Shift Register Waveform-Shaping Unit for LCD Feed-Through Reduction
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Solution Overview
Problem
The feed-through effect in shift registers used in liquid crystal display (LCD) driving circuits causes image flicker due to parasitic capacitors, degrading display quality by pulling down pixel voltages with each falling edge of square waveform gate signals.
Innovation Solution
A shift register design incorporating a plurality of shift register units with a clock signal input terminal, starting signal input terminal, shift signal output terminal, and feedback terminals, featuring a pull-up unit, pull-down unit, control unit, and waveform-shaping unit to manage clock signals and control the timing of shift signals, reducing the feed-through effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If square waveform gate signals are used to write data signals to pixel units, then the shift register can provide periodic pulse signals for scanning, but the falling edge of each pulse causes pulling down of pixel voltages due to parasitic capacitors, resulting in feed-through effect and image flicker
Solution Approach 1:
The patent applies preliminary anti-action by introducing a compensation signal before the feed-through effect occurs. The compensation signal is generated in advance to counteract the voltage drop caused by parasitic capacitors, thereby preventing the harmful effect rather than correcting it after occurrence
Solution Approach 2:
The patent uses an intermediary approach by introducing a compensation signal as a mediator between the gate signal and the pixel voltage. This compensation signal acts as an intermediate element that offsets the harmful coupling effect of parasitic capacitors, allowing the square waveform gate signals to be used without causing feed-through effect
2Speed
If square waveform gate signals are used for scanning, then the circuit operation is simple and fast, but the display quality is degraded due to image flicker caused by feed-through effect
Solution Approach 1:
The compensation signal serves as an intermediary that bridges the conflict between fast square waveform signals and display quality. It mediates the interaction by canceling out the harmful effects, allowing high-speed operation without compromising display reliability
Solution Approach 2:
The patent implements feedback by using the output signal to generate a compensation signal that feeds back to counteract the feed-through effect. This feedback mechanism ensures that the harmful effects of square waveform signals are continuously compensated, maintaining display quality at high speeds
Data Source
AI summary
A shift register for an LCD display includes N shift register units. Each shift register unit outputs a shift signal. An Nth shift register unit includes a waveform-shaping unit electrically coupled to an shift signal output terminal of the Nth register to perform a waveform-shaping operation on the Nth shift signal according to the (N+1)th shift signal output by an (N+1)th shift register, to reduce the feed-through effect which causes display flicker.