Comparator Level Shifting for Low Oxide Breakdown Voltages
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Solution Overview
Problem
Process node scaling reduces gate oxide thickness, leading to lower oxide breakdown voltages in comparators, which can result in gate oxide stress and damage from common mode input voltages exceeding the breakdown voltage, compromising performance and reliability.
Innovation Solution
Incorporating a level shifter and body bias controller within the comparator architecture to mitigate gate oxide stress and bias temperature instability, using internal components to adjust input voltage levels and body bias control, thereby supporting a wide input voltage range without external components that increase system size and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If process node scaling is used to improve circuit speed and power efficiency, then transistor gate oxide thickness is reduced, but oxide breakdown voltage decreases leading to gate oxide stress and damage
Solution Approach 1:
A level shifter circuit is introduced as an intermediary component between the comparator input and the transistor input pair. This level shifter translates the input voltage to prevent excessive voltage differential across the gate oxide, thereby protecting the scaled transistors from breakdown while allowing continued process scaling for speed improvement.
Solution Approach 2:
The patent modifies the voltage parameters at the transistor gate by using a level shifter that adjusts the input voltage level. This parameter change ensures that the voltage differential across the gate oxide remains within safe limits even when common mode input voltages are present, resolving the reliability issue without sacrificing speed.
2Reliability
If external components are added to protect against oxide breakdown, then reliability improves, but system size and cost increase
Solution Approach 1:
The level shifter and body bias control circuitry are merged into the comparator architecture itself rather than being implemented as separate external components. This integration provides oxide breakdown protection while minimizing system size and cost increases, as the protective functionality is combined with the signal processing functionality.
Solution Approach 2:
The level shifter serves multiple functions: it protects the gate oxide from breakdown, establishes proper bias conditions for the transistor input pair, and enables the comparator to handle common mode input voltages. This multi-functionality reduces the need for additional dedicated protection components.
3Adaptability or versatility
If gate oxide thickness is reduced for scaling, then common mode input range is reduced, but process node scaling benefits are lost
Solution Approach 1:
The level shifter acts as an intermediary that decouples the relationship between common mode input voltage and the voltage differential across the gate oxide. This allows the comparator to accept a wide common mode input range while the scaled transistors remain protected, preserving both adaptability and speed benefits.
Data Source
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Figure 3~6
AI summary
A circuit (100) includes a transistor input pair (114, 153), a differential input having a comparator input (102, 104), and a level shifter (116, 157). The transistor input pair (114, 153) is adapted to be coupled between a voltage supply and a comparator output (106, 108). The transistor input pair (114, 153) includes a first transistor having a gate and a drain. The drain of the first transistor is coupled to the comparator output (106, 108). The level shifter (116, 157) is coupled between the transistor input pair (114, 153) and the differential input. The level shifter (116, 157) includes a second transistor having a gate and a source. The gate of the second transistor is coupled to the comparator input (102, 104). The source of the second transistor is coupled to the gate of the first transistor.