Audio Amplifier Coupling Circuit for Ripple Attenuation
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Solution Overview
Problem
High-frequency ripple currents in class D amplifiers lead to significant heat dissipation in class A amplifiers, limiting the performance and linearity of high-fidelity audio amplifiers, particularly at frequencies above 10 kHz, due to switching losses and inductive coupling effects.
Innovation Solution
Incorporating an attenuation impedance with a low-value attenuation inductance and a series capacitor, along with a resistance, to form an RLC circuit that reduces high-frequency ripple current, allowing multiple phase-shifted class D amplifiers to cancel ripple and distribute power voltage effectively, thereby reducing heat dissipation and enhancing linearity and bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a low inductance value is used in the coupling impedance to reproduce high audio frequencies, then the slew rate in the audio band is improved, but the amplitude of the ripple current at the class D switching frequency increases significantly
Solution Approach 1:
An attenuation impedance (comprising resistance and capacitance) is introduced as an intermediary element connected to the midpoint between the two series coupling inductances. This intermediary component specifically targets and attenuates the high-frequency ripple current generated by the class D amplifier's PWM switching, while allowing the audio frequency signal to pass through the coupling inductors with minimal impedance. This resolves the contradiction by providing frequency-selective impedance management.
Solution Approach 2:
The patent changes the impedance parameters of the coupling network by introducing frequency-dependent elements (resistance and capacitance in the attenuation impedance) that modify the overall impedance characteristics. The attenuation impedance's resistance and capacitance values are selected to create a frequency response that presents high impedance to ripple frequencies while maintaining low impedance for audio frequencies, thus changing the parameter behavior across different frequency ranges.
2Loss of energy
If the switching frequency of the class D amplifier is increased to reduce ripple current amplitude, then the ripple current is reduced, but the switching losses of the MOS transistors increase proportionally
Solution Approach 1:
The attenuation impedance serves as a mediator that allows the system to operate at practical switching frequencies (below 500 kHz for voltages greater than 100 volts) while still achieving effective ripple current reduction. By providing a dedicated path for ripple current attenuation, the system doesn't need to rely solely on increasing switching frequency, thus avoiding excessive switching losses in the MOS transistors.
3Reliability
If the class A amplifier absorbs the high-frequency ripple current, then the linearity and performance of the amplifier are improved, but significant heat dissipation occurs in the class A amplifier
Solution Approach 1:
The harmful high-frequency ripple current is extracted from the main audio signal path by the attenuation impedance, which is specifically designed to target and remove this unwanted component. The attenuation impedance connected at the midpoint between the coupling inductors selectively extracts ripple frequencies, preventing them from being absorbed by the class A amplifier and causing heat dissipation, while allowing the useful audio signal to pass through.
Solution Approach 2:
The attenuation impedance converts the harmful ripple current into a beneficial filtering action. By introducing the resistance and capacitance elements, the system transforms what would be a harmful thermal load on the class A amplifier into a controlled attenuation mechanism that improves overall system linearity and reduces unwanted high-frequency content in a predictable and manageable way.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution significantly reduces heat dissipation in class A amplifiers, increases the working bandwidth, and improves linearity by effectively attenuating high-frequency ripple currents, allowing the amplifiers to handle higher frequencies without significant distortion.
Implementation Method 1
a coupling impedance (30) including two coupling inductances (32A, 32B) mounted in series between the output of the reference generator and the output of the power voltage generator
Implementation Method 2
the attenuation impedance includes an attenuation inductance (44A), a capacitor (44B) and a resistance (44C) connected in series to one another
Data Source
AI summary
Disclosed is the audio amplifier comprising an input for an audio signal to be amplified and an output for powering a load on the basis of the amplified audio signal; a generator of reference voltage of very high linearity and low output impedance, able to receive, as input, the audio signal to be amplified; a power current generator comprising a power voltage generator whose output is connected to the output of the reference voltage generator through a coupling impedance. The coupling impedance comprises two coupling inductances mounted in series between the output of the reference generator and the output of the power voltage generator and an attenuation impedance linking a mid-point between the two coupling inductances and a reference potential, wherein the attenuation impedance includes an attenuation inductance.