Cascaded RF Switching Amplifier for Lower Switching Losses
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Solution Overview
Problem
High-power, high-efficiency broadband DC to RF switching amplifiers face challenges due to significant switching losses in semiconductor switches, particularly due to output capacitance and intrinsic diode recovery times, which limit their operational efficiency across a wide frequency range.
Innovation Solution
The design employs a cascaded multi-level inverter topology with GaN HEMT devices and a control scheme that identifies the least-recently-switched switching devices to minimize switching losses by adjusting their states, using a control circuit to manage the switching frequency and voltage across multiple switch modules in a cascade or parallel configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If Class D, E, or F switched amplifiers are used to achieve 100% efficiency, then efficiency is improved, but output filter complexity increases and broadband operation becomes difficult
Solution Approach 1:
The amplifier is divided into multiple parallel switching amplifiers, each operating at a different switching frequency. This segmentation allows each amplifier to handle specific frequency ranges without requiring complex output filters, as each amplifier's output filter only needs to handle its designated frequency band.
Solution Approach 2:
The system dynamically selects and adjusts the operating switching amplifiers based on the input signal frequency. By dynamically changing which amplifiers are active and at what switching frequencies, the system maintains high efficiency across a broad frequency range without requiring a single complex filter design.
2Adaptability or versatility
If Class S amplifier is used with high switching frequency to achieve broadband operation, then frequency range is improved, but switching losses increase significantly
Solution Approach 1:
The broadband frequency range is segmented into multiple bands, with each switching amplifier dedicated to a specific frequency range. This allows each amplifier to operate at optimized switching frequencies rather than requiring one amplifier to handle the entire broadband range at high switching frequencies.
Solution Approach 2:
The system changes the operating parameters (switching frequency) of different amplifiers based on the input signal frequency. By adjusting which amplifiers are active and at what switching frequencies, the system maintains adaptability across broadband while minimizing switching losses in each individual amplifier.
3Speed
If semiconductor switches with output capacitance are used, then switching speed is improved, but capacitive switching losses increase
Solution Approach 1:
The total power handling is segmented across multiple switching amplifiers, each with smaller switches. This reduces the output capacitance of individual switches, thereby reducing capacitive switching losses while maintaining overall high switching speed through parallel operation.
Data Source
AI summary
A RF amplifier is provided that includes a plurality of switch modules connected in a cascade configuration and divided into disjoint sets in accordance with their corresponding distinct peak DC voltages or currents, each switch module including a plurality of switch devices connected in a half-bridge or full-bridge circuit and a DC voltage or current source electrically connected with the half-bridge or full-bridge circuit, and a control circuit configured to determine an output voltage or current of the RF amplifier at the next switching interval, examine the states of the switching devices in the respective switch modules to identify a combination of least-recently-switched switching devices within each set of switch modules that, when switched to an opposite state, will produce the determined output voltage or current, and switch to an opposite state, at the next switching interval, the switching devices in the identified combination.