Headphone Load Current Sensing With Off-Chip Reference Noise Isolation
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Solution Overview
Problem
Conventional methods for sensing load current in headphones degrade the signal-to-noise ratio due to board-level noise, which affects the performance of auxiliary devices with features like frequency equalization and biometrics authentication.
Innovation Solution
An audio codec system with a first path for driving the auxiliary device and a second path that includes a sense resistor, a bias circuit, and an off-chip voltage reference is used to detect the load current, applying the reference voltage between resistors to reduce board-level noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sense resistor is added in series with the headphone load to measure voltage and sense load current, then load current sensing capability is improved, but board-level noise increases and signal-to-noise ratio degrades
Solution Approach 1:
The patent divides the audio system into two separate paths: a first path for driving the auxiliary device and a second path for sensing operations. The second path includes dedicated sensing resistors and bias circuits that are isolated from the main audio driver path, preventing noise coupling while enabling accurate current sensing through separate measurement circuitry.
Solution Approach 2:
The patent introduces an off-chip voltage reference as an intermediary element that provides a stable reference potential for the sensing circuitry. This voltage reference acts as a mediator between the bias circuits and the sensing resistors, enabling precise measurements without introducing additional noise into the audio signal path.
2Measurement precision
If conventional measurement implementations are used to sense load current, then current sensing is enabled, but signal-to-noise ratio is degraded
Solution Approach 1:
The patent segments the measurement function from the audio driver function by creating a dedicated second path with its own sensing resistors and bias circuits. This segmentation allows current sensing to occur in an electrically isolated environment, preventing noise from the audio path from degrading the signal-to-noise ratio of the measurement.
Solution Approach 2:
The patent applies local quality by providing specialized sensing circuitry with appropriate biasing and reference voltages in the second path, rather than using the general-purpose audio driver circuitry. This localized optimization ensures that the measurement function has the precise electrical conditions needed for high signal-to-noise ratio performance.
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
This approach effectively reduces board-level noise, enhancing the signal-to-noise ratio and enabling accurate load current sensing for diverse auxiliary devices, including headphones with ancillary features.
Implementation Method 1
A conventional way to sense a load current is to add a sense resistor in series with the headphone load and measure the voltage across the sense resistance
Implementation Method 2
The off-chip voltage reference is associated with the auxiliary device load and can be coupled between the first bias circuit and the second bias circuit
Data Source
AI summary
An audio codec system includes an audio driver path coupled to a first node of the audio codec system. A first terminal of a sense resistor external to the audio codec system is coupled to the first node and a second terminal of the sense resistor is coupled to an auxiliary device load. The audio codec system includes a second path having a first bias circuit, a second bias circuit and an off-chip voltage reference. The first bias circuit is coupled to a second node of the audio codec system. The second bias circuit is coupled to a third node of the audio codec system. The off-chip voltage reference is associated with the auxiliary device load coupled between the first bias circuit and the second bias circuit.