Cascoded Level Shifting Circuit for Wide Voltage Swing
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Solution Overview
Problem
Conventional level shifting circuits face reliability issues due to high voltage stress on transistors, require multiple supply voltages, and exhibit slower switching speeds, making them impractical for wide supply voltage ranges and multiple output voltage domains in modern SOC designs.
Innovation Solution
A single-stage cascoded level shifting circuit using four supply voltages (VLOW, VMIDL, VMIDH, and VHIGH) to achieve a maximum voltage swing of twice the maximum operating voltage, with cascode transistors and drive transistors configured to avoid voltage stress and ensure proper output node driving.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional level shifting circuit is used with high voltage levels, then voltage level conversion is achieved, but transistor voltage stress increases causing reliability issues
Solution Approach 1:
The level shifting function is divided into multiple stages, each handling a portion of the total voltage conversion. The first stage converts VLOW to VMID, and the second stage converts VMID to VHIGH, so that no single transistor experiences the full voltage difference between VLOW and VHIGH.
Solution Approach 2:
An intermediate voltage level VMID is introduced as a mediator between VLOW and VHIGH. This intermediate level allows the system to achieve high voltage conversion while keeping individual transistor voltage stress within safe operating limits by using VMID as a stepping stone.
2Reliability
If multi-stage level shifting circuit is used to reduce voltage stress, then transistor reliability improves, but circuit complexity and number of supply voltages increases
Solution Approach 1:
Multiple level shifting stages are merged into a single integrated circuit block. The first and second level shifting circuits are combined with shared components and interconnected in a unified structure, reducing overall system complexity despite the multi-stage functionality.
Solution Approach 2:
The circuit is designed to handle multiple voltage domains (VLOW, VMID, VHIGH) simultaneously with a single integrated structure. The level shifting circuit can operate with different voltage combinations and configurations, making it universally applicable to various SOC designs with different supply voltage requirements.
3Speed
If conventional level shifting circuit is used, then simple circuit structure is maintained, but switching speed is slow
Solution Approach 1:
The circuit employs dynamic control mechanisms where the level shifting operation is actively managed through controlled switching of transistors. The circuit adapts its operation mode based on input conditions, enabling faster response and switching speeds compared to static conventional designs.
Solution Approach 2:
The level shifting operation maintains continuous useful action by ensuring that at least one transistor in each series pair remains conductive during the transition process. This continuous conduction path enables faster switching by avoiding complete cutoff states and maintaining signal flow continuity throughout the voltage conversion process.
Data Source
AI summary
A level shifting circuit operates at a high voltage level without stressing the transistors. The circuit has the ability to swing between large supply domains. Multiple output voltage levels are supported for the level shifted signal. Additionally, output nodes are stably driven to supply voltage levels that do not vary with respect to process corner and temperature.