RF modulator design for a low level pilot sub-system

This paper presents an adaptive duplexer using cancelling instead of filtering to obtain sufficient transmitter (Tx) leakage and noise isolation in the receiver. A low level pseudo-noise (PN) pilot signal is introduced in order to adjust the cancelling coefficients. To modulate the pilot signal to radio frequencies a straightforward direct up-conversion mixer with low carrier feedthrough has been designed. This structure has been implemented in the silicon-on-sapphire (SOS) 250 nm GC process.