Level Shift Circuit for Display Devices Resistant to Transistor Variations
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Solution Overview
Problem
Conventional level shift circuits for display devices, such as liquid crystal display devices and OLEDs, are susceptible to variations in transistor characteristics, leading to operational instability and high power consumption due to leakage currents.
Innovation Solution
A level shift circuit design incorporating a first and second switch, each turning on/off based on specific voltage thresholds, along with capacitors and a voltage setting circuit to manage node voltages, ensuring stable operation and minimizing leakage currents by setting nodes in a floating state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a current mirror circuit is used for level shifting, then the circuit can perform signal level conversion, but the circuit operation becomes susceptible to variations in transistor characteristics
Solution Approach 1:
The patent introduces a voltage setting circuit as an intermediary component that generates reference voltages for the switch thresholds. This mediator decouples the switch operation from direct dependence on transistor characteristic variations, as the reference voltages are independently set and stable, thereby improving operational reliability while reducing sensitivity to transistor parameter changes
Solution Approach 2:
The patent changes the operational parameters by using voltage threshold comparison instead of direct current mirroring. The switches are controlled by comparing node voltages against stable reference voltages generated by the voltage setting circuit, rather than relying on matched transistor characteristics. This parameter change from current-based to voltage-based control reduces sensitivity to transistor variations
2Loss of energy
If conventional level shift circuit components are used, then the circuit can function, but power consumption increases due to leakage currents
Solution Approach 1:
The patent extracts and removes the sources of leakage currents from the conventional current mirror circuit configuration. By replacing the continuous current-mirroring transistors with voltage-controlled switches that operate in a more controlled manner, the harmful leakage paths are eliminated, thereby reducing power consumption while maintaining the level-shifting function
Solution Approach 2:
The patent converts the potential harm of leakage currents into a benefit by using voltage setting circuits that establish stable reference levels. These reference voltages enable the switches to operate with precise threshold control, minimizing unintended current flow while the voltage stabilization process itself becomes useful for reducing power consumption through controlled operation
3Ease of manufacture
If transistor characteristics vary, then manufacturing tolerances are accommodated, but circuit operation becomes unstable
Solution Approach 1:
The voltage setting circuit acts as an intermediary that stabilizes the circuit operation against transistor characteristic variations. By providing externally controllable reference voltages that are independent of transistor parameters, the mediator allows manufacturing tolerances to be accommodated while maintaining stable operation, as the reference voltages compensate for component variations
Data Source
AI summary
A level shift circuit, a shift register, and a display device in which circuit operation is resistant to influence of variations in characteristics of elements such as transistors. The level shift circuit, includes a first switch turning on or off in accordance with a voltage of a first node, switching ON and OFF when the voltage is a first threshold value, and outputting a first voltage when ON state; a second switch turning on or off in accordance with the voltage of a second node, switching ON and OFF when the voltage is a second threshold value, and outputting a second voltage when ON state; a first capacitor receiving a first input signal at one terminal and connected at the other terminal to the first node; a second capacitor receiving a second input signal at one terminal, and connected at the other terminal to the second node; and a circuit for setting the voltage of the first node at the first threshold value and setting the voltage of the second node at the second threshold value in a predetermined period and setting the first node and the second node in a floating state after the predetermined period.