A gate bias circuit for a plurality of GaAs amplifier stages is a transistor coupled to a temperature compensation current received from a CMOS control stage. A plurality of pHEMPT amplifier stages are coupled to the gate bias circuit and to a control voltage which switches the amplifier stage. A selectively controlled stage pass transistor enables a current mirror between the gate bias circuit and each stage amplifying transistor. The penultimate pHEMPT amplifier stage is coupled to a CMOS amplifier. A CMOS circuit provides both the temperature compensation current by a proportional to absolute temperature (PTAT) circuit and the control voltage enabling each pHEMPT transistor to receive its input signal in combination with the gate bias voltage.

A power amplifier apparatus includes: an amplifier configured to amplify an input signal; a sensing circuit connected to the amplifier and configured to sense a bias of the amplifier; and a biasing circuit connected to the sensing circuit and configured to provide a biasing current to the amplifier, wherein the sensing circuit is configured to change the biasing current based on the bias of the amplifier.

A power amplifier apparatus includes: an amplifier configured to amplify an input signal; a sensing circuit connected to the amplifier and configured to sense a bias of the amplifier; and a biasing circuit connected to the sensing circuit and configured to provide a biasing current to the amplifier, wherein the sensing circuit is configured to change the biasing current based on the bias of the amplifier.

An audio amplifier and a warning sound amplifier are connected in parallel to each other, relative to a voice coil of a loudspeaker. A resistor having an impedance greater than an impedance of the voice coil is connected to the voice coil and is also connected to the warning sound amplifier. An audio signal from the warning sound amplifier is input to the voice coil via the resistor. Thus, since the warning sound amplifier is connected to the resistor having the impedance greater than the impedance of the voice coil of the loudspeaker, even in a case where only the audio amplifier is operated, a large current is prevented from flowing into the warning sound amplifier.

An amplifying circuit is provided. The amplifying circuit includes a bias circuit receiving an operating voltage from a power supply circuit and generating a first bias voltage, a resistance circuit connected between the bias circuit and a gate node and transferring the first bias voltage to the gate node, a start-up circuit generating a high-level start-up voltage and supplying the start-up voltage to the gate node before the operating voltage is supplied, based on a control signal, and an amplifier started-up by receiving the start-up voltage and then receiving the operating voltage and the first bias voltage to amplify a high frequency signal input through the gate node.

Radio Frequency (RF) amplifiers with voltage limiting using non-linear feedback are presented herein. According to one aspect, an RF amplifier comprises an amplifier circuit having an input terminal and an output terminal and a non-linear feedback circuit having an input terminal and an output terminal. The input terminal of the non-linear feedback circuit is connected to the output terminal of the amplifier circuit and the output terminal of the non-linear feedback circuit is connected to the amplifier circuit to reduce the gain of the amplifier circuit when an RF voltage swing present at the input terminal of the non-linear feedback circuit exceeds a predefined threshold. In one embodiment, the output terminal of the non-linear feedback circuit is connected to the input terminal of the amplifier circuit. In another embodiment, the output terminal of the non-linear feedback circuit is connected to a bias circuit of the amplifier circuit.

Radio Frequency (RF) amplifiers with voltage limiting using non-linear feedback are presented herein. According to one aspect, an RF amplifier comprises an amplifier circuit having an input terminal and an output terminal and a non-linear feedback circuit having an input terminal and an output terminal. The input terminal of the non-linear feedback circuit is connected to the output terminal of the amplifier circuit and the output terminal of the non-linear feedback circuit is connected to the amplifier circuit to reduce the gain of the amplifier circuit when an RF voltage swing present at the input terminal of the non-linear feedback circuit exceeds a predefined threshold. In one embodiment, the output terminal of the non-linear feedback circuit is connected to the input terminal of the amplifier circuit. In another embodiment, the output terminal of the non-linear feedback circuit is connected to a bias circuit of the amplifier circuit.

This application relates to circuitry for monitoring for instability of an amplifier. The amplifier (100) has a first signal path between an amplifier input (IN.sub.N) and an amplifier output (V.sub.OUT) and a feedback path from the output to form a feedback loop with at least part of the first signal path. A comparator (212) has a first input configured to receive a first signal (IN.sub.N) derived from a first amplifier node which is part of said feedback loop and a second input configured to receive a second signal (IN.sub.P) derived from a second amplifier node which varies with the signal at the amplifier input but does not form part of said feedback loop. The comparator is configured to compare the first signal to the second signal and generate a comparison signal (COMP), wherein in the event of amplifier instability the comparison signal comprises a characteristic indicative of amplifier instability.

This application relates to circuitry for monitoring for instability of an amplifier. The amplifier (100) has a first signal path between an amplifier input (IN.sub.N) and an amplifier output (V.sub.OUT) and a feedback path from the output to form a feedback loop with at least part of the first signal path. A comparator (212) has a first input configured to receive a first signal (IN.sub.N) derived from a first amplifier node which is part of said feedback loop and a second input configured to receive a second signal (IN.sub.P) derived from a second amplifier node which varies with the signal at the amplifier input but does not form part of said feedback loop. The comparator is configured to compare the first signal to the second signal and generate a comparison signal (COMP), wherein in the event of amplifier instability the comparison signal comprises a characteristic indicative of amplifier instability.

Apparatus and methods for overload protection of low noise amplifiers (LNAs) are provided herein. In certain configurations, an LNA system includes an input switch having an analog control input that controls an impedance of the input switch, an LNA that amplifies a radio frequency (RF) input signal received from the input switch, and an overload protection circuit that provides feedback to the input switch's analog control input based on detecting a signal level of the LNA. The overload protection circuit detects whether or not the LNA is overloaded. Additionally, when the overload protection circuit detects an overload condition, the overload protection circuit provides feedback to the analog control input of the switch to increase the impedance of the switch and reduce the magnitude of the RF input signal received by the LNA.