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.
High-Efficiency Envelope-Tracking Transmitter With Optimized Class-${\hbox{F}}^{-1}$  Amplifier and 2-bit Envelope Amplifier for 3G LTE Base Station
In this paper, a high-efficiency envelope-tracking (ET) transmitter incorporating a novel efficiency-boosting function is proposed and implemented. An inverse Class-F power amplifier is utilized and optimized using the proposed output loading condition, which enhances its efficiency at the high probability region. This matching network can be conveniently implemented by controlling the nonlinear capacitance of the power transistor. For an accurate analysis, the output waveforms are modeled in terms of the nonlinear capacitance, and the efficiency and output power are subsequently analyzed and successfully optimized. For a high-efficiency envelope amplifier (EA), we propose a new EA utilizing a 2-bit switching stage in place of a 1-bit switching stage. This proposed architecture effectively reduces the ripple current, improving the efficiency of the EA. To verify our analysis, we have fully implemented a 3.54-GHz high-efficiency ET transmitter including a digital processing block. The experimental results show that the ET transmitter using a commercial 60-W peak-envelope-power GaN device operates at a drain efficiency of 44% and power-added efficiency of 39.6% with a gain of 10.1 dB at an average output power of 40 dBm for a 10-MHz third-generation long-term evolution signal with 8.5-dB peak-to-average power ratio. Using a digital pre-distortion function, the adjacent channel leakage ratio is less than -47.5 dBc.
Role of the coronoid process in varus osteoarticular stability of the elbow.
The role of the coronoid process in varus osteoarticular stability of the elbow was investigated in 10 cadaveric elbows. Testing was performed at multiple flexion angles after incremental removal of the coronoid. At each flexion angle, removal of more than 50% of the coronoid produced a statistically significant decrease in the load resisting varus displacement compared with all lesser resection levels (P < .003). There was a trend for decreasing load after removal of 50% of the coronoid. The mean decrease in load across all flexion angles was 10.1%, 50.4%, and 75.4% after removal of 50%, 75%, and 100% of the coronoid, respectively. Resistance to varus displacement tended to decrease more as a percent of control at lower flexion angles than at higher flexion angles after removal of more than 50% of the coronoid. The coronoid process was found to be a key varus stabilizer in the elbow and may contribute more to elbow stability in extension than in flexion.