Analyzing the improvement in efficiency through the integration of class-F power amplifiers compared to class-AB in an envelope tracking architecture
This paper investigates the performance of a class-F mode power amplifier (PA) integrated in an envelope tracking (ET) environment, compared to the conventional class-AB mode of operation in the same setting. A 10W high voltage laterally diffused metal oxide semiconductor (HVLDMOS) device is used to perform the comparison at 900MHz using an active load pull system in an emulated ET environment at 900MHz. The analysis looks at three scenario of optimization: when the class-F and class-AB PA's are optimized at individual drain voltage within the ET range, optimized at peak drain voltage, and optimized at the average drain voltage. The challenges of maintaining the device in class-AB and class-F modes throughout the ET range due to the variation of the device output capacitance are also presented in terms of the trajectory of the fundamental and harmonic loads, as well as the degradation in drain efficiency.
An 8 W GaAs Class-AB amplifier for operation in envelope tracking systems
In this paper an 8 W GaAs HEMT power amplifier for operation in envelope tracking systems is presented. The application targeted is UMTS downlink operation with a peak-to-average ratio of about 7 dB. By varying the drain bias voltage between 5 V and 12 V the compression point can be shifted in the required area. Power-added efficiency is more than 45 % in this area and above 52 % in the area of average output power of a UMTS signal. Gain can be kept above 14 dB in this operation mode with a variation of 3 dB.
Mathematical Modeling of Scour and Deposition
Electronic computers are opening up the field of sedimentation engineering by permitting the analysis of problems which heretofore have required too much time and effort. Movable stream bed profiles are being calculated in addition to water surface profiles. The initial gradation of sediment material in the stream bed may be prescribed to facilitate the calculation of an armor layer. This gradation is continually changed by the computer program in response to sediment particles being deposited on the stream bed and material on the stream bed being removed to satisfy transport capacity. Hydraulic sorting of sediment by grain size is accomodated. The stream bed does not have to be represented by a single grain size. Retardance of motion because of armor layer is calculated.