具線路響應暫態補償之模擬電流模式控制升壓轉換器之建模與設計

Abstract

主動矩陣有機發光二極體（AMOLED）已成為手機顯示器的主流。AMOLED顯示器需要三個電源來運作，其中之一是通過升壓轉換器提供的。然而TDMA通訊協議會造成顯示器的輸入電壓的下降，這會導致顯示器發生閃頻的現象。因此，AMOLED的功率轉換器需要嚴格的線性瞬態響應。立錡科技提出了兩種Emulated-Current-Mode（ECM）控制架構的線性瞬態響應補償技術，分別是電感電流峰值補償技術和輸入前饋補償技術。通過添加這兩種技術，可以最小化PWM比較器輸入端的電壓變化，從而大大減少線性瞬態期間的輸出電壓變化。然而，新的控制方案缺乏用於預測和分析多回路控制系統的小信號模型。在現有的固定頻率控制架構中，Ridley的模型在切換頻率之前具有足夠的精度，並且可以通過更簡潔易懂的模型來構建，因此本文選擇使用Ridley的模型作為模型的基礎。提出的小信號模型不僅可以用於設計電壓反饋補償，還可以通過模型來改善線性瞬態響應。通過立錡科技提供的晶片進行驗證，測量結果顯示該模型的預測結果和改善後的瞬態響應有約30％的降低。

Active matrix organic light-emitting diodes (AMOLED) have become the mainstream in cellphone displays. AMOLED displays require three power sources, one of which is provided through a boost power converter. If the power supply voltage of the display deviates due to the change in the input voltage, display screen flickering issue occurs. Therefore, stringent line transient response is required for AMOLED’s power converters. Richtek technologies proposed two line transient response compensation technologies for the Emulated-Current-Mode (ECM) control architecture, namely the inductor current peak compensation technology and the input feedforward compensation technology. By adding these two technologies, the voltage change at the input of the PWM comparator is minimized, thereby greatly reducing the output voltage change during line transients. However, the new control scheme lacks models to predict and analyze the small-signal characteristics of this multi-loop control system and to improve the transient response. In the existing fixed-frequency control architecture, Ridley's model currently has sufficient accuracy before switching frequencies and can be constructed through a more concise and easy-to-understand model, so this paper chooses to use Ridley's model as the basis for the new model. The proposed small-signal model can not only be used to design voltage feedback compensation but also can improve the transient response of the line through the model. The improvement result is verified by the chip provided by Richtek technologies. The measurement shows that the predicted results of this model and the improved transient response of undershoot and overshoot about 30%.