利用擴頻功率控制避免物聯網系統中的噪聲

　　物聯網設備的一個重要特征是他們能夠通過低能量無線鏈路傳輸數據。需要傳輸和接收的數據的敏感性質意味著需要采取措施來保護鏈路。以及使用加密通信，竊聽的風險，可以減少通過限制在網絡上的節點的發送功率，并使用編碼方案，使比特難以區分隨機噪聲。

　　其結果是，RF靈敏度起著很大的作用，在提高安全性，因為它允許使用較低的功率電平，并采用更先進的編碼方案。然而，接收靈敏度的要求，嚴格的要求，可以容忍的設備內的噪聲電平。低能量的無線電接收器通常易受窄帶噪聲，集中在特定的頻率，特別是協議常常使用窄帶信道的干擾，使得更難避免。

　　Although it is possible to tune clock sources so that the main causes of internal interference avoid generating harmonics that interfere with a particular RF transmission band， the demand for flexibility is making this harder to achieve in practice. White-space radio systems such as Weightless demand that the RF subsystem is frequency agile – so that at times， the receiver needs to contend with interference generated locally. As a result， the suppression of electromagnetic interference （EMI） in the circuit design is becoming increasingly important.

　　A key source of EMI in any electronic system is the power subsystem. Most designs providing stable power rails at the point of load （POL） have moved from the use of analog low-dropout （LDO） regulators to provide stable power rails to switched-mode DC/ DC converters. Although switched-mode DC/DC converters provide high efficiency， maximizing the energy that can be recovered from a single battery charge， their switching behavior can be a major source of noise. The primary source is the clock used to drive the pulse-width PWM conversion circuitry.