Bias-Controlled Level Shifter for Low-Voltage EMI Reduction

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Solution Overview

Problem

The decreasing voltage level of logic signals in display devices causes level shifters to fail in normal operation due to insufficient threshold voltage, leading to issues with peak current generation and electromagnetic interference (EMI) characteristics.

Innovation Solution

A level shifter design incorporating input and output transistors with bias units and switches, which control voltage drops and current flow to prevent simultaneous transistor activation, reducing peak current and improving EMI characteristics.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by stationary object

If the voltage level of logic signals is decreased, then power consumption is reduced, but the level shifter cannot be normally driven due to insufficient threshold voltage

Engineering Contradiction:

Improvepower consumptionVSAvoidlevel shifter operation

Core Design Contradiction:

Use of energy by stationary objectVSReliability

Solution Approach 1:

The level shifter is divided into multiple stages including a first level shifter for initial voltage level conversion and a second level shifter for further voltage level adjustment. This segmentation allows the circuit to handle low-voltage input signals effectively by progressively boosting the voltage level through multiple transistor stages, ensuring reliable operation while maintaining low power consumption.

Inventive Principle:

Principle #1Segmentation

2Device complexity

If conventional level shifter design is used, then circuit simplicity is maintained, but peak current is generated causing EMI issues

Engineering Contradiction:

Improvecircuit simplicityVSAvoidpeak current and EMI

Core Design Contradiction:

Device complexityVSObject-generated harmful factors

Solution Approach 1:

Bias circuits are introduced to pre-establish appropriate voltage levels at the gates of output transistors before the main switching operation occurs. This preliminary biasing action ensures that when input signals transition, the output transistors switch smoothly without generating peak currents, thereby reducing EMI while maintaining relatively simple circuit architecture.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Bias circuits act as intermediary elements between the input and output stages of the level shifter. These bias circuits generate and supply bias voltages that mediate the switching process, preventing direct abrupt transitions that would cause peak currents. The bias circuits smooth out the switching action, reducing electromagnetic interference while keeping the overall circuit design straightforward.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS10447252B2Level shifter, and source driver, gate driver and display device including the same

Publication Date: 2019.10.15 DB GLOBALCHIP CO LTD

AI summary

A level shifter includes (a) an input unit including (i) a first input transistor configured to receive a first voltage and connected to a first connection node, and (ii) a second input transistor configured to receive the first voltage and connected to a second connection node, (b) an output unit including (i) a first output transistor connected to a first output terminal and configured to receive a second voltage, and (ii) a second output transistor connected to a second output terminal and configured to receive the second voltage, (c) a first bias unit configured to control voltage drop between the output terminals and the connection nodes based on a first bias signal, and (d) a second bias unit configured to control a first voltage drop between the first output transistor and the second output terminal and a second voltage drop between the second output transistor and the first output terminal based on a second bias signal.