Voltage Level Shifter Latch Current Control Across Wide Voltage Ranges
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Solution Overview
Problem
Conventional level shifters face challenges in providing optimal performance over varying input signal levels and sub-threshold voltage conditions, as they are often optimized for specific voltage domains and suffer from increased parasitic capacitance and reduced speed due to larger transistor sizes, making them inefficient for wide voltage ranges.
Innovation Solution
A level shifter design that incorporates a latch circuit and a current limiting circuit, such as a current mirror, to control the current based on the supply voltage, allowing the drive circuit to maintain sufficient drive strength over a wide range of input signal levels, including sub-threshold voltages, by adjusting the current sourced to the latch circuit in proportion to the supply voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If larger transistor sizes are used to accommodate larger VDDH to VDDL ratios, then the level shifter can operate over wider voltage ranges, but parasitic capacitance increases and speed decreases
Solution Approach 1:
The patent implements dynamic transistor sizing where the width-to-length ratio of the NMOS transistor is adjusted based on the detected VDDH to VDDL ratio. When the ratio is large, the NMOS transistor uses a larger aspect ratio to provide sufficient drive strength. When the ratio is small, a smaller aspect ratio is used to reduce parasitic capacitance and increase switching speed. This dynamic adaptation resolves the contradiction between voltage range adaptability and operating speed.
Solution Approach 2:
The patent changes the electrical parameters of the transistor (specifically the aspect ratio W/L) based on operating conditions. By detecting the voltage domain ratio and selecting appropriate transistor dimensions, the system optimizes the balance between drive strength needed for large voltage ratios and speed needed for small voltage ratios, effectively resolving the performance trade-off.
2Power
If transistor size is increased to handle larger voltage ratios, then drive strength improves, but parasitic capacitance increases reducing operational speed
Solution Approach 1:
The system dynamically adjusts the transistor aspect ratio based on the detected voltage ratio. For large VDDH to VDDL ratios, a larger NMOS aspect ratio provides the necessary drive strength to overcome the latch. For smaller ratios, a smaller aspect ratio reduces parasitic capacitance and maintains high switching speed. This dynamic parameter adjustment resolves the contradiction between drive strength and switching speed.
3Reliability
If the level shifter is optimized for a specific voltage ratio, then performance at that ratio is maximized, but performance degrades at other voltage levels
Solution Approach 1:
The patent implements a detection and adaptation mechanism that identifies the actual VDDH to VDDL ratio and selects the appropriate NMOS transistor aspect ratio accordingly. This dynamic configuration allows the level shifter to maintain optimal performance across different voltage domains rather than being fixed for a single ratio, resolving the contradiction between performance consistency and voltage domain flexibility.
Solution Approach 2:
The level shifter is designed to handle multiple voltage domain scenarios by incorporating detectable elements that identify the operating voltage ratio and adjust the transistor characteristics accordingly. This multi-functional design enables the same circuit to optimally serve multiple voltage domain configurations, achieving both reliability and adaptability.
Data Source
AI summary
A level shifter shifts the level of an input signal from a second voltage domain to a first voltage domain. To accommodate different input signal levels (e.g., including sub-threshold input signal levels) that may arise due to changes in the supply voltage for the second voltage domain, current for a latch circuit of the level shifter is limited based on the supply voltage for the second voltage domain. In this way, a drive circuit of the level shifter that controls the latch circuit based on the input signal is able to initiate a change of state of the latch circuit over a wide range of input signal levels.