Transistors may be manufactured with a shared drain to reduce die area consumed by circuitry. In one example, two transistors can be manufactured that include two body regions that abut a shared drain region. The two transistors can be independently operated by coupling terminals to a source and a gate for each transistor and the shared drain. Characteristics of the two transistors can be controlled by adjusting feature sizes, such as overlap between the gate and the shared drain for a transistor. In particular, two transistors with different voltage requirements can be manufactured using a shared drain structure, which can be useful in amplifier circuitry and in particular Class-D amplifiers.

This application relates to amplifier circuits for amplifying an audio signal. An amplifier circuit (100) has a voltage regulator (201) for outputting a supply voltage to an amplifier (104). An output capacitor (103) coupled to an output node of the voltage regulator. The voltage regulator is operable in a voltage-control mode to maintain the output voltage (V.sub.S) at a nominal output voltage and in current-control mode to limit the input current drawn to exceed a defined limit. A controller (301) is operable in a first mode to define the nominal output voltage so as not to exceed a first voltage magnitude and in a second mode to define the nominal output voltage to be equal to a second, higher, voltage magnitude. The controller (301) monitors the audio signal for a high-amplitude part of the audio signal, that could result in the voltage regulator operating in the current-control mode to apply current limiting and, on such detection swaps from the first to the second mode until such a high-amplitude part of the audio signal has been amplified. The second voltage magnitude is greater than required for voltage headroom for amplifying the high-amplitude part of the audio signal so as to allow for a voltage droop of the output voltage over a plurality of switching cycles of the voltage regulator when operating in the current-control mode.

This application relates to amplifier circuits for amplifying an audio signal. An amplifier circuit (100) has a voltage regulator (201) for outputting a supply voltage to an amplifier (104). An output capacitor (103) coupled to an output node of the voltage regulator. The voltage regulator is operable in a voltage-control mode to maintain the output voltage (V.sub.S) at a nominal output voltage and in current-control mode to limit the input current drawn to exceed a defined limit. A controller (301) is operable in a first mode to define the nominal output voltage so as not to exceed a first voltage magnitude and in a second mode to define the nominal output voltage to be equal to a second, higher, voltage magnitude. The controller (301) monitors the audio signal for a high-amplitude part of the audio signal, that could result in the voltage regulator operating in the current-control mode to apply current limiting and, on such detection swaps from the first to the second mode until such a high-amplitude part of the audio signal has been amplified. The second voltage magnitude is greater than required for voltage headroom for amplifying the high-amplitude part of the audio signal so as to allow for a voltage droop of the output voltage over a plurality of switching cycles of the voltage regulator when operating in the current-control mode.

An apparatus includes an envelope detecting unit for detecting an envelope of a signal to be amplified, and a variable power supply applies, to an output terminal of a carrier amplifier, a voltage increased with increase in the envelope detected by the envelope detecting unit. As a result, highly efficient operation can be implemented without including a phase shifter including a quarter wavelength line or the like.

An apparatus includes an envelope detecting unit for detecting an envelope of a signal to be amplified, and a variable power supply applies, to an output terminal of a carrier amplifier, a voltage increased with increase in the envelope detected by the envelope detecting unit. As a result, highly efficient operation can be implemented without including a phase shifter including a quarter wavelength line or the like.

A Class-D amplifier includes a plurality of power rails, a quantizer, and a driver stage. The quantizer and the driver stage have a combined gain. For each power rail of the plurality of power rails, the Class-D amplifier senses a voltage value for the power rail and determines a ramp amplitude based on the sensed voltage value. The Class-D amplifier concurrently switches from the driver stage using a first power rail to a second power rail of the plurality of power rails and switches from the quantizer using the ramp amplitude associated with the first power rail to using the ramp amplitude associated with the second power rail so that the combined gain is constant.

A Class-D amplifier that includes a driver stage operable in a plurality of modes having different respective output impedances, a loop filter having an output, and a circuit configured to sense a current at a load of the Class-D amplifier, determine, based on the sensed current, an IR drop for a respective output impedance of the driver stage, and add the IR drop to the loop filter output to compensate for the respective output impedance of the driver stage to reduce distortion.

Embodiments disclosed herein describe a wireless power receiver including a synchronous rectifier using a Class-E or a Class-F amplifier. The voltage waveform generated from a power source, for example an antenna, is tapped to create a feed-forward tap-line to provide a gate voltage to the transistor of the Class-E or the Class-F amplifier. In some instances, a constant phase shift across the feed-forward tap-line may be provided using a micro-strip of a predetermined length that is selected such that the transistor switches at the zero-crossings of the voltage waveform arriving at the drain terminal of the transmitter. In other instances, a feed-forward circuit is used for controlling the phase across the feed-forward loop.

A filter includes M filter circuits. The M filter circuits are sequentially cascaded from an input terminal to an output terminal, in order to generate an output signal according to an input signal, in which M is a positive integer greater than or equal to 2. The M filter circuits include at least one first filter circuit and at least one second filter circuit. Each of the at least one first filter circuit is set to be an active filter circuit, and each of the at least one second filter circuit is set to be a passive filter circuit.

A filter includes M filter circuits. The M filter circuits are sequentially cascaded from an input terminal to an output terminal, in order to generate an output signal according to an input signal, in which M is a positive integer greater than or equal to 2. The M filter circuits include at least one first filter circuit and at least one second filter circuit. Each of the at least one first filter circuit is set to be an active filter circuit, and each of the at least one second filter circuit is set to be a passive filter circuit.