Latch-Based Level Shifter for Power-Loss Output Hold
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Solution Overview
Problem
Conventional level shifter circuits face issues with indeterminate output signals and static power consumption when one of the supply voltages becomes high impedance, leading to potential cross conduction and increased power consumption during normal activity.
Innovation Solution
A level shifter device with a storage circuit, specifically a latch, that stores the output signal value and forces the output terminal to maintain the last stored voltage value when the primary supply voltage is no longer available, preventing undesired changes and ensuring no power consumption when the primary voltage is absent.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the first supply voltage VA becomes high impedance (externally removed), then the level shifter should consume no power, but the gate terminals of transistors M1 and M2 are not correctly polarized causing leakage currents and cross conduction leading to indeterminate output signal
Solution Approach 1:
The inverter I3 is configured to automatically generate the complement signal at its output terminal even when the first supply voltage VA is removed. This preliminary action ensures that the gate terminals of transistors M1 and M2 maintain correct polarization before any leakage currents can cause cross conduction, thereby preventing indeterminate output signals while consuming no power during standby
Solution Approach 2:
The inverter I3 provides feedback by continuously generating the complement signal based on the state of the first supply voltage VA. When VA is present, the inverter produces the correct complement signal; when VA is removed, the inverter's output naturally transitions to a state that prevents cross conduction, creating a self-regulating system that maintains reliability without additional power consumption
2Reliability
If conventional level shifter circuit is used with proper polarization, then output signal remains determined, but static power consumption occurs when first supply voltage is removed due to leakage currents
Solution Approach 1:
The inverter I3 serves dual purposes: it provides the necessary complement signal for proper transistor polarization while simultaneously preventing cross conduction when the first supply voltage is removed. The circuit serves itself by using the inverter's natural behavior to prevent leakage currents without requiring additional active components or power-consuming protection circuits
Data Source
AI summary
A level shifter includes a first terminal configured to receive a first supply voltage, a second terminal configured to receive a second supply voltage, an input terminal configured to receive an input signal and an output terminal. The level shifter is configured to shift the input signal from the level of the first supply voltage to the level of the second supply voltage in outputting the output signal. The level shifter includes a storage circuit for storing the output signal value and configured, when the first supply voltage is no longer available, to force the output terminal to assume the last output voltage value stored by the storage circuit when the first supply voltage was available and before the first supply voltage was not available.