An amplifier unit includes an amplifier, a bias circuit, an inductor, a variable resistor circuit, and a control circuit. The amplifier includes an amplifier transistor that amplifies an input radio-frequency signal. The bias circuit is connected to the amplifier. The inductor is connected between and in series with the amplifier and the bias circuit. The variable resistor circuit is connected to the inductor. The control circuit includes a measuring circuit and a comparison circuit. The measuring circuit measures an amplification characteristic value of the amplifier transistor. The comparison circuit compares the amplification characteristic value measured by the measuring circuit with a reference value. The control circuit controls the variable resistor circuit based on a comparison result of the comparison circuit.

An example apparatus includes: a folded cascode circuit including a first input terminal, a second input terminal, a first output terminal, and a second output terminal; a first feedback loop including a third output terminal, the third output terminal coupled to the first output terminal; a second feedback loop including a fourth output terminal, the fourth output terminal coupled to the second output terminal; and a first driver including a first control terminal and a fifth output terminal, the first control terminal coupled to the third output terminal; and a second driver including a second control terminal and a sixth output terminal, the second control terminal coupled to the fourth output terminal, the sixth output terminal coupled to the fifth output terminal.

In an example, a system includes an amplifier configured to produce a bandgap voltage reference. The system also includes a current source configured to provide a current to bias the amplifier. The system includes a switching circuit configured to receive a first current replica signal and a second current replica signal, the switching circuit further configured to cause the current source to provide the current to bias the amplifier based on either the first current replica signal or the second current replica signal.

A circuit portion comprises a load circuit portion and a bias circuit portion. The load circuit portion comprises a load transistor. The bias circuit portion comprises a replica transistor matched to the load transistor and connected to the load transistor at a node such that when a current flows through the replica transistor, a current proportional to the current through the replica transistor flows through the load transistor. The bias circuit portion also comprises a current input for receiving an input current, a supply voltage input for receiving a supply voltage, and a feedback loop arranged to: adjust a voltage at the node connecting the replica transistor and the load transistor such that the replica transistor conducts a current proportional to the input current, and counteract variations in the voltage at the node connecting the replica transistor and the load transistor arising from changes in the supply voltage.

Temperature compensation circuits and methods for adjusting one or more circuit parameters of a power amplifier (PA) to maintain approximately constant Gain versus time during pulsed operation sufficient to substantially offset self-heating of the PA. Some embodiments compensate for PA Gain “droop” due to self-heating using a Sample and Hold (S&H) circuit. The S&H circuit samples and holds an initial temperature of the PA at commencement of a pulse. Thereafter, the S&H circuit generates a continuous measurement that corresponds to the temperature of the PA during the remainder of the pulse. A Gain Control signal is generated that is a function of the difference between the initial temperature and the operating temperature of the PA as the PA self-heats for the duration of the pulse. The Gain Control signal is applied to one or more adjustable or tunable circuits within a PA to offset the Gain droop of the PA.

An audio signal reproduction apparatus includes a temperature detection unit detecting a temperature of a battery pack, a voltage detection unit detecting a voltage of the battery pack, and a control unit performing an output control on a basis of temperature information detected by the temperature detection unit and voltage information detected by the voltage detection unit.

An integrated cinema amplifier comprises a power supply stage that distributes power over a plurality of channels for rendering immersive audio content in a surround sound listening environment. The amplifier automatically detects maximum and net power availability and requirements based on audio content by decoding audio metadata and dynamically adjusts gains to each channel or sets of channels based on content and operational/environmental conditions. A power supply stage provides power to drive a plurality of channels corresponding to speaker feeds to a plurality of speakers. The amplifier has a front panel having an LED array with each LED associated with a respective channel or group of channels of the multi-channel amplifier, and a control unit configured to light the LEDs according to display patterns based on operating status or error conditions of the amplifier.

An amplifier includes an input circuit that amplifies a difference between a first input voltage and a second input voltage to generate a first current and a second current. A positive feedback circuit amplifies a difference between the first current and the second current to generate a third current and a fourth current and outputs a difference between the third current and the fourth current through an output node. A temperature compensation circuit adjusts an amplification factor of the positive feedback circuit in response to a change of temperature.

In an example, a system includes an amplifier configured to produce a bandgap voltage reference. The system also includes a current source configured to provide a current to bias the amplifier. The system includes a switching circuit configured to receive a first current replica signal and a second current replica signal, the switching circuit further configured to cause the current source to provide the current to bias the amplifier based on either the first current replica signal or the second current replica signal.

A circuit system for providing thermal stability to a transistor may include: a comparing circuit in electrical communication with the transistor for receiving a present voltage from the transistor and comparing a present voltage to a predetermined bias voltage; a logic gate electronically coupled to an output of the comparing circuit, the logic gate, gate having a high, open position and a low, closed position; and a heating element thermally coupled to the transistor and electrically coupled to the output of the comparing circuit, wherein when the present voltage is lower than the predetermined bias voltage, the gate is in the high, open position providing current to the heating element, and wherein when the present voltage is higher than the predetermine bias voltage the gate is in the low, closed position.