Abstract: A method and attendant circuitry reduces the number of regulatory and switching devices in a multi-reference switching amplifier. In the preferred embodiment, multiple independently-modulated effective references are summed at a load through use of both linear and switched control of switching devices.

Abstract: A method and apparatus for detecting output current in switching power supplies forgoes the need for any resistor or other components in series with the load. A method according to the invention includes the steps of inferring the peak current through the inductor as a function of input voltage and inductor charge time, and deriving the current available to the load based upon the flyback voltage during discharge of the inductor. Although a disclosed example is based upon a buck/boost topology, other converter topologies are anticipated. In terms of apparatus, in a switching power supply of the type wherein a switching device is used to charge an inductor that discharges to a load, the invention provides devices arranged for detecting output current without the need for a resistor or other component in series with the load.

Abstract: A method and circuitry are disclosed that provide for linear operation of a flyback converter through zero output. Broadly, the preferred embodiment enforces a minimum control pulse width thereby isolating energy derived thereby from the eventual load, and dissipating the energy from the minimum control pulse width. The net effect is linear operation inclusive of zero output.

Abstract: A method of adding a minimum pulse width to the switching devices of both outputs of a switching differential pair enhances the performance of a switching amplifier. When used with similar switching devices at similar temperatures, this results in injecting a similar error term into both sides of a differential output, thus presenting it as a null common-mode output. That is, by correlating the output to differences between the differential pairs, accurate representations by the switching device outputs are achieved. Although the invention is described in conjunction with two switching devices per side of the differential output pair, operation with three or more switching devices per side, as seen in multi-reference amplifiers, may be accommodated by the invention.

Abstract: A method of enhancing the performance of an inductive boost amplifier includes the steps of detecting the specific load impedance being drive by the amplifier, and adjusting the operation of the amplifier to accommodate the detected load impedance. Various load impedances may be connected to the improved amplifier while accommodating the impedance of different amplifier loads subject to change under various conditions such as temperature, voltage, frequency, etc. Thus, in addition to compensation of static load impedance variances, the present invention is quite effective in compensating for dynamic variances as well. Although the description focuses on variable load impedance compensation, it is anticipated that simpler implementations of the technique may be used to selectively switch output filter components into operation in response to specific load impedance ranges, yielding a similar, albeit coarser, net result.

Abstract: A method and apparatus for greatly increasing the output voltage or current transformation ratio in an impedance transformation amplifier are disclosed. Broadly, the method takes advantage of multiple, phase-synchronized impedance transformation stages, each of which preferably contributes an equal portion of the eventual output voltage or current.

Abstract: Circuitry generates a secondary reference voltage in a multi-reference amplifier as a function of a primary reference. As such, the secondary reference equals a known, fixed portion of the primary reference, thereby minimizing distortion due to variations in voltage (or current) ratio. A zero detector is used to monitor incoming data. When the input data is zero, the integral of primary or high-voltage reference represents pulse-width data of ‘one.’ This integral is compared with the integral presented to load through the buffer amplifier, such that the high-voltage reference integral commands a non-inverted output. The output of the amplifier across the load drives the digital integrator to produce higher or lower data values at its output, when enabled by the zero detector. The data value output of digital integrator is converted to a pulse-width train by pulse-width modulator, filtered, buffered, and switched to the load as the secondary reference voltage.

Abstract: The filtered output of multiple possible voltage levels are AC-coupled to a load. An incoming data stream provides input to a pulsewidth modulator which issues control voltages to three or more switching devices, respectively. A first switching device provides a controlled connection to the incoming power supply (V+), a second switching device provides a controlled connection to a lower reference voltage (VR), and a third switching device provides a controlled connection to common, or ground. The common connection of switching devices provides an input to an inductor, which, in conjunction with a capacitor removes out-of-band components before presentation of the output to one side of load. Another capacitor provides a pseudo-ground for the second side of load in a manner consistent with the art of AC-coupled power amplifiers.

Abstract: A method and apparatus facilitate a voltage multiplication into the output stage of a switching amplifier. A plurality of switching devices are used to modulate the interconnection between a power supply, a reactance and a load in accordance with a modulation signal, such that the voltage across the load exceeds the supply voltage. In the situation where the reactance is a capacitor, the voltage across the load exceeds the supply voltage by two or an integer multiple thereof. In the preferred embodiment, a pair of reactances and attendant switching devices are used to modulate the interconnection between the supply voltage relative to both sides of the load depending upon the sign of the modulation signal.

Abstract: A method of improving modulation resolution in a flyback converter by pulsewidth- and/or position-modulation of a subtractive constant current with specific timing considerations is applicable to boost or buck/boost topologies. A typical system of this type uses a pulsewidth-modulated (PWM) circuit to provide a control pulsewidth in response to an incoming data stream. The control pulsewidth is used to drive a switching device which, when energized, charges an inductor. When the switching device is released the energy stored in the inductor “flies back” through a diode into a capacitor and load resistance. According to this invention, a constant current sink, gated under control of the PWM controller, is used to improve modulation resolution through pulsewidth- and position-modulation of a subtractive constant current with specific timing considerations. In the preferred embodiment, the constant current sink is implemented using a transistor in conjunction with a resistor network.

Abstract: An analog voltage is used to directly alter the timebase of a pulse-width converter, thereby modifying a digitally-generated system output with an analog source. The input to the amplifier is coupled to a first counter (101) clocked by a voltage-controlled oscillator (VCO) (113), and second counter (104) driven by a fixed clock (114). The output of the first counter is ultimately delivered to a load device following appropriate filtering (107 and 111). The non-inverting input of a differential amplifier (112) is coupled to the load device, and the inverting input is coupled to the output of the second counter (104). The output of the differential amplifier forms the control voltage input to the VCO, which increases output frequency in response to increasing input voltage. An increase in frequency at the output of the VCO ultimately reduces the load voltage, thereby linearizing an otherwise digital amplifier with an analog signal.

Abstract: A distortion reduction technique finds particular utility in inductive boost amplifiers. In contrast to existing arrangements, the invention uses the boost voltage itself, rather than the output voltage(s), as feedback to linearize the output. As such, the boost voltage is not subject to the severe time delay of the output filter, yet is sensitive to the effects of back-EMP from inductive loads, which tend to exist at frequencies well below the cutoff frequency of the output filter. The invention is applicable to bridged and non-bridged configurations using analog and/or digital circuitry.

Abstract: Apparatus and methods minimize propagation delay distortion in a switching amplifier (111) without impacting system efficiency. Circuitry (400) is used to detect when the width of an output pulse is approaching, or is less than, the propagation delay of switching devices in the output stage and, if this is the case, the width of the output pulse is artificially adjusted a function of the delay. More particularly alternate pulses, the invention adds the width “N”, being twice the minimum accurate width, to the desired width for output, or subtracts the desired width from the width “N” for the output while inverting the polarity of the output. In so doing, the desired width is alternately added to, and subtracted from, the width “N”, thus enforcing an accurately achievable minimum pulse width without irpposing error. When applied to a bridged switching output stage, system switching losses remain those of a single switching output.

Abstract: A switching amplifier employs a plurality of independent output stages in a bridged configuration, with each output stage presenting the product of an independent duty cycle and two or more static of dynamic reference voltages, currents or powers to a single terminal of a common output load. A plurality of electrically controlled switches (207, 208, 209, 210, 211, 212) interconnect the references to the load (218), with a waveform generator (220) controlling the switches for a coarse and fine control of power to the load. The waveform generator preferably uses pulse-code modulation (PCM), though the invention is not limited in this regard, and is applicable to any modulation scheme or waveform suitable to sequence the electrically controlled switches. The load is preferably filtered on either side, and return paths for the power supplies (i.e., ground) are connected through separate switches to the load through the filters (213, 214, 215, 216, 217).