Voltage Rail Generation Circuit Using Single Flying Capacitor
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Solution Overview
Problem
Existing voltage rail generation circuits require dedicated flying capacitors for each generated voltage rail, leading to increased costs and complexity due to tighter ESR requirements and additional pins needed for integrated circuits.
Innovation Solution
A voltage rail generation circuit utilizing a single flying capacitor and multiple switches to generate multiple voltage rails, with additional storage capacitors to smooth the voltage, reducing the need for multiple flying capacitors and minimizing pin count.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dedicated flying capacitors are used for each voltage rail, then voltage rail generation reliability is improved, but device complexity and cost increase
Solution Approach 1:
The patent implements a single flying capacitor that serves multiple voltage rail generation functions through switched capacitor techniques. The same capacitor is reused across different charge pump circuits to generate multiple voltage rails (e.g., VDD/2, VDD/4, VDD/8), eliminating the need for dedicated flying capacitors for each rail. This multi-functional approach reduces component count and circuit complexity while maintaining reliable voltage rail generation.
Solution Approach 2:
The patent merges multiple flying capacitor functions into a single shared capacitor. By combining the flying capacitor resources across different charge pump circuits and using time-multiplexed switching, the system achieves multiple voltage rail generation with minimal components. The storage capacitors are also strategically shared between adjacent charge pumps, further consolidating the overall capacitor requirements.
2Reliability
If dedicated flying capacitors are used for each voltage rail, then voltage stability is improved, but manufacturing cost increases
Solution Approach 1:
The single flying capacitor is designed to serve multiple voltage rail generation functions simultaneously through efficient switching control. By making this capacitor multi-functional across different charge pump circuits, the patent reduces the total capacitor count and associated ESR requirements, thereby lowering manufacturing costs while maintaining voltage stability through proper capacitor selection and switching design.
Solution Approach 2:
The patent optimizes the flying capacitor's electrical parameters (capacitance value, ESR characteristics) to accommodate its multi-functional role across different voltage rails. By carefully selecting capacitor parameters that satisfy the most stringent requirements, the design achieves cost-effective manufacturing while maintaining voltage stability for all generated rails.
3Loss of energy
If multiple flying capacitors are used, then power efficiency is improved, but pin count and device area increase
Solution Approach 1:
The patent merges multiple flying capacitor functions into a single capacitor, significantly reducing the device area occupied by capacitor structures and their associated pins. The switched capacitor charge pump architecture maintains power efficiency by using the same capacitor in different configurations across multiple charge pump circuits, achieving area efficiency without sacrificing the power transfer efficiency that characterizes charge pump operation.
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 allows for efficient generation of multiple voltage rails with reduced component count and cost, while maintaining high efficiency and lowering output impedance, as demonstrated by power efficiency and impedance simulation results.
Implementation Method 1
The charge pump is built around a flying capacitor CF
Implementation Method 2
The storage capacitor CP is coupled between the output terminal and the ground voltage reference supply in order to store the charge packets delivered by CF and to smooth the voltage at 50P
Data Source
AI summary
A voltage reference generation circuit having switch pairs coupled to systematically commutate a flying capacitor among adjacent pairs of voltage rail outputs. The circuit requires only a single flying capacitor, N+1 switch pairs, and N storage capacitors, to generate N intermediate voltage references between VDD and GND. A signal generator produces N+1 non-overlapping switch enable signals to systematically enable the switch pairs and commutate the single flying capacitor between the rail pairs. The flying capacitor remains charged to VDD/(N+1). The N storage capacitors hold their respective reference outputs at VDD*N/(N+1), VDD*(N−1)/(N+1), VDD*(N−2)/(N+1), and so forth.