MEMS Accelerometer Bias Injection to Eliminate Sigma-Delta Idle Tones
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Sigma-delta analog-to-digital converters in microelectromechanical acceleration sensors, such as those used in in-ear headphones, exhibit undesirable idle tone behavior, where oscillations above the noise background can generate audible tones when idle signals are applied, leading to noise interference.
Innovation Solution
Incorporating a first signal generator element that applies a signal value greater than average gravity acceleration to the output signals of the acceleration sensor, and a second signal generator element to correct digital output signals, preventing the analog-to-digital converter from entering an idle state and thus eliminating idle tones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sigma-delta analog-to-digital converter is used for converting acceleration sensor signals, then measurement precision and signal-to-noise ratio are improved, but idle tone behavior occurs generating audible oscillations above the noise background
Solution Approach 1:
The patent applies preliminary action by pre-setting a bias current in the sigma-delta analog-to-digital converter that ensures the converter never enters the idle state, even when the acceleration sensor output is zero. This bias current is configured in advance to maintain a minimum activity level in the converter, preventing idle tone generation before it can occur.
Solution Approach 2:
The patent changes the operating parameters of the sigma-delta converter by adjusting the bias current level to a specific value that prevents idle state entry. By modifying this electrical parameter, the converter maintains continuous operation above the idle threshold, eliminating the harmful idle tone while preserving measurement precision.
2Use of energy by moving object
If the acceleration sensor outputs a zero signal in resting position, then the sensor system operates efficiently, but the analog-to-digital converter enters idle state and generates audible tones
Solution Approach 1:
The patent introduces an intermediary bias current between the acceleration sensor and the sigma-delta converter. This bias current acts as a mediator that prevents the converter from receiving a true zero signal, thereby avoiding the idle state and audible tone generation while allowing the sensor to maintain its low-power resting operation.
3Loss of energy
If the analog-to-digital converter operates in idle state with zero input signal, then power consumption is reduced, but oscillations above noise background become measurable and audible
Solution Approach 1:
The patent applies preliminary action by pre-configuring the bias current to prevent the converter from entering the idle state in the first place. This proactive measure ensures continuous operation above the idle threshold, eliminating noise interference before it can manifest as audible tones, while maintaining acceptable power consumption levels.
Data Source
AI summary
A microelectromechanical acceleration sensor system including a microelectromechanical acceleration sensor element for detecting acceleration values acting on the acceleration sensor element, a sigma-delta analog-to-digital converter for converting the analog output signals of the acceleration sensor element into digital output signals, and a first signal generator element and a second signal generator element. The first signal generator element is connected between the acceleration sensor element and the analog-to-digital converter and being configured to apply a predetermined signal value to the output signals of the acceleration sensor element. The signal value of the first signal generator element corresponding to an acceleration value that is greater than the average gravity acceleration, and the second signal generator element being connected in a signal processing direction downstream from the analog-to-digital converter and being configured to correct the digital output signals of the analog-to-digital converter by the signal value of the first signal generator element.