The crystal oscillator plays a role in the application details. The clock source of the microcontroller can be divided into two categories: clock sources based on mechanical resonant devices, such as crystal oscillators and ceramic resonant tank circuits; RC (resistance, capacitance) oscillators. One is the Pierce oscillator configuration, which is suitable for crystal oscillators and ceramic resonant tank circuits.

    The other is a simple discrete RC oscillator. Oscillators based on crystal oscillators and ceramic resonant tank circuits usually provide very high initial accuracy and low temperature coefficients. The RC oscillator can be started quickly and the cost is relatively low, but the accuracy is usually poor in the entire temperature and operating power supply voltage range, and it will vary within the range of 5% to 50% of the nominal output frequency. However, its performance is affected by environmental conditions and the choice of circuit components. The component selection and circuit board planning of the oscillator circuit must be taken seriously. In use, the ceramic resonant tank circuit and the corresponding load capacitance must be optimized according to a specific logic series. A crystal oscillator with a high Q value is not sensitive to the choice of amplifier, but it is prone to frequency drift (and may be damaged) when over-driving. Nowadays, many system crystal oscillators have high clock frequency and strong interference harmonic energy. In addition to being conducted from the input and output traces, interference harmonics will also radiate from space. If the planning is unreasonable, it will easily constitute strong noise radiation. The problem is difficult to deal with by other methods, so it is very important to plan the crystal oscillator and CLK signal line when planning the PCB board.

    The environmental factors that affect the operation of the oscillator are: electromagnetic interference (EMI), mechanical vibration and shock, humidity and temperature. These factors will increase the output frequency change, increase instability, and in some cases, will also constitute the oscillator to stop vibration. Most of the above problems can be avoided by using the oscillator module. These modules have their own oscillator, provide low-impedance square wave output, and can guarantee operation under certain conditions. The two most commonly used types are crystal oscillator modules and integrated RC oscillators (silicon oscillators). The crystal oscillator module provides the same accuracy as a discrete crystal oscillator. The precision of the silicon oscillator is higher than that of the discrete RC oscillator, and in most cases it can provide the same precision as the ceramic resonant tank circuit. With the development of electronic components, the size of the crystal oscillator is getting smaller and smaller, and the power consumption is getting lower and lower. Crystal oscillators are used in almost all electronic products.