Charge Pump Bias Circuit for MEMS Microphone Temperature Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
MEMS microphones experience a decrease in sensitivity with increasing temperature due to temperature-dependent properties of their electrical and mechanical components, necessitating a solution for maintaining constant high sensitivity over a large temperature range.
Innovation Solution
A charge pump assembly with a bias circuit that applies a temperature-dependent bias voltage, featuring a piecewise linear temperature dependence, is used to counteract temperature-induced sensitivity deterioration by transferring a controlled amount of charge to the MEMS capacitor, utilizing a temperature sensor and selection circuits to adjust voltages based on temperature intervals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional charge pump assembly is used, then the circuit design is simple, but the sensitivity of the MEMS microphone decreases with increasing temperature
Solution Approach 1:
The bias voltage is divided into multiple segments corresponding to different temperature intervals. Each segment has a specific slope that compensates for temperature-induced sensitivity changes in that interval. This segmentation allows precise temperature compensation without requiring a single complex circuit design, as the bias voltage can be adjusted in discrete steps across the temperature range.
Solution Approach 2:
The bias circuit dynamically adjusts the bias voltage based on the operating temperature. The circuit transitions from a static bias voltage design to a dynamic one where the bias voltage changes with temperature. This dynamic adjustment compensates for temperature effects on capacitor sensitivity, maintaining stable microphone performance across varying temperatures while using relatively simple circuit components.
2Manufacturing precision
If a high number of temperature intervals are chosen for piecewise linear bias voltage, then the temperature compensation is better, but the circuit complexity increases
Solution Approach 1:
The patent applies partial action by implementing piecewise linear compensation with a moderate number of temperature intervals rather than attempting continuous compensation. This approach provides sufficient temperature compensation precision for practical applications without implementing an excessively complex circuit. The bias voltage is adjusted in discrete steps that are adequate for the required performance level, avoiding unnecessary complexity.
Solution Approach 2:
The patent changes the parameter of bias voltage slope for different temperature intervals. By varying the slope parameter across temperature intervals rather than using a single fixed slope, the circuit achieves better temperature compensation precision. This parameter change approach allows the same basic circuit topology to adapt to different temperature conditions without requiring fundamentally different circuit designs for each interval.
3Reliability
If the exact voltage for temperature compensation is determined precisely, then the sensitivity remains constant over large temperature range, but the determination and application becomes difficult
Solution Approach 1:
The complex task of determining the exact compensation voltage across the entire temperature range is segmented into multiple simpler tasks, each handling a specific temperature interval. For each interval, a linear approximation with a constant slope is used, which is much easier to determine and implement than a single exact voltage curve. This segmentation makes the manufacturing and calibration process more manageable while maintaining sensitivity constancy.
Solution Approach 2:
The patent implements a dynamic voltage adjustment mechanism that automatically adapts the bias voltage to the operating temperature. Rather than requiring manual determination and application of a single exact compensation voltage, the circuit dynamically selects and applies the appropriate bias voltage level based on the current temperature interval. This dynamic approach simplifies manufacturing by eliminating the need for precise manual calibration while maintaining temperature compensation effectiveness.
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 effectively maintains high sensitivity of MEMS microphones across a wide temperature range by compensating for temperature-induced sensitivity losses, simplifying the circuit design and reducing complexity while ensuring precise temperature compensation.
Implementation Method 1
The bias voltage has a temperature dependence. The temperature dependence of the bias voltage is chosen such that the temperature dependence of the electrical charge provided at the output port by the charge pump counteracts a temperature-induced deterioration of an external circuit environment of the charge pump assembly.
Implementation Method 2
The charge pump CP further has an output port OP via which electric charge can be transferred, e.g. to a capacitor.
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A charge pump assembly allowing MEMS microphones being temperature-compensated in a large temperature range and corresponding microphones are provided. An assembly comprises a charge pump and a bias circuit electrically connected to the charge pump. A bias voltage provided by the bias circuit has a temperature dependence.