The timing crystal is used as the time or frequency reference source in the circuit and can be called the heart of the device. Quartz resonator is also called passive crystal oscillator or resonator, and its English name is crystal resonator.

    In 1880, the Curie brothers Jacques and Pierre Curie discovered that when the crystal is under pressure, an electric charge will be generated on the surface, and the amount of electric charge is proportional to the external mechanical force. This phenomenon is the piezoelectric effect. Objects with piezoelectric effect are called piezoelectric bodies. If pressure is applied to the wafer at the same time, a charge will be generated on the wafer. Conversely, when a voltage is applied to electrodes across the wafer, the crystal deforms mechanically. The frequency of wafers depends on the dicing and size of the wafers. The higher the q value of the chip, the more stable the frequency. Since there is no IC inside the passive crystal oscillator, the external circuit needs to be coordinated, so the stability of the passive crystal oscillator largely depends on the user's matching of the external circuit.

    The piezoelectric resonance phenomenon of the time-strained crystal can be simulated by an equivalent circuit. The equivalent circuit includes static capacitance C0, dynamic capacitance C1, resonance resistance R1 and dynamic inductance L1.

    Passive crystal itself cannot generate oscillating signal, so it needs an external oscillating circuit, which can be divided into series oscillating circuit and parallel oscillating circuit. A series crystal oscillator is a feedback oscillator consisting of an amplifier and a feedback network. The quartz resonator and load capacitor are connected in series. The resonator is purely resistive.

    In a parallel crystal oscillator, a quartz resonator is connected in the feedback branch, operating between the series and parallel resonant frequencies, and the resonator is inductive. Used as an inductive element in a circuit. The matching capacitances C1C1 and C2 of the circuit plus the stray capacitance Cstray of the circuit are closer to the load capacitance of the crystal, and the frequency output by the crystal is more accurate.

    The passive crystal oscillator has a simple structure, but cannot avoid the calculation of complex formulas. Active crystal oscillator is to put passive crystal oscillator and related oscillation circuit together, no need to match peripheral circuits and so on. If you have any questions about matching capacitors, Kean Kaiqing Dongguang has professional technicians to provide you with online guidance.