Bootstrap Class-D RF Power Amplifier With Single-Phase Driver
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Solution Overview
Problem
Designing radio frequency power amplifiers (RF PAs) that can efficiently produce high-power RF signals at microwave frequencies over a wide range is challenging due to complexity, energy inefficiency, and large footprint requirements.
Innovation Solution
A high-power, high-frequency RF PA with a single-phase driver and nonlinear switch-based design using aluminum gallium nitride / gallium nitride (AlGaN/GaN) high electron mobility transistors (GaN HEMTs), eliminating the need for a large drain inductor and simplifying the circuitry, allowing for compact monolithic microwave integrated circuit (MMIC) fabrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a conventional single-ended RF PA design is used, then high RF output power is achieved, but a large drain inductor is required increasing the footprint
Solution Approach 1:
The patent divides the single-ended amplifier into a push-pull configuration with two separate FETs (Q1 and Q2) operating in complementary phases. This segmentation eliminates the need for a large drain inductor by using two smaller output matching networks, thereby reducing the overall PA footprint while maintaining high RF output power capability
Solution Approach 2:
The invention transitions from a single-phase single-ended architecture to a two-phase push-pull architecture, adding a temporal dimension to the operation. By alternating the conduction phases of Q1 and Q2, the design achieves high power output without requiring large inductive components, thus reducing the stationary object area
2Adaptability or versatility
If a two-phase driver is used to achieve wide bandwidth operation, then frequency range is improved, but circuit complexity increases
Solution Approach 1:
The single-phase driver circuit is designed to control both Q1 and Q2 FETs through a common gate network. The driver performs multiple functions: it provides the drive signal for both transistors, establishes the 180-degree phase relationship between them, and enables wide bandwidth operation without requiring separate driver circuits for each phase, thus reducing overall circuit complexity
3Reliability
If a non-switched linear RF PA is used, then linearity is maintained, but energy efficiency deteriorates
Solution Approach 1:
The patent employs class-D switching operation where Q1 and Q2 are alternately switched on and off in a periodic manner controlled by the single-phase driver. This periodic switching enables the amplifier to operate in a highly efficient mode while maintaining signal linearity through proper pulse-width modulation and output filtering, thereby improving energy efficiency without sacrificing signal quality
4Power
If AlGaN/GaN HEMTs are used instead of conventional transistors, then power handling capability is improved, but manufacturing complexity increases
Solution Approach 1:
The patent utilizes AlGaN/GaN heterostructure HEMTs which combine aluminum gallium nitride and gallium nitride layers to create a composite material system. This composite structure provides high breakdown voltage and high electron mobility, enabling superior power handling capability. The design accepts the manufacturing complexity of these advanced materials as necessary to achieve the desired high-power performance
Data Source
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AI summary
A high-power, high-frequency radio frequency power amplifier includes an output stage and a single-phase driver. The output stage is arranged in a Class-D amplifier configuration and includes a first depletion mode field effect transistor (FET), a second depletion mode FET, and a bootstrap path that couples the output of the output stage to the gate of the second FET. The first and second depletion mode FETs are switched out-of-phase and between fully-ON and fully-OFF states, under the direction of the single-phase driver. The single-phase driver directly controls the ON/OFF state of the first depletion mode FET and provides a discharge path through which the input gate capacitor of the second depletion mode FET in the output stage can discharge to turn OFF the second depletion mode FET. The bootstrap path provides a current path through which the input gate capacitor of the second depletion mode FET can charge to turn the second depletion mode FET ON.