Adjacent channel power and error-vector magnitude performance of reduced complexity CALLUM systems

The combined analogue locked-loop universal modulator (CALLUM) is a power efficient linear RF transmitter based on the LINC principle (linear amplification with nonlinear components). The system provides both upconversion and amplification of a baseband input signal, within a closed-loop control scheme. The variant known as CALLUM1 is optimal, but difficult to implement practically. Simplifications to this system can be made so that the processing requirement is reduced. The simulated performance of these systems is compared to that of CALLUM1, in terms of adjacent channel power (ACP) and error-vector magnitude (EVMrms), in response to a TETRA (terrestrial trunked radio) baseband modulation signal. The existing CALLUM systems and the simplified versions proposed in the paper meet the TETRA ACP specification of -60dBc if enough stable loop gain can be provided.