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模擬和數字的本質區別是什么?數字電視中哪里有數字?

發布時間:2018-09-10 11:50:14     閱讀次數:484

來源: 作者:王珂

我們經常聽說,模擬與數字的區別是:模擬信號是連續的,而數字信號是離散的。
 
這其實并不是本質區別。
 
模擬信號
 
“模擬”的本質,是用一種物理量,來“轉換并類比”另一種物理量。
 
比如,水銀溫度計。
 
溫度越高,水銀受熱膨脹,水銀液位就越高,所指示的溫度就越高。
它是用水銀液位的高度,來“成比例地模擬”溫度的高低。
 
因此,對應到電路中,就是用“電壓或電流的大小”,來“模擬表征”其它的物理量。
 
又比如,我們用的麥克風(話筒),也是一個模擬電路系統。
 
麥克風將我們說話聲音的大小,成比例地轉換成電壓的高高低低。聲音越大,信號的電壓就越大;聲音越小,信號的電壓就越小,這就是在“模擬”。
 
因此,模擬信號確實是連續信號,但這只是它的表面特征,并不是本質。
 
數字信號
 
數字信號也是電信號,但它是表征“邏輯”意義的電信號,信號本身的電壓大小往往不攜帶信息。
 
比如,我們可以將電路的邏輯規定為:
0V至2V表示邏輯“0”,稱之為低電平;
2V至5V表示邏輯“1”,稱之為高電平;
這樣一來,1.5V就是邏輯上的“0”,而1.5數值本身并沒有意義。
 
當然,具體閾值在不同數字電路系統中可能不同,這里的2V僅僅是舉例。
 
有了邏輯上的“0”和“1”,就能用二進制來表示數字了。
 
假設,這一刻我說話的聲音大小是3(單位略)。
 
那么,3就可以表示為二進制0011,而0011,可以進一步表示為(低電平,低電平,高電平,高電平)。
 
這樣,物理量“聲音”,就轉換成了“數字形式的電信號”。
 
我們經常耳熟能詳的“數字電視”,指的是,其像素點的色彩信息,是通過“二進制01”的形式傳輸的,而不是直接用電壓的高高低低來表示并傳輸。
 
古老的黑白電視,是一種“模擬電視”,它直接用電壓的高低,來表示畫面色彩的灰度(黑白程度)。
 
信號中電壓越高,畫面就越黑或越白,這就是“模擬”。
 
但是,由于電壓不可能是完美的幾伏,因此,模擬系統的精度和抗干擾性都比較差,這也是為什么模擬電視已被淘汰的原因。
總結
 
數字電路和模擬電路的主要區別是:
 
模擬電路直接用電壓或電流的大小,來表示物理量的大小,并進行計算或處理;
 
而數字電路,是用電壓表示“0”和“1”,然后用“0”和“1”來表示物理量的大小并進行運算、傳輸。

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