Tektronix - Hunting Noise Sources in Wireless Embedded Systems

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When integrating a radio chip or module into a typical embedded system, a common task designers must face is tracking down and eliminating noise and spurious signals. Potential noise sources include switching power supplies, digital noise from other parts of the system, and external sources. Noise considerations also include any possible interference generated by the radio; an important consideration to avoid interfering with other radios as well as to meet radio agency requirements. In this application note, tips and techniques for hunting noise sources with the MDO4000 Series Mixed Domain Oscilloscope Series will be explored.

Integrating Wireless Capability into Embedded Systems

In adding wireless capability to embedded systems, there are a number of issues typically encountered in the integration. For battery powered systems, a switching regulator is typically used to have the highest practical efficiency at the lowest cost. The size of the power supply is also often an issue. This can lead to the use of high switching frequencies to minimize the size and requirements of output filtering. These power supplies often have ripple on the output voltage which can show up on the RF transmitter output, especially when under load or under low battery conditions. To avoid this, additional power supply filtering may be needed to avoid unwanted impairment of the radio signal, even though the cost or size is undesirable.

The hardware circuits and the software configuration of the radio chip or module can affect the quality of the transmitted signal. If not properly set up and filtered, the radio can cause interference to other radio systems and/ or fail to conform to applicable agency regulations. Some radio systems will need channel filters, RF Surface Acoustic Wave, or other relatively expensive filters to meet agency regulations for out-of-channel and out-ofband emissions...

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