A novel adaptive power-divider (APD) structure is introduced to overcome the limitations of practical Doherty power amplifiers (DPA). This technique provides a new structure for which the primary distinction from conventional structures is that it adjusts power division ratio to reduce the work load during measurement. Because the base station power amplifiers have a low efficiency due to the power back-off operation, efficiency enhancement techniques become very important. In this article, the efficiency simulation and measurements show that power-added efficiency of 52.5% can be achieved at 11-dB back-off. The power-added efficiency of an adaptive power-divider Doherty power amplifier is 5-10% larger than a conventional Doherty power amplifier. Furthermore, it is shown that this new structure can be used to improve the efficiency of the amplifier and bring a little effect of the third-order intermodulation distortion.
This paper presents a low-power imaging diversity front-end receiver employing the maximum-ratiocombining algorithm for free-space optical communication. It consists of seven signal channels and an output stage, each channel has a front-end transimpedance amplifier, a signal-to-noise ratio (SNR) estimator and a variable gain amplifier (VGA). The imaging receiver circuit was implemented in a 90 nm CMOS process. The maximum-ratio weighting is achieved with the SNR estimator and VGA, which provides the signal with a gain proportional to the signal amplitude. The maximum ratio combining feature was demonstrated with two channels driven by photodiode emulation circuits for electrical characterization. The power dissipation for the whole chip is 43 mW from a single 1.2 V supply.
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