應用於切換式直流至直流轉換器之高性能互補金氧半控制器

Abstract

本論文針對切換式直流至直流轉換器提出數種創新之高性能控制器。為了要達到快速暫態反應、高效率、穩定運作以及固定的切換頻率等需求，新型控制器的分析與設計在本論文裡有完整的探討，並利用CMOS類比及數位混合式積體電路技術實現控制電路。

現存之自由運行控制電路具有架構簡單和反應極為快速之優點，然而切換頻率不固定，因此無法運用在對電磁干擾敏感的裝置中，同時相關的論文質與量皆相當缺乏，在理論分析方面仍有進一步探討的空間。在本論文中對於常見的兩種自由運行控制型式--漣漪控制和固定開啟時間控制進行理論研究，並針對缺點提出改進的電路架構。 在固定開啟時間控制方面，設計可依據輸入輸出電壓調整開啟時間的電路，因此切換頻率幾乎不隨輸入輸出電壓以及負載電流變動。在論文中探討自由運行控制的不穩定現象，容易被回授信號上的雜訊干擾，因此提出創新的補償電路，可改善頻率響應以及雜訊免疫能力，利用內建積分器產生的斜坡信號用來觸發比較器，具有良好的雜訊免疫能力，可以達到穩定且快速的動作。控制電路利用1微米的互補式金氧半導體積體電路技術來實現，包含輸入輸出接腳的面積為5.2毫米平方，實驗結果顯示暫態反應十分快速，在輸入電壓5伏特，輸出電壓2.476伏特，負載電流10毫安培至3安培的情況下，效率可達86 %至93 %，負載穩壓度和線穩壓度分別為0.032 %/A和0.034 %/V，均優於傳統電壓模式和電流模式的脈寬調變控制方式。

在漣漪控制方面，提出了嶄新的方法，利用相鎖迴路調整延遲，用以鎖定切換頻率，並針對buck和boost兩種功率級分別提出電壓模式與電流模式之漣漪控制器。穩態反應分析、輸出電壓電流轉換函數、切換頻率函數以及頻率響應函數在論文中有推導及分析，根據頻率響應設計出補償網路，分析漣漪控制之各種特性。同時，將切換頻率與延遲的關係線性化之後，可得到一個線性模型，根據此模型，我們可以設計迴路參數和分析相鎖迴路的穩定度。穩壓器電路經由SPICE模擬，buck穩壓器在輸入20伏特輸出1.5伏特的情況下，穩態切換頻率鎖定300 kHz，負載穩壓度和線穩壓度分別為0.0046 %/A和0.028 %/V；boost穩壓器在輸入2.4伏特輸出3.3伏特的情況下，穩態切換頻率鎖定300 kHz，負載穩壓度和線穩壓度分別為0.96 %/A和0.75 %/V，其他模擬結果也包含在本論文內。

傳統之類比式控制器存在調整困難，容易隨製程參數與外在環境漂移之缺點，數位式控制器則受限於電路數量較多與成本較高，針對此一問題，提出一種混合式控制電路，利用比例式電流回授技術加速電源穩壓器之暫態反應，配合特別電路設計，簡化類比數位轉換與數位運算電路，具有架構簡單與高性能之優點，且容易調整控制參數。一般數位類比混合電路多利用電晶體等級的模擬分析系統的時域反應，在本論文中利用行為模型模擬系統的時域反應，可以大幅減少模擬的時間。控制電路利用0.6微米的互補式金氧半導體積體電路技術來實現，包含輸入輸出接腳的面積為1.8乘1.8毫米平方。當輸出電流由2安培增加至20安培時，輸出電壓最多降低150毫伏，並於100微秒內回到靜態容忍的界線內，大電流暫態反應符合嚴格的電源需求，並且與模擬的結果相符。

Several high performance controllers for switching-mode DC–DC converter are proposed. In order to achieve fast transient response, high efficiency, stable operation, and low switching noise, analysis and circuit design of the controllers are comprehensively investigated in this dissertation. Controllers are realized by CMOS analog and digital mixed-mode integrated circuits techniques.

Free-running control is the simplest among all control topologies of switching power supply. However, the switching frequency depends on the operating conditions and power filters. Thus, the use is limited in noise sensitive devices. Besides, only few related literatures provide analytical insights into this kind of control. Two common free-running control topologies, ripple control and constant on-time control, are investigated. Circuits architectures are proposed to improve these controllers. Switching frequency of the constant on-time regulator can be also stabilized by adjusting the on time according to input and output voltages. Unstable operation of free-running control due to noise on feedback signal is discussed. A novel compensation circuit is proposed to improve the frequency response and noise immunity of constant on-time control. This compensation circuit uses a built-in integrator to generate a ramp signal to trigger the comparator. Therefore, it is less susceptible to noise. Stable operation and fast response are obtained. The proposed control circuits are realized in a 1 um CMOS technology with area of 5.2 mm^2 including the I/O pads. Experimental results showed fast response during load and line transients. Efficiency from 86 % to 93 % is obtained over a load range from 10 mA to 3 A under 5 V input voltage and 2.476 V output voltage. The load and line regulations are 0.032 %/A and 0.034 %/V that are superior to conventional current-mode and voltage-mode PWM control.

Switching frequency of the ripple control regulator can be synchronized by a novel method that uses a phase-locked loop to lock the switching signal with an input clock. Voltage-mode and current-mode control circuits are presented for the buck and boost power stages, respectively. Both steady-state response and small-signal model are discussed. Derived transfer functions are useful for designing the control loop and compensation network. By taking linearization of the relationship of switching frequency and delay, a linear model is obtained for loop parameter design and PLL stability analysis. The proposed regulators were simulated in transistor level using SPICE. Input voltage and output voltage are 20 V and 1.5 V respectively for the buck regulator. During the steady state, the switching frequency was locked at 300 kHz. Load regulation is 0.0046 %/A and line regulation is 0.028 %/V. Input voltage and output voltage are 2.4 V and 3.3 V respectively for the boost regulator. During the steady state, the switching frequency was locked at 300 kHz. Load regulation is 0.96 %/A and line regulation is 0.75 %/V. More simulation results are also shown in this dissertation.

Analog controllers are sensitive to noise, process, temperature and component variations. Tuning these controllers is quite complicated as well. The uses of digital controllers are limited by their complex circuits and higher cost. In this thesis, the proportional current feedback technique is proposed to accelerate transient response of the voltage-mode switching regulators. With this technique, the complexity of analog-to-digital conversion circuits and digital computation circuits is greatly reduced. Performance can be easily tuned by adjusting the parameters. Instead of transistor-level simulation, a Matlab behavior model is build to simulate time-domain system response. Fast and accurate results can be obtained from this model. The proposed control circuits are realized in a 0.6 um CMOS technology with area of 1.8×1.8 mm^2 including the I/O pads. Experimental results showed the output voltage dropped 150 mV and recovered to static tolerance in 100 us during a load transient from 2 A to 20 A. The performance of the regulator met strict requirements and verified the simulation results.