Differential Audio Amplifier Bias Compensation for Pop Noise
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Solution Overview
Problem
Audio amplifying circuits often produce audible popping noise due to mismatched input currents at their input nodes, leading to voltage differences that are amplified and perceived as noise, especially when power supply fluctuations occur, and this noise is further exacerbated by electromagnetic interference.
Innovation Solution
The amplifying circuit employs a differential configuration with current mirrors to provide offset currents that match the input currents, ensuring no voltage difference when no signals are received, and includes capacitors and resistors to filter noise and adjust frequency response, thereby reducing popping noise and improving power supply rejection ratio (PSRR).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If input currents at input nodes are not matched, then the circuit can operate with simple design, but voltage difference is introduced causing audible popping noise
Solution Approach 1:
The patent applies preliminary action by providing offset currents to the non-inverting input nodes before signal input to ensure current matching. The offset current source generates compensation currents that are applied in advance to balance the input currents of the differential amplifiers, preventing voltage differences and popping noise before they occur during state transitions.
2Object-generated harmful factors
If offset currents are provided to match input currents, then popping noise is reduced, but circuit complexity increases
Solution Approach 1:
The patent applies universality by designing the offset current source to serve multiple functions: it provides current matching to eliminate popping noise, maintains input bias current compensation, and works across different operating conditions (play/mute states). This multi-functional design reduces the need for separate compensation circuits, thereby limiting the increase in overall circuit complexity.
3Device complexity
If power supply fluctuations occur, then the circuit can operate with basic components, but noise is exacerbated and PSRR deteriorates
Solution Approach 1:
The patent applies feedback by implementing a circuit that continuously monitors and compensates for power supply fluctuations. The offset current source is designed to respond to changes in power supply voltage and adjust the compensation currents accordingly, creating a feedback mechanism that maintains input current matching under varying power conditions and improves power supply rejection ratio.
Data Source
AI summary
An amplifying circuit includes a first circuit component configured to receive and amplify first and second input voltages to generate an output voltage. The first circuit component is formed by a first amplifier and a second amplifier. A second circuit component is configured to provide a first offset current that is associated with a first input current of the first amplifier. The first offset current compensates for variation in the first input current. A third circuit component is configured to provide a second offset current that is associated with a second input current of the second amplifier. The second offset current compensates for variation in the second input current.