A crystal element that incorporates an IC to form an oscillation circuit within its package is called a crystal oscillator. These products are typically packaged in metal casings, but glass, ceramic, or plastic casings are also available.
working principle of crystal oscillators
A quartz crystal oscillator is a resonant device made using the piezoelectric effect of quartz crystals. Its basic structure is roughly as follows: a thin slice is cut from a quartz crystal at a specific azimuth angle; silver layers are coated on two corresponding surfaces to serve as electrodes; a lead is soldered to each electrode and connected to a pin; and finally, a casing is added to form the quartz crystal resonator, also simply called a quartz crystal or crystal oscillator. These products are generally packaged in metal casings, but glass, ceramic, or plastic casings are also available.
If an electric field is applied to the two electrodes of a quartz crystal, the crystal will undergo mechanical deformation. Conversely, if mechanical pressure is applied to the sides of the crystal, an electric field will be generated in the corresponding direction of the crystal. This physical phenomenon is called the piezoelectric effect.
01. Basic Knowledge of Crystal Oscillators A crystal oscillator, also known as a crystal oscillator, is an electromechanical device made by precisely cutting and grinding a quartz crystal, then plating it with electrodes and soldering leads onto it. This crystal exhibits electromechanical effects, meaning it generates mechanical oscillations when energized and produces electricity when mechanical force is applied. Its oscillation frequency is closely related to its shape, material, and cutting direction. Because quartz crystals have stable chemical properties and a small coefficient of thermal expansion, their oscillation frequency is very stable and accurate.
❒ The working mechanism of a crystal oscillator
A crystal oscillator is a device that generates an oscillation frequency through the electromechanical effect of a quartz crystal. Its frequency is determined by the shape, material, and cutting direction of the crystal. Chemical stability and a small coefficient of thermal expansion ensure stable and accurate frequency operation.
Applications in clock circuits
In clock circuits, crystal oscillators play a crucial role, providing a reference frequency for components such as graphics cards, network cards, and motherboards, much like a precise ruler. Crystal oscillators provide the reference frequency in clock circuits, supporting the stable operation of devices such as graphics cards, network cards, and motherboards. With improvements in manufacturing processes, the technical specifications of crystal oscillators, such as frequency deviation, temperature stability, aging rate, and sealing, have all improved significantly, greatly reducing the failure rate. However, when selecting a crystal oscillator, it is still necessary to pay attention to its quality to ensure its stability and reliability.
02 Application Scenarios of Crystal Oscillators ❒ Applications in Microcontrollers
Furthermore, crystal oscillators have wide applications in microcontrollers. Their clock source configurations typically include oscillators based on mechanical resonant devices such as crystals and ceramic resonant tank circuits, as well as RC (resistor-capacitor) oscillators. Crystal oscillators, used as clock sources in microcontrollers, offer high initial accuracy and a low temperature coefficient; compared to RC oscillators, they provide more stable performance. While the former offers high initial accuracy and a low temperature coefficient, the latter offers rapid startup and low cost, but its accuracy may vary depending on environmental conditions and the selection of circuit components. Therefore, various factors must be considered comprehensively when selecting and using crystal oscillators to ensure they function stably.
❒ Resonance condition and capacitance matching
The load capacitance of a crystal element is a crucial concept for satisfying the resonance condition. During crystal oscillator operation, the load capacitance of the crystal must be satisfied to achieve resonance. It refers to the total effective external capacitance connected across the crystal in the circuit, which is the external capacitance required for the crystal oscillator to function normally. Typically, the purpose of the external capacitor is to make the equivalent capacitance across the crystal equal to or close to the load capacitance. Not all crystal oscillator circuits require a matching capacitor; whether or not it is needed depends on the specific form of the oscillator circuit. In analysis, an equivalent model of the crystal should be used to understand this process.
03 Oscillator Selection and Precautions ❒ Environmental Factors
Environmental factors affecting oscillator operation include electromagnetic interference (EMI), mechanical vibration and shock, humidity, and temperature. Oscillator operation can be affected by external factors such as electromagnetic fields, mechanical vibration, humidity, and temperature, leading to frequency instability or even oscillation failure. These factors can cause output frequency variations, increase instability, and may even cause the oscillator to stop oscillating. However, these problems can be effectively avoided by using oscillator modules. These modules not only have a built-in oscillator but also provide a low-impedance square wave output and ensure stable operation under certain conditions.
❒ Power consumption and grounding issues
When selecting an oscillator, power consumption is also a factor to consider. The power consumption of different types of oscillators varies significantly. The power consumption of discrete oscillators is greatly affected by the power supply current and capacitance value of the feedback amplifier, and grounding design is also crucial for the stability of the resonant circuit. The power consumption of discrete oscillators is mainly affected by the power supply current of the feedback amplifier and the internal capacitance value of the circuit. In contrast, the power consumption of crystal modules and silicon oscillators is relatively low. Grounding is equally important in crystal oscillator circuits. The two capacitors next to the crystal are grounded, effectively forming a voltage divider in a three-point capacitor circuit. The choice of grounding point is crucial because it directly affects the voltage divider effect. With the grounding point as a reference, the input and output of the oscillation pins are out of phase. However, from the perspective of the parallel resonant circuit, i.e., the two ends of the quartz crystal, this positive feedback mechanism ensures the continuous oscillation of the circuit.
Crystal oscillators, acting as the "precise pulse" of LED smart TVs, provide a stable clock signal to ensure smooth operation of every frame, every sound, and every network connection. Whether it's the presentation of high-definition picture quality or the rapid response of smart functions, crystal oscillators silently support the process. This article will delve into the technical applications of crystal oscillators in LED smart TVs and introduce SJK crystal oscillator's superior solutions.
What is a crystal oscillator?
A crystal oscillator, also known as a quartz crystal oscillator, is an electronic component used to generate precise clock signals. In modern electronic devices, the crystal oscillator acts like the heart, providing a stable beat for the device.
The core role of crystal oscillators in LED smart TVs
As an electronic product integrating numerous advanced technologies, smart TVs have extremely high requirements for clock signal accuracy. The stability of the crystal oscillator directly affects the picture and sound quality of the TV, as well as the normal operation of various smart functions.
1. Image quality: The frequency stability of the crystal oscillator directly affects the image refresh rate. Unstable frequency can lead to problems such as image jitter and tearing.
2. Sound quality: The frequency accuracy of the crystal oscillator affects the sampling rate of the audio signal, which in turn affects the clarity and fidelity of the sound.
3. Smart Functions: The various smart functions of smart TVs, such as voice recognition, image processing, and network connectivity, all require precise clock signals to coordinate their operation.
Crystal Oscillator
Common Crystal Oscillator Models and Their Functions in LED Smart TVs
• 32.768KHz crystal oscillator: Mainly used for real-time clocks (RTCs) to control the time display on televisions.
• 24MHz crystal oscillator: Used as the clock source for the main chip, affecting the overall operation of the TV.
• 24.576MHz crystal oscillator: Mainly used in the audio section, affecting the sound output quality.
• 25MHz crystal oscillator: Commonly used in network modules, it affects the stability of network connections.
• 26MHz crystal oscillator: Primarily used in wireless modules, affecting the performance of wireless connections.
• 27MHz crystal oscillator: Used in the video processing module, affecting image display quality.
The impact of crystal oscillator failure on television
If the crystal oscillator in a television malfunctions, it may cause the following problems:
Unable to power on
• Image is unstable
• Sound distortion
• Unstable network connection
• Smart function malfunction
The 49S series crystal oscillators are commonly used on LED smart TV motherboards, while high-end motherboards often use more stable SMD surface mount crystal oscillators.
working principle of crystal oscillators
1. Piezoelectric effect
The core principle of a crystal oscillator is the piezoelectric effect. When pressure is applied to a crystal, an electric charge is generated inside the crystal; conversely, when an electric field is applied to a crystal, the crystal undergoes mechanical deformation. Utilizing this property, a crystal oscillator can generate a stable oscillation frequency under the influence of an electric field. Common piezoelectric crystal materials include quartz crystals and ceramic crystals, among which quartz crystals are widely used due to their stable physical properties and high precision.
2. Oscillating circuit
Crystal oscillators are typically used in conjunction with oscillation circuits. The oscillation circuit provides the necessary excitation signal to the crystal, enabling it to oscillate continuously. Common oscillation circuits include parallel oscillation circuits and series oscillation circuits. Parallel oscillation circuits are suitable for high-frequency applications, while series oscillation circuits are suitable for low-frequency applications. By properly designing the oscillation circuit, the performance of the crystal oscillator can be optimized, and its frequency stability improved.
Characteristics of crystal oscillators
1. Frequency stability
Frequency stability is one of the most important characteristics of a crystal oscillator. It represents the crystal's ability to maintain a constant frequency under different environmental conditions (such as temperature, humidity, and power supply voltage). High-precision crystal oscillators typically employ temperature compensation technology (such as temperature-compensated crystal oscillators, TCXOs) or isothermal control technology (such as oven-controlled crystal oscillators, OCXOs) to improve their frequency stability. For example, OCXOs can maintain extremely high frequency stability under extreme temperature conditions, making them suitable for applications requiring extremely high precision, such as satellite communication and precision measurement.
2. Phase noise
Phase noise is an important indicator of crystal oscillator frequency jitter. It reflects the short-term stability of the crystal oscillator's output signal. Low phase noise crystals can provide a cleaner clock signal, reducing jitter and bit error rate during signal transmission. In communication systems, low phase noise crystals are crucial for improving signal quality and communication bandwidth.
3. Power consumption
Power consumption is a crucial factor to consider in the practical application of crystal oscillators. Low-power crystal oscillators can effectively extend the battery life of electronic devices, making them particularly suitable for portable devices and IoT terminals. With technological advancements, the performance of low-power crystal oscillators continues to improve, employing advanced circuit design and low-voltage drive technology to reduce power consumption while maintaining high performance.
Key points for crystal oscillator selection
1. Frequency range
The frequency range of the crystal oscillator should be selected based on the specific application requirements. Different electronic devices have different requirements for the frequency of the clock signal. For example, computer systems typically require high-frequency crystal oscillators (such as above 100MHz), while some low-power sensors may only require low-frequency crystal oscillators (such as 32.768kHz).
2. Accuracy Requirements
Choose the appropriate crystal oscillator type based on the accuracy requirements of the application. For high-precision applications, such as satellite navigation and precision measurement, an oven-controlled crystal oscillator (OCXO) or a high-precision temperature-compensated crystal oscillator (TCXO) should be selected. For general applications, ordinary crystal oscillators (such as passive or active crystal oscillators) are sufficient.
3. Packaging Form
The crystal oscillator's package type should be selected based on the size and mounting method of the electronic device. Common package types include SMD (Surface Mount Device) and DIP (Dual In-line Package). SMD-packaged crystal oscillators are small in size and suitable for high-density mounting; DIP-packaged crystal oscillators are easier to solder and adjust manually.
