IC693MDL731LT 為了控制目的,僅關(guān)注電流的平均分量。要提取平均分量,常見的方法是對(duì)與PWM_SYNC同步的信號(hào)進(jìn)行采樣。在此情況下,電流為平均值,因此,如果能對(duì)采樣時(shí)刻進(jìn)行嚴(yán)格控制,就可以實(shí)現(xiàn)欠采樣而不會(huì)發(fā)生混疊。
使用常規(guī)逐次逼近型(SAR) ADC時(shí),采樣由采樣保持電路執(zhí)行,用戶得以嚴(yán)格控制采樣時(shí)刻。然而,Σ-Δ轉(zhuǎn)換是一個(gè)連續(xù)采樣過程,需要通過其它方式來提取電流平均值。為了地了解這個(gè)問題,看一下Σ-Δ信號(hào)鏈視圖會(huì)有幫助
IC693MDL731LT第一個(gè)元件是轉(zhuǎn)換器本身。以數(shù)MHz的速率對(duì)模擬信號(hào)進(jìn)行采樣,將其轉(zhuǎn)換為1位數(shù)據(jù)流。此外,轉(zhuǎn)換器對(duì)量化噪聲進(jìn)行整形,將其推到更高頻率。轉(zhuǎn)換器之后是通過濾波和抽取方式執(zhí)行的解調(diào)。濾波器將1位信號(hào)轉(zhuǎn)換為多位信號(hào),抽取過程將更新速率降低,使之與控制算法相匹配。濾波和抽取可以分兩級(jí)完成,但極常見的方法是使用一個(gè)sinc濾波器,它能在一級(jí)中完成這兩個(gè)任務(wù)。sinc濾波器可以在FPGA中實(shí)現(xiàn),或者也可以是微處理器中的標(biāo)準(zhǔn)外設(shè)(這已是司空見慣)。無論sinc濾波器如何實(shí)現(xiàn),三階(sinc3)流行的形式。
IC693MDL731LT
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