On-Chip MEMS Capacitance Measurement Circuit
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Solution Overview
Problem
The existing methods for producing digital cameras with MEMS capacitors require expensive off-chip equipment and lengthy test times to measure capacitance versus applied potential, increasing production costs.
Innovation Solution
An on-chip MEMS actuator circuit that can both drive a MEMS capacitor to a preselected potential and measure its capacitance, eliminating the need for external test setups by using a current mirror, voltage divider, operational amplifier, and switch to calculate capacitance based on discharge time and resistor values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If off-chip equipment is used to measure capacitance of MEMS capacitor, then measurement accuracy is improved, but production cost increases and test time increases
Solution Approach 1:
The patent merges the capacitance measurement function with the existing on-chip test circuitry by integrating a voltage divider, current mirror, and timing circuit into the same chip as the MEMS capacitor. This eliminates the need for separate off-chip measurement equipment while maintaining measurement accuracy through precise on-chip voltage division and timing detection.
Solution Approach 2:
The MEMS capacitor chip performs its own capacitance measurement using integrated on-chip circuitry. The voltage divider network and current mirror circuitry enable the chip to self-test its capacitance characteristics without requiring external measurement equipment, thereby reducing production costs and simplifying the manufacturing process.
2Measurement precision
If off-chip equipment is used to measure capacitance of MEMS capacitor, then measurement accuracy is improved, but test time increases
Solution Approach 1:
The patent combines the capacitance measurement function with the existing on-chip test circuitry, enabling measurements to be performed directly on the chip during the manufacturing process. This integration eliminates the time-consuming transfer and setup required for off-chip measurements while maintaining measurement accuracy through precise on-chip voltage division and timing detection.
Solution Approach 2:
The on-chip circuitry is pre-configured with voltage divider networks and current mirror circuits that are ready to perform capacitance measurements immediately during the manufacturing process. This preliminary preparation of measurement circuitry on the chip eliminates the need for subsequent off-chip setup and measurement steps, significantly reducing total test time.
3Measurement precision
If separate capacitance measurement setup is used for each camera, then individual capacitance characterization is achieved, but device complexity increases
Solution Approach 1:
The patent merges multiple functions (capacitance measurement, voltage division, current mirroring, and timing detection) into a single integrated on-chip circuit. This consolidation eliminates the need for separate off-chip measurement setups for each camera, reducing overall system complexity while maintaining the capability for individual capacitance characterization of each MEMS capacitor.
Solution Approach 2:
The on-chip circuitry is designed with universal functionality that can perform capacitance measurements for different MEMS capacitors using the same integrated circuit architecture. The voltage divider network and current mirror circuits can be configured to measure various capacitance values, providing a universal solution that reduces the need for multiple specialized measurement setups.
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
Enables on-chip capacitance measurement and automatic focal range adjustment, reducing production costs and eliminating the need for separate capacitance measurement setups for each camera.
Implementation Method 1
an operational amplifier having a first amplifier input coupled to the interior contact, a second amplifier input, and an amplifier output; and a switch having a first switch contact coupled to the first mirror contact, a second switch contact coupled to the amplifier output, and a switch control contact
Implementation Method 2
a current mirror having a first mirror contact, a second mirror contact, and a third mirror contact; a first current flowing through the first mirror contact being mirrored by a second current flowing through the second mirror contact
Implementation Method 3
a voltage divider having an interior contact and coupled between the second mirror contact and a first potential; a second current flowing through the voltage divider
Implementation Method 4
a MEMS fabricated capacitor includes two conducting plates whose spacing varies as the potential between two plates is changed which in turn adjusts the capacitance of the MEMS capacitor
Data Source
AI summary
A micro-electro-mechanical system (MEMS) actuator circuit and method. The circuit includes a current mirror, a voltage divider having an interior contact and coupled between the mirror output and a potential, an operational amplifier having an input coupled to the interior contact and a switch having input/output contacts separately coupled to the amplifier output and the mirror input and having a switch control. The amplifier output can be coupled to a digital control circuit which can be coupled to the switch control contact and to a digital to analog circuit (DAC) which can be coupled to the digital control circuit and to another amplifier input. An enable signal at the switch control couples the switch input/output contacts together. The capacitance of a MEMS capacitor coupled to the mirror output is determined by measurement of time for the amplifier output to switch from one level to another following a change in DAC output potential.