Dj. Jennings et al., Adjacent channel power and error-vector magnitude performance of reduced complexity CALLUM systems, IEE P-COMM, 146(5), 1999, pp. 297-302
The combined analogue locked-loop universal modulator (CALLUM) is a power e
fficient linear RF transmitter based on the LINC principle (linear amplific
ation with nonlinear components). The system provides both upconversion and
amplification of a baseband input signal, within a closed-loop control sch
eme. The variant known as CALLUM1 is optimal, but difficult to implement pr
actically. Simplifications to this system can be made so that the processin
g requirement is reduced. The simulated performance of these systems is com
pared to that of CALLUM1, in terms of adjacent channel power (ACP) and erro
r-vector magnitude (EVMrms), in response to a TETRA (terrestrial trunked ra
dio) baseband modulation signal. The existing CALLUM systems and the simpli
fied versions proposed in the paper meet the TETRA ACP specification of -60
dBc if enough stable loop gain can be provided.