線性調節器驅動噪聲降低

　　低壓差穩壓器（LDO）長期以來一直是降壓電壓轉換的選擇，不僅在成本是一個問題，但在噪聲性能是至關重要的。

　　線性技術公司的創始人Robert Dobkin發明的，他曾在美國國家半導體的構思時，調節器的核心架構是非常簡單而有效的。Dobkin把一個固定的電壓調整器和適應它的輸出可以使用一個分壓器的輸出進行調整。1

　　在經典的線性調節器中，晶體管充當電勢分配器的一半。它的輸出電壓是控制一個反饋電路，在MOSFET的情況下控制晶體管的門，這通常是LDO穩壓器的情況。通過柵極電壓反饋的恒定控制在基準電路設置的電平上提供穩定的輸出電壓。由于使用了分壓器結構，線性調節器只能產生比輸入電壓低的電壓。舊的穩壓器電路可能會下降2 V或更多。LDO是設計來提供更容易的控制輸出電壓和限制這個電壓差小于2 V.

　　LDO的主要變化是從一個射極跟隨器拓撲到一個集電極開路或開漏拓撲結構，使晶體管能在飽和狀態下工作，從而使壓降降到最小。

One reason why linear regulators are not used in all cases for buck regulation is that their efficiency is poor compared to that of a switched regulator. Even when the regulator is quiescent, it passes a small amount of current that is dissipated as wasted heat. The LDO attacks the efficiency problem on one front by minimizing the difference between input and output voltage, which helps in situations where the input voltage is reasonably constant. For example, this is often the case when a linear regulator follows a switching regulator and is present primarily to provide a stable voltage to the target circuit. However, designers must account for the quiescent current that remains.?