2023.05.18 - Unraveling Temperature Controlled Crystal Oscillators
Welcome to the Harmony Electronics (HELE) blog! Today, we're diving into the fascinating world of temperature-controlled crystal oscillators. These devices, known by various acronyms such as VC TCXO, OCXO, and more, play a critical role in our digital world. So, let's get started!
A temperature-controlled crystal oscillator (TCXO) adjusts itself as the temperature changes. It does this using an on-board circuit. The circuit provides a consistent clock signal. It adjusts for temperature and uses a crystal unit that functions in various temperatures.
The TCXO and VC-TCXO are temperature-controlled crystal oscillators that compensate for temperature and voltage.
Another type of temperature-controlled oscillator is the OCXO or oven-controlled oscillator. The OCXO oscillators operate with 3.3VDC and function in temperatures ranging from -40°C to +85°C. This oscillator type features a temperature-controlling circuit to maintain a consistent crystal temperature and other vital components.
OCXO products feature several innovative features, including frequency stability over wide temperature ranges, long-term reliability, and low power consumption. Many OCXO products are available that provide excellent performance and high-precision timing requirements for various applications. These products range from simple one-time clock oscillators to complex embedded systems with multiple frequency outputs.
Crystal temperature stability is an essential factor when considering a crystal oscillator. The TCXO and VC-TCXO have frequency temperature stabilities of ±2ppm to ±50ppm, respectively. On the other hand, the OCXO has an impressive frequency stability rating of 0.005ppm or better over the given temperature range.
The OCXO has the broadest operating temperature range of all oscillator types, ranging from -40°C to +85°C. The TCXO operates in temperatures ranging from -20°C to +70°C. On the other hand, the VC-TCXO works in temperatures ranging from 0°C to +60°C.
The supply voltage for an OCXO is typically between 15V and 28V, while the TCXO requires a 5V power supply. The VC-TCXO operates on 3.3V.
A TCXO or temperature-compensated crystal oscillator maintains the same frequency over a wide range of temperatures. Many applications, such as satellites, network infrastructure, wireless communications, and portable base stations, widely use this oscillator type. The TCXO includes a temperature-sensing circuit that adjusts the output frequency to compensate for variations in operating temperature.
We measure the accuracy of the oscillator by how well it maintains a specific frequency over time. The standard unit for expressing this number is parts-per-million (ppm). Oscillators with higher ppm ratings are more expensive but offer better performance. High stability oscillators have ppm ratings of under 100, while manufacturers typically rate low stability oscillators at over 500.
TCXOs come in different sizes. Some are miniature surface mount packages with less than 1 mm in height. Others are oversized DIP packages that use more power.
When selecting a TCXO, you need to think about the power requirements. Generally speaking, higher accuracy requires more power, whereas lower accuracy oscillators will have lower power requirements.
Using temperature control improves the accuracy of TCXOs. Constant temperature control (CTC) is a technique that uses thermistors and voltage regulation to maintain a constant temperature for the oscillator. This helps maintain accuracy over a broader range of temperatures and reduces power consumption.
TCXOs can use SC cut crystals to improve frequency stability and accuracy. Quartz makes these crystals.
They can control frequency more accurately. They can do this across a wider temperature range than AT or BT cut crystals. Because of their reduced power consumption, lower-power applications can also use SC-cut crystals.
The size of the TCXO package affects the accuracy and frequency stability. Smaller containers increase accuracy but can also reduce power consumption and cost. Larger packages provide more space for components, increasing accuracy and making them suitable for higher-power applications.
Different methods, like CMOS, LVDS, LV-PECL, HCSL, etc., can divide quartz oscillators into more timing product categories. These include popular devices such as the TCXO, the VCXO, and the VC-TCXO.
Quartz-based timing devices are the purest form of timing. These products convert signal frequencies, filter noise, and ensure electrical circuits work correctly and at the right speed. A quartz crystal resonator achieves this function.
A commonly used timing device in circuit design is the quartz oscillator. The quartz oscillator combines the quartz crystal resonator and an IC within an oscillation circuit design.
Temperature-controlled crystal oscillators (TCXO, VC-TCXO, or OCXO) are important for maintaining the accuracy and stability of electronic devices. At Harmony Electronics, we're proud to provide these essential components that help power our digital world.
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