A mobile device can have a transceiver configured to generate a radio frequency signal and a power management system with envelope tracking. The device can also have a power amplifier system having a driver transistor coupled to a radio frequency signal input, a transformer balun having a main primary coil connected between the driver transistor and a voltage supply node of the power amplifier system, a secondary coil magnetically coupled to the main primary coil and an additional primary coil configured to generate a feedback signal related to a signal of the main primary coil. The power amplifier system can also have a push-pull amplifier with a first transistor having a base connected to a first end of the secondary coil and a second transistor having a base connected to a second end of the secondary coil. Accordingly, push-pull stage neutralization can deploy two transistors cross-connected to opposite ends of an output coil in a transformer balun.

An amplifier includes a P-type transistor and an N-type transistor that are connected in series, an operation amplifier, a transformer, and a variable attenuator. In the operation amplifier, an output terminal is coupled to a gate side of one of the P-type transistor and the N-type transistor, one of an inverting input terminal and a non-inverting input terminal is coupled to drain sides of both of the P-type transistor and the N-type transistor, and a reference voltage is to be applied to the other of the inverting input terminal and the non-inverting input terminal. In the transformer, a primary coil is coupled to a source side of one of the P-type transistor and the N-type transistor. The variable attenuator is provided between a secondary coil and gate terminals of both of the N-type transistor and the P-type transistor.

A radio frequency amplifier includes a transistor, an input impedance matching circuit (e.g., a single-section T-match circuit or a multiple-section bandpass circuit), and a fractional harmonic resonator circuit. The input impedance matching circuit is coupled between an amplification path input and a transistor input terminal. An input of the fractional harmonic resonator circuit is coupled to the amplification path input, and an output of fractional harmonic resonator circuit is coupled to the transistor input terminal. The fractional harmonic resonator circuit is configured to resonate at a resonant frequency that is between a fundamental frequency of operation of the RF amplifier and a second harmonic of the fundamental frequency. According to a further embodiment, the fractional harmonic resonator circuit resonates at a fraction, x, of the fundamental frequency, wherein the fraction is between about 1.25 and about 1.9 (e.g., x≈1.5).

A multi-mode envelope tracking (ET) amplifier circuit is provided. The multi-mode ET amplifier circuit can operate in a low-resource block (RB) mode, a mid-RB mode, and a high-RB mode. The multi-mode ET amplifier circuit includes fast switcher circuitry having a first switcher path and a second switcher path and configured to generate an alternating current (AC) current. A control circuit activates the fast switcher circuitry in the mid-RB mode and the high-RB mode, while deactivating the fast switcher circuitry in the low-RB mode. More specifically, the control circuit selectively activates one of the first switcher path and the second switcher path in the mid-RB mode and activates both the first switcher path and the second switcher path in the high-RB mode. As a result, it is possible to improve efficiency of ET tracker circuitry and the multi-mode ET amplifier circuit in all operation modes.

A MIMO amplifier circuit operable to couple one or more selectable input ports to one or more selectable output ports. The circuit includes N input transistors and M output transistors. Each input transistor has its base coupled to a respective input port node, its emitter coupled to ground, and its collector connected to an intermediate node. Each output transistor has its base coupled to a bias node, its emitter connected to the intermediate node, and its collector coupled to a respective output port nodes. Each input transistor enables the respective input port node when its base is biased. Each output transistor enables the respective output port node when its bias node is asserted. The base of the input transistor for each enabled port is biased to provide a quiescent current I.sub.0*m/n through that input transistor, where m is the number of enabled output ports and n is the number of enabled input ports.

Methods and devices used in mobile receiver front end to support multiple paths and multiple frequency bands are described. The presented devices and methods provide benefits of scalability, frequency band agility, as well as size reduction by using one low noise amplifier per simultaneous outputs. Based on the disclosed teachings, variable gain amplification of multiband signals is also presented.

Methods and devices to fabricate low-cost wideband LNAs that are tunable to multiple frequency bands. Decoupling capacitors are used as part of a tuning circuit implemented at the LNA input. The capacitors are switchably selectable to also tune a signal into desired frequency bands.

A wireless access point is configured to regularly monitor the status of WLAN, WAN and ePDG data links to determine whether the current connections are sufficient to support VoWiFI services. When a device connects to the WLAN of the hub and attempts to switch from its VoLTE service to VoWiFi via the hub, the hub is configured to determine whether the current conditions can satisfy a VoWiFi connection. If the VoWiFi service can support the connection, the request is routed to the ePDG associated with the mobile device's subscriber LTE network. However, if the current conditions cannot satisfactorily support a VoWiFi connection such that incoming calls may be missed or the quality of active calls would not be clear, then the hub is configured to block the request so that the client device will time out and remain connected to VoLTE.

Techniques for monitoring a distortion signal of a power amplifier circuit, where the output of a distortion monitoring circuit includes little or no fundamental signal and closely represents the actual distortion of the amplifier circuit of a wired communications system. The power amplifier circuit can generate a distortion feedback signal that does not affect the power amplifier's output power capability, e.g., no inherent loss in the fundamental output of the amplifier. That is, using a distortion monitor circuit, the power amplifier circuit can resolve a distortion feedback signal from the intended output signal of the output power amplifier circuit.

A radio frequency amplifier includes a transistor, an input impedance matching circuit (e.g., a single-section T-match circuit or a multiple-section bandpass circuit), and a fractional harmonic resonator circuit. The input impedance matching circuit is coupled between an amplification path input and a transistor input terminal. An input of the fractional harmonic resonator circuit is coupled to the amplification path input, and an output of fractional harmonic resonator circuit is coupled to the transistor input terminal. The fractional harmonic resonator circuit is configured to resonate at a resonant frequency that is between a fundamental frequency of operation of the RF amplifier and a second harmonic of the fundamental frequency. According to a further embodiment, the fractional harmonic resonator circuit resonates at a fraction, x, of the fundamental frequency, wherein the fraction is between about 1.25 and about 1.9 (e.g., x≈1.5).