Current Sample-and-Hold Circuit for Faster Display Demultiplexing

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Solution Overview

Problem

Conventional current demultiplexers in current-driven display devices, such as AMOLEDs, face challenges in reducing the number of data drivers while maintaining high resolution, as they require longer data writing times, which is difficult to achieve with conventional demultiplexers.

Innovation Solution

A sample-and-hold circuit with an input terminal in current source format and an output terminal in current sink format is used, employing transistors and switches to sample and hold data current, allowing for efficient demultiplexing without reducing data writing time, and can be used with driver ICs having current sink output terminals.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If conventional demultiplexers are used to reduce the number of data drivers, then the number of data drivers is reduced, but the data writing time increases

Engineering Contradiction:

Improvenumber of data driversVSAvoiddata writing time

Core Design Contradiction:

Quantity of substanceVSLoss of time

Solution Approach 1:

The sample-and-hold circuit performs preliminary sampling of the data current during a first time period before the demultiplexing operation. This pre-sampled data is then held and used during the demultiplexing phase, allowing the pixel to be driven without requiring the full data writing time to occur during the active display period, thus resolving the contradiction between reducing driver count and maintaining writing speed

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The circuit separates the data writing process into distinct time periods: a sampling period where data is captured, a holding period where data is maintained, and a display period where the pixel is driven. This temporal segmentation allows the data to be prepared in advance and reused across multiple pixel columns, reducing the number of drivers needed while maintaining high resolution

Inventive Principle:

Principle #1Segmentation

2Ease of manufacture

If driver ICs with current sink output terminals are used, then production costs are reduced and power consumption decreases, but compatibility with current source format pixels is lost

Engineering Contradiction:

Improveproduction costVSAvoidcompatibility with pixel formats

Core Design Contradiction:

Ease of manufactureVSAdaptability or versatility

Solution Approach 1:

The sample-and-hold circuit acts as an intermediary between the current sink output driver and the current source pixel. The driver outputs current in sink format, the sample-and-hold circuit processes and converts it, and the pixel receives data in source format. This intermediary conversion enables compatibility between mismatched formats, allowing cost-effective current sink drivers to work with standard current source pixels

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS7636075B2Current sample and hold circuit and method and demultiplexer and display device using the same

Publication Date: 2009.12.22 SAMSUNG DISPLAY CO LTD

AI summary

A data current sample and hold circuit having an input terminal of a current source type and an output terminal of a current sink type. The sample and hold circuit includes a first transistor, a capacitor, and a plurality of switches, for sampling and holding the data current sunk to an output terminal of a data driver. When the sampled and held data current is applied to the data line, the data current is sunk to an output terminal of the sample and hold circuit. The sample and hold circuit is used together with a data driver having an output terminal of the current sink type.