線性調(diào)節(jié)器驅(qū)動噪聲降低

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

　　線性技術(shù)公司的創(chuàng)始人Robert Dobkin發(fā)明的，他曾在美國國家半導(dǎo)體的構(gòu)思時，調(diào)節(jié)器的核心架構(gòu)是非常簡單而有效的。Dobkin把一個固定的電壓調(diào)整器和適應(yīng)它的輸出可以使用一個分壓器的輸出進行調(diào)整。1

　　在經(jīng)典的線性調(diào)節(jié)器中，晶體管充當(dāng)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(wěn)壓器的情況。通過柵極電壓反饋的恒定控制在基準(zhǔn)電路設(shè)置的電平上提供穩(wěn)定的輸出電壓。由于使用了分壓器結(jié)構(gòu)，線性調(diào)節(jié)器只能產(chǎn)生比輸入電壓低的電壓。舊的穩(wěn)壓器電路可能會下降2 V或更多。LDO是設(shè)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(jié)構(gòu)，使晶體管能在飽和狀態(tài)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.?