Level Shifter Bias Compensation for Transistor Drive Variation
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Solution Overview
Problem
Level shifters face challenges in accurately translating signals between voltage domains due to variations in transistor drive strength caused by process, voltage, temperature, and aging, leading to timing issues and potential latch misoperation.
Innovation Solution
The implementation of a level shifter circuit with compensated biasing voltage for bias transistors in each current path, which adjusts to account for drive strength variations, ensuring accurate voltage shifting and minimizing the impact of transistor strength variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If transistors are sized to handle the voltage differential between voltage domains, then breakdown voltage requirement is met, but resistance increases and speed decreases
Solution Approach 1:
The current path is segmented into multiple transistor stages (first transistor, second transistor, third transistor) that collectively handle the voltage differential. Each transistor operates within its safe voltage breakdown limits while contributing to the overall voltage translation function, thereby maintaining higher speed performance.
Solution Approach 2:
An intermediate voltage domain is introduced between the first and second voltage domains. The level shifter translates signals through this intermediate domain using multiple transistor stages, allowing each transistor to operate at lower voltage stress while achieving the overall voltage translation function.
2Strength
If transistors with larger breakdown voltages are used, then voltage differential handling is improved, but transistor area increases
Solution Approach 1:
The voltage translation function is segmented across multiple smaller transistors rather than using a single large transistor. This segmentation allows the use of smaller area transistors that individually cannot handle the full voltage differential but collectively achieve the function through staged voltage translation.
3Manufacturing precision
If bias transistors are added to reduce voltage drop across transistors, then voltage translation accuracy is improved, but device complexity increases
Solution Approach 1:
The bias transistors are configured to automatically adjust their operation based on the voltage conditions in the circuit. The compensation mechanism uses the inherent characteristics of the transistors and biasing networks to self-correct for drive strength variations without requiring external control circuits or complex adjustment mechanisms.
4Reliability
If compensated biasing voltage is applied to account for drive strength variation, then reliability is improved, but device complexity increases
Solution Approach 1:
The compensated biasing voltage is generated using a feedback mechanism that monitors the operation of the level shifter and adjusts the biasing accordingly. This feedback-based compensation improves reliability by adapting to actual operating conditions while keeping the complexity manageable through efficient feedback circuit design.
Data Source
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AI summary
A level shifter circuit (101) is described herein for shifting a signal from a first voltage domain (Vdd1) to a second voltage domain (Vdd2). The level shifter circuit includes two current paths (113, 115) between a supply terminal of the first voltage domain (Vss1) and a supply terminal of the second voltage domain (Vdd2). The first and second current paths each include a differential transistor (155, 157) that receives a signal from a pulse generator in a first voltage domain. The pulse generator provides pulses to the differential transistors based on an input signal (INPUT) to be translated to the second voltage domain. The level shifter includes a latch circuit (107) in the second voltage domain that includes two inputs where each input is biased at a node of one of the current paths. Each current path includes a bias transistor whose control terminal receives a compensated biasing voltage (CBV) for biasing the bias transistor. The compensated biasing voltage is compensated to account for drive strength variation of at least one transistor in each current path.