Application FAQs

Application Guide

1) Selection of Load Capacitance

Load capacitance, together with the quartz resonator, determines the operating frequency of the oscillator. By adjusting the load capacitance, the operating frequency of the oscillator can generally be tuned to the nominal value. The load capacitance specified in the product datasheet serves as both a test condition and an operating condition. This value can be appropriately adjusted according to specific requirements. When the load capacitance is too large, the effect of stray capacitance is reduced, but the tuning range decreases. When the load capacitance is small, the tuning range increases, but the effect of stray capacitance increases, the load resistance increases, and oscillation start-up may become difficult. A load capacitance specified as (series) indicates series resonance. When the crystal operates at the fundamental mode, the standard load capacitance value is 12~20 pF.

2) Typical Application Circuit for Fundamental Mode Oscillation:

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When applied to CMOS oscillator circuits, in order to maintain the drive level within a specific range for stable oscillation, the resistor Rd in the circuit diagram is essential.

3) Effect of Drive Level:

Generally speaking, for AT-cut crystals, an increase in drive level results in a positive frequency shift. The drive level value specified for each product in the datasheet is both a test condition and an operating condition. In actual use, the drive level can be appropriately adjusted. Excessive drive level may cause nonlinear effects, leading to spurious oscillation, severe thermal frequency drift, overstress frequency drift, and resistance step. When the drive level is too low, it may result in difficulty in overcoming the start-up threshold, poor operation, and unstable performance specifications. Common standard values are 50 μW and 100 μW.

4) Negative Impedance Check of the Oscillation Circuit:

The negative impedance value should be 5 to 10 times the resonant impedance. When the negative impedance of the circuit is too small, oscillation will become unstable.

Ordering and Usage Precautions

1) Product Ordering Requirements

The product order form should clearly specify the following items: product model, temperature range, nominal frequency, load capacitance, frequency tolerance, temperature frequency tolerance, and any additional notes or special conditions.

2) Product Usage Precautions

• The external capacitors of the electronic circuit should match the load capacitance of the crystal.

• Use the product in accordance with the technical specifications. The drive power and other parameters must not exceed the specified limits during use.

• Handle with care. Avoid dropping from height or subjecting the product to external impact, which may cause product failure.

• Avoid scratching or friction on the housing, which may cause surface damage or unclear markings.

• Avoid over-bending or stretching the product leads, which may damage or crack the insulator.

• Avoid further bending of the product leads after initial processing.

• During soldering, avoid short-circuiting the product leads and housing with solder.

• Soldering temperature should not exceed 265°C, and soldering time should not exceed 5 seconds.

• Products should be stored in a warehouse with ambient temperature between -10°C and 40°C, relative humidity not exceeding 80%, and free from acidic, alkaline, and other harmful gases.

Determining the condition of a crystal oscillator typically requires a combination of visual inspection, basic tool measurement, and professional instrument testing. The following are several commonly used methods:

I. Visual Inspection

First, perform a visual observation, as many physical damages can be detected by the naked eye:

Inspect the housing and pins: Check whether the crystal oscillator surface has cracks, chips, or scratches, which usually indicate that the internal crystal has fractured. Also check whether the pins are blackened from oxidation or have green rust spots, as poor contact may cause signal interruption.

Inspect the package condition: For active crystal oscillators (typically 4-pin), if the metal housing is bulging or deformed, it often indicates that the internal circuit has been damaged.

II. Multimeter Preliminary Screening (Applicable to Passive Crystals)

A multimeter can quickly rule out obvious short-circuit faults, but cannot precisely determine whether the frequency is normal:

Resistance Method for Short Circuit: Set the multimeter to the R×10k range (or diode test range), and measure the resistance across the two terminals of the crystal oscillator. A normal passive crystal is non-conductive at rest, with resistance approaching infinity. If the resistance is very low (e.g., tens of ohms or close to 0Ω), it indicates that the crystal oscillator is internally shorted and damaged.

Capacitance Method as Auxiliary Reference: Use the capacitance range of a digital multimeter to measure the capacitance. A normal, undamaged crystal oscillator typically has a capacitance in the range of tens to hundreds of pF. If the measured capacitance is significantly lower, it may indicate that the crystal oscillator is damaged.

Voltage Method for Oscillation Check: With the circuit board powered on, use the DC voltage range to measure the voltage from each pin of the passive crystal oscillator to ground. Under normal conditions, the voltage at both pins should be close to half of the supply voltage (e.g., approximately 2.5V for a 5V supply), and there should be a slight voltage difference between the two pins. If both pins have the same voltage or both are close to 0V, oscillation may not have started.

III. Oscilloscope Testing (Most Accurate Method)

An oscilloscope is the core tool for determining whether a crystal oscillator is functioning properly, allowing direct visualization of the waveform and frequency:

Probe Settings: Always use the 10X attenuation setting to minimize circuit loading, and keep the ground lead as short as possible (preferably using a spring ground clip). It is recommended to enable bandwidth limiting to reduce noise interference.

Measurement Point: It is not recommended to measure directly across the crystal oscillator terminals, as this may disturb the oscillation. Instead, measure the OSC_OUT pin of the MCU or FPGA (where the signal is stronger), and avoid probing the weaker OSC_IN pin.

Waveform Observation: When oscillation starts normally, the waveform should approximate a sine wave, with a peak-to-peak amplitude typically between 0.2V and 1V, and the frequency should equal the nominal frequency of the crystal. Due to the action of the internal feedback amplifier in the MCU, the waveform may exhibit slight clipping distortion, which is normal.

IV. Substitution Method (Definitive Verification)

If the above methods still cannot determine the fault, or if professional instruments are unavailable, the substitution method is the most reliable verification approach:

Select a normal crystal oscillator with the same frequency and package (for active oscillators, also verify the operating voltage) for substitution. During soldering, pay attention to temperature control to avoid thermal damage. If the device functions normally after substitution, the original crystal oscillator can be confirmed as failed.

Supplementary Note: Ensure power is disconnected before performing any operation to prevent electric shock. Additionally, the method circulating on the market of using a test pen inserted into the mains live wire to test crystal oscillators poses significant safety risks and should not be attempted by non-professionals.

In the manufacturing process, the raw quartz crystal material must first be cut and ground. One critical step is angle setting. Due to different cutting angles and orientations of the quartz plate, the piezoelectric characteristics, elastic characteristics, and mechanical strength vary, resulting in different performance of the resonators manufactured from them. Through extensive research, dozens of useful cut orientations have been identified.

Conventional Cut Designation:

AT, BT, CT, DT, ET, FC, SC, LC, etc.

Commonly used crystal cuts are divided into two types: AT-cut and BT-cut.

AT-cut: Small temperature coefficient, low cost, widely used, with a larger C₀ (static capacitance) compared to BT-cut.

BT-cut: Suitable for oven-controlled operation. For the same frequency, the crystal is thicker than AT-cut, therefore the Q factor is higher than AT-cut.

A crystal oscillator serves as the "heart clock source" of an electronic circuit, with the following primary functions:

1. Frequency Reference: A crystal oscillator can precisely generate a signal at a specific frequency, typically used as the clock source in a system. This stability is critical for digital circuits (such as microcontrollers and microprocessors), as it ensures synchronization of both internal and external operations.

2. Synchronized Clock: Most digital circuits rely on clock signals to control data acquisition, processing, and transmission. The stable clock signal provided by the crystal oscillator ensures that different circuits or components can interact at correct time intervals.

3. Signal Modulation and Demodulation: In wireless communication modules, crystal oscillators are used for modulation and demodulation, maintaining frequency coherence between the transmitter and receiver to ensure a stable and reliable communication link.

4. Frequency Multiplication and Division: A crystal oscillator can serve as the basis for a frequency synthesizer, generating other required frequency signals through multiplication or division techniques to meet the needs of different circuits.

A crystal oscillator plays the role of the "heart" in an electronic circuit. Its most fundamental function is to provide a precise and stable clock frequency signal for the circuit.

Specifically, the functions of a crystal oscillator are mainly reflected in the following aspects:

1. Providing a Reference Clock Signal (Core Function)

Digital circuits (such as microcontrollers, CPUs, FPGAs, etc.) operate synchronously and require a unified "timing beat" to coordinate the actions of various components. A crystal oscillator generates an extremely stable high-frequency oscillation signal through the piezoelectric effect, serving as the system reference clock to ensure that all logic operations and data transmissions proceed in an orderly manner.

2. Ensuring Precision and Stability of System Timing

Crystal oscillators have extremely high frequency stability (minimally affected by temperature and voltage variations). This stability ensures:

Accurate Timekeeping: For example, electronic watches and Real-Time Clock (RTC) modules must rely on high-precision 32.768 kHz crystal oscillators to maintain accurate timekeeping.

Data Synchronization: In communication systems (such as USB, Ethernet, Bluetooth), the transmitter and receiver must maintain strict frequency synchronization, otherwise data packet loss or communication failure may occur.

3. Providing Operating Frequency for Specific Function Modules

In addition to serving as the "heartbeat" for the main processor, crystal oscillators are also commonly used to drive specific function modules, such as:

• RF Communication: Providing carrier frequency for wireless transmit/receive modules.

• Audio Processing: Providing sampling clock for audio codecs to ensure distortion-free sound quality.

• Display Driving: Providing timing reference for screen refresh.

Supplementary: Difference Between Active and Passive Crystal Oscillators

In practical applications, crystal oscillators are generally divided into two categories. They serve the same function but differ slightly in usage:

Passive Crystal Oscillator (Crystal Resonator): Requires external capacitors and the internal oscillation circuit of the chip to start oscillation. Lower cost and most widely used.

Active Crystal Oscillator (Oscillator): Has an integrated oscillation circuit internally. Outputs a complete clock signal upon power-up, with higher accuracy and stability, but at the cost of higher cost and power consumption.

In summary, without crystal oscillators, processors in modern electronic equipment would be unable to operate in an orderly manner, communication systems would lose synchronization, and timing devices would completely stop. The crystal oscillator is the cornerstone that ensures the orderly operation of electronic equipment.

Both quartz oscillators and MEMS oscillators are core components used in modern electronic systems to provide precise clock signals and frequency references. However, they differ significantly in core materials, manufacturing processes, and performance characteristics. The following is a detailed comparison:

1. Core Materials and Working Principles

Quartz Oscillator: Based on natural or synthetic silicon dioxide (SiO₂) crystal. The core principle utilizes the "piezoelectric effect" of quartz crystal — when an alternating electric field is applied to the crystal surface, the crystal produces precise mechanical vibrations, thereby outputting an extremely stable frequency signal.

MEMS Oscillator: Based on semiconductor silicon material. It is manufactured using Micro-Electro-Mechanical Systems (MEMS) technology to create a miniature mechanical resonance structure, typically consisting of an all-silicon MEMS resonator and a programmable CMOS driver chip in a single package, forming a programmable silicon oscillator.

2. Manufacturing Process and Supply Chain

Quartz Oscillator: Belongs to a traditional labor-intensive semi-automated industry. Production involves complex processes such as quartz cutting, grinding, silver plating, special adhesive bonding, and metal packaging. Different frequencies require different raw materials and processes, resulting in longer production cycles and weaker emergency supply capability.

MEMS Oscillator: Uses advanced semiconductor batch manufacturing processes (such as photolithography, etching, deposition, etc.) and is fully automatically produced in integrated circuit (IC) fabrication plants. This process not only achieves large-scale, high-consistency mass production but also significantly shortens supply lead times and improves demand responsiveness.

3. Performance Comparison

4. Reliability and Flexibility

Quartz Oscillator: Prone to fragility, impact sensitivity, and hermeticity issues. Long-term reliability is significantly affected by manufacturing processes and quality management.

MEMS Oscillator: Uses standard chip packaging (such as QFN), offering extremely high cleanliness levels and reliability. Additionally, its programmable platform allows system designers to flexibly configure frequencies, simplifying system design (e.g., a single MEMS oscillator can replace multiple quartz oscillators), and complies with lead-free manufacturing environmental trends.

Summary: Quartz oscillators, with their extremely high Q factor and mature technology, remain the preferred choice for many high-precision reference sources. Meanwhile, MEMS oscillators,thanks to their miniaturization, excellent vibration and temperature resistance, low power consumption, and cost and supply chain advantages from semiconductor mass production, are rapidly replacing traditional quartz oscillators, becoming the ideal clock source solution for modern high-performance electronic systems such as smartphones, wearable devices, automotive electronics (such as ADAS systems), IoT, and AI data centers.