Shift Register Multi-Signal Generation for OLED Displays
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Solution Overview
Problem
Existing shift registers for flat panel display devices, particularly those using oxide thin film transistors, face challenges with leakage currents due to negative threshold voltages, which affect the output of gate pulses and limit the generation of multiple signals required for OLED display devices, and are difficult to operate with extended signal output times.
Innovation Solution
A shift register design that includes a start signal unit, end signal unit, and multiple stages using dual pull-down TFTs to manage threshold voltage shifts, allowing for the generation of multi-signals by employing two start pulse signals and two clock signals to control the output signals effectively, thereby extending the output time and preventing threshold voltage shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If oxide TFTs with negative threshold voltage are used in the shift register, then the manufacturing process is simplified and manufacturing cost is reduced, but leakage current occurs when gate voltage is 0V, preventing normal gate pulse output
Solution Approach 1:
The shift register is divided into multiple stages, with each stage independently generating gate pulses through controlled threshold voltage shifts. This segmentation allows each stage to manage leakage current locally while maintaining overall system reliability for normal gate pulse output.
Solution Approach 2:
The invention dynamically changes the threshold voltage parameter of oxide TFTs from negative to positive through controlled voltage application. By shifting the threshold voltage to a positive value, the TFTs operate in a mode that eliminates leakage current at 0V gate voltage while maintaining the simplified manufacturing process using existing equipment.
2Reliability
If the threshold voltage of oxide TFTs is shifted to positive voltage to eliminate leakage current, then leakage current is reduced, but driving power increases
Solution Approach 1:
The invention applies periodic voltage pulses to shift the threshold voltage of oxide TFTs temporarily to positive values only when needed for gate pulse generation. After completing the gate pulse output, the threshold voltage returns to negative, reducing leakage current. This periodic action eliminates continuous power consumption associated with maintaining positive threshold voltage, thereby reducing overall driving power while maintaining reliability.
3Device complexity
If a 1HT driving scheme layout is used for the shift register, then the layout is simplified, but the output signal timing cannot be adjusted and signal cannot be output for extended periods
Solution Approach 1:
The invention introduces dynamic control mechanisms that allow the shift register to adapt its output signal timing based on operational requirements. By implementing controllable threshold voltage shifting and multi-stage configuration, the system can extend signal output duration beyond the limitations of fixed 1HT layouts while maintaining layout simplicity. The dynamic adjustment of voltage levels enables flexible timing control without increasing layout complexity.
Data Source
AI summary
A shift register for flat panel display devices includes a start signal unit configured to control a start of an output signal, an end signal unit configured to control an end of the output signal, and a plurality of stages configured to increase the output signal to a high-level driving voltage according to a signal supplied from a first node connected to the start signal unit, and decrease the output signal to a low-level driving voltage according to a signal supplied from a second node connected to the end signal unit. Each of the plurality of stages generates multi signals for diving a pixel circuit of a display device.