MEMS Variable Capacitor Cell Segmentation for RF Parasitic Control
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Solution Overview
Problem
MEMS devices in RF and microwave applications face issues with unwanted capacitive coupling and series inductance due to parasitic capacitances, which make it difficult to achieve customized capacitance without impacting mechanical performance and matching dynamic performance with full cells.
Innovation Solution
Designing variable capacitors with cells having the same control capacitance irrespective of RF capacitance, allowing the use of the same isolation resistor and parasitic capacitance, enabling optimization of CMOS control circuits and matching dynamic performance across cells, while allowing for easy scaling of RF capacitance and reuse of controller circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the number of MEMS switches in a cell is reduced to achieve customized capacitance, then the RF capacitance is customized, but the parasitic capacitance increases due to larger isolation resistors
Solution Approach 1:
The patent divides the cell into multiple groups where each group contains a subset of MEMS switches. By selectively activating different groups, the patent achieves customized capacitance values without reducing the total number of switches in the cell, thereby avoiding the need for larger isolation resistors and associated parasitic capacitance.
Solution Approach 2:
The patent changes the control capacitance parameter to match the RF capacitance scaling, ensuring that the isolation resistor remains the same size across different capacitance configurations. This parameter adjustment allows customized RF capacitance without increasing parasitic capacitance from oversized isolation resistors.
2Adaptability or versatility
If partial cells are designed with fewer switches to scale RF capacitance, then the RF capacitance is reduced, but the mechanical performance and dynamic performance matching becomes difficult
Solution Approach 1:
The patent segments the cell into multiple groups with identical mechanical structures, allowing selective activation of different groups to achieve capacitance scaling while maintaining the full mechanical structure of each group. This ensures that mechanical performance is preserved regardless of which groups are activated.
Solution Approach 2:
The patent designs all groups to have identical mechanical structures and control capacitances, making each group universally functional. This universality allows any combination of groups to be activated while maintaining consistent mechanical performance and dynamic characteristics across all capacitance configurations.
3Reliability
If isolation resistors are increased in value to maintain RF performance in partial cells, then the RF performance is maintained, but the parasitic capacitance increases
Solution Approach 1:
The patent adjusts the control capacitance parameter to match the scaled RF capacitance, which allows the use of the same isolation resistor value across all cell configurations. This parameter change eliminates the need to increase isolation resistor values, thereby preventing the associated increase in parasitic capacitance while maintaining RF performance.
4Adaptability or versatility
If custom cells are designed with different numbers of switches, then the desired capacitance is achieved, but the control circuit optimization and dynamic performance matching becomes complex
Solution Approach 1:
The patent segments the cell into multiple identical groups that can be selectively activated. This segmentation allows capacitance customization through simple group selection rather than custom cell design, greatly simplifying the control circuit architecture and enabling reuse of the same control circuitry across different capacitance configurations.
Solution Approach 2:
The patent creates universal groups with identical structures and characteristics that can serve multiple capacitance values when combined in different configurations. This universality allows a single control circuit design to optimize and match dynamic performance across all capacitance settings without requiring custom control circuits for each configuration.
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 enables the production of DVC cells with customized capacitance without parasitic capacitances, optimizing dynamic performance and allowing for the reuse of controller circuitry across multiple products, thereby maximizing yield and reducing new product development time.
Implementation Method 1
The MEMS devices have a suspended structure that moves between at least two positions to modify the electrical impedance to the flow of continuous or alternate current
Implementation Method 2
a large-value isolation resistor is required between the control-electrodes and the CMOS driver to make sure that the control-electrodes are RF-floating, which ensures that the RF currents don't flow into the CMOS driver
Data Source
AI summary
A variable capacitor (300) comprises cells (200, 400) that have an RF electrode (202, 402) coupled to a bond pad (30). Each cell comprises a plurality of MEMS devices (100) the capacitance of which can be changed by means of a movable electrode. The MEMS devices are placed in a sealed cavity of the cell and are arranged next to each other along the length of the RF electrode of the cell. The RF electrode of each cell can be trimmed so as to obtain an RF line (402) and a further ground electrode (404) and so as to scale the RF capacitance of the cell without impacting the mechanical performance of the MEMS cells. Each cell has the same control capacitance irrespective of the RF capacitance. This allows each cell to use the same isolation resistor required for RF operation and thus each cell has the same parasitic capacitance. This allows the CMOS control circuit to be optimized and the dynamic performance of the cells to be matched.