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1. Interference between digital circuit modules and analog circuit modules
Analog circuits (RF circuits) and digital circuits may work well if they are worked separately. However, once you put them on the same RF PCB and work together using the same power supply, the entire system is likely to become unstable.
This is mainly because digital signals often oscillate between ground and a positive source (>3 V), and the period is extremely short, often on the order of nanoseconds. Due to the large amplitude, the switching time is short. These digital signals contain a large number of high-frequency components that are independent of the switching frequency. In the analog part, the signal from the wireless tuning loop to the receiving part of the wireless device is generally less than 1μv.
Therefore, the difference between digital and RF signals can be up to 120 dB. Obviously if we can't separate the digital signal from the RF signal. Weak RF signals can be corrupted, causing wireless devices to degrade or even fail to work.
RF circuit design
2. Noise interference from power supply
RF circuits are very sensitive to power supply noise, especially voltage glitches and other high-frequency harmonics. The microcontroller will suddenly draw most of the current for a short period of time each internal clock cycle. This is because modern microcontrollers are manufactured using CMOS technology.
So, assuming the microcontroller is running at an internal clock frequency of lmhz, it will draw current from the power supply.
Improper power supply decoupling can cause voltage glitches on the power lines. If voltage glitches reach the power pins of the RF portion of the circuit, it may cause operational malfunctions.
3. The ground wire is unreasonable
If the ground wire of the RF circuit is not handled properly, some strange phenomena may occur. For digital circuit designs, most digital circuits will work fine even without a ground plane. At RF frequencies, even very short ground wires can act as inductors.
As a rough calculation, the inductance per millimeter is about lnH, and the inductance of a 10 Toni PCB is about 27 Ω at 433 MHz. Without a ground plane, most ground traces would be much longer and the circuit would not behave as designed.
4. Radiation interference from the antenna to other analog circuit parts
In PCB circuit design, there are usually other analog circuits on the board.
For example, many circuits have an analog-to-digital converter (ADC) or a digital-to-analog converter (DAC). A high-frequency signal from the RF transmitter antenna may reach the analog input signal of the ADC, which will be sent to the F signal. If the ADC input is not handled properly, the RF signal may self-excite in the ESD diode of the ADC input. This causes ADC bias.