Level Shifter Circuit with Keeper Path for Low-Voltage Switching
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Solution Overview
Problem
Conventional level shifting circuitry fails to operate effectively with low input voltage domains due to high threshold voltage of pulldown transistors, limiting power savings and voltage reduction capabilities.
Innovation Solution
The proposed level shifting circuitry includes a pulldown path with greater maximum drive current than a keeper path, along with pullup control circuitry that renders the pullup path non-conductive after pulling the output signal to the higher voltage level, allowing the pulldown path to overcome the keeper path and maintain the output signal at the higher voltage level until the pulldown path can pull it down.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the VDD level is reduced to save power, then power consumption decreases, but the pulldown transistors cannot overcome the pullup transistors to switch the output to ground level
Solution Approach 1:
The pullup function is segmented into two separate paths: a pullup path for switching the output to the high voltage level, and a keeper path for maintaining the high voltage level. This segmentation allows the pullup path to be sized for strong pulling capability while the keeper path uses minimal strength, enabling the pulldown path to overcome the keeper path even with low VDD levels.
Solution Approach 2:
The pullup path is dynamically controlled to be non-conductive after successfully pulling the output to the high voltage level. This dynamic switching ensures the pullup path does not compete with the pulldown path during the pull-down operation, allowing the system to operate reliably at low VDD levels.
2Power
If the pullup transistors are sized to pull the output to the high voltage level, then the pullup capability is sufficient, but the pulldown transistors cannot overcome them when switching to ground level
Solution Approach 1:
The pullup function is divided into a pullup path and a keeper path. The pullup path is sized to provide strong pulling capability for switching to the high voltage level, while the keeper path uses minimal strength. This segmentation resolves the contradiction by allowing strong pullup capability while enabling the pulldown transistors to overcome the weaker keeper path.
Solution Approach 2:
The pullup path performs its function of pulling the output to the high voltage level first, then is rendered non-conductive before the pulldown operation begins. This preliminary action ensures that when the pulldown transistors need to switch to ground level, they only need to overcome the weak keeper path rather than the strong pullup path.
3Reliability
If the pulldown transistors are sized to overcome the pullup transistors, then the pulldown switching is reliable, but the pullup transistors cannot effectively pull the output to the high voltage level
Solution Approach 1:
The pullup function is segmented into a pullup path and a keeper path. The pullup path is sized to provide strong pulling capability, while the keeper path uses minimal strength. This allows the pulldown transistors to be sized to overcome the weak keeper path while the strong pullup path effectively pulls the output to the high voltage level.
Solution Approach 2:
Different parts of the pullup function have different strength requirements. The pullup path uses strong transistors for effective pulling to the high voltage level, while the keeper path uses weak transistors that can be easily overcome by the pulldown transistors. This local differentiation of quality resolves the contradiction.
Data Source
AI summary
Level shifting circuitry is provided for generating an output signal in response to an input signal. The level shifting circuitry includes a pulldown path for pulling the output signal to a lower output voltage level in response to a first transition of the input signal and a pullup path for pulling the output signal to a higher output voltage level in response to a second transition of the input signal. Pullup control circuitry places the pullup path in a non-conductive state in response to the output signal being pulled to the higher output voltage level. A keeper path keeps the output signal at the higher output voltage level while the pullup path is non-conductive until the pulldown path pulls the output signal low. A maximum drive current of the pulldown path is greater than a maximum drive current of the keeper path.