Power amplifier system with reduced gain variation for envelope tracking applications

A power amplifier system for amplifying a radio frequency signal, the power amplifier system comprising:

• 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, 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 induced in the main primary coil;
• and
• a neutralization diode connected between the additional primary coil and the driver transistor, the neutralization diode configured to neutralize an inter-electrode capacitance generated in the driver transistor based on the feedback signal.

A radio frequency module comprising:

• a packaging substrate configured to receive a plurality of components;
• a power amplifier system implemented on the packaging substrate, the power amplifier system including a driver transistor in communication with a radio frequency signal;
• 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 induced in the main primary coil;
• and
• a neutralization diode connected between the additional primary coil and the driver transistor, the neutralization diode configured to neutralize an inter-electrode capacitance generated in the driver transistor based on the feedback signal.

A mobile device comprising:

• a transceiver configured to generate a radio frequency signal;
• a power management system including an envelope tracker configured to generate a power amplifier supply voltage that changes is relation to an envelope of the radio frequency signal;
• and
• a front end module including a power amplifier system including a driver transistor coupled to an input of the radio frequency signal;
• a transformer balun having a main primary coil connected between the driver transistor and a voltage supply node, 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 induced in the main primary coil;
• and a neutralization diode connected between the additional primary coil and the driver transistor, the neutralization diode configured to neutralize an inter-electrode capacitance generated in the driver transistor based on the feedback signal.