Two-State Charge-Pump Control Loop for MEMS DVC Voltage Stability
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Solution Overview
Problem
Digital variable capacitors (DVC) in MEMS devices face challenges in achieving stable high-voltage output for electrostatic actuation, as existing charge-pumps suffer from voltage ripple, slow response, and high power consumption, leading to potential device failure and reduced lifespan due to overshoot during startup and operation.
Innovation Solution
A charge-pump system incorporating a combination of resistive and capacitive dividers with a control loop that adjusts operating frequency and uses a waveform controller to manage voltage levels, along with additional signals like HVREADY and Reset, to ensure stable high-voltage delivery and minimize power consumption during startup and operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If existing charge-pumps are used to generate high voltage for MEMS DVC, then voltage boosting from VDD to HV is achieved, but voltage ripple and overshoot occur during startup and operation
Solution Approach 1:
A control loop with comparator is implemented that continuously monitors the high voltage output and adjusts the charge-pump frequency accordingly. When voltage reaches the target level, the comparator triggers a frequency reduction, preventing overshoot and maintaining stable operation. This feedback mechanism eliminates the need for external voltage monitoring circuitry while ensuring reliable voltage delivery to the MEMS device.
Solution Approach 2:
The charge-pump operates with dynamically adjustable frequency rather than a fixed frequency. The system automatically transitions between high-frequency operation (during startup and voltage droop) and low-frequency operation (when voltage is stable), optimizing performance across different operating conditions. This dynamic frequency adjustment reduces voltage ripple and improves overall voltage stability.
2Reliability
If charge-pump operates at high frequency to reduce voltage ripple, then voltage stability improves, but power consumption increases
Solution Approach 1:
The charge-pump frequency is dynamically adjusted based on real-time voltage conditions. During startup or when voltage droops, the system operates at high frequency to quickly restore voltage levels. When voltage is stable, the frequency automatically reduces to minimize power consumption. This dynamic operation achieves voltage stability only when necessary, significantly reducing average power consumption compared to continuous high-frequency operation.
Solution Approach 2:
The system changes the operating frequency parameter in response to voltage conditions. The comparator detects voltage levels and triggers frequency transitions, allowing the charge-pump to adapt its power consumption to actual operational needs. This parameter change strategy maintains voltage stability during critical periods while minimizing energy consumption during stable operation.
3Device complexity
If charge-pump uses simple voltage boosting, then device complexity is reduced, but response speed becomes slow during voltage transitions
Solution Approach 1:
A control loop with comparator is implemented that continuously monitors the high voltage output and adjusts the charge-pump frequency accordingly. When voltage reaches the target level, the comparator triggers a frequency reduction, preventing overshoot and maintaining stable operation. This feedback mechanism eliminates the need for external voltage monitoring circuitry while ensuring reliable voltage delivery to the MEMS device.
Solution Approach 2:
The charge-pump employs periodic frequency modulation based on voltage feedback. The system alternates between high-frequency charging phases (when voltage is below target) and low-frequency maintenance phases (when voltage is stable). This periodic action pattern enables fast voltage establishment during transitions while maintaining simplicity in the overall circuit design.
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 solution provides a stable high-voltage output with reduced ripple and overshoot, ensuring reliable MEMS device operation and extended lifespan by controlling voltage levels and power consumption effectively.
Implementation Method 1
The charge pump comprises a first capacitor; a second capacitor coupled to the first capacitor at a first capacitor node
Implementation Method 2
a second resistor coupled to the first resistor at a first resistor node, wherein the first resistor node is coupled to the first capacitor node
Implementation Method 3
a comparator, wherein the first capacitor node is coupled to the comparator
Implementation Method 4
a force is acting on the moveable MEMS element when a voltage V is applied between the MEMS element and a control electrode. This electrostatic force scales with (V/gap)2
Data Source
AI summary
The present invention generally relates to a DVC having a charge-pump coupled to a MEMS device. The charge-pump is designed to control the output voltage delivered to the electrodes, such as the pull-in electrode or the pull-off electrode, that move the switching element within the MEMS device between locations spaced far from and disposed closely to the RF electrode.