Multiphase PDM Direct-Drive Power Amplifier for Low RF Distortion
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Solution Overview
Problem
Existing radio frequency power supplies for plasma generation suffer from significant distortion due to large reflected signals during the initial stage of plasma establishment, which can harm the power supply and require complex filtering to reduce noise interference.
Innovation Solution
A novel low-distortion digitally modulated direct-drive power amplifier apparatus using an exciter and PDM pulse distribution unit to generate multiphase PDM modulated waveform pulses, improving sampling rates through Δ-Σ oversampling and interpolated filtering, and controlling the power amplifier in an on-off state to minimize distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If radio frequency signals are modulated with trapezoidal waves or exponential function waves to reduce reflected energy accumulation, then the harm to radio frequency power supply is reduced, but the system complexity and distortion increase
Solution Approach 1:
The patent changes the modulation parameter from traditional trapezoidal or exponential waveforms to PDM (Pulse Duration Modulation) waveforms. This parameter change allows the system to reduce reflected energy accumulation while maintaining simpler system architecture, as PDM naturally limits duty cycle to 50% and reduces harmonic distortion without requiring complex modulation waveforms
Solution Approach 2:
The patent replaces complex analog modulation circuits with digital PDM modulation implemented through a microcontroller unit. This substitution simplifies the hardware architecture by using digital logic and software-based modulation, eliminating the need for complex analog waveform generation circuits while achieving the same protective effect
2Use of energy by moving object
If class-D power amplifiers are used for high efficiency, then energy consumption is reduced, but filtering requirements and distortion increase at low switching frequencies
Solution Approach 1:
The patent changes the switching frequency parameter to operate above 20 kHz, which is the human hearing threshold. This parameter change allows the use of simple first-order RC low-pass filters instead of complex higher-order filters, as the higher switching frequency pushes the filter cutoff requirements to simpler implementations while maintaining class-D efficiency
Solution Approach 2:
The patent applies different filtering approaches for different frequency ranges. For audio frequencies below 20 kHz, simple RC filtering is sufficient. For the PDM carrier frequency above 20 kHz, the same RC filters effectively attenuate the carrier while passing the audio signal, eliminating the need for complex dual-stage filtering
3Manufacturing precision
If multiphase PDM modulation is implemented to reduce distortion, then harmonic distortion is reduced, but the system complexity increases
Solution Approach 1:
The patent segments the single PDM signal into multiple phased PDM signals (typically 3 phases). Each phase is generated by time-multiplexing the same PDM bitstream with appropriate phase shifts. This segmentation reduces harmonic distortion through phase cancellation of odd harmonics while maintaining simple implementation using basic timing circuits and phase-shift registers
Solution Approach 2:
The patent combines multiple phased PDM signals into a single composite drive signal that drives the power amplifier. The combining is achieved through simple additive superposition in the time domain, where the phased signals are summed to produce the final drive waveform. This merging reduces distortion while keeping the combining circuitry simple
Data Source
AI summary
Provided is an implementation method of a novel low-distortion digitally modulated direct-drive power amplifier apparatus. The method can achieve acquisition of modulated waveform signals by Δ-Σ oversampling technique, and further improves a sampling rate of the modulated waveform signals by an interpolated filter. An exciter can generate multiphase PDM modulated waveform pulses and carrier drive pulses to directly drive power amplifier modules to complete carrier generation and waveform modulation. However, to reduce complexity of a system and take the modulated waveform THD indicators into account, the multiphcontrolled within 12 phases.