In electronic circuits, the crystal is a crucial frequency control component, providing a stable and accurate clock signal for the system. The crystal load capacitance and crystal capacitance on both sides of the normal operation of the crystal oscillator are playing a key role, although they are related, but actually have different characteristics and functions.

I. The crystal load capacitance
Crystal load capacitance is a parameter closely linked with the characteristics of the crystal itself, it refers to the crystal oscillation circuit, in order to make the crystal can work stably at its nominal frequency, and the equivalent capacitance value configured in the external. Essentially, the crystal load capacitance is designed to match the internal parameters of the crystal to ensure that the crystal produces a stable oscillating signal at a specific frequency.
Different types of crystals have different load capacitance requirements, which are usually determined by the manufacturing process and design parameters of the crystal. For example, the load capacitance value of a common quartz crystal is generally between 10pF and 30pF, and the specific value will be clearly given in the product manual of the crystal. When circuit designers use the crystal in actual applications, they need to meet the load capacitance value provided in the manual through the reasonable configuration of external capacitors to achieve this requirement. If the load capacitance is not properly configured, the oscillation frequency of the crystal will be shifted, which will lead to the deviation of the clock signal of the whole electronic system and affect the normal operation of the system. For example, in some of the clock frequency accuracy requirements of communication equipment, such as cell phone base station RF transceiver module, if the crystal load capacitance is inaccurate, may make the signal modulation demodulation error, resulting in communication quality degradation or even communication interruption.

II. The capacitance on both sides of the crystal
The capacitance on both sides of the crystal oscillator usually refers to the specific capacitive components connected to both ends of the crystal oscillator pins in the actual oscillation circuit. The main role of these capacitors is to form a complete oscillation circuit with the equivalent capacitance inside the crystal, in order to meet the conditions for the crystal to vibrate and maintain stable oscillation.
From the way the circuit is connected, the capacitors on both sides of the crystal and the crystal form a capacitive three-point oscillation circuit (or other types of oscillation circuits, depending on the specific circuit design). These two capacitors interact with the internal capacitance of the crystal to determine the resonant frequency and feedback coefficient of the oscillator circuit. In actual circuit design, the value of these two capacitors should not only consider the load capacitance requirements of the crystal, but also take into account other parameters of the circuit, such as the supply voltage, operating temperature, and stability of the circuit. For example, in some low-power electronic equipment, in order to reduce the power consumption and cost of the circuit, will choose a smaller capacitance value of the capacitor, but at the same time need to more accurately calculate and adjust the capacitance value to ensure that the crystal oscillator can be reliably vibration and stable operation.

III. The difference between the two
1. Concept and essence
Crystal load capacitance is an abstract equivalent capacitance value, a parameter defined from the crystal can work stably under ideal conditions, reflecting the overall demand for external capacitance of the crystal, its purpose is to make the crystal in the nominal frequency to achieve the best working condition. The capacitance on both sides of the crystal is a specific capacitive element that actually exists in the circuit, and they are the physical components that realize the oscillation of the crystal, and build the oscillation circuit through the interaction with the crystal.
2. Determinants of the value
The value of crystal load capacitance is mainly based on the model and specifications of the crystal, which is determined by the crystal manufacturer through experiment and design, and is clearly given in the product specification, and the circuit designer needs to configure the external capacitance in strict accordance with this value, in order to ensure the frequency accuracy of the crystal. And although the value of capacitance on both sides of the crystal should also consider the requirements of the crystal load capacitance, but also by the overall performance of the circuit, cost, space and other factors. In some cases, in order to meet other circuit design requirements, may be within a certain range of the crystal capacitance on both sides of the value of fine-tuning, but this fine-tuning must be carried out to ensure that meet the requirements of the crystal load capacitance under the premise of the crystal oscillator, otherwise it will affect the normal operation of the crystal oscillator.
3. Impact on the circuit
Crystal load capacitance if inaccurate, the direct impact is the oscillation frequency of the crystal, which in turn affects the clock synchronization and timing accuracy of the entire electronic system. For example, in digital circuits in the microprocessor system, if the clock frequency deviation is too large, it may lead to program operation errors, data transmission errors and other problems. The change in the parameters of the capacitance on both sides of the crystal, in addition to affecting the oscillation frequency, may also affect the stability of the oscillation circuit, starting conditions and phase noise and other performance indicators. For example, in some of the phase noise requirements of the strict requirements of the radio frequency circuit, the crystal on both sides of the capacitance of the quality factor and capacitance stability will have a direct impact on the spectral purity of the signal and the sensitivity of the receiver.

IV. The connection between the two
Although the crystal load capacitance and crystal capacitance on both sides of the difference between the above, but they also have a close connection. The capacitance on both sides of the crystal and the crystal internal capacitance together constitute the oscillation circuit, the equivalent capacitance value should be matched with the crystal required load capacitance value. In the actual circuit design, the designer needs to choose the capacitance value of the capacitors on both sides of the crystal according to the load capacitance requirement of the crystal to realize the precise adjustment of the equivalent capacitance of the oscillation circuit, so as to ensure that the crystal can work stably and accurately.

In summary, although the crystal load capacitance and the capacitance on both sides of the crystal are related to the oscillation of the crystal oscillator, there are obvious differences in the concept, the value of the determining factors and the impact on the circuit. Understand these differences and similarities, for electronic circuit designers is crucial, only accurately grasp their characteristics and role, in order to correctly select and configure the capacitance in the circuit design, to ensure that the crystal oscillator's stable operation, and then ensure that the entire electronic system of reliable operation and performance optimization.