loop sampling frequency is increased to deal with any resulting instability. Thus, an oversampled, noise shaping signal processor is described having at least one integrator stage in a feedback loop. A sampling stage in the feedback loop is coupled to the at least one integrator stage. The sampling stage samples an analog signal at a sample frequency.

Abstract: A class D amplifier utilizing first and second switches connected in series to conduct current from a power source in a sequential manner. The switches have a common output node between them. A pulse width modulator is utilized to produce first and second signals identified as the high and low side. The first switch connects to a drive which receives the first signal from the pulse width modulator to close the first switch. A second switch drive receives a second signal from the pulse width modulator to operate the second switch in a sequential manner. A toggle or commutator device utilizes third and fourth switches in series with an inductor. The toggle device is connected to the common node between the first and second switches in order to closely control the switching of the first and second switches to eliminate loss of energy associated with the rapid switching normally found in a class D amplifier.

Abstract: A circuit for generating an accurate reproduction of the output of a Class D amplifier for error-correction purposes includes a reference signal amplifier circuit. The reference signal amplifier circuit includes an op-amp configured as a differential amplifier that combines the digital outputs of the internal output stage of the amplifier into a single reference signal. By reducing the bandwidth of the op-amp, switching noise is removed from the digital signals, without adding any phase shift to the generated reference signal. In addition, by using the digital signals directly from the output stage rather than the filtered analog outputs of the amplifier, distortion due to external speaker-induced back-EMF is prevented. The reference signal can then be compared to the original signal input to the amplifier for error-correcting purposes.

Abstract: A method and apparatus for efficient power amplification of a modulated signal includes an envelope detector (220), an multi-output class S modulator (270), a driver amplifier (250), and a power amplifier (260). The multi-output class S modulator (270) amplifies the envelope of the input signal and generates a primary amplified envelope signal and at least one offset amplified envelope signal. The offset amplified envelope signal is used to modulate the driver amplifier (250), and the primary amplified envelope signal is used to modulate the power amplifier (260).

Abstract: A method and apparatus for detecting pulse data is accomplished by a low voltage data detection circuit that includes a preamplifier circuit, an amplification stage, and a scaling circuit. The preamplifier circuit has a differential input, a predefined gain, and a maximum output limit and receives an input signal, which has a wide dynamic range. The preamplifier circuit amplifies the input signal based on the predefined gain to produce a preamplified data signal. The preamplified data signal is again amplified by the amplification stage and subsequently provided to the scaling circuit which scales the amplified data signal to a predetermined level. The resulting scaled data signal maintains the pulse width fidelity of the input data signal.

Abstract: A pulse-width modulation (PWM) circuit in a Class D audio amplifier includes output-limiting logic and an automatic gain control (AGC) circuit. When an out-of-range, or overmodulated, input signal is received by the PWM, mono-stable multivibrator circuits provide discharge pulses that ensure that the PWM output will not spend excessive time in a single state. By using discrete mono-stable multivibrators, uniform and repeatable pulses can be generated at precise intervals. In addition, when an out-of-range input signal is detected, the AGC circuit lowers the gain on the input signal until it falls within the acceptable range of the PWM, enabling more faithful reproduction of the original signal.

Abstract: An amplifier (100) includes an output node (114) having an output voltage (V.sub.out), and a switching amplifier (104) having a first output (132) coupled to the output node for delivering a switching amplifier output current (I.sub.SW) to the output node. The amplifier further includes a modulator (136) coupled to the switching amplifier for controlling the switching amplifier, and a linear amplifier (102) producing a linear amplifier output current (I.sub.lin) through a second output (118) coupled to the output node. The amplifier also includes a feedback network (106) coupled to the modulator for controlling the modulator, the feedback network also coupled to a reference signal (V.sub.ref) which the amplifier apparatus tracks, the feedback network further coupled to a current sense signal (I.sub.sen) proportional to the linear amplifier output current, and coupled to a switching amplifier signal (V.sub.

Abstract: A continuous cardiac output monitor a general-purpose monitoring console with local display and communication facilities, and a module removably interfacing with the console to configure the latter for performing continuous cardiac output monitoring. The module includes a switch-mode high efficiency power amplifier for providing electrical heating power at a selected voltage, frequency, and wave form to a heating element of a continuous cardiac output monitoring catheter, which catheter at a distal end portion thereof is immersed in the blood flow of a patient. The catheter effects a temperature transient in the patient's blood flow by the controlled application of electrical resistance heating utilizing electrical power from the power amplifier, and this temperature transient is sensed and used to derive a value for the patient's cardiac output.

Abstract: A delta-modulated magnitude amplifier is used to amplify the magnitude component of an RF power amplifier that employs envelope elimination and restoration. The delta-modulated amplifier introduces a smaller amount of non-linearity than traditional approaches, which are based upon pulse-width modulation. The disclosed technique can be implemented using switched-capacitor circuits in a standard MOS technology with only two external components, i.e., an inductor and a capacitor. Thus, the disclosed technique allows the implementation of an efficient and yet linear RF power amplifier using low-cost MOS technology.

Abstract: An input limiting circuit limits the maximum signal voltage value of input signal voltage supplied from a signal source through an input terminal. A power amplifying circuit converts the signal voltage from the input limiting circuit to a switching signal having the input signal included in a low frequency component using, for example, a PWM modulation, and then amplifies the output power of the modulated signal using a D-class amplification. A signal demodulating circuit selects the switching frequency signal received from the power amplifying circuit, and demodulates it into a signal similar to the signal generated by the original source. The demodulated signal from the signal demodulating circuit is then supplied to a reproducing device.

Abstract: A signal processing circuit is provided which includes a frequency selective network in a feedback loop for noise shaping purposes. A sampling analog-to-digital converter in the feedback loop operates at a sample frequency substantially above the Nyquist frequency. A switching device is driven by the sampling analog-to-digital converter and produces a continuous-time output signal which is continuously monitored by and fed back to the frequency selective network for noise and distortion correction in the feedback loop. This is in contrast to traditional techniques which employ only state feedback. State feedback (i.e., digital or sampled) of the output of the analog-to-digital converter may also be employed in combination with the continuous-time feedback of the switching device output.

Abstract: A Class D (audio) amplifier and method in which an input signal for the amplifier is pulse width modulated outside of the amplifier's feedback loop, and in which the pulse width modulated input signal and a pulsed signal from the feedback loop are summed in the feedback loop and fed back to the amplifier. The removal of the pulse width modulation stage and signal integration stage from the feedback loop improves distortion.

Abstract: An all digital switching amplifier wherein linearization of the power switch is accomplished solely by using three states. A small, fixed width, bi-state compensating carrier waveform is added to the leading or training edges of an oversampled main input pulse producing a compensated composite waveform. This compensating carrier linearizes output from a power switch by effecting common mode cancellation of switch time errors. Output pulse width combinations for the compensating carrier are obtained from a look-up table stored in memory. A correction mechanism is implemented to correct for harmonic distortion that is dependent on the modulation level or index and results from the compensating carrier modulation. The correction mechanism applies the inverse of the modulation induced distortion to the oversampled compensated composite input signal to null distortion products resulting from the modulation scheme used to apply the small carrier to linearize the performance of the tri-state power switch.

Abstract: A continuous cardiac output monitor includes a general-purpose monitoring console with local display and communication facilities, and a module removably interfacing with the console to configure the latter for performing continuous cardiac output monitoring. The module includes a switch-mode high efficiency power amplifier for providing electrical heating power at a selected voltage, frequency, and wave form to a heating element of a continuous cardiac output monitoring catheter, which catheter at a distal end portion thereof is immersed in the blood flow of a patient. The catheter effects a temperature transient in the patient's blood flow by the controlled application of electrical resistance heating utilizing electrical power from the power amplifier, and this temperature transient is sensed and used to derive a value for the patient's cardiac output.

Abstract: A low earth orbiting satellite communication terminal includes a data signal generator, a modulator, and a class E switching amplifier. The modulator converts a data signal from the data signal generator into a phase modulated signal which is then amplified by the class E switching amplifier for transmission to a low earth orbiting satellite. In a preferred embodiment, the modulator converts the data signal into a symmetric differential phase shift keyed data signal. The class E switching amplifier amplifies the phase modulated signal at frequencies between about 148 and 150 MHz. The class E switching amplifier includes a switching transistor, an input matching network, a class E load network, and an output matching network. The class E load network is electrically connected to the switching transistor and loads the transistor for phase linear class E operation over a predetermined bandwidth.

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 amplifier (1) used with a pulse width modulated signal which improves the efficiency of a low level input signal comprises two or more switching devices (7,9) with common source/drain or emitter/collector connections. The gates or the bases of the devices are independently driven to optimize the efficiency of the various Rds (on) resistance values of the transistors (61, 63, 65, 89, 91, 93) used in the devices. The amplifier is operated so that during the highest output levels, select switching devices (61, 63, 65) are utilized to reduce in series resistance with the load (13). As output power decreases, devices (89, 91, 93) with higher Rds (on) resistance values are activated by a control signal which greatly improves DC to DC conversion efficiency with improved output voltage resolution, dynamic range and reduced electromagnetic interference potential.

Abstract: A two-state modulation system includes a hysteretic comparator with variable thresholds, a two-state processor and an integrating element. A summing circuit combines a signal coupled from the output of the two-state processor, the signal output, the signal input and a delay compensating signal feedback input and a feedback input from an integrating element at the output of the two-state processor. The hysteretic comparator receives a hysteresis control signal that varies the threshold. The hysteresis control signal may be provided by analog switches switched by the switching signal to provide the switched two-state levels to a low pass filter. Rectifying circuitry may also be used for supplying the hysteresis control signal. Limiters and compressors may be connected to the input with the limiter limiting levels tracking the two-state levels, and the compression proportional to the switching frequency.

Abstract: A circuit for combining first and second signals having the same frequency. The signals have a relative phase shift, 2a(t). The circuit generates a signal that is proportional to the sum or difference of signals. The circuit appears to be a resistive load; however, the circuit can be constructed from purely reactive circuit elements, and hence, does not dissipate energy. In one embodiment, the circuit is constructed from a transformer and two LC circuits in which the capacitance is varied in response to a(t). The circuit may be used to construct a high efficiency RF amplification stage.

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: A combining circuit for Class-E RF power amplifiers includes a transformer for each power amplifier to be combined, the respective secondaries of the transformers being connected in series to the RF load of the system. Each of the transformers further has a tertiary winding, with one end connected to a first common circuit node, and the other end being connected to a second common circuit node via an inductance. A switchable reactive network is connected to the second common circuit node, and in the event that one of the power amplifiers is removed from the circuit, such as due to failure thereof, the primary terminating impedance of the transformer connected thereto will become a high impedance, and by appropriate switching of the reactive network, in combination with the remaining circuit components, the matching impedance necessary to maintain optimum operation of the remaining power amplifiers is achieved, with a benign VSWR being presented to the remaining power amplifiers.

Abstract: An improved digital switching amplifier is disclosed. The amplifier utilizes a low-pass filter at the input of the switching comparator to give an improved signal to noise ratio at the final output. In another aspect of the invention, a propagation delay is used to produce the steady-state oscillation of the amplifier circuit.

Abstract: A multilayered ceramic electromagnetic coupler apparatus includes coils formed on ceramic substrates. The coils are laminated and have insulting layers between the ceramic substrates, a modulator section having an oscillator and a demodulator for outputting a transmitted signal.

Abstract: An amplifier has at least several stages activated only to one of two bi-level states controlled in response to the value of an input source exceeding a threshold for each stage. Each stage has a different threshold. The thresholds and source are arranged so that the stages change between the bi-level states as the value of the source changes relative to the thresholds of the different stages. Bi-level outputs of the stages are summed together. The values of the thresholds are continuously varied by a small amount relative to a predetermined maximum value for the source in response to a noise source that is independent of the signal source. A power supply for the stages includes an AC-DC converter having plural primary windings and several secondary windings, one for each of the stages. The windings are coupled together so that at all times loading of the primary windings by the secondary windings as a result of activation of the output stages is approximately equal.

Abstract: Disclosed are both methods and a circuit to achieve powers of many kilowatts in radio frequency amplification using a switch mode amplifier in a new class of operation. In operation the invention utilizes internal switch characteristics. Methods create a substantial voltage step at the end of a response time period which allows greater output power without increasing the maximum switch voltage, reduces the maximum switch voltage for the same power, and which permits reduction of the stress on the switch element. Utilization of internal varactor capacitance avoids undesirable circulating currents and avoids the effects of lead inductance. The design allows use of less expensive components and high voltage switches not manufactured for radio frequency applications by preferring a substantial internal capacitance to establish maximum power. Other components of the network circuitry are also coordinated with the internal varactor capacitance.

Abstract: The disclosure relates to fast amplification circuits that are designed to provide an output current of some amperes, proportional to an input voltage, and have a frequency spectrum that may go beyond 1 MHz. A linear amplifier follows the fast variations in the input voltage and gives a load all the output current so long as this current is low. As soon as the output current from the linear amplifier reaches a given value, a chopper amplifier gives a current that causes a reduction in the output current of the linear amplifier. The circuit may be applied, in particular, to the control of deflection coils and as a high efficiency amplification circuit for audiofrequencies.

Abstract: A power amplifier for amplifying analog input signals includes one or a plurality of amplifier modules which are connected in series on their output sides, which preferably each include a double mains unit having three outputs and a mains transformer connected in a wye pattern on its secondary side, with the two outer outputs each being connected by way of a main switch with the filter choke of a lowpass filter and by way of a free running diode connected between the main switch and the filter choke with the middle output while the middle output, in turn, is connected directly with the secondary side wye point of the transformer and, on the other hand, directly with the junction of the two series connected filter capacitors of the two lowpass filters.

Abstract: A hysteresis-type pulse width modulator for a class D audio amplifier converts an input voltage into a pulse width modulated waveform. The width of the pulses is related to the input voltage amplitude. The modulator comprises a window comparator, a supply voltage source having a pair of terminals across which a supply voltage is provided, and a hysteresis voltage source having a pair of terminals across which a hysteresis voltage is provided. The hysteresis voltage source comprises a multiplier, a comparator for adding the supply voltage and input voltage to generate a sum voltage, and a comparator for subtracting the input voltage from the supply voltage to generate a difference voltage. The audio amplifier output stage comprises first and second solid state devices, each having a controlled current conducting path comprising first and second terminals and a controlling current conducting path comprising at least a third terminal.

Abstract: A dual feedback control system for a Class-D power circuit maximizes efficiency by controlling the magnitude and phase angle of the resonant load circuit using two separate feedback loops. The first feedback loop changes the value of a first variable capacitor in response to difference in magnitude between the actual load impedance and the desired load impedance. The second feedback loop changes the value of a second variable capacitor in response to the phase difference between the actual phase angle and the desired phase angle. In this way, the real and imaginary components of the load impedance are controlled so that the Class-D circuit is in tune, and hence efficiency is maximized, over a wide range of load impedances. The dual feedback control of the present invention may be advantageously employed in the ballast of an electrodeless HID lamp system.

Abstract: A wideband high efficiency amplification system for amplifying radio frequency signals to high power levels. The system includes components adapted for generating an RF carrier signal having a multi-level waveform which may be characterized as a "modified square wave" including one or more intermediate voltage levels. This RF carrier waveform allows the power of the signal to be amplified with high efficiency beyond the efficiency levels which can ordinarily be achieved with conventional wideband class D amplifiers. The preferred embodiment of the invention describes an amplification system generating and using a three level waveform although waveforms having more than three levels may also be used.