Methods and apparatus for limiting the input voltage (swing) of a power amplifier, such as a power amplifier in a radio frequency (RF) front-end of a wireless device. One example radio frequency front-end circuit generally includes a power amplifier, a matching circuit having an output coupled to an input of the power amplifier, and an overvoltage protection circuit coupled to the matching circuit. With an overvoltage protection circuit coupled to the matching circuit in this manner, the power amplifier may have enhanced ruggedness performance.

An amplifier overload power limit circuit, system, and a method thereof comprising a monitoring of a current gain of a BJT based on a current detector and limiting power to the BJT based on the monitored current gain to prevent the BJT from driven into a saturation mode and the amplifier overdrive.

Differential input circuits employ protection transistors and feedback paths to limit the differential voltage applied to input transistors. In an example arrangement, a differential input voltage is applied to terminals of the protection transistors, and current paths couple the respective protection transistors to control terminals of the input transistors, respectively. A control terminal drive voltage source is coupled to the control terminals of the input protection transistors to control the drive voltage applied to those terminals. Feedback paths, one for each of the input transistors, control voltages applied to the control terminals of the input transistors, maintaining the input differential voltage at a relatively low level and defined by the product of a specified current value and a specified resistance value.

Differential input circuits employ protection transistors and feedback paths to limit the differential voltage applied to input transistors. In an example arrangement, a differential input voltage is applied to terminals of the protection transistors, and current paths couple the respective protection transistors to control terminals of the input transistors, respectively. A control terminal drive voltage source is coupled to the control terminals of the input protection transistors to control the drive voltage applied to those terminals. Feedback paths, one for each of the input transistors, control voltages applied to the control terminals of the input transistors, maintaining the input differential voltage at a relatively low level and defined by the product of a specified current value and a specified resistance value.

A current control circuit controls a base current of a first transistor included in a bias circuit outputting a bias current to a power amplifier based on a base-collector voltage of the first transistor. The current control circuit includes a first circuit that outputs a signal associated with the base-collector voltage of the first transistor, and a second circuit that, based on the signal, provides electrical continuity between a base of the first transistor and a reference potential.

A current control circuit controls a base current of a first transistor included in a bias circuit outputting a bias current to a power amplifier based on a base-collector voltage of the first transistor. The current control circuit includes a first circuit that outputs a signal associated with the base-collector voltage of the first transistor, and a second circuit that, based on the signal, provides electrical continuity between a base of the first transistor and a reference potential.

Methods and apparatus are provided. In an example aspect, an amplifier protection circuit is provided. The amplifier protection circuit comprises an input for receiving a signal from a first amplifier, and an isolation circuit between the input and an output of the amplifier protection circuit. The isolation circuit is configured to sense a backward signal propagating from the output of the amplifier protection circuit towards the input to provide a sensed signal, and to provide at least one cancellation signal based on the sensed signal to at least partially cancel the backward signal.

Methods and apparatus are provided. In an example aspect, an amplifier protection circuit is provided. The amplifier protection circuit comprises an input for receiving a signal from a first amplifier, and an isolation circuit between the input and an output of the amplifier protection circuit. The isolation circuit is configured to sense a backward signal propagating from the output of the amplifier protection circuit towards the input to provide a sensed signal, and to provide at least one cancellation signal based on the sensed signal to at least partially cancel the backward signal.

In described examples, a circuit includes a reference voltage, a driving circuit with a driving input and a driving output, an output transistor, and a clamp circuit with a clamp input and a clamp output. The output transistor includes a source, a drain, and a gate; the source is coupled to receive the reference voltage. The clamp input is coupled to the driving output and to the gate. The clamp output is coupled to either the driving input or to the driving output, the gate, and the clamp input. The clamp circuit is configured to detect an operating region of the output transistor and to generate a clamping current after the output transistor enters a triode region. The clamping current is selected to prevent an absolute value of a source-gate voltage of the output transistor from equaling or exceeding a gate oxide tunneling voltage of the output transistor.

According to one embodiment, a semiconductor circuit includes a first transimpedance amplifier and a second transimpedance amplifier. The first transimpedance amplifier is configured to convert an input current to a first output voltage and output the first output voltage from a first output terminal when a reference voltage is supplied to a first input terminal and the input current is supplied to a second input terminal. The second transimpedance amplifier has a circuit configuration similar to a circuit configuration of the first transimpedance amplifier. The second transimpedance amplifier is configured to output a second output voltage from a second output terminal when the reference voltage is supplied to a third input terminal.