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Active crystals oscillator are powerful electronic components designed to produce precise and stable clock signals for modern devices. Active crystals combine a quartz crystal and an internal oscillator into one compact unit. Their built-in circuitry makes them easy to integrate while ensuring reliable timing performance in both consumer and industrial applications. This article will discuss about active crystals types, functions, applications and more.
Active crystals are compact oscillator modules that generate precise clock signals for electronic circuits. Unlike passive crystal resonators, which require an external circuit to function, active crystals integrate a quartz crystal and an internal oscillator circuit into a single package. Once powered, they deliver a stable and accurate output waveform, usually in square or CMOS form, making them easy to use and reliable for timing applications.
They typically operate on standard DC voltages such as 3.3V or 5V and cover a wide frequency range from kilohertz to hundreds of megahertz. Their combination of frequency stability, low noise, and consistent performance makes them ideal for microcontrollers, communication systems, computers, and other digital devices. With their built-in circuitry, active crystals simplify design requirements while ensuring precise timing across various industrial and consumer electronics.
A Temperature-Compensated Crystal Oscillator, or TCXO, is designed to maintain stable frequency performance despite temperature variations. It achieves this by using a thermal compensation network that senses changes in ambient temperature and adjusts the oscillator’s output accordingly. This compensation method ensures that the frequency remains accurate over a wide temperature range. TCXOs are commonly used in precision communication systems, navigation equipment, and portable electronics where high stability is required. They typically operate within a frequency range of 1 to 40 MHz and provide outstanding frequency stability levels from 5 × 10⁻⁶ to 5 × 10⁻⁷, making them ideal for applications exposed to fluctuating environmental conditions.
The Simple Packaged Crystal Oscillator, often abbreviated as SPXO, is the most basic type of active crystal oscillator. It functions purely through the natural vibration of the quartz crystal without any additional compensation or voltage control. SPXOs are widely used in systems that do not require extremely tight frequency accuracy but still need a consistent clock signal. They are appreciated for their simple design, low cost, and dependable performance. The typical operating frequency of an SPXO ranges from 1 kHz to 250 MHz, with stability between 10⁻⁴ and 10⁻⁵. Because of their straightforward structure, SPXOs are suitable for timing sources, reference signals, and general-purpose electronic devices.
A Voltage-Controlled Crystal Oscillator, or VCXO, allows the output frequency to be adjusted through an external control voltage. This type of oscillator is especially useful in circuits that require precise synchronization, such as phase-locked loops, frequency modulation systems, and signal generators. By applying a varying control voltage, users can fine-tune the oscillator frequency to match system requirements. VCXOs are known for their flexibility, covering frequencies from 1 to 250 MHz with tunable frequency stability ranging from 10⁻³ to 10⁻⁷, depending on design and application. They are widely used in communication systems, broadcast equipment, and other devices that rely on accurate timing and frequency alignment.
The Voltage-Controlled Temperature-Compensated Crystal Oscillator, or VC-TCXO, combines the functions of both voltage control and temperature compensation to deliver superior frequency stability and tunability. It maintains accuracy across varying temperatures while allowing frequency adjustment through an external voltage input. This hybrid design makes VC-TCXOs highly reliable in environments with frequent temperature changes or where precision frequency control is essential. They are commonly used in advanced communication systems, GPS modules, and navigation equipment that require both stability and flexibility. With their ability to adapt to environmental and operational conditions, VC-TCXOs represent one of the most advanced and versatile forms of active crystal oscillators available today.
| Pin Number | Pin Name | Description |
| Pin 1 | Enable/Disable (OE or ST) | Controls the output signal. When set high (logic “1”), the oscillator output is active. When set low (logic “0”), the output is disabled or high-impedance. |
| Pin 2 | Ground (GND) | Connected to the system ground. Serves as the reference point for all internal and output signals. |
| Pin 3 | Output (OUT) | Provides the oscillator’s frequency output, typically in CMOS or square-wave form. The output frequency depends on the crystal specification (e.g., 125 MHz). |
| Pin 4 | Supply Voltage (Vcc) | Provides the DC power supply for the oscillator, usually 3.3V or 5V depending on model. Proper decoupling (e.g., 0.1 µF capacitor) is recommended near this pin. |
Active crystals like Lithium Triborate (LBO) and Beta Barium Borate (BBO) are used in lasers to generate new light frequencies. Lithium Niobate (LiNbO₃) supports optical modulation in fiber networks, while Nd:YAG and Ti:Sapphire crystals serve as laser gain media for industrial and medical use.
Quartz crystals generate accurate timing signals in clocks and communication systems. Piezoelectric crystals detect pressure or motion by converting mechanical stress into electric signals. Scintillator crystals such as NaI:Tl and LYSO convert radiation into visible light for imaging and detectors.
Protein crystals help scientists analyze molecular structures for drug design. Scintillator crystals improve clarity in X-ray and PET imaging, while piezoelectric crystals in ultrasound probes deliver real-time diagnostic images.
Monocrystalline silicon crystals are used in solar cells for high power efficiency. Metal-organic framework (MOF) crystals aid in gas storage, hydrogen production, and pollution control. Piezoelectric and optical crystals detect vibration, pressure, and gas concentration in environmental monitoring.
• High Precision and Stability - Active crystals provide excellent frequency and signal stability, which is crucial in oscillators, lasers, and communication systems.
• Efficient Energy Conversion - They can convert mechanical, electrical, or optical energy with minimal loss, making them ideal for sensors, transducers, and laser systems.
• Strong Temperature and Chemical Resistance - Many crystal materials, like quartz and lithium niobate, maintain stable performance across wide temperature ranges and resist corrosion.
• Long Lifespan and Reliability - Active crystals have no moving parts, allowing them to operate for years with consistent performance and minimal maintenance.
• Compact and Lightweight Design - Their small size allows easy integration into compact devices such as smartphones, medical sensors, and high-speed communication modules.
• High Manufacturing Cost - Producing high-quality single crystals requires precise growth and cutting processes, increasing material and production costs.
• Fragility and Handling Sensitivity - Crystals are brittle and can easily crack or fracture during handling, mounting, or thermal stress.
• Limited Operating Range - Some crystal types may lose performance or accuracy under extreme temperature, pressure, or radiation conditions.
• Complex Integration - Active crystals often require additional circuits or thermal management systems to function properly in advanced devices.
• Availability and Supply Issues - Specialized crystals or doped materials may have limited suppliers, causing sourcing challenges or long lead times.
Catalogue
FPGA / CPLD
Memory
MOS 
MCU 
DSP
OCEP
Secondary 
Other