臺灣博碩士論文加值系統

摘要

在現今的影像科技產業中，液晶顯示器(Liquid Crystal Display monitor) 異軍突起，產量越來越高，也就是說有越來越多的人使用LCD的產品。因為高頻的要求及整體組裝的品質，時脈及影像訊號所產生出來的電磁波干擾在LCD 顯示器中變得常見，也之所以如此，解決LCD 顯示器的電磁波方法也變得日益重要。在這篇的論文中，運用了各種不同的方法，例如: 接地(grounding)、遮蔽(shielding)、鐵心(ferrite core)、吸波材 (absorbing material)和電路佈線(layout)等等;並會提到頻移(frequency shifting)和展頻(spread spectrum)的技術。在這論文中，我也將會討論上述的各種方法的原理，並將各方法應用於一個有問題的LCD顯示器中，我們將會比較出其中最有效的方法並加以改善，以求最佳的解決方案。
在這篇論文中，我們將提出以下的貢獻：
(1) 我們提出幾個更有效的方法來改善電磁波的強度並降低成本(23吋HP monitor)
(2) 我們提出兩個有效的方法(frequency shifting 和spread spectrum)，這兩個方法可以不花任何額外成本且有效的降低電磁波強度(20吋 Philips monitor)。
最後，我們相信這些做出來的最後結果可以有效的解決電磁波干擾的問題，並可減少資源及成本的浪費。

Abstract

In this thesis, it is based on EMC theories to make efficient improvements such as signal grounding, system shielding, PCB layout, and noise filtering have been proposed in order to reduce the electromagnetic interference. Furthermore, the methods without external EMI materials such as frequency shifting and spread spectrum are proposed to reduce EMI level and product cost as well. Finally, the comparison is made for practical consideration.
In the proposed scheme, at first, we offer couples of ways to soften EMI problem, such as grounding between control board and panel frame; putting a ferrite core on the LVDS twisted-pair wires between panel and scaler connector; and a better grounding between panel frame and super ergo base. Basically, all methods can provide a good solution to reduce EMI problem. However, in order to reduce product cost at the same time, we attempt to find an optimized way to compromise EMI problem solving over system cost. Because of the above consideration, firstly, we try to use solutions without any external EMI material since it is much less costly. For example, shift vertical refresh rate of input signal from 60 Hz to 75Hz sufficiently for avoid trouble point. This measure can shift the problematic frequency (shown on the EMI receiver) to a different frequency. For another example, the spread spectrum technique is applied to disperse energy generated from the problematic frequency to reduce EMI level. These methods form a practical way will lower down EMI level without much extra system cost.
In this thesis, the following contributions are gained:
1. Base on our knowledge, we use many methods to lower down EMI level radiated from TFT-LCD monitor such as signal grounding, system shielding, EMI absorber and ferrite core and noise filtering. We suggest an efficient way for reducing EMI level. That uses the smallest effort to get an impressive outcome.
2. We provide two approaches, which are frequency shifting and spread spectrum without extra cost for EMI reduction. These methods have not been used in this monitor yet and will not influence video quality and performance as well.
We strongly believed that the results of our study would be very helpful in practical applications. Also, it is quite feasible for the future design too.

Contents

Abstract……………………………………………………………..I

List of Figures………………………………………………………III

List of Tables……………………………………………………….V

Chapter 1. Introduction……………………………………………..1
1.1 Introduction……………………………………………………..1
1.2 The Proposed Schemes…………………………………………4
1.3 Organization of This Thesis…………………………………….5

Chapter 2. Overview of Electromagnetic Interference……………..6
2.1 Basic Concepts of EMI…………………………………………6
2.2 Theory of Grounding…………………………………………...12
2.2.1 Single-Point Ground…………………………………...13
2.2.2 Multi-Point Ground……………………………………14
2.3 Absorbing Material……………………………………………..15
2.3.1 Absorber……………………………………………….15
2.3.2 Ferrite Core……………………………………………16
2.4 Frequency Shifting……………………………………………..18
2.5 Theory of Spread Spectrum…………………………………….20
2.6 Theory of Layout……………………………………………….23

Chapter 3. Experiments and Comparison…………………………..30
3.1 Experiments…………………………………………………….30
3.1.1 23” HP Monitor………………………………………..31
3.1.1.1 EMI by Using Grounding…………………….34
3.1.1.2 EMI by using Ferrite Core & Absorber………39
3.1.2 20” Philips Monitor ……………………………………42
3.1.2.1 EMI by Using Spread Spectrum……………...45
3.1.2.2 EMI by Using Frequency Shifting……………51
3.2 Comparisons……………………………………………………53
3.2.1 Comparison of 23” HP Monitor……………………….53
3.2.2 Comparison of 20” Philips Monitor…………………...54

Chapter 4. Conclusion and Future Research……………………….56

References………………………………………………………….57


List of Figures

Figure 1.1 Diagram of Electromagnetic Compatibility ……………….3
Figure 2.1 Demonstration of radiated and conducted emission, and
susceptibility to noise ……………………………………...8
Figure 2.2 EMI paths ………………………………………………….9
Figure 2.3 Diagram of electronic and magnetic waves.………………11
Figure 2.4 Relationship between wave impedance and distance……. 11
Figure 2.5 Multipoint grounding……………………………………...15
Figure 2.6 Diagram of the absorbing material………………………..16
Figure 2.7 Equivalent circuit at high frequency……………………....17
Figure 2.8 Characteristic of ferrite core material……………………..17
Figure 2.9 Impedance of characteristic……………………………….18
Fig 2.10 Block Diagram of Programmable Spread Spectrum………...21
Figure 2.11 Flow chart of PFD state condition……………………….23
Figure 2.12 Intensity of magnetic field of different wiring configurations.…………………………………………..27
Figure 3.1 Instruments………………………………………………..31
Figure 3.2 Antennas and turn table in the chamber…………………..31
Figure 3.3 EMI of 23”HP without solution…………………………..32
Figure 3.4 Character of letter H……………………………………...33
Figure 3.5 Pixel clock and waveform………………………………..33
Figure 3.6 EMI of 23”HP with H-Pattern off………………………..33
Figure 3.7 Ground wire b/w control board and panel………………..35
Figure 3.8 Conductive gasket b/w panel ground and LVDS
connector…………………………………………………36
Figure 3.9 Conductive gasket b/w panel and LVDS connecter……...36
Figure 3.10 Conductive tape b/w the panel and the base…………….38
Figure 3.11 43.3 cm conductive tape………………………………...38
Figure 3.12 23.5cm conductive tapes………………………………..39
Figure 3.13 Ferrite core on LVDS twisted-paired wire……………...40
Figure 3.14 Absorber on scaler IC…………………………………...41
Figure 3.15 Absorbing material on scaler IC………………………...41
Figure 3.16 Absorbers on scaler and transmitter ICs………………...42
Figure 3.17 Absorber on both scaler and transmitter IC……………..42
Figure 3.18 Original waveform of frequency 154.36 MHz………….43
Figure 3.19 Solution with an absorber on Tcon IC…………………..45
Figure 3.20 Absorbers on Tcon and buffers………………………….45
Figure 3.21 spread spectrum value of 9 …………………………...47
Figure 3.22 spread spectrum value of 11 ………………………….48
Figure 3.23 Spread spectrum value of 13 …………………………49
Figure 3.24 spread spectrum 7 with a ferrite core…………………50
Figure 3.25 spread spectrum 9 with a ferrite core…………………50
Figure 3.26 Frequency shifting………………………………………53


List of Tables

Table 2.1 Product classification of 3C…………………………………6
Table 2.2 Specification of panel……………………………………....19
Table 2.3 Timing table of panel...…………………………………….19
Table 3.1 7 & 9 in binary ……………………………………………46
Table 3.2 spread Spectrum Control...…………………………………46
Table 3.3 11 in binary……………………………………………........47
Table 3.4 13 in binary…………………………………………………48
Table 3.5 Specification of panel………………………………………52
Table 3.6 Specification of panel clock and frame rate………………..52
Table 3.7 Timing table of panel………………………………………52
Table 3.8 Comparison for 23” HP monitor…………………………...54
Table 3.9 Comparison for 20” Philips monitor……………………….55

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