Cartesian feedback amplifier with soft landing

The author describe the results of several experiments conducted on a Cartesian feedback amplifier with soft landing. This amplifier uses a new method for adaptively controlling the local signal phase in a Cartesian demodulator. They tested the soft-landing Cartesian feedback (SLCFB) method in the 900 MHz band using π/4-shifted QPSK modulation to determine its applicability for pocket terminals in Japanese digital cellular systems. They developed a smooth loop-gain control mechanism using a variable gain amplifier with an FET and a continuous phase-shifter control circuit for digital processing in the IF band. They showed that the SL-CFB method can maintain the optimum local signal phase in the demodulator. This method therefore solves the problem at applying CFB amplifiers. They adopted circuit configurations that are easy to incorporate into LSI chips so that the amplifier can be used in compact terminals. The results show that the SL-CFB amplifier is a promising candidate for developing highly efficient linear amplifiers, which are very important in digital cellular telephone terminals