濾波器選擇與設(shè)計(jì)：系統(tǒng)性能的網(wǎng)關(guān)

　　通常，設(shè)計(jì)師要花那么多的時(shí)間專注于其復(fù)雜的規(guī)范和選擇成本較高的設(shè)備，如處理器、FPGA與ADC，他們沒有充分考慮到的主要性能的影響，以及成本和功耗問題，這是由選擇和整合的所謂“低端“部件如過濾器。

　　事實(shí)上，濾波器電路的規(guī)格和設(shè)計(jì)常常是決定整個(gè)系統(tǒng)成功的最重要因素。例如，如果在相對(duì)低帶寬應(yīng)用中的濾波設(shè)計(jì)不能消除信號(hào)鏈前端的高帶寬噪聲，則系統(tǒng)必須燒毀額外的能量，以將不必要的噪聲傳播到信號(hào)鏈上。或者，在處理某些帶寬的信號(hào)時(shí)，例如在基于信道的無線電接收機(jī)中，不適當(dāng)?shù)臑V波設(shè)計(jì)會(huì)導(dǎo)致從相鄰信道的信號(hào)進(jìn)行不必要的處理。這就導(dǎo)致了電源的浪費(fèi)和目標(biāo)信號(hào)的潛在退化。

　　Proper filter design also prevents the signal path from contributing noise to other parts of the system， such as keeping high-frequency signals from coupling back into the power circuit and causing instability or fluctuations. In essence， bypass capacitors are actually the simplest category of analog filters and are widely used in all types of designs.

　　Below is a brief overview of the role of filters， the types of filters， and differences between digital and analog approaches as well as between passive and active filtering designs. Then there are some specific design tips for simulating and selecting analog filters for an example application to drive high-performance analog-digital converters （ADCs）。