Microwave amplifier

摘要

The level wide dynamic signals of the modulation envelope involved in the present invention are, for instance, the QAM modulated carriers characterised by multipoint constellations and by an assigned roll-off of the transmission filter, or by the usual radio signals AM transmitted. In the system of the invention the IF transmission signal is subjected to a compression of the level dynamic before being sent to a GaAsFET final microwave power amplifier, thus alleviating the AM/AM and AM/PM distortions due to gain saturation. The compression introduces a given distortion degree in the IF signal such to enable the observance of ETSI masks by the RF signal. In reception, the IF signal is subjected to an expansion of the level dynamic, having trend opposite to the compression one, before being sent to the demodulator. A feedback network measures the FEC rate (Forward Error Correction) at the demodulator and corrects in an adaptive mode a voltage defining the expansion degree. The expansion causes the signal spectrum to coincide with the spectrum of the modulated signal, obtaining a perfect linearity of the channel and the reaching of a BER in the order of 10<-14>, that enables to employ multipoint QAM constellations, for instance 1024. In an analogue implementation, the compression and expansion devices employ a polarized GaAsFET, in the first case, close to the knee and in the second case close to the pinch-off (Fig. 7).