MEMS Capacitive Readout Circuit Without High-Bias Amplifiers
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Solution Overview
Problem
Conventional MEMS inductive capacitance conversion techniques require high bias voltage and high-quality amplifiers, leading to increased chip size, cost, and signal errors, making it difficult to integrate into low-voltage ICs and limiting sensitivity and noise immunity.
Innovation Solution
An apparatus using a reference voltage circuit, switches, and a controller to directly convert MEMS inductive capacitance to digital signals without a high bias circuit or high-quality amplifier, employing a single-end or differential ADC with integral circuits to simplify the design and improve noise resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high bias voltage (10V or higher) is used to increase MEMS sensing sensitivity, then sensitivity is improved, but device complexity and integration difficulty increase
Solution Approach 1:
The patent changes the voltage parameter from high bias voltage (10V or higher) to low operating voltage (compatible with standard IC processes). The invention achieves this by using a voltage converter circuit that generates the necessary high voltage only when needed for sensing, while the rest of the system operates at low voltage, thus improving sensitivity without permanently increasing device complexity
Solution Approach 2:
The patent implements dynamic voltage switching where the high bias voltage is applied only during the sensing phase through a controlled voltage converter, while the processing and output stages operate at low voltage. This dynamic approach allows the system to achieve high sensitivity when needed without the permanent complexity of a high-voltage bias circuit
2Reliability
If a high quality amplifier is used to amplify the 1-mV MEMS output signal, then signal quality is improved, but chip area increases
Solution Approach 1:
The patent merges the amplifier function with the ADC input stage by directly connecting the MEMS capacitor to the ADC's sampling circuit. The ADC's internal switching and integration circuits perform the amplification and conversion functions that would otherwise require a separate high-quality amplifier, thus maintaining signal quality while reducing chip area
Solution Approach 2:
The ADC circuit performs multiple functions: it directly samples the MEMS capacitor voltage, performs the amplification function through its internal integration, and converts the signal to digital format. This multi-functionality eliminates the need for a separate amplifier component, reducing chip area while maintaining signal quality
3Ease of manufacture
If a sensor amplifier and bias circuit are used in the conventional configuration, then signal conversion is achieved, but chip area and cost increase
Solution Approach 1:
The patent extracts and eliminates the separate sensor amplifier and bias circuit from the conventional configuration. By directly connecting the MEMS capacitor to the ADC and using the ADC's internal circuits to perform the necessary signal conditioning, the invention removes unnecessary components, reducing chip area and manufacturing cost while maintaining signal conversion capability
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 reduces chip area, eliminates the need for a bias circuit and high-quality amplifiers, enhances sensitivity, and improves noise immunity by directly sampling MEMS capacitor voltage, enabling more compact and efficient MEMS signal conversion.
Implementation Method 1
ADC 40 converts the amplified signal into digital signals
Implementation Method 2
a comparator 45, where first-stage converter circuit 41 further includes a subtracter 42, an adder 43, a delay relay 44 and a digital-to-analog converter (DAC) 46
Data Source
AI summary
An apparatus for converting MEMS inductive capacitance to digital is provided, for converting the induced analog voltage of MEMS element into digital signal. The apparatus includes an ADC, a reference voltage circuit and a controller. With the integral circuit and the comparator of the ADC and the reference voltages generated by the reference voltage circuit, the apparatus of the present invention uses the switch signals generated by the controller to generate digital signals. The present invention can also be integrated with MEMS element into a single chip to achieve single-chip MEMS.