Level Shifter Transition Sequencing to Prevent Output Spikes
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Solution Overview
Problem
Existing level shifter circuits face reliability issues due to transient excessive voltages across semiconductor devices, which can lead to failure, especially when operating at higher voltages and power levels, making them costly and unreliable.
Innovation Solution
The proposed method and apparatus for level shifting generate control outputs with a significantly wider voltage range by using upper and lower source supply signals that transition in a controlled manner, preventing source supply signals from transitioning away from a 'common' state until the other signal has completed a significant portion of its transition, thereby avoiding excessive transient voltages across semiconductor devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If level shifter circuits operate at higher voltage and power levels, then the voltage range and power handling capability are improved, but transient excessive voltages across semiconductor devices occur leading to reliability degradation
Solution Approach 1:
The patent applies preliminary action by pre-charging source supply nodes to intermediate voltage levels before allowing transitions to final voltage levels. This preparatory step prevents excessive voltage transients by ensuring that voltage differences across semiconductor devices remain within safe limits during switching operations, thereby maintaining reliability at higher power levels
Solution Approach 2:
The patent implements beforehand cushioning by introducing intermediate voltage states that act as buffer zones during voltage transitions. These cushioning states prevent direct large-voltage jumps that would cause harmful transients, allowing the circuit to handle higher power levels safely through controlled, stepped voltage changes
2Speed
If source supply signals transition simultaneously, then the switching speed is improved, but excessive transient voltages are generated across semiconductor devices
Solution Approach 1:
The patent applies segmentation by dividing a single simultaneous voltage transition into multiple sequential stages. Instead of transitioning all source supply signals at once, the patent segments the transition process into controlled steps with intermediate states, thereby maintaining fast overall switching speed while preventing harmful transient voltage spikes that would result from simultaneous transitions
3Reliability
If controlled transition sequencing is implemented to prevent transient voltages, then reliability is improved, but the transition time and complexity increase
Solution Approach 1:
The patent applies merging by combining multiple control functions into a unified control mechanism. The control circuit integrates transition sequencing, intermediate state management, and timing control into a coordinated system that achieves reliable voltage transitions without requiring separate complex control circuits for each function, thereby limiting the increase in overall device complexity
Data Source
AI summary
A level shifter, or method, producing a final output from a driver supplied by a high-side source driver providing VDD or common, and a low-side source driver providing common or VSS. A delay is introduced to prevent a source driver output at common from beginning to transition toward a supply rail until a delaying source driver at a rail begins transitioning toward common. The level shifter may be single-ended or differential, and the delaying source driver may be coupled to the same final output driver as is the delayed source driver, or may be coupled to a different final output driver. The level shifter may have a second level shifter front end stage, which may have high-side and low-side intermediate source driver outputs coupled by a capacitor, and/or may couple one of the supplies to all intermediate source drivers via a common impedance or current limit Zs.