Flash Cell Voltage Reference Generator for Compact IC Design
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Solution Overview
Problem
Conventional voltage reference circuits using resistors on integrated circuits are imprecise and occupy space, while precision resistors outside the circuit require additional space, posing challenges in achieving accurate and compact voltage reference generation.
Innovation Solution
The use of 'big flash cells' with floating gate transistors and programmable threshold voltages in closed loop voltage reference circuits, along with current mirror and source follower configurations, allows for precise and trimmable reference voltage generation, enabling efficient power management and compact design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a precision resistor is placed outside the integrated circuit, then voltage reference precision is improved, but device area increases
Solution Approach 1:
The patent combines the voltage reference function with flash memory cell structure, integrating what would traditionally be external precision resistors into on-chip flash cells. The flash cell's floating gate transistor serves dual purposes: memory storage and voltage reference generation, eliminating the need for separate external precision resistors and reducing overall device area.
Solution Approach 2:
The flash memory cell is designed to perform multiple functions: it serves as both a memory storage element and a voltage reference generator. The floating gate transistor's threshold voltage, traditionally used only for memory data storage, is repurposed to provide a stable reference voltage, allowing one component to fulfill multiple roles and reduce the need for additional dedicated reference voltage circuitry.
2Area of stationary object
If conventional resistors are placed on the integrated circuit die, then device area is reduced, but voltage reference precision deteriorates
Solution Approach 1:
The patent changes the fundamental parameter used for voltage reference from resistor value to transistor threshold voltage. By utilizing the floating gate transistor's threshold voltage characteristic, which can be precisely controlled during fabrication and programming, the system achieves high precision without requiring large-area precision resistors. The threshold voltage serves as the reference parameter instead of resistance.
Solution Approach 2:
The patent replaces the traditional resistor-based voltage reference mechanism with a transistor-based mechanism. Instead of using ohmic resistance to generate reference voltage, the system uses the transistor's threshold voltage characteristic, substituting one physical mechanism (resistive division) with another (transistor threshold voltage reference), thereby achieving both area reduction and maintained precision.
3Measurement precision
If flash cells are used for voltage reference, then voltage precision and trimmability are improved, but power consumption increases
Solution Approach 1:
The patent implements periodic refreshing of the flash cell threshold voltages to maintain precision without continuous power consumption. The flash cells are programmed during manufacturing or initialization, and then periodically refreshed or re-programmed as needed, rather than requiring continuous power to maintain the reference voltage. This allows the system to achieve high precision with low average power consumption by using pulsed or periodic action instead of continuous operation.
Data Source
AI summary
A voltage reference generator includes multiple closed loop voltage references. Each of the closed loop voltage references uses a flash cell with a variable threshold voltage and a feedback loop to trim a reference voltage. The voltage reference generator includes sample and hold capacitors in output stages to allow reference voltages to be refreshed during a standby mode of operation.