A semiconductor devices comprises a first member including a first circuit partially formed by an elemental semiconductor element at a surface layer, a first conductive raised portion at the first member, and a second member smaller than the first member in plan view joined to the first member. The second member includes a second circuit partially formed by a compound semiconductor element. A second conductive raised portion is at the second member. A power amplifier includes a first-stage amplifier circuit included in the first or second circuit and a second-stage amplifier circuit included in the second circuit. The first circuit includes a first switch for inputting to the first-stage amplifier circuit a radio-frequency signal inputted to a selected contact, a control circuit to control the first- and second-stage amplifier circuits, and a second switch for outputting from a selected contact a radio-frequency signal outputted by the second-stage amplifier circuit.

A filter includes a series arm circuit connected between an input-output terminal and an input-output terminal and a parallel arm circuit connected between a ground and a node. The parallel arm circuit includes a first circuit and a second circuit. The first circuit has a parallel arm resonator. The second circuit is connected in parallel with the first circuit and has a parallel arm resonator. At least one of the first and second circuits includes a variable frequency circuit. The variable frequency circuit is connected in series with the parallel arm resonator or the parallel arm resonator included in the corresponding one of the first and second circuits. The variable frequency circuit has an impedance element and a switch connected in parallel with each other. The parallel arm resonator has a resonant frequency different from the parallel arm resonator and an anti-resonant frequency different from the parallel arm resonator.

A half-power buffer and/or amplifier is disclosed. The half-power buffer and/or amplifier includes an amplifying unit including first and second transistors connected between a first voltage source having a first voltage and a third voltage source having a third voltage, and a first output node configured to connect the first and second transistors and to output a voltage over a first voltage range between the first and third voltages, a second output buffer unit including third and fourth transistors connected between a second voltage source having a second voltage and the third voltage source, and a second output node configured to connect the third and fourth transistors and to output a voltage over a second voltage range between the second and third voltages, and a first charge share switch unit connected between the gate of the second transistor and the first voltage source, and configured to perform a charge share and/or equalization operation.

Apparatus and methods for envelope tracking systems with automatic mode selection are provided herein. In certain configurations, a power amplifier system includes a power amplifier configured to provide amplification to a radio frequency signal and to receive power from a power amplifier supply voltage, and an envelope tracker including a signal bandwidth detection circuit configured to generate a detected bandwidth signal based on processing an envelope signal corresponding to an envelope of the radio frequency signal. The envelope tracker further includes a switch bank configured to receive a plurality of regulated voltages, a filter configured to filter an output of the switch bank to generate the power amplifier supply voltage, and a mode control circuit configured to control a filtering characteristic of the filter based on the detected bandwidth signal.

A signal coupling apparatus for transmitting transmission signals between a terminal and an antenna includes a terminal-side interface, at least one attenuation device and at least one connection signal arm for connecting the terminal-side interface with the attenuation device. At least a first transmission activity detection device is coupled with the connection signal arm for signaling purposes. The first transmission activity detection device is capable of generating a protection signal for controlling the attenuation device if a transmission power of a transmission signal is greater than a predetermined power. There is also described a method for operating such a signal coupling apparatus.

Front-end integrated circuit for wireless local area network WLAN applications. In some embodiments, a semiconductor die can include a semiconductor substrate, and a power amplifier implemented on the semiconductor substrate and configured for WLAN transmit operation associated with a frequency range. The semiconductor die can further include a low-noise amplifier (LNA) implemented on the semiconductor substrate and configured for WLAN receive operation associated with the frequency range. The semiconductor die can further include a transmit/receive switch implemented on the semiconductor substrate and configured to facilitate the transmit and receive operations.

Embodiments of radio frequency (RF) systems include a transmit/receive switch integrated with one or more power amplifiers and/or other components. The power amplifiers can have transformer-based architectures. A compensation circuit can act to protect the receive path during an RF transmit mode.

In a sensor reader, an IC chip has a function for amplifying and outputting a sensor signal from each sensor element included in a sensor array, and includes a plurality of channel amplifiers connected each of the sensor elements. When an output switch is closed and the IC chip is in the outputting state, channel switches operate sequentially, and sensor amplification signals are output sequentially from the channel amplifiers. When the output switch is open and the IC chip is in the non-outputting state, a bias current of an operational amplifier of the channel amplifier is decreased, the IC chip is set to a low power consumption state, and gain of the operational amplifier is decreased.

Embodiments of radio frequency (RF) systems include a power amplifier having a primary winding and a secondary winding. The primary winding can be biased in different states in transmit and receive modes such that a difference between center frequencies of the primary winding and the secondary winding are significantly different in the different modes.

Envelope trackers providing compensation for power amplifier output load variation are provided herein. In certain configurations, a radio frequency (RF) system includes a power amplifier that amplifies an RF signal, an output detector coupled to an output of the power amplifier and that generates an output detection signal, an input detector coupled to an input of the power amplifier and that generates an input detection signal, and an envelope tracker that generates a power amplifier supply voltage for the power amplifier based on an envelope of the RF signal. The envelope tracker compensates the power amplifier for output load variation based on the output detection signal and the input detection signal.