Cartesian feedback amplifier with soft landing

Abstract

This paper describes 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. We tested the soft-landing Cartesian feedback (SL-CFB) method in the 900 MHz band using d4-shifted QPSK modulation to determine its applicability for pocket terminals in Japanese digital cellular systems.We developed a smooth loopgain control mechanism using a variable gain amplifier with an FET and a continuous phase-shifter control circuit for digital processing in the IF band. We 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. We 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.

Digitally Assisted RF Architectures: Two Illustrative Designs

“…14.1 acts as two independent feedback loops: one for the I channel and one for the Q channel. However, these systems are vulnerable to an apparent phase difference between the local oscillator (LO) sources, and the associated problems are mentioned in practically all literature on the subject [4][5][6][7][8][9][10][11][12][13][14]. This phase difference is represented as φ in the figure.…”

“…We demodulate by multiplying (14A.18) by −( j/2)(e jω 0 t e jφ − e − jω 0 t e − jφ ). Keeping only the low-frequency terms (it can be safely assumed that terms involving 2ω 0 are filtered out), we are left with 12 We emphasize "ordinary" in the sense that its imaginary part implies nothing about the signal on the Q channel. In our development, we treat I and Q as two separate signals, as opposed to the real and imaginary parts of the complex signal I + j Q.…”

“…26.5% PA power savings FIGURE 14 12. Comparison of the power required to maintain the required level of linearity between the linearized and nonlinearized cases.…”

Increasing the talk-time of mobile radios with efficient linear transmitter architectures

“…Noise (particularly wideband) in the Cartesian loop can be increased by insufficient stability and inattention to gain distribution around the loop [17,18]. The phase shifter is needed to counter for RF delays [19,20]. This must be set uniquely for every channel, and generally requires a training sequence to optimise the setting.…”