MEMS DC-DC Converter Biasing Circuit for Startup and Ripple Control
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Solution Overview
Problem
DC-DC converters for MEMS devices face issues such as capacitor damage due to excessive middle node voltage during startup, inadequate ripple reduction in output voltage, and the need for large, high-value resistors consuming significant circuit layout, which are not effectively addressed by existing solutions.
Innovation Solution
A DC-DC converter design incorporating a biasing circuit with level shifters and switch circuits to maintain node voltages at half the supply voltage, reducing the need for calibrated resistors and using substrate selection MOS transistors to manage voltage levels and control signals, along with filtering to minimize ripple and parasitic components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-value resistors are used to create biasing voltages, then the voltage levels can be established, but the circuit layout area increases and output impedance increases
Solution Approach 1:
The patent changes the parameter of resistance value from high-value resistors to low-value resistors in the voltage division network. By using resistors with values of 1kΩ instead of high-value resistors, the circuit achieves the required voltage levels while minimizing layout area and output impedance. This parameter change directly resolves the contradiction between voltage accuracy and circuit area.
2Productivity
If middle node voltage is not controlled during startup, then the circuit can start up, but the capacitor C2 may be damaged due to voltage exceeding 5.5V
Solution Approach 1:
The patent implements preliminary action by adding a startup control circuit that detects the output voltage level and selectively connects or disconnects the middle node biasing circuit. During startup, when output voltage is below 10.5V, the biasing circuit is disconnected to prevent overvoltage damage to C2. Once the output voltage stabilizes above 10.5V, the biasing circuit is activated to maintain proper middle node voltage levels. This preliminary control action resolves the contradiction between startup capability and capacitor safety.
3Power
If conventional DC-DC converter design is used, then basic voltage conversion is achieved, but output ripple exceeds the specification of below 10 uV
Solution Approach 1:
The patent introduces an intermediary middle node biasing circuit that actively controls the voltage at the middle node between capacitors C1 and C2. This biasing circuit, using operational amplifiers and resistors, serves as a mediator to stabilize the middle node voltage and reduce voltage fluctuations. By adding this intermediary control mechanism, the output ripple is reduced from conventional levels to below 10 uV, resolving the contradiction between power conversion capability and output precision.
Data Source
AI summary
The invention relates to a DC-DC converter adapted to supply a MEMS device comprising an input for receiving a DC voltage (Vs), an output for transmitting a supplied voltage (V1) to the MEMS device. The DC-DC converter further comprises a biasing circuit (MNBC) for biasing a first node (Vmi) and a second node (Vme) with a first biasing voltage (Vm1) and a second biasing voltage (Vm2).