液晶顯示器與有機發光二極體顯示器為現今主流顯示技術，液晶顯示器製程技術成熟且成本低，但其需一背光板提供光源，導致面板厚度提高及對比度下降；有機發光二極體顯示器具有自發光的特性故對比度高且視角廣，但在長時間操作後其元件容易老化導致發光效率下降，進而縮短顯示器壽命。近年來，為改善現今主流顯示器的缺點以產生高品質之畫面，具有使用壽命長、對比度高及適用於可撓基板特點的次毫米發光二極體被用以做為液晶顯示器之背光板，但次毫米發光二極體之驅動電流高達毫安等級，導致面板整體功率消耗上升及此大電流流經電源線上負載會產生巨大的壓差而使畫面均勻度下降。
針對上述問題，本論文提出四個低溫多晶矽薄膜電晶體製程之脈波寬度調變次毫米發光二極體背光模組，透過補償電晶體之臨界電壓變異及電流流經電源所造成之電壓變異，提高輸出電流均一性及灰階控制能力，並模擬當驅動電晶體的臨界電壓變異0.3 V及電流流經電源所造成之電壓變異0.5 V時的電流變化，驗證輸出電流的均勻度。首先，本論文提出一由十一顆電晶體及兩顆電容組成之脈波寬度調變控制之次毫米發光二極體背光模組，其透過將次毫米發光二極體操作於最佳發光效率點減少面板整體功率消耗，根據模擬結果顯示，輸出電流之誤差皆小於9.96%，且各灰階功率消耗與6T1C電路相比 [24]，皆改善16.09%以上。為更精準地控制各灰階發光時間，本論文利用N型及P型低溫多晶矽薄膜電晶體設計一使次毫米發光二極體快速轉態之背光模組，此背光模組由十個電晶體及三顆電容組成，可透過減少發光路徑上的開關電晶體個數和使次毫米發光二極體操作於最佳發光效率的方式降低功率消耗。根據模擬結果，輸出電流誤差小於9.9%，且與6T1C相比各灰階功耗均改善21.84%以上 [24]。但考慮到產生VSWEEP的成本高，本論文提出一背光模組利用定電流放電方式控制灰階故無需使用VSWEEP訊號，此電路由十二顆電晶體及三顆電容所組成，可透過減少發光路徑上的開關電晶體及將次毫米發光二極體操作於最佳發光效率降低功率消耗，模擬結果證明，輸出電流誤差均在10%以內，且與6T1C電路相比各灰階之功率消耗均下降21.84%以上 [24]。為了精簡電路架構，本論文提出一採用同步式發光之Mini LED背光模組，只需由八顆電晶體及三顆電容構成，此電路之VSWEEP訊號可全面板共用以減少產生VSWEEP訊號之成本，模擬結果證明，此電路之輸出電流誤差均在9.88%以內，並透過發光路徑上無開關電晶體的設計及將次毫米發光二極體操作於最佳發光效率以減少功率消耗，故與6T1C電路相比 [24]，各灰階之功率消耗均降低21.84%以上。根據以上模擬結果驗證本論文所提出之四個脈波寬度調變次毫米發光二極體背光模組均具有高均一度的輸出電流、低功率消耗及精準控制灰階的特色，使其能適用於液晶顯示器之背光板。

Nowadays, liquid crystal displays (LCDs) and organic light emitting diode (OLED) displays have become the mainstream in display technology. LCDs have several advantages such as mature technology and low cost. However, they need a backlight to provide the light source, increasing the thickness and decreasing the contrast ratio of LCDs. In contrast, OLED displays have the advantages of high contrast ratio and wide viewing angle, but the luminance efficiency of OLEDs degrades after long-term operation, shortening the lifetime of OLED displays. To resolve the problems of LCDs and OLED displays for generating the high-quality images, mini light-emitting diodes (Mini LEDs) with high contrast ratio, long lifetime, and suitability of flexible substrate are widely used as the backlight of LCDs. Moreover, the driving currents achieve milliamp levels. Therefore, such large currents will increase the power consumption of displays and suffer from severe current-resistance rise in the VSS line which in turn causes low uniformity of driving currents for images.
To solve the aforementioned problems, this thesis proposes four Mini LED backlight circuits based on LTPS TFTs with pulse width modulation (PWM). By compensating for threshold voltage (VTH) variations of LTPS TFTs and current-resistance rise in the VSS line (VSS I-R rise), the highly uniform driving currents and precise controllability of the gray level can be achieved. The uniformity of the driving currents is verified by the simulation when the VTH of driving TFT varies by 0.3 V and VSS I-R rises 0.5 V. First of all, this thesis proposes a Mini LED backlight circuit that is composed of 11 TFTs and two capacitors to operate the Mini LED at best-luminance-efficacy for reducing the power consumption of displays. According to the simulation results, the relative error rates of the driving currents are less than 9.96%. Compared with the previously developed 6T1C circuit [24], power consumption is improved by more than 16.09% for all gray levels. To more accurately control emission time for each gray level, a Mini LED backlight circuit consisting of ten TFTs and three capacitors is proposed. By using both N-type and P-type LTPS TFTs, the Mini LED is turned on rapidly. Notably, the driving current path has no switch TFT, saving power consumption. The simulated results show that the current error rate is less than 9.9%. Compared with the 6T1C circuit [24], the power consumption of this circuit decreases at each gray level by more than 21.84%. To decrease the complexity of the display system, the thesis proposes a Mini LED backlight circuit comprised of 12 TFTs and three capacitors without using the signal of VSWEEP. This circuit adopts a discharging method with a constant current to control the gray level. Based on the simulated results, the current error of this circuit is less than 10%. The power consumption of the 6T1C circuit is saved by more than 21.84% [24]. To simplify the circuit, this thesis develops a Mini LED backlight circuit utilizing the simultaneous emission (SE) driving scheme, so the structure is only composed of eight TFTs and three capacitors. Furthermore, the applied VSWEEP signal can be shared by the whole panel to decrease the complexity of displays. The output currents of this circuit are uniform after the compensation. Moreover, the power consumption can be successfully diminished by operating Mini LEDs at best-luminance-efficacy point and only using driving TFTs on the driving current path. Simulation results demonstrate that the error rate of the emission current is less than 9.88%. Compared with the 6T1C circuit [24], the power consumption improves to above 21.84%. According to the aforementioned simulation results, all circuits proposed in this thesis that can provide low power consumption, highly uniform driving currents, and precise controllability for each gray level are suitable for use in LCD backlights.

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