A communication device having an RF power amplifier stage with a Cartesian feedback loop is provided. The loop has forward paths whose outputs are combined to form an output signal that is fed back to a single feedback path. Each forward path has a common path with a filter that filters the overall loop response and a unique split path. The main and auxiliary split paths have a power amplifier and carry signals respectively of lower and higher frequencies. The auxiliary amplifier is faster than the main amplifier. Different phases of the carrier signal are used during upconversion such that the overall phase response through the split paths is equal. Instability recovery problems introduced by higher-order loop filters are mitigated by baseband loop filters with switchable order. Upon detecting instability, the loop filter order is reduced and is subsequently increased after eliminating the unstable operation.
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