The following is a rewritten and improved version of the original content, written in English with added details to make it more natural and comprehensive:
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**1. The Difference Between Crystal and Crystal Oscillator**
1) A **crystal oscillator**, also known as an *active crystal*, is a device that generates a stable frequency signal on its own. Its English name is "oscillator." On the other hand, a **crystal** (also called a *passive crystal*) is a resonator that requires an external circuit to produce oscillation. It is typically used in a two-pin configuration and does not generate a signal by itself. Common packages for crystals include 49U and 49S.
2) A **passive crystal** is generally a non-polar component that is directly connected between two pins. It needs to be paired with a clock circuit to generate an oscillating signal. In contrast, an **active crystal oscillator** (or crystal oscillator) is a four-pin device that contains an internal clock circuit. It can generate a stable output signal simply by being powered. These are commonly available in sizes like 7050, 5032, 3225, and 2520.
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**2. MEMS Silicon Crystal Oscillator vs. Quartz Crystal Oscillator**
MEMS (Micro-Electro-Mechanical Systems) silicon crystal oscillators are made using advanced semiconductor technology and offer several advantages over traditional quartz crystal oscillators. Here are some key benefits:
1) They use fully automated chip-level manufacturing, eliminating air-tightness issues and ensuring long-term stability.
2) They include an internal temperature compensation circuit, providing high accuracy across a wide temperature range (-40°C to +85°C).
3) They have an average mean time between failures of up to 500 million hours.
4) Their seismic performance is 25 times better than that of quartz oscillators.
5) They support frequencies from 1 MHz to 800 MHz with high precision (up to five decimal places).
6) They are compatible with various supply voltages, including 1.8V, 2.5V, 2.8V, and 3.3V.
7) They support multiple levels of frequency accuracy, such as 10ppm, 20ppm, 25ppm, 30ppm, and 50ppm.
8) They come in standard package sizes like 7050, 5032, 3225, and 2520.
9) They are available in both four-pin and six-pin configurations, making them easy to replace quartz oscillators without design changes.
10) They support various output types, including differential, single-ended, voltage-controlled (VCXO), and temperature-compensated (TCXO).
11) They are growing rapidly in the market, with a 300% growth rate and expected to replace over 80% of the quartz oscillator market within three years.
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**3. Equivalent Circuit of a Crystal Resonator**
The equivalent circuit of a crystal resonator is a simplified model that represents its impedance characteristics near the resonant frequency. The components include:
- **C1**: Dynamic capacitor (equivalent series capacitance)
- **L1**: Dynamic inductor (equivalent series inductance)
- **R1**: Dynamic resistance (equivalent series resistance)
- **C0**: Static capacitor (equivalent parallel capacitance)
There are two main frequencies in this circuit: the **series resonant frequency (Fr)** and the **parallel resonant frequency (Fa)**. When a crystal is used in an oscillator circuit, it is usually coupled with a load capacitor to operate between these two frequencies. Adjusting the reactance of the circuit allows for fine-tuning of the crystal's frequency.
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**4. Key Parameters of Crystal Components**
**4.1 Nominal Frequency**
This is the specified frequency of the crystal component, which is the target frequency for the user in circuit design.
**4.2 Frequency Tolerance**
This is the maximum allowable deviation from the nominal frequency at a reference temperature, usually expressed in parts per million (ppm). For example, 1 ppm = 0.0001%.
**4.3 Temperature Drift**
This refers to the change in frequency due to temperature variations over the entire operating range. It is also measured in ppm.
**4.4 Aging Rate**
This is the gradual frequency drift caused by time under specified conditions. It is important for high-precision crystals but is not always strictly defined in specifications.
**4.5 Resonant Resistance (Rr)**
This is the equivalent resistance of the crystal at resonance. It affects the quality factor (Q) and determines the stability of the oscillation.
**4.6 Load Resistor (RL)**
This is the resistance seen at the load resonant frequency when a specific external capacitor is connected.
**4.7 Load Capacitance (CL)**
This, together with the crystal, determines the effective external capacitance at the load resonant frequency. It is crucial for tuning the actual working frequency of the crystal.
**4.8 Static Capacitance (C0)**
This is the capacitance of the static arm in the equivalent circuit and depends on the electrode area, wafer thickness, and processing.
**4.9 Dynamic Capacitance (C1)**
This is the capacitance of the dynamic arm in the equivalent circuit and depends on the electrode area and wafer alignment.
**4.10 Inductance (L1)**
This is the inductance in the dynamic arm of the equivalent circuit and is related to the dynamic capacitance.
**4.11 Resonant Frequency (Fr)**
This is the frequency at which the crystal’s impedance becomes purely resistive. It is the natural frequency of the crystal.
**4.12 Load Resonance Frequency (FL)**
This is the frequency at which the crystal, when combined with a load capacitor, shows a resistive impedance. It is the actual operating frequency in most applications.
**4.13 Quality Factor (Q)**
This measures the performance of the resonator and is calculated based on L1, C1, and R1. A higher Q value means better frequency stability.
**4.14 Drive Level**
This is the power applied to the crystal. It affects the frequency and resistance, and must be carefully controlled during design.
**4.15 Drive Level Dependency (DLD)**
This refers to the variation in frequency and resistance with different drive levels. Poor manufacturing or contamination can cause DLD failure.
**4.16 DLD2 (Ohms)**
This is the difference between the maximum and minimum load resonance resistance at different drive levels.
**4.17 RLD2 (Ohms)**
This is the average load resonance resistance across different drive levels.
**4.18 Spurious Response**
This refers to unwanted frequency responses in the crystal. It can be reduced through careful design and processing.
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**5. Classification of Crystal Oscillators**
**5.1 SPXO (Standard Package Quartz Oscillator)**
These do not include temperature control or compensation. Their frequency stability depends on the quartz crystal itself.
**5.2 TCXO (Temperature-Compensated Crystal Oscillator)**
These add a temperature compensation loop to reduce frequency drift caused by temperature changes.
**5.3 VCXO (Voltage-Controlled Crystal Oscillator)**
These allow the output frequency to be adjusted using an external voltage.
**5.4 OCXO (Oven-Controlled Crystal Oscillator)**
These maintain a constant temperature inside a sealed chamber, ensuring high frequency stability despite ambient temperature changes.
With the development of technologies like PLL, digital control, and memory, new types of crystal oscillators continue to emerge, offering greater flexibility and performance.
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