Param Convert

The load capacitance of the crystal oscillator is connected to the two pins of the crystal oscillator and the capacitance to the ground, which is generally dozens of PF. It will affect the resonant frequency and output amplitude of the crystal oscillator. When customers ask us about the crystal oscillator, we will ask them what the load capacitance of the crystal oscillator is. A resistor connected to the crystal oscillator is a feedback function, which makes the oscillator easy to vibrate. The load capacitance of crystal oscillator is directly related to the accuracy of frequency modulation. If the load capacitance value in the actual circuit is not accurate enough, the accuracy of the crystal oscillator purchased will have a deviation. The calculation method for the load capacitance is to see the sum of the capacitance from both ends of the crystal. Calculation formula: load capacitance of crystal oscillator=[(Cd * Cg)/(Cd+Cg)]+Cic+△ C; In the formula, Cd and Cg are respectively connected to the two feet of the crystal oscillator and the capacitance to the ground; Cic (internal capacitance of integrated circuit); △ C (capacitance on PCB) is generally 3 to 5pf. 1. Matching capacitance: load capacitance refers to the capacitance required for normal oscillation of crystal oscillator. Generally, the external capacitance is used to make the equivalent capacitance at both ends of the crystal oscillator equal to or close to the load capacitance. When the requirements are high, the capacitance to ground of ic input should also be considered. Generally, the capacitance connected at both ends of crystal oscillator is twice of the required load capacitance. In this way, the parallel connection is close to the load capacitance. 2. Load capacitance refers to the total external effective capacitance across the two ends of the crystal in the circuit. It is a test condition and also a use condition. In application, the accurate frequency can be obtained by adjusting the load capacitance value. The magnitude of this capacitor mainly affects the load resonant frequency and the equivalent load resonant resistance. 3. In general, increasing the load capacitance will reduce the oscillation frequency, while decreasing the load capacitance will increase the oscillation frequency. 4. Load capacitance refers to the sum of all effective capacitances inside and outside the IC block connected by the two leads of the crystal oscillator, which can be regarded as the series capacitance of the crystal oscillator in the circuit. Different load frequencies determine different oscillation frequencies of oscillators. The load capacitance of crystal oscillators with the same nominal frequency may not be the same. Because the quartz crystal oscillator has two resonant frequencies, one is the low load capacitor crystal oscillator which is used to wipe the crystal oscillator in series, and the other is the high load capacitor crystal oscillator which is used to wipe the crystal oscillator in parallel. Therefore, when the crystal oscillators with the same nominal frequency are exchanged, the load capacitance must be up to, and they cannot be exchanged rashly, otherwise the electrical appliances will work abnormally.