OC5SC25

The OC5SC25 is a high-performance Oven-Controlled Crystal Oscillator (OCXO) manufactured by CTI (Crystal Technology Inc.). Designed for applications requiring extreme frequency stability, this 10 MHz oscillator uses an SC-cut crystal resonator enclosed in a precision temperature-controlled oven, maintaining the crystal at a constant temperature (typically around 85°C) to virtually eliminate frequency drift caused by ambient temperature variations. The ‘OC5’ prefix indicates a 5V supply voltage, while ‘SC25’ refers to the SC-25 package form factor (25x25mm footprint). The OC5SC25 delivers exceptional frequency stability of ±0.01 ppm at room temperature, and maintains ±0.1 ppm stability across the full -40°C to +85°C operating temperature range. This level of performance is typically 100-500 times better than standard XO crystals and 10-50 times better than TCXOs. The square wave output provides clean, fast-edged digital signals compatible with TTL and CMOS logic families, making it ideal for direct interfacing with FPGAs, microcontrollers, and digital systems. The output rise and fall times of 10ns/12ns ensure crisp signal edges for high-speed digital applications. The device features a built-in heater and temperature control circuitry that maintains the crystal at its turnover point temperature. Warm-up time is typically 3-5 minutes to reach within ±0.2 ppm of the final frequency. Steady-state power consumption is approximately 600mW (120mA @ 5V), with higher draw during the warm-up phase. Many versions include a voltage control pin (VCXO capability) for fine frequency adjustment, useful for synchronization applications.

The OC5SC25 operates on the principle of oven-controlled crystal oscillation, providing exceptional frequency stability through active temperature control: 1) Crystal Resonator: An SC-cut (Stress Compensated) quartz crystal resonator forms the resonant element of the oscillator. SC-cut crystals have an inflection point (turnover temperature) where the frequency-temperature coefficient is near zero, providing inherently better stability than AT-cut crystals. 2) Oscillation Circuit: A sustaining amplifier drives the crystal at its resonant frequency, producing a stable sinusoidal or square-wave output. The oscillation circuit is designed for low phase noise and high frequency purity. 3) Oven (Heater) Assembly: The crystal and critical oscillator components are enclosed inside a thermally insulated oven chamber. An electric heater maintains the chamber at a constant temperature (typically 75-85°C), which is set to match the crystal’s turnover temperature. At this temperature, the crystal’s frequency is least sensitive to temperature variations. 4) Temperature Control Loop: A precision temperature sensor (often a thermistor or diode) inside the oven feeds back to a control circuit that regulates the heater current. This closed-loop control maintains the oven temperature to within millidegrees of the setpoint, even as ambient temperature varies over a wide range. 5) Output Buffer: A high-speed output buffer amplifies and shapes the oscillator signal to produce a clean square wave with specified logic levels (CMOS/TTL compatible) and fast rise/fall times. 6) Frequency Tuning (Optional): Many OCXO variants include a varactor diode or voltage-controlled tuning capability. Applying a control voltage to the tuning pin slightly shifts the oscillator frequency, allowing fine adjustment for calibration or synchronization purposes (e.g., locking to a GPS reference). 7) Warm-up Phase: When power is first applied, the oven is at ambient temperature and the heater draws maximum current. As the oven warms up, the frequency stabilizes. The warm-up time (3-5 minutes for the OC5SC25) is the time required to reach the specified frequency stability after power-on.

Note: Pin configuration may vary by manufacturer. SC-25 packages typically have pins on the bottom or sides. Refer to specific datasheet for exact pinout.

• Cellular base station reference clock sources (GSM, LTE, 5G)
• Precision frequency references for test and measurement instruments
• GPS-disciplined oscillators (GPSDO)
• Network timing and synchronization (PTP/IEEE 1588, SyncE)
• Optical networking and DWDM system clock sources
• Military communications and radar systems
• Spectrum analyzers, signal generators, and frequency counters
• High-speed data converter clocking (ADC/DAC)