電路功能與優勢
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title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" title="穩壓器">穩壓器" 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　　這種高效率可以降低系統級功耗，而AD9268的性能則不會下降。ADP2114是一款低噪聲DC-DC穩壓器，提供兩個同步降壓通道（2 A/2 A或3 A/1 A組合），效率最高可達95%。該器件具有300 kHz、600 kHz或1.2 MHz的可選開關頻率，也可以與200 kHz至2 MHz范圍內的外部頻率同步。
　
　　AD9268是一款低功耗ADC，針對通信應用進行了優化，能夠對最高300 MHz的模擬輸入頻率進行數字化處理。這款ADC的信噪比(SNR)超過78 dB，非常適合高動態范圍和低功耗至關重要的通信應用。AD9268內置片內時鐘分頻器(1:8)，可以改善輸入時鐘信號的抖動性能，從而改善較高模擬輸入頻率時的噪聲性能。可以使能AD9268的片內擾動功能，以改善積分非線性(INL)和無雜散動態范圍(SFDR)性能。
　
電路描述
　　圖1顯示該ADP2114電源解決方案，它為AD9268 ADC提供所需的全部輸入供電軌。ADP2114的輸入為+3.6 V低紋波直流總線電源。ADP2114的兩路輸出與AD9268所需的兩個電源相連，包括AVDD供電軌(+1.8 V/390 mA)和DRVDD供電軌(+1.8 V/55 mA)。ADP2114的開關頻率通過與FREQ引腳相連的27 kΩ電阻設置為1.2 MHz。高開關頻率允許使用較小的外部器件，從而降低該電源解決方案的整體電路板空間需求。與OPCFG引腳相連的電阻設置為4.75 kΩ時，可將ADP2114設置為雙2 A強制PWM輸出模式。
　
　　利用同步降壓DC-DC穩壓器ADP2114為雙通道、16位、125 MSPS模數轉換器AD9268供電，以提高效率 (CN0137)

圖1. ADP2114與AD9268相連（原理示意圖，未顯示去耦和所有連接）

　　各輸出均采用一個兩級LC濾波器，第一級利用一個電感(L1/L2)，第二級則利用一個鐵氧體磁珠(FB1/FB3)，反饋環路圍住兩級閉合。為保持穩定性，環路交越頻率必須較低。穩壓器之后還有一個鐵氧體磁珠(FB2/FB4)，以便進一步濾波。經過此鐵氧體磁珠之后，這些電壓分配至PCB的電源層，其中AD9268采用局部去耦。
　
　　圖2顯示70 MHz模擬輸入頻率和125 MSPS采樣時鐘時AD9268的FFT。如圖所示，與線性穩壓器電源解決方案相比，FFT本底噪聲性能沒有下降，而且沒有任何與開關頻率相關的可測量頻率成分或雜散。
　
利用同步降壓DC-DC穩壓器ADP2114為雙通道、16位、125 MSPS模數轉換器AD9268供電，以提高效率 (CN0137)

圖2. 輸出頻譜（70 MHz AIN，–1 dBFS，采樣速率 = 125 MSPS，采用ADP2114電源）

　　表1顯示采用ADP1706系列線性穩壓器和采用DC-DC穩壓器ADP2114兩種情況下，AD9268 (125 MSPS)上測得的交流性能數據。主要是10.3 MHz至200.3 MHz的各種模擬輸入頻率范圍內的滿量程信噪比(SNRFS)和無雜散動態范圍(SFDR)。結果表明，采用ADP2114開關穩壓器設計與采用傳統LDO解決方案相比，SNR、SFDR或動態范圍性能沒有任何下降。　 

  　　表1. 采用ADP2106系列LDO與采用ADP2114 DC-DC穩壓器時的AD9268性能對比
　
　　表2中的效率結果將LDO穩壓器設計與基于ADP2114的開關穩壓器設計的整體效率進行了比較。為了合理比較利用各穩壓器方案的輸入至輸出計算得到的功率損失，本實驗所用的兩種評估板均采用相同的3.6 V線內或總線電壓。開關穩壓器(ADP2114)設計的整體效率提高了35%。對于單個AD9268，這大約節省600 mW功耗。如果系統中使用多個器件，節省的功耗將相當可觀。
 

 表2. 線性與開關穩壓器效率對比

　　采用ADP2114等DC-DC穩壓器時，適當的布局和電路分割是確保設計成功的關鍵。PCB堆疊（電源層和接地層）應緊密耦合，以改善旁路。開關穩壓器電感應遠離ADC及ADC時鐘和信號路徑中的敏感器件而安裝，或者安裝在PCB背面，以利于消除耦合至敏感器件的磁通量。還應仔細了解電流流向，以及器件或相鄰電路布局。電路之間應有良好的隔離。
　
　　欲了解設計和測試結果的更多信息，請參考Rob Reeder和Michael Cobb主持的網絡研討會高速模數轉換器應用中的開關穩壓器設計，以及Michael Cobb撰寫的技術文章“利用開關電源為高速模數轉換器供電”。
　
常見變化
　　AD9258、AD9251、AD9269、AD9231和AD9204 與AD9268尺寸兼容，在要求較低分辨率或采樣速率的應用中可以代替AD9268。ADP2114的電流能力可以驅動一個以上的AD9268。如果只需要為一個器件供電，則可以考慮ADP2108。在這種情況下，只要AVDD與DRVDD供電軌之間提供適當的隔離濾波，就可以利用單個穩壓器給這兩個電源域供電。
　
　　若為ADC供電，低壓差(LDO)穩壓器與開關電路解決方案都可行。LDO電路的效率較低。開關解決方案可提高效率、降低功耗，ADC性能則不會下降。使用多個器件時，可實現更高效率，并節省更多功耗。