How to test and debug the frequency accuracy of radio frequency

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How to test and debug the frequency accuracy of radio frequency [Copy link]

For any RF chip, frequency accuracy is the most important indicator of its RF performance. It may cause problems such as failure to connect, poor transmission indicators, and poor receiving sensitivity.
Test method:
It is an incorrect method to test the frequency error directly on the oscillation circuit, because the probe will introduce parasitic capacitance and change the characteristics of the oscillation circuit. What needs to be done is to make the chip generate RF CW (constant amplitude wave) waves, and use the method of testing RF to test the frequency accuracy. The commonly used instrument is a spectrum analyzer (Note: oscilloscopes cannot measure).
Debugging method:
According to the requirements of different chips/protocols for frequency accuracy, adjust the two load capacitors until the measured frequency accuracy reaches the target.

The selection of crystal/crystal oscillator
Mainly includes:
1. Frequency point - refer to the support list described in the datasheet
2. Accuracy - For most RF chips of the Internet of Things, AFC (automatic frequency control) is not available, and all accuracy is guaranteed by the crystal oscillator. Here, taking wifi technology (CC3100/CC3200) as an example, the specification requires +/-20ppm. Therefore, when selecting the device, the crystal (or external clock) needs to meet the total accuracy within 20ppm, including: a) inherent accuracy b) drift with temperature c) aging
3. Load capacitance and ESR - choose the same as the specification and reference design. When debugging the product board, the accuracy needs to be adjusted according to the load capacitance. For details, refer to the "How to test and debug the frequency accuracy of the RF" section.