Dual-Amplifier Audio Circuit for Glitch Suppression
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Solution Overview
Problem
Class D power amplifiers in portable devices often produce higher noise levels, making them less suitable for earpiece applications, and integrating both earpiece and hands-free speakers in a single sub-system increases noise glitches due to inductive kickback and voltage spikes.
Innovation Solution
A dual-amplifier circuit system that uses a class D amplifier for hands-free operation and a class AB amplifier for earpiece operation, with feedback circuits and switch configurations to isolate noise glitches from the audio signal input, reducing unwanted noise reproduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a class D power amplifier is used for hands-free operation, then power consumption is reduced, but noise level increases making it unsuitable for earpiece applications
Solution Approach 1:
The audio output system is segmented into two separate amplifier channels: a class D amplifier for hands-free operation and a class AB amplifier for earpiece operation. This segmentation allows each amplifier type to be optimized for its specific application, with the class D handling high-power hands-free output and the class AB handling low-noise earpiece output, thereby resolving the contradiction between power efficiency and noise level.
2Area of stationary object
If a single speaker is coupled to both class AB and class D amplifier outputs, then printed circuit board space and component costs are reduced, but noise glitches increase due to inductive kickback and voltage spikes
Solution Approach 1:
A glitch suppression circuit is introduced as an intermediary between the class D amplifier output and the shared speaker. This circuit includes a glitch suppression capacitor connected between the class D amplifier output and ground, which acts as a mediator to filter out voltage spikes and inductive kickback before they can couple into the speaker and cause noise glitches, thereby allowing space savings without sacrificing audio quality.
3Object-affected harmful factors
If feedback circuits are used to suppress noise glitches, then noise reproduction is reduced, but device complexity increases
Solution Approach 1:
The glitch suppression capacitor value is carefully selected based on the switching frequency of the class D amplifier and the inductance of the speaker. By optimizing this parameter, the circuit achieves effective noise suppression without requiring complex active feedback circuits. The capacitor creates a frequency-dependent impedance that blocks high-frequency noise while passing audio frequencies, resolving the contradiction between noise suppression and circuit simplicity.
Data Source
AI summary
An apparatus includes first and second amplifiers, each having an input coupled to an audio signal input and an output coupled to an audio signal output. The second amplifier also has a feedback path from its output to its input. A first switch can be operated to selectively couple and uncouple the audio signal input and the input to the first amplifier to and from a first node. A second switch can be operated to selectively couple and uncouple the input of the second amplifier to and from a second node. A third switch can be operated to selectively couple and uncouple the first node to and from ground.