1. Interference between digital circuit modules and analog circuit modules
If the analog circuit (RF) and the digital circuit work separately, they may work well individually. However, once they are placed on the same circuit board and work together using the same power supply, the entire system is likely to be unstable. This is mainly because digital signals swing frequently between ground and positive power supply (> 3 V), and the cycle is particularly short, often at the nanosecond level. Due to the large amplitude and short switching time, these digital signals contain a large amount of high-frequency components independent of the switching frequency. In the analog part, the signal transmitted from the radio tuning loop to the receiving part of the radio device is generally less than 1 μV. Therefore, the difference between the digital signal and the RF signal can reach 120 dB. Obviously, if the digital signal and the RF signal cannot be well separated, the weak RF signal may be damaged, resulting in deterioration of the performance of the wireless device, or even complete failure to work.
2. Noise interference from the power supply
RF circuits are quite sensitive to power supply noise, especially to voltage spikes and other high-frequency harmonics. The microcontroller will suddenly draw most of the current for a short time in each internal clock cycle, because modern microcontrollers are manufactured using CMOS technology. Therefore, assuming a microcontroller runs at an internal clock frequency of 1 MHz, it will extract current from the power supply at this frequency. If proper power supply decoupling is not adopted, it is bound to cause voltage spikes on the power line. If these voltage spikes reach the power pin of the RF part of the circuit, it may cause failure in severe cases.
3. Unreasonable ground wire