Stacked Voltage Reference Circuit for Stable Low-Power IoT Biasing
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Solution Overview
Problem
Existing voltage reference circuits face challenges in providing a stable reference voltage with low power consumption and insensitivity to parameter variations such as temperature and supply voltage fluctuations, particularly in IoT devices that operate in a subthreshold region.
Innovation Solution
A voltage reference circuit design incorporating stacked transistors with regulating transistors to compensate for voltage changes at multiple nodes, ensuring stable reference voltages with added transistors contributing to power consumption while maintaining insensitivity to parameter variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If stacked pMOS transistors are used to increase output reference voltage, then the reference voltage level increases, but power consumption increases and noise increases
Solution Approach 1:
The voltage reference circuit is divided into multiple independent stacked transistor branches (first branch with first and second transistors, second branch with third and fourth transistors). Each branch contributes to the overall reference voltage, allowing the circuit to achieve higher voltage levels without proportionally increasing power consumption in a single branch. The segmentation enables parallel current paths that share the power consumption burden.
Solution Approach 2:
The stacked transistor structure serves multiple functions simultaneously: it generates the reference voltage, provides temperature compensation through matched transistor pairs, and enables scalable voltage output by adjusting the number of stacked transistors. The same transistor stack configuration can be used to generate different voltage levels by selecting different tap points or adjusting transistor dimensions.
2Temperature
If stacked pMOS transistors are used to increase output reference voltage, then the reference voltage level increases, but noise increases
Solution Approach 1:
By dividing the voltage generation function across multiple transistor branches, the noise contribution from each individual transistor is reduced. The segmented structure allows noise to be distributed and partially cancelled across parallel paths, resulting in lower overall noise compared to a single long stack.
Solution Approach 2:
Multiple transistor branches are merged in parallel to achieve the desired voltage level. The combining of multiple low-noise paths results in a lower overall noise floor compared to using a single high-voltage path, as the noise contributions from each branch add incoherently while the voltage contributions add coherently.
3Stability of the object's composition
If voltage reference circuit is always-on to provide stable reference voltage, then reference voltage stability is maintained, but power consumption increases
Solution Approach 1:
The circuit operates in the subthreshold region of transistor operation, where transistors conduct current at very low levels while maintaining their voltage regulation function. By changing the operating parameter from above-threshold to subthreshold, the power consumption is reduced by orders of magnitude while the reference voltage stability is preserved through the exponential current-voltage relationship in subthreshold operation.
Data Source
AI summary
A voltage reference circuit comprises: first transistor, second transistor, first regulating transistor, and second regulating transistor arranged in a stacked connection, wherein first voltage is provided at first node between first and second transistor, second voltage is provided at second node between second transistor and first regulating transistor, third voltage is provided at third node between first and second regulating transistor; wherein first regulating transistor and second regulating transistor are connected to first node and second node, respectively, for compensating changes in first voltage and second voltage, respectively, to maintain stable voltage levels; wherein voltage reference circuit outputs at least one of the first, second or third voltage as a reference voltage.