Level Shifter Circuit Using Intermediate Voltage to Cut Switching Loss
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Solution Overview
Problem
Level shifters in LCD applications experience high power dissipation due to significant voltage drops across MOSFET devices when switching, leading to increased temperature and reliability issues, especially when driving capacitive loads with small resistance.
Innovation Solution
A level shifter configuration with a third auxiliary voltage supply providing an intermediate voltage between the low and high output voltages, minimizing voltage drops by reducing the voltage step across active MOSFET devices through a specific switching sequence and allowing the auxiliary supply to sink and source current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If MOSFET devices are used as switches in the level shifter, then low ON resistance is achieved, but significant voltage drop occurs during switching leading to high power dissipation
Solution Approach 1:
The voltage transition is segmented into multiple stages by introducing an intermediate voltage level. Instead of a single direct transition from low to high voltage, the level shifter first transitions to an intermediate voltage and then to the final high voltage, dividing the switching process into smaller steps that reduce instantaneous power dissipation.
Solution Approach 2:
An intermediate voltage supply is introduced as a mediator between the low and high voltage supplies. This intermediate voltage acts as a buffer during transitions, allowing the MOSFET to operate at lower voltage differences during switching events, thereby reducing power dissipation while maintaining the ability to achieve the full voltage range.
2Power
If the voltage difference between low and high levels is increased to meet LCD drive requirements, then appropriate drive signals are provided, but power dissipation increases due to larger voltage drops across switches
Solution Approach 1:
The large voltage transition required for LCD drive signals is segmented into smaller incremental steps using an intermediate voltage level. This allows the system to achieve the necessary high drive voltage while reducing the instantaneous voltage drop across switching devices, thereby lowering power dissipation during transitions.
Solution Approach 2:
The intermediate voltage supply pre-establishes a middle voltage level that can be used as a stepping stone during transitions. By having this intermediate level ready in advance, the system can perform preliminary switching actions at lower voltage differences before completing the full voltage transition, reducing overall power dissipation.
3Speed
If switching frequency is increased to improve signal response, then faster signal transmission is achieved, but power dissipation increases due to more frequent switching events
Solution Approach 1:
By segmenting the voltage transition into smaller steps through an intermediate voltage level, each individual switching event dissipates less energy. This allows the system to maintain high switching frequencies for fast signal response while the reduced energy per switch event keeps total power dissipation manageable.
Data Source
AI summary
An electronic device comprising a level shifter and a method. The level shifter includes an input adapted to receive an input signal switching between a low input voltage level and a high input voltage level and a first switch and a second switch coupled in series between a low output voltage supply and a high output voltage supply. An output is coupled to an interconnection node between the first and the second switch and is adapted to be coupled to a load. The first and second switches are controlled by the input signal. The level shifter further includes a third switch which is coupled between the interconnection node and an auxiliary voltage supply which has a voltage level between the low output voltage level and the high output voltage level.