Crystals
1. Crystals Overview
Crystals (crystal resonator) is a passive electronic component based on quartz crystal, which generates an oscillation signal of precise frequency through the natural electromechanical effect of quartz crystal. Its main function is to provide clock signals for digital circuits and control the timing operation of the system. It is often likened to the “heart of electronic circuits”.
2. What are the Types of Crystals?
Passive Crystal Oscillator (Crystals): It needs to rely on external circuit drive, only quartz crystal slices and pins, and external capacitors and other components are required to form a resonant circuit.
Active Crystal Oscillator (Oscillator): Integrated oscillation circuit, directly outputs stable square wave signal, no additional drive required.
3. How do Crystals Work?
Using the piezoelectric effect of quartz crystal: When an alternating electric field is applied, the crystal will generate mechanical vibrations, thereby outputting an oscillation signal of a specific frequency. Its frequency range is usually from a few kHz to tens of MHz, and the frequency can be fine-tuned by adjusting the external load capacitor.
4. What are the Structural Features of Crystals?
Packaging Form: Common small packages, such as HC-49U, only contain crystal slices and pins.
Circuit Dependency: It needs to work with external capacitors (usually 10-22pF) and oscillation circuits to work properly.
Stability: The temperature characteristics of quartz materials determine their frequency stability. Temperature compensation or constant temperature crystal oscillators need to be selected in high-precision applications.
5. What are Crystals Used for?
Provide reference clock signals for microprocessors and digital circuits to ensure system timing synchronization.
Frequency generation modules in communication equipment, such as RF signal modulation and demodulation.
6.Technical Parameter Considerations for Crystals
Frequency Accuracy: Indicators such as frequency difference adjustment and temperature frequency difference affect system performance.
Load Capacitance Matching: It is necessary to select appropriate external capacitance values according to circuit design to ensure the accuracy of the resonant frequency.
7. Selection and Design Recommendations for Crystals
Low Power Consumption Scenarios: Passive crystal oscillators are preferred to simplify circuit design.
High Stability Requirements: Active crystal oscillators or temperature compensation/constant temperature crystal oscillators are recommended to avoid frequency drift caused by environmental interference.
High Frequency Applications: It is necessary to pay attention to the crystal oscillator bandwidth and quality factor (Q value) to ensure signal purity.
8. Crystals FAQs
1) How to choose a suitable nonlinear optical crystal?
It is necessary to consider laser parameters (such as wavelength, power/energy, divergence angle) and crystal performance (such as transmittance, damage threshold, effective nonlinear optical coefficient, phase matching type, and angle). Different application scenarios need to match the spectral acceptance bandwidth and temperature stability of the crystal.
2) How do crystals ensure accurate timing in electronic devices?
Crystals generate stable frequency signals through the piezoelectric effect. For example, tuning fork crystals generate electrical signals through mechanical vibrations. Their resonant frequency is controlled by geometry and material properties. This stability makes it a core component of timing circuits such as quartz clocks and communication modules.
3) How to keep the crystal oscillator stable in PCB layout?
Shorten the wiring distance between the crystal and the chip to reduce interference;
Avoid high-frequency signal lines close to the crystal area;
Use ground planes to isolate noise;
Choose a package design with low parasitic capacitance.
4) Can the crystal oscillator operate outside the specified temperature range?
Exceeding the nominal temperature range may cause frequency drift or failure. Industrial and automotive grade crystals usually have a wider temperature adaptability range (such as -40°C to 125°C), but the limit parameters need to be confirmed according to the specific model manual.
5) What is the difference between AT-cut and SC-cut crystals?
AT-cut crystals: lower cost, frequency-temperature characteristics are cubic curves, suitable for conventional environments; SC-cut crystals: better temperature stability, strong resistance to thermal shock, suitable for high-precision or extreme temperature scenarios.
6) How does the crystal damage threshold affect the application?
The damage threshold determines the maximum laser power density that the crystal can withstand. If this value is exceeded, it will cause optical performance degradation or physical damage. In high-power applications, crystals with high damage thresholds (such as LBO, BBO) must be selected and combined with heat dissipation design.
7) What is the future development trend of tuning fork crystals?
Smaller size (such as SMD packaging) to adapt to miniaturized devices;
Low power design to extend battery life;
Improve resistance to vibration and environmental interference, and expand its application in the fields of Internet of Things, automotive electronics, etc.