Bidirectional Shift Register for Image Display Devices
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Solution Overview
Problem
Bidirectional shift registers used in image display devices face instability in operation due to shifting threshold voltage of switch elements when continuously driven in one direction, affecting the reliability of both forward and backward shift operations.
Innovation Solution
A bidirectional shift register design incorporating a shift register part with cascade-connected unit register circuits, a clock signal generation part, and a trigger signal generation part, which includes forward and backward direction set and reset terminals, and uses double-gate structure transistors to stabilize the operation by managing the potential levels and timing of trigger signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If bidirectional shift register continuously drives in one direction, then shift operation can be performed, but threshold voltage of switch elements shifts causing operation instability
Solution Approach 1:
The patent implements periodic action by alternating the driving direction of the shift register between forward and backward directions in regular intervals. This periodic direction switching prevents continuous unidirectional operation that causes threshold voltage drift, thereby maintaining operation stability while preserving shift functionality.
Solution Approach 2:
The patent applies parameter changes by dynamically switching the driving direction parameter of the shift register. By changing the operation direction (forward/backward) as a controllable parameter, the system prevents threshold voltage accumulation in one direction, thus resolving the instability issue while maintaining productive shift operations.
2Adaptability or versatility
If frame memory is provided to change image data sequence, then display direction can be changed, but device structure becomes complex
Solution Approach 1:
The patent applies universality by making the shift register capable of performing multiple functions: it can shift data in both forward and backward directions directly, eliminating the need for separate frame memory structures. This multi-functional approach achieves display direction flexibility while keeping the device structure simple.
Solution Approach 2:
The patent uses inversion by reversing the conventional approach of using frame memory to change display direction. Instead, the shift register itself is designed to shift in opposite directions (backward direction capability), thereby achieving display direction flexibility through the inverse method of direct bidirectional shifting rather than through external memory buffering.
Data Source
AI summary
A bidirectional shift register capable of performing a stable shift operation in both directions and an image display device using the same are provided. In forward shift operation, when reference point N1 is at H level, (n+4)-th unit register circuit as a rear stage of the bidirectional shift register outputs pulse G(n+4) in synchronization with clock pulse V(n+4) inputted to (n+4)-th unit register circuit. A backward direction trigger signal VSTB is generated not only at the time of start of backward shift, but also, for example, in period (time t4 to t5) of one-phase clock immediately after G(n+4) is outputted in vertical blanking interval of the forward shift. The backward direction trigger signal VSTB is inputted to gate of a transistor provided to set reference point N1 of (n+4)-th unit register circuit to H level at the time of start of the backward shift.