利用扩频功率控制避免物联网系统中的噪声

　　利用扩频功率控制避免物联网系统中的噪声

　　物联网设备的一个重要特征是他们能够通过低能量无线链路传输数据。需要传输和接收的数据的敏感性质意味着需要采取措施来保护链路。以及使用加密通信，窃听的风险，可以减少通过限制在网络上的节点的发送功率，并使用编码方案，使比特难以区分随机噪声。

　　其结果是，RF灵敏度起着很大的作用，在提高安全性，因为它允许使用较低的功率电平，并采用更先进的编码方案。然而，接收灵敏度的要求，严格的要求，可以容忍的设备内的噪声电平。低能量的无线电接收器通常易受窄带噪声，集中在特定的频率，特别是协议常常使用窄带信道的干扰，使得更难避免。

　　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.