Adjustable Biasing Circuits for MEMS Microphones
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Solution Overview
Problem
Process variations in MEMS capacitive microphones, such as plate stiffness and gap variations, affect sensitivity and electrostatic forces, leading to inconsistent signal production due to fixed bias voltage.
Innovation Solution
An adjustable bias voltage system using a non-volatile memory element and a charge pump architecture with multiple stages, enabling voltage regulation and adjustment to trim sensitivity and electrostatic forces, while maintaining power supply compatibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed bias voltage is used, then the circuit is simple, but the sensitivity and electrostatic forces vary due to process variations
Solution Approach 1:
The patent applies the Dynamics principle by transforming the fixed bias voltage into an adjustable one. The biasing circuit includes a non-volatile memory element (such as an anti-fuse or fuse) that can be programmed to different resistance values, allowing the bias voltage to be dynamically adjusted to compensate for process variations in plate stiffness and gap, thereby achieving consistent sensitivity across different microphones.
2Manufacturing precision
If an adjustable bias voltage system is used, then sensitivity and electrostatic forces can be trimmed, but the device complexity increases
Solution Approach 1:
The patent applies theParameter changesprinciple by modifying the resistance value of a non-volatile memory element (such as an anti-fuse or fuse) to adjust the bias voltage. By changing the resistance parameter of this single component, the circuit achieves the ability to trim sensitivity and electrostatic forces without requiring a completely complex adjustable voltage source, thus minimizing the increase in device complexity.
Solution Approach 2:
The patent introduces a non-volatile memory element (anti-fuse or fuse) as an intermediary component between the fixed voltage source and the capacitor. This intermediary element allows for precise adjustment of the bias voltage by changing its resistance value, enabling sensitivity trimming while keeping the overall circuit structure relatively simple.
3Measurement precision
If finer voltage resolution is provided, then sensitivity variations can be compensated, but power consumption increases
Solution Approach 1:
The patent applies thePreliminary actionprinciple by programming the non-volatile memory element (anti-fuse or fuse) during the manufacturing or initialization process to achieve the desired bias voltage setting. Once programmed, the setting is stored and does not require continuous power to maintain, thus achieving fine voltage resolution for sensitivity compensation without incurring ongoing power consumption penalties.
Solution Approach 2:
The non-volatile memory element (anti-fuse or fuse) serves itself by maintaining its programmed resistance value without requiring external power or control circuits during normal operation. The element automatically provides the correct bias voltage setting based on its programmed state, eliminating the need for complex, power-consuming voltage regulation circuits.
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 system provides finer voltage resolution to compensate for sensitivity variations, improving microphone sensitivity and electrostatic force control, while optimizing power consumption and compatibility with various power supply voltages.
Implementation Method 1
The charge pump includes a plurality of stages. A first stage is coupled to the voltage adjustment circuit and the clock circuit and comprises a plurality of switched latches. The first stage receives the driver voltage and the regulated voltage and outputs a first stage output voltage approximately equal to the sum of the driver voltage and the regulated voltage.
Implementation Method 2
By using a non-volatile memory element it is possible to trim both the sensitivity and consequently the electrostatic forces on the sensor by adjusting the bias voltage.
Data Source
AI summary
An adjustable charge pump system. The system includes a voltage regulator, a clock circuit, a voltage adjustment circuit, and a charge pump. The voltage regulator is configured to receive an input voltage and output a regulated voltage. The clock circuit is coupled to the voltage regulator and receives the regulated voltage. The voltage adjustment circuit is coupled to the voltage regulator and is configured to receive the regulated voltage and to output a driver voltage. The charge pump includes a plurality of stages. The output of the adjustable charge pump system is adjusted by disabling one or more stages of the first stage and the plurality of subsequent stages.