Front-End Module And Coupling Compensation For Closed-Loop Digital Pre-Distortion System

A method implementable in a closed-loop digital pre-distortion (DPD) circuit, comprising:

• phase shifting a phase of either a power amplifier (PA) input signal received by a PA of the closed-loop DPD circuit or a PA output signal outputted by the PA to cause a loopback path of the closed-loop DPD circuit to output a first loopback signal and a second loopback signal with a non-zero phase shift from the first loopback signal;
• and
• processing the first loopback signal and the second loopback signal to replicate the PA output signal,
• wherein the PA is configured to receive the PA input signal and amplify the PA input signal to provide the PA output signal,
• wherein the loopback path is coupled to receive the PA output signal to provide an output, and
• wherein a forward coupling and a backward coupling exist between the PA input signal and the output of the loopback path.

An apparatus, comprising:

• a front-end module (FEM) coupled between an antenna and a transceiver, the FEM comprising:
• a first combining element coupled to the antenna to transmit and receive signals through the antenna;
• a power amplifier (PA) configured to receive an outgoing signal from the transceiver as a PA input signal and amplify the PA input signal to provide a PA output signal to the antenna through the first combining element;
• and
• a low-noise amplifier (LNA) configured to receive a pre-amplified incoming signal from the antenna through the first combining element, the LNA further configured to amplify the pre-amplified incoming signal to provide an incoming signal to the transceiver;
• and
• a loopback circuit configured to sense the PA output signal and generate a loopback signal corresponding to characteristics of the PA output signal,
• wherein the loopback signal is received by the transceiver.