Differential Capacitive Sensor Layout Without Negative Charge Pump
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Solution Overview
Problem
Existing capacitive sensor arrangements, particularly in MEMS microphones, require complex differential architectures and negative charge pumps, which increase design and integration challenges, and are not easily integrated into semiconductor devices.
Innovation Solution
A sensor arrangement comprising two single-ended capacitive sensors connected to a positive charge pump, eliminating the need for a negative charge pump and allowing for a differential output with reduced integration effort, using a positive bias voltage to suppress DC portions and achieve differential signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If differential MEMS with two backplates and a diaphragm are used, then differential output is achieved, but device complexity increases
Solution Approach 1:
The patent divides the differential sensor system into two separate single-ended capacitive sensors instead of using one complex differential sensor. Each sensor operates independently with its own readout circuit, simplifying the mechanical structure while maintaining differential output capability through electronic processing of the two separate signals.
Solution Approach 2:
The patent introduces an intermediary processing stage that takes the outputs from two single-ended sensors and combines them to produce a differential signal. This intermediary electronic processing replaces the need for complex mechanical differential structures, achieving the same functional result with simpler components.
2Reliability
If negative charge pump is used for differential MEMS, then proper bias voltage is achieved, but integration effort increases
Solution Approach 1:
The patent extracts the need for negative voltage generation by using only positive bias voltages from a single charge pump. The differential output is achieved not through negative voltage but through the differential processing of two single-ended sensor signals, both biased with positive voltage, thereby eliminating the complex negative charge pump circuitry.
Solution Approach 2:
The patent changes the voltage parameter approach from requiring both positive and negative voltages to using only positive voltages. By maintaining both sensors on positive supply rails and using differential signal processing, the system achieves proper biasing without the need for negative voltage generation, simplifying integration into standard CMOS processes.
3Measurement precision
If two single-ended MEMS with positive and negative charge pump voltages are used, then differential signal is achieved, but device complexity increases
Solution Approach 1:
The patent segments the differential sensing function into two independent single-ended sensors, each with its own readout circuit operating on positive voltage. This segmentation eliminates the need for a single complex differential sensor structure and the associated negative voltage requirement, while still achieving differential output through electronic combination of the two signals.
Solution Approach 2:
The patent makes the charge pump universal by using it to provide positive bias voltage to both single-ended sensors simultaneously. This single positive charge pump serves the function that would otherwise require separate positive and negative charge pumps, reducing overall device complexity while maintaining differential signal 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 solution simplifies the integration of differential capacitive sensors into semiconductor devices, reduces the complexity of ASIC technology, and maintains the advantages of differential sensor architectures without the need for negative charge pumps, enhancing signal-to-noise ratio and power supply rejection ratio performance.
Implementation Method 1
A charge pump is coupled to the first capacitive sensor and to the second capacitive sensor. The charge pump is operable to deliver a positive bias voltage
Implementation Method 2
MEMS (micro electro mechanical systems) microphone. Such MEMS microphones comprise a MEMS as a pressure dependent capacitor
Data Source
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AI summary
A Sensor arrangement is provided, comprising a first capacitive sensor (1) and a second capacitive sensor (2). A charge pump (3) is coupled to the first capacitive sensor and to the second capacitive sensor, the charge pump being operable to deliver a positive bias voltage. A differential output has a first terminal (OUTN) coupled to the first capacitive sensor and a second terminal (OUTP) coupled to the second capacitive sensor.