All-MOSFET Voltage Reference With Feedback Against Process Variation
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Solution Overview
Problem
Existing ultra-low power voltage reference circuits, such as those described by Yang Liu, are highly susceptible to process variations, leading to significant percentage errors in generated reference voltages, with errors reaching up to 50% at extreme process corners.
Innovation Solution
An all-MOSFET voltage reference circuit design featuring cascaded branches with specific configurations of current sources and N-type transistors, including diode-connected transistors and an amplifier, where the first N-type transistor uses a standard-type threshold voltage and the third N-type transistor is adaptable to a higher power supply voltage, reducing process variation sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If an all-MOSFET voltage reference circuit is designed to reduce power consumption, then power consumption is reduced, but susceptibility to process variations increases leading to high percentage error
Solution Approach 1:
The patent changes the operating parameters of MOSFETs by utilizing the subthreshold region operation and carefully selecting threshold voltage parameters. By operating MOSFETs in the subthreshold region and selecting specific threshold voltage values for different transistors, the circuit achieves both low power consumption and reduced sensitivity to process variations, resolving the contradiction between low power and high accuracy
Solution Approach 2:
The patent implements a feedback mechanism using an operational amplifier that continuously monitors and adjusts the voltages at interconnected nodes. This feedback loop compensates for process variations by dynamically adjusting transistor gate voltages, thereby maintaining reference voltage accuracy while keeping power consumption low
2Device complexity
If standard MOSFET configurations are used in voltage reference circuits, then device complexity is reduced, but manufacturing precision suffers due to high sensitivity to process variations
Solution Approach 1:
The patent applies local quality by assigning different threshold voltage characteristics to specific MOSFETs within the circuit. By carefully selecting which transistors have higher or lower threshold voltages and placing them in specific positions within the cascaded branches, the circuit optimizes performance for reduced process variation sensitivity while maintaining overall structural simplicity
Solution Approach 2:
The patent segments the voltage reference circuit into multiple cascaded branches with distinct functions. Each branch is designed with specific transistor configurations that address particular aspects of process variation compensation, allowing the overall circuit to achieve high manufacturing precision through modular functional segmentation
Data Source
AI summary
An all-MOSFET voltage reference circuit includes a first cascaded branch configured to generate a bias current and composed of a first current source and a diode-connected first N-type transistor connected at a first interconnected node; a second cascaded branch composed of a second current source, a diode-connected second N-type transistor and a third N-type transistor connected with the second N-type transistor disposed in between, wherein the second N-type transistor and the third N-type transistor are connected at a second interconnected node; a third cascaded branch composed of a third current source and a diode-connected fourth N-type transistor connected at an output node that provides a reference voltage; and an amplifier with a non-inverting node coupled to the first interconnected node and an inverting node coupled to the second interconnected node. A threshold voltage of the third N-type transistor is larger than a threshold voltage of the second N-type transistor.