2022.11.09 - TCXO vs OCXO Crystal Oscillators
Crystal oscillators are essential components in many electronic devices and systems. They provide a stable clock signal for timing and synchronization purposes. Two common crystal oscillators are the primary crystal oscillator (XO) and the temperature-compensated crystal oscillator (TCXO). This article compares TCXOs and XOs to help engineers choose the right oscillator for their electronic designs.
First, you must understand the differences between crystal and oscillator. When you apply pressure to a crystal, it creates an electrical signal. A crystal oscillator is an electronic circuit with a crystal and other parts that produce a steady electrical signal.
The difference between crystal and oscillator includes function, size, and cost. Distinctions between oscillator and crystal include:
The crystal oscillator has two functions. It provides a stable clock signal and adjusts incoming signals. On the other hand, a crystal serves a single purpose - providing a stable clock signal.
The following article will provide additional clarity.
A crystal oscillator consists of a quartz crystal and an oscillator circuit. The quartz crystal acts as a frequency-determining element because of its piezoelectric properties. When connected to an oscillator circuit, it will vibrate at its resonant frequency upon applying DC voltage. This generates the clock signal.
Crystal oscillators provide good frequency stability at room temperature. However, their frequency stability degrades significantly with temperature changes. A regular XO can vary in frequency by 10 to 100 parts per million, depending on the temperature.
Standard crystal oscillator circuits use quartz crystals in a parallel resonance configuration, known as the “parallel resonant crystal oscillator.” Many people use this circuit because it stays stable at different temperatures and requires only a few extra parts. If you do not use additional filtering, the output signal distorts and can have harmonics up to the 10th order.
A designer creates an oven-controlled crystal oscillator (OCXO) to mitigate temperature variations. The OCXO employs an oven to maintain the crystal at a constant temperature and provide higher frequency accuracy. It varies by about five parts per million or less, depending on the model and frequency range.
A TCXO resists temperature changes by using a thermistor and capacitors in its circuit. This design keeps a steady output frequency of ten parts per million or more, depending on the model and frequency range.
High stability and accuracy are critical to the performance of any frequency product. An OCXO or TCXO offers a great solution when choosing an oscillator for your application. Both oscillators are more stable and accurate than regular crystals, but the choice depends on the specific application's needs.
Electronic components with stable and exact frequencies are essential in many applications, such as radio communications, medical imaging systems, and digital control systems. In any of these cases, choosing the proper oscillator is essential to get the desired accuracy for an application.
Precise frequency and stable frequency stability are key requirements when selecting an oscillator. OCXOs and TCXOs offer higher stability, accuracy, and jitter than other oscillators. Strategic applications often use the two technologies that require high-performance solutions.
TCXO vs. crystal oscillator time accuracy depends on the type of application. In general, TCXOs offer better accuracy and stability than traditional crystals. The frequency tolerance is lower for an OCXO or a TCXO when compared to a regular crystal oscillator. Additionally, TCXO oscillator vs crystal oscillator power consumption is more efficient.
A TCXO-temperature compensated crystal oscillator is a specialized crystal oscillator that incorporates temperature compensation. Adding temperature stabilization techniques to temperature-controlled crystal oscillators achieves this.
TCXOs can achieve 1 to 5ppm frequency stability over the operating temperature range with temperature compensation. Some premium TCXOs can even reach 0.5ppm stability. This is a 10x to 100x improvement over basic XOs.
TCXO stability is essential for precision frequency control in communications, GPS, and IoT applications. RF transceivers, base stations, Wi-Fi systems, and other wireless communication equipment also utilize TCXOs.
A temperature-compensated voltage-controlled oscillator (TCVCXO or VC-TCXO) is also available. This oscillator is like a TCXO but can change the frequency with an external voltage control signal. They are perfect for GPS receivers and radios that need to quickly and accurately adjust tuning.
Different types of TCXOs exist, such as analog, digital, microcontroller-compensated, and MEMS, based on the compensation technique used. Applications like satellite receivers, test equipment, telecom base station clocks, and medical diagnostics use TCXO Clock oscillators.
Aerospace systems use OCXO Clock oscillators for applications that require even higher stability. Temperature-compensated oscillators achieve their high stability by using an electronic circuit to adjust the oscillator frequency in response to changes in temperature. This keeps the output frequency more constant, improving accuracy and stability.
Temperature-compensated crystal oscillator circuits are used to accurately adjust the oscillator's tuning, compensating for temperature-induced errors. You can adjust the oscillator circuit to a certain frequency at one temperature and keep it the same at different temperatures. The TCXO is perfect for tasks needing accurate timing despite temperature changes, as it has minimal drift.
Battery-powered devices benefit from TCXOs as they need low power and can withstand varying temperatures.
XTAL ppm (parts per million) measures frequency stability in TCXOs and other crystals. The lower the ppm, the better the temperature compensation and less drift.
Digital temperature-compensated crystal oscillators (DTCXOs) are an extension of TCXOs and provide a higher frequency stability than traditional TCXOs. They use digital temperature compensation algorithms to improve accuracy and enable more precise tuning over a wider range of temperatures.
The VC-TCXO is a new type of TCXO. It reduces power usage by using different voltages. It also adjusts the oscillator frequency with voltage changes.
Here are the main differences between TCXO and crystal oscillator:
Temperature Stability: The critical difference is that TCXOs offer substantially better frequency stability over temperature variations compared to a basic XO.
Accuracy: TCXOs provide higher frequency accuracy. Their temperature-compensated design minimizes the effects of ambient temperature on frequency.
Complexity: TCXOs are more complex than basic crystal oscillators, which impacts pricing for improved performance.
Power Consumption: TCXOs consume slightly more power because of the additional compensation circuitry.
Warm-up Time: TCXOs need time after power-on to stabilize to rated accuracy. An uncompensated XO can reach stability faster.
Size: TCXOs tend to be larger than basic crystal oscillators. However, miniaturized SMD packages are commonly available.
High Precision: TCXOs have excellent short-term stability and accuracy over temperature. They are ideal for ultra-high precision timing applications like frequency synthesizers, communication systems, and medical devices.
Highest Frequency: temperature compensated crystal oscillators (TCXOs) can reach higher frequencies than basic crystal oscillators.
Long-Term Stability: TCXOs also offer superior long-term stability over temperature, making them a better choice than crystal oscillators in applications where the frequency may drift over time.
TCXO Oven crystal oscillator (OCXO): A higher level of accuracy and long-term stability is offered by oven crystal oscillators (OCXOs). These are self-heated with an internal heater to maintain optimal performance in temperature-sensitive applications. OCXOs offer the highest frequency stability and accuracy available.
Here are some guidelines for selecting the correct type of oscillator:
TCXO vs OCXO: Choose OCXO if your system requires more excellent frequency stability and accuracy over extended temperature ranges. Synchronizing multiple devices, such as communication networks, is especially important.
Frequency references are an exact type of oscillator. They enable frequency measurements and transfer, optimize systems or component performance, and provide reference signals for other oscillators.
Temperature-controlled oscillator circuits use a thermistor or thermal diode to sense temperature and adjust the oscillator output. Temperature-compensated oscillator circuits help with performance changes from conditions or aging parts, leading to more stable frequency accuracy.
Oscillator selection depends on application requirements like accuracy, phase noise, stability, temperature range, cost, size constraints, and power consumption. Contact an expert to determine the right solution for your specific use case.
A VCTCXO oscillator uses a crystal to control temperature and adjust the frequency for different temperatures. It provides improved stability, accuracy, and repeatability compared to traditional oscillators.
Temperature-compensated crystal oscillator suppliers offer a broad selection of products to meet any application needs. Additionally, they offer customization services for custom design requests. For example, some suppliers will customize an existing oscillator with alternative frequencies and temperature ranges. Furthermore, customers can obtain complete support and custom services directly from Harmony Electronics.
In conclusion, the proper oscillator is essential for optimal system performance and stability. TCXOs provide superior temperature stability and frequency accuracy compared to basic crystal oscillators. They are perfect for systems that require accurate and dependable timing signals in different environmental conditions.