Pa coarse complex vswr detection (quadrant) for analog-assisted dpd and pa load modulation optimization

A method of linearizing a radio frequency (RF) signal transmitted by a power amplifier system, the method comprising:

• amplifying an RF input signal with a power amplifier that defines an amplification path between an RF input and an RF output;
• sampling, at one or more locations within the amplification path, a voltage signal representative of the output voltage of the power amplifier and a current signal representative of the output current of the power amplifier;
• determining a voltage standing wave ratio (VSWR)-phase indication from a phase relationship between sampled voltage and current signals;
• determining a VSWR-amplitude indication from a ratio of the magnitude of the sampled voltage signal to the magnitude of the sampled current signal;
• combining the VSWR-phase indication with the VSWR-amplitude indication to identify a VSWR region (quadrant);
• measuring reflected power at an isolation port of an antenna coupler;
• generating an enable signal to activate coarse VSWR-detection circuitry to cause the determination steps for VSWR phase, amplitude, and region to be performed when the measured reflected-power level exceeds a predetermined threshold;
• selecting, from a memory that stores a plurality of digital pre-distortion (DPD) coefficient sets, a DPD coefficient set associated with the identified VSWR region;
• and
• shaping a pre-distortion applied to the RF signal in accordance with the selected DPD coefficient set to increase linearity of the amplified RF signal.

A wireless communication device comprising:

• a baseband processor;
• transmit circuitry configured to receive encoded data from the baseband processor and to modulate a carrier signal with the encoded data, wherein the transmit circuitry comprises:
• a power amplifier having a radio frequency (RF) input and an RF output, the power amplifier defining an amplification path between the RF input and the RF output;
• detector circuitry coupled to at least one sample location within the amplification path, the detector circuitry including
• a voltage detector configured to provide a voltage signal representative of the output voltage of the power amplifier, and
• a current detector configured to provide a current signal representative of the output current of the power amplifier;
• a reflected-power detector located at an isolation port of an antenna coupler, the reflected-power detector being configured to generate an enable signal that activates coarse power-amplifier VSWR detection when a measured reflected-power level exceeds a predetermined threshold;
• a voltage standing wave ratio (VSWR) quadrant data generator coupled to outputs of the detector circuitry, the VSWR quadrant data generator being configured to:
• derive a VSWR phase indication from a phase relationship between the voltage and current signals;
• derive a VSWR amplitude indication from a ratio of the voltage magnitude to the current magnitude;
• and
• combine the VSWR phase and VSWR amplitude indications to determine a VSWR region;
• baseband circuitry comprising:
• a memory storing a plurality of digital pre-distortion (DPD) coefficient sets, each DPD coefficient set being associated with at least one VSWR region;
• and
• a DPD processor having an input coupled to the VSWR quadrant data generator, the DPD processor being configured, in response to the determined VSWR region, to select one of the stored DPD coefficient sets and to apply the selected coefficients to shape a pre-distortion applied to the RF signal propagated through the power amplifier, thereby increasing linearity of the amplified RF signal.