Comparator Level Shifting for Low-Oxide-Breakdown Input Range
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Solution Overview
Problem
Process node scaling reduces gate oxide thickness in transistors, leading to a narrower common mode input range (CMIR) for comparators, which can result in gate oxide stress and damage from common mode input voltages exceeding the oxide breakdown voltage, and existing solutions using external components increase costs and system size while compromising performance.
Innovation Solution
A comparator design incorporating a level shifter and body bias controller to mitigate gate oxide stress by applying voltage shifts and dynamically adjusting body bias, respectively, without adding external components, thereby supporting a wider input voltage range and CMIR while maintaining performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If gate oxide thickness is reduced for process node scaling, then circuit speed and power efficiency are improved, but common mode input range is reduced and gate oxide breakdown risk increases
Solution Approach 1:
A level shifter circuit is introduced as an intermediary component between the comparator input and the transistor input pair. The level shifter translates the common mode input voltage to a suitable level that does not exceed the reduced oxide breakdown voltage of the scaled transistors, thereby enabling the comparator to accept a wider input voltage range while protecting the sensitive scaled transistors.
Solution Approach 2:
The patent dynamically adjusts the body bias voltage of the transistor input pair based on the common mode input voltage level. By changing the body bias parameter, the transistor threshold voltages are adjusted to accommodate different input voltage ranges, effectively expanding the common mode input range while preventing gate oxide breakdown in scaled transistors.
2Adaptability or versatility
If external components are added to expand input voltage range, then comparator adaptability is improved, but system size and cost increase
Solution Approach 1:
The level shifter and body bias controller are integrated within the comparator circuit itself, merging multiple functions into a single unified device. This integration eliminates the need for external components, reducing system size and cost while maintaining the expanded input voltage range capability.
Solution Approach 2:
The internal level shifter and body bias controller serve multiple functions: they expand the input voltage range, protect against gate oxide breakdown, and maintain comparator performance across different operating conditions. This multi-functionality reduces the need for separate external protection circuits and components.
Data Source
AI summary
A circuit includes a transistor input pair, a differential input having a comparator input, and a level shifter. The transistor input pair is adapted to be coupled between a voltage supply and a comparator output. The transistor input pair includes a first transistor having a gate and a drain. The drain of the first transistor is coupled to the comparator output. The level shifter is coupled between the transistor input pair and the differential input. The level shifter includes a second transistor having a gate and a source. The gate of the second transistor is coupled to the comparator input. The source of the second transistor is coupled to the gate of the first transistor.