A. Direct up conversion transmitter
1) Classical I/Q transmitter: The classical I/Q ZIF transmitter is presented on Fig. 1. The in phase and quadrature components of the baseband signals, digitally generated and converted into analog signals, are sent at the input of the I/Q modulator after low pass filtering. The local oscillator drives the mixer for RF modulation. The RF signal is then fed to the power amplifier, after preamplification and filtering. Although this architecture is very simple, it suffers from various imperfections: I/Q imbalance, noise floor and linearity of the power amplifier. The imbalance can be thwart by fine tuning of the modulator with either feedback or calibration techniques . The output noise remains a weak point because it imposes a filter at the output of the mixer and according to the system, at the output of the PA (GSM case).