LCD Multiplexer Feed-Through Compensation Circuit
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Solution Overview
Problem
Liquid crystal displays (LCDs) face significant feed-through voltage drops due to increased channel widths in multiplexers, necessitating additional compensation circuits to recover the lost voltage, which complicates the design and increases power consumption.
Innovation Solution
The implementation of a multiplexer feed-through compensation circuit with parallel-connected switches and carefully timed control signals to manage the switching of video signals across data lines, reducing voltage drops by optimizing the timing of switch activation and deactivation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the channel widths of the switches are increased to provide better charging capability for the data lines, then the charging capability is improved, but the feed-through voltage drops increase
Solution Approach 1:
The patent divides each multiplexer channel into two separate switches (first switch and second switch) connected in series between the signal line and data line. This segmentation allows independent control of each switch through separate control signals, enabling the first switch to be turned off earlier than the second switch to compensate for feed-through voltage drops while maintaining adequate charging capability through properly sized channel widths.
Solution Approach 2:
The patent applies preliminary action by turning off the first switch before turning off the second switch during the multiplexer operation cycle. This timing sequence allows the first switch to stop charging the data line early, preventing excessive voltage drops before the second switch is deactivated. The staggered switching timing compensates for the feed-through effect without requiring larger channel widths.
2Reliability
If additional compensation circuits are added to recover feed-through voltage drops, then the voltage recovery is improved, but the device complexity increases
Solution Approach 1:
The patent makes the existing multiplexer switches serve dual functions: they perform their primary function of selectively transmitting video signals to data lines, and simultaneously function as compensation elements for feed-through voltage drops through staggered switching. The first and second switches in each channel work together to both route signals and compensate for voltage drops, eliminating the need for separate compensation circuits and reducing overall device complexity.
Solution Approach 2:
The multiplexer's own switches perform the compensation function for themselves through the staggered switching mechanism. The first switch's early turn-off automatically compensates for the feed-through voltage drops generated by the second switch's later turn-off, allowing the system to self-correct without external compensation circuits. This self-service approach simplifies the overall display device architecture.
Data Source
AI summary
In one aspect, an LCD includes a display panel with a pixel matrix having M scan lines and N data lines, and a multiplexer feed-through compensation circuit, which includes P signal lines for providing P video signals, P multiplexers, and K pairs of control lines providing K pairs of control signals. Each multiplexer is electrically coupled to a corresponding signal line and has K channels. Each channel includes first and second switches parallel-connected between the signal line and a corresponding data line for selectively transmitting the video signal to the corresponding data line. Each pair of control lines is respectively electrically coupled to the first and second switches of a corresponding channel of each multiplexer. Each pair of control signals are configured such that a time turning off one of the first and second switches is earlier than that turning off the other switch.