Output-Latched Level Shifter for Power Domain Shutdown
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Solution Overview
Problem
Microcontrollers may not be aware when secondary power domains are powered down, leading to unpredictable output signals and unnecessary current drain due to floating input signal voltage levels in prior level shifters.
Innovation Solution
A level shifter that shifts input voltage levels between power domains only when both domains are operative, using cross-coupled inverters and an enable signal to latch the output and prevent current flow when one domain is powered down, ensuring stable logic levels and preventing current leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the level shifter continuously monitors input signal voltage levels to ensure proper operation, then output signal reliability is improved, but current drain increases due to continuous operation of the cross coupled transistors
Solution Approach 1:
The level shifter transitions from a static continuous operation mode to a dynamic mode where the cross coupled transistors are enabled only when both power domains are operative. The enable signal dynamically controls the activation state, allowing the circuit to adapt its operation based on power domain status, thereby reducing current drain while maintaining reliability when needed.
Solution Approach 2:
The level shifter incorporates self-monitoring capability through the enable signal that detects when the second power domain is powered down. This self-service mechanism automatically disables the cross coupled transistors when unnecessary, eliminating the need for external continuous monitoring while preventing current drain and floating voltage issues.
2Stability of the object's composition
If the level shifter allows continuous operation of cross coupled transistors to maintain signal levels, then signal stability is improved, but current leakage occurs when secondary power domains are powered down
Solution Approach 1:
The circuit dynamically adjusts its operation based on the enable signal status. When the second power domain is powered down, the enable signal disables the cross coupled transistors, preventing current leakage. When both domains are operative, the transistors are enabled to provide stable signal levels, thus achieving both signal stability and energy efficiency at different operational states.
3Device complexity
If the level shifter uses a simple voltage shifting mechanism without latching, then device complexity is reduced, but floating input signal voltage levels cause unpredictable output signals
Solution Approach 1:
The enable signal performs a preliminary check of the second power domain status before allowing the level shifting operation to proceed. By evaluating the power domain state in advance and only enabling the cross coupled transistors when appropriate, the circuit prevents floating voltage conditions and ensures predictable output signals without requiring complex latching mechanisms.
Data Source
AI summary
A level shifter for a microcontroller shifts an input voltage in a first power domain to an output voltage level consistent with a second power domain. The level shifter is enabled to shift the voltages when both power domains are operative.