Power amplifier systems with control interface and bias circuit

A power amplifier system comprising:

• a digital control interface configured to receive a voltage input/output signal at a voltage/input output pin, operate as a serial interface in response to the voltage input/output signal having a first logic value, operate as a general purpose input/output interface in response to the voltage input/output signal having a second logic value, and provide an output signal;
• a power amplifier that is controllable based at least partly on the output signal;
• a resistor having a resistance that depends on a condition of a die that includes the resistor and the power amplifier;
• and
• a bias circuit included on a different die than the power amplifier, the bias circuit configured to generate a bias signal based at least partly on an indication of the resistance of the resistor.

A power amplifier system comprising:

• a power amplifier configured to amplify a radio frequency signal;
• a control interface including a serial interface and a general purpose input/output interface, the control interface configured to set a mode of the power amplifier;
• a passive component having an electrical property that depends on a condition of a die that includes the passive component and the power amplifier;
• and
• a bias circuit included on a different die than the power amplifier, the bias circuit configured to generate a bias signal based at least partly on an indication of the electrical property of the passive component.