Switching Amplifier FIR Filtering for Carrier Harmonic Rejection
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Solution Overview
Problem
Class D amplifiers generate strong carrier signal harmonics, requiring large output filters to attenuate these harmonics, which occupy significant circuit area and have limited bandwidth, affecting efficiency and performance.
Innovation Solution
Incorporating an embedded harmonic rejection filter that generates multiple drive signals with different delays, applied to output circuits to sum and attenuate carrier signal harmonics, allowing for a smaller and more efficient output filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a large output filter is used to attenuate carrier signal harmonics, then harmonic attenuation is improved, but circuit area occupied increases
Solution Approach 1:
The filter function is segmented into two parts: an embedded harmonic rejection filter within the amplifier that handles specific harmonic frequencies, and a smaller output filter that handles remaining filtering. This division allows each filter to be optimized for its specific function, reducing the total circuit area while maintaining effective harmonic attenuation.
Solution Approach 2:
The embedded harmonic rejection filter performs preliminary filtering of carrier signal harmonics before the signal reaches the output filter. By pre-attenuating the harmonics, the output filter only needs to handle residual filtering, significantly reducing its size and the total circuit area required.
2Object-generated harmful factors
If a large output filter is used to attenuate carrier signal harmonics, then harmonic attenuation is improved, but bandwidth is limited
Solution Approach 1:
The filtering function is divided between the embedded harmonic rejection filter and the output filter, allowing each to be optimized for different frequency ranges. The embedded filter targets specific harmonic frequencies while the output filter handles the broader bandwidth signal, maintaining both harmonic attenuation and wide bandwidth performance.
Solution Approach 2:
Different parts of the frequency spectrum are handled by different filtering mechanisms: the embedded harmonic rejection filter provides targeted attenuation at specific harmonic frequencies, while the output filter provides broad bandwidth filtering. This localized approach to filtering maintains both harmonic rejection and wide bandwidth.
3Loss of energy
If class D amplifier operates in switching regions, then power efficiency is improved, but harmonic distortion increases
Solution Approach 1:
The embedded harmonic rejection filter converts the harmful carrier signal harmonics generated by switching operation into a manageable filtering problem. By integrating this filter, the amplifier maintains its high efficiency switching operation while the filter systematically eliminates the resulting harmonics, turning the efficiency-harmonics trade-off into a solved design challenge.
Solution Approach 2:
The embedded harmonic rejection filter acts as an intermediary between the high-efficiency switching amplifier and the output stage. It mediates the conflict between switching efficiency and harmonic generation by providing targeted harmonic attenuation, allowing the amplifier to operate in efficient switching regions while maintaining clean output signals.
Data Source
AI summary
A switching amplifier with an embedded harmonic rejection filter is disclosed. In an exemplary design, the switching amplifier includes a generator circuit and a plurality of output circuits. The generator circuit receives an input signal and a carrier signal at a carrier frequency and generates a plurality of versions of a drive signal associated with different delays. The drive signal may be a pulse width modulation (PWM) signal. The plurality of versions of the drive signal may be generated by delaying the carrier signal, or the input signal, or the drive signal. The output circuits receive the plurality of versions of the drive signal and provide an output signal. The output circuits have outputs that are coupled together and implement a finite impulse response (FIR) filter based on the plurality of versions of the drive signal. The FIR filter has a frequency response with zeros at harmonics of the carrier frequency.