傳統的切換式轉換器使用固定開關頻率的PWM(Pulse Width Modulation)做為控制電路，可以達到高效率，但其控制方法容易在輸出上看到固定頻率的漣波電壓。對於較雜訊敏感的RF電路或混訊電路而言，這些漣波與其產生的高次項諧波雜訊容易耦合到基板及供應線上，影響此類電路。因此本篇論文以一離散時間的三階串接積分器回授型三角積分調變器(Discrete Time 3rd Order CIFB Delta Sigma Modulator)當作控制電路的降壓轉換器。
為了達到低雜訊影響的降壓轉換器，利用三角積分調變器的超取樣及雜訊移頻特性，減少頻寬內的開關雜訊並將其移至高頻。將調變器的輸出結果透過一位元的量化之後，作為控制Power-MOS的開關訊號。量化器調變結果為一頻率不固定且佔空比不固定的訊號，與傳統型的降壓轉換器相比，可降低在輸出看到的雜訊，且頻譜上不會存在明顯的開關頻率。
本篇論文晶片使用TSMC 0.18um製程，操作電壓為3.3V，降壓轉換器的輸入電壓範圍為3V-3.6V，輸出電壓範圍為1V-3V，取樣頻率為4.95MHz，最大可承受負載電流為800mA，頻譜展示開關頻率在輸入電壓3.3V輸出電壓1.8V時達到-85.32dBm，在輸入電壓3.6V輸出電壓3V且負載電流為200mA時測得最高效率為89.068%，晶片總面積2.76 mm2。

The traditional switching converter uses a fixed switching frequency PWM (Pulse Width Modulation) as the control circuit, which can achieve high efficiency, but the converters output usually possesses a ripple at the switching frequency. For noise-sensitive RF circuits or mixed circuits, these ripples and their high-order harmonics easily coupled to the substrate and supply lines, affecting the performance of such circuits. Therefore, in this thesis, a discrete time 3rd order cascade integrator feedback(CIFB) delta-sigma modulator (DSM) is used in the buck converter as its control circuit.
To design a low noise buck converter, oversampling and noise shaping characteristics of a DSM are employed to reduce the in-band switching noise by moving it out of bandwidth. After the 1 bit quantizer, it is used as a switching signal for the power-MOS. The result that the control signal has is a variable frequency and a variable duty cycle. Compared with traditional buck converters, the noise seen at the output can be reduced, and its output spectrum has a relative small tone at the clock frequency.
The chip is fabricated using the TSMC 0.18um process, .The nominal operating voltage is 3.3V, The input voltage range of the buck converter is 3V-3.6V and the output voltage range is 1V-3V, the DSM clock frequency is 4.95MHz, and the maximum load current is 800mA at 3.3V. The output spectrum shows that the clock tone is suppressed down to -85.32dBm at 3.3V input and 1.8V output. The peak efficiency measured at 3.6V input and 3v output with 200mA load current is 89.068%.The total chip area is 2.76 mm2.

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