Bidirectional Level Shifter Circuit for Wide-Range Fast Conversion
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Solution Overview
Problem
Current level shifters face challenges in achieving high-speed and wide-voltage-range operation, particularly in covering both sub-threshold and super-threshold voltages, while being insensitive to manufacturing technology variations and operation environments, and they often have limited bidirectional level conversion capabilities.
Innovation Solution
A level shifter circuit comprising a comparison circuit, a delay circuit, and a selection circuit that compares and delays input signals to select the higher voltage signal, ensuring balanced rising and falling delays and enabling bidirectional voltage conversion across a wide range from sub-threshold to standard voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional cross-coupled level shifters are used to convert sub-threshold input signal to super-threshold output signal, then the level conversion function is achieved, but the delay time becomes very slow in some combinations of input-to-output voltages
Solution Approach 1:
The level shifter circuit dynamically adjusts its operating mode based on the voltage levels of input and output signals. It automatically selects between different transistor configurations (standard-threshold or low-threshold) depending on whether the voltage difference is large or small, thereby optimizing conversion speed across the entire voltage range from sub-threshold to super-threshold levels
Solution Approach 2:
The invention changes the threshold voltage parameter of transistors based on operating conditions. By using both standard-threshold and low-threshold transistors in different stages, the circuit adapts its electrical parameters to match the voltage conversion requirements, achieving fast conversion across wide voltage ranges
2Ease of manufacture
If Wilson current mirror is used for stable conversion, then only standard-threshold transistors are needed, but the rising delay becomes much greater than the falling delay making it not practical for IC application
Solution Approach 1:
The circuit introduces asymmetric transistor configurations to balance the symmetric rising and falling delays. By strategically placing low-threshold transistors in specific positions within the push-pull output stage, the circuit compensates for the inherent delay imbalance of Wilson current mirror, making both rising and falling edges equally fast
3Speed
If cross-coupled NOR gates are used with inverted input signal, then the speed of the level shifter is accelerated, but the available voltage of the input signal is confined to a near-threshold value
Solution Approach 1:
The level conversion function is segmented into multiple stages: a first stage for differential sensing using cross-coupled NOR gates that handles near-threshold voltages, and a second stage that extends the input voltage range to accommodate sub-threshold and super-threshold levels. This segmentation allows each stage to be optimized for its specific voltage range while maintaining overall high speed
Data Source
AI summary
A level shifter transfers a first voltage signal to a second voltage signal. The level shifter comprises a comparison circuit, a delay circuit, and a selection circuit. The comparison circuit generates a first signal according to the comparison result between the first voltage signal and the reverse-phase signal of the first voltage signal. The delay circuit generates a second signal according to the first voltage signal. The selection circuit receives the first and the second signals and chooses the higher voltage one from the first signal and the second signal to be the second voltage signal.