Bidirectional Shift Register Pre-Charge Circuit
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Solution Overview
Problem
The reliability of bidirectional shift registers in liquid crystal displays (LCDs) is compromised due to stress effects on transistors from constant on-off cycles, leading to abnormal operations and reduced reliability, especially when dummy shift registers are omitted to reduce fabrication costs.
Innovation Solution
A bidirectional shift register apparatus is designed with N shift registers connected in series, including pre-charge, pull-up, and pull-down units, which receive specific signals to generate and control scan signals, eliminating the need for dummy shift registers and reducing stress on transistors by optimizing signal timing and voltage control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dummy shift registers are added to protect against stress effects, then reliability of shift registers is improved, but device complexity and fabrication cost increase
Solution Approach 1:
The pre-charge unit pre-charges the node before the pull-up unit activates the scan signal, ensuring that when the scan signal transitions, the node is already in a charged state. This preliminary action prevents the stress effect that would otherwise occur during constant on-off cycles of dummy shift registers, maintaining reliability without adding dummy registers.
Solution Approach 2:
The pre-charge unit acts as an intermediary between the clock signal and the scan signal generation. It receives the clock signal and prepares the node by charging it before the actual scan signal activation, thereby mediating the stress effect and eliminating the need for dummy shift registers while maintaining system reliability.
2Reliability
If dummy shift registers are added to protect against stress effects, then reliability of shift registers is improved, but fabrication cost increases
Solution Approach 1:
The pre-charge unit performs preliminary charging of the node using the clock signal before scan signal activation. This eliminates the need for dummy shift registers, thereby reducing fabrication complexity and cost while maintaining shift register reliability through proper timing control.
Solution Approach 2:
The shift register apparatus uses its own clock signal to charge the node through the pre-charge unit, rather than requiring external dummy shift registers. This self-service approach eliminates additional fabrication steps and reduces manufacturing cost while maintaining reliability.
3Device complexity
If dummy shift registers are omitted to reduce fabrication cost, then device complexity and fabrication cost are reduced, but reliability of shift registers deteriorates due to stress effects
Solution Approach 1:
The pre-charge unit charges the node in advance using the clock signal before the pull-up unit activates the scan signal. This preliminary charging action maintains node voltage stability without requiring dummy shift registers, thereby preserving reliability while reducing device complexity.
Solution Approach 2:
The pre-charge unit serves as an intermediary that uses the clock signal to prepare the node state before scan signal activation. This mediation eliminates the stress effect on transistors that would otherwise require dummy shift registers, maintaining reliability without the added complexity.
4Reliability
If pre-charge unit charges node before scan signal activation, then stress effect on transistors is reduced and reliability is improved, but device complexity increases
Solution Approach 1:
The pre-charge function is merged into the existing shift register apparatus structure, sharing components and signal paths with the pull-up and pull-down units. This integration adds minimal complexity while achieving the reliability benefit of reduced stress effects through proper timing control.
Solution Approach 2:
The pre-charge unit utilizes the existing clock signal for its charging function, making the clock signal serve dual purposes: clocking the shift register operation and charging the node to prevent stress effects. This multi-functionality reduces the need for separate dedicated circuits, minimizing added complexity.
Data Source
AI summary
An LCD and bidirectional shift register apparatuses thereof are provided. One of the bidirectional shift register apparatuses includes Nth shift registers. An ith shift register includes a pre-charge unit, a pull-up unit and a pull-down unit. When i is greater than or equal to 3 and less than or equal to N−2, the pre-charge unit receives outputs of an (i−2)th and an (i+2)th shift register. When i is equal to 1 or 2, the pre-charge unit receives a first start pulse signal and the output of the (i+2)th shift register. When i is equal to (N−1) or N, the pre-charge unit receives a second start pulse signal and the output of the (i−2)th shift register. The pre-charge unit outputs a pre-charge signal. The pull-up unit outputs a scan signal. The pull-down unit receives the pre-charge signal to control a level of the scan signal.