The application of oven-controlled crystal oscillator (OCXO) in ground satellite receivers

The Oven-Controlled Crystal Oscillator (OCXO) is a type of crystal oscillator that achieves ultra-high frequency stability through temperature control technology. Its core principle involves placing the crystal in a temperature-controlled chamber, where heating and temperature control circuits maintain a constant operating temperature for the crystal, significantly reducing the impact of temperature variations on frequency.

The main advantages of the temperature-compensated crystal oscillator in ground satellite receivers are as follows:

1. High Frequency Stability

·Requirement Background: Satellite signals (e.g. communication, navigation satellites) usually use high-frequency carriers (e.g. L-band, C-band), and receivers need to extract data through down-conversion and coherent demodulation, which requires very high frequency stability of the local oscillator.
·OCXO Advantage: OCXO controls the crystal temperature within ±0.1°C by means of a thermostatic bath, and the typical frequency stability can reach ±1×10-⁹ to ±1×10-¹¹¹ (daily drift), which is far superior to that of an ordinary crystal oscillator (XO) or temperature-compensated crystal oscillator ( TCXO). This stability significantly reduces the bit error rate (BER) during signal demodulation.

2. Low Phase Noise

· Application Scenario: Satellite signal transmission rate is high (e.g. QPSK, 16APSK modulation), and too much phase noise will cause blurring of the signal constellation diagram and increase the BER.
·OCXO Role: OCXO's phase noise at 1 kHz offset is usually lower than -150 dBc/Hz, which ensures the spectral purity of locally oscillated signals and improves signal demodulation accuracy.

3. Resistance to temperature fluctuations.

· Environmental Challenge: Ground receivers may be exposed to extreme temperature variations (e.g. -40°C to +70°C), where ordinary crystals can drift due to temperature drift resulting in frequency shifts.
· Thermostatic Mechanism: OCXO's internal heater actively maintains the crystal temperature at a constant level (e.g., +75°C), so that frequency drift is suppressed to the ppb (parts-per-billion) level even when the external temperature changes drastically, guaranteeing all-day reliability of the receiver.

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4. Doppler Frequency Shift Compensation

·Satellite Dynamics: Low-orbit satellites (e.g., Starlink, GPS) generate Doppler shifts (typical range of ±10 kHz to ±100 kHz) due to high-speed motions, and receivers need to track frequency changes in real time.
·OCXO support: OCXO's highly stable reference clock provides a reference for the phase-locked loop (PLL), ensuring that the local oscillator can quickly and accurately track the frequency deviation to avoid signal loss.

5. Long-term Aging Compensation

· Long-term stability: The annual aging rate of OCXO is typically <±0.1 ppm, whereas a common crystal may reach ±2 ppm/year. This is particularly important for satellite ground stations (e.g., deep space communications) that require long-term continuous operation, reducing the frequency of calibration maintenance.

6. Common Frequency Range

The commonly used frequencies for OCXOs in satellite receivers are concentrated in the following range:
·10 MHz: as the base reference frequency, widely used to generate high-frequency intrinsic oscillator signals (via PLL frequency doubling) or directly as baseband processing clocks.
·100 MHz: suitable for high-speed digital signal processing (e.g. ADC/DAC sampling clocks) or to directly drive RF front-ends.
· Other special frequencies: e.g. 10.230 MHz, 20 MHz, 25 MHz, 50 MHz, etc., to be customized according to system requirements.

7. The Basis for Frequency Selection

(1) Satellite Signal Frequency Bands and Downconversion Requirements
Satellite receivers need to downconvert high frequency signals (e.g., L, C, Ku bands) to intermediate frequency (IF), and OCXO is typically used in the following scenarios:
· Local Oscillation (LO) reference source:
o For example: when receiving L-band (1-2 GHz) signals, a 10 MHz OCXO may be used as a PLL reference to generate a high-frequency LO (e.g., 1 GHz) by frequency doubling.
o C-band (4-8 GHz) receivers may use a 100 MHz OCXO to synthesize a high-frequency LO signal through a phase-locked loop.
· direct IF processing:
o If the IF is 70 MHz or 140 MHz, the OCXO may directly provide a clock at that frequency to drive an ADC/DAC or demodulator chip.
(2) System Architecture and Standard Specifications
GNSS receiver (GPS/BeiDou):
o Baseband chips typically require a reference frequency of 16.368 MHz (GPS L1) or 10.23 MHz (raw GPS clock), which is generated by an internal PLL to generate the desired frequency.
o High precision receivers (e.g. RTK) may directly use a 10 MHz OCXO as an external reference to improve clock stability.
· satellite TV (DVB-S2/S2X):
oLNBs (Low Noise Downconverters) typically have a 9.75 GHz or 10.6 GHz (Ku-band) fundamental frequency, but their reference clock may be generated by a 10 MHz OCXO driving a phase-locked loop.
· Satellite Communications Earth Station (VSAT):
o Following the ITU-T G.813 synchronization standard, the master clock is often a 10 MHz or 20 MHz (E1 interface clock) OCXO.
(3) Digital signal processing requirements
·ADC/DAC sampling clock:
o If the receiver utilizes a 100 MSPS (Mega Samples Per Second) ADC, a 100 MHz OCXO may be required to provide the sample clock directly to reduce jitter. o If the receiver utilizes a 100 MSPS (Mega Samples Per Second) ADC, a 100 MHz OCXO may be needed to provide the sample clock directly.
·FPGA/ASIC baseband processing:
o The parallel data interface to the baseband chip may require a 25 MHz, 50 MHz, or 125 MHz synchronization clock.

8. Typical Application Cases

(1) GPS receiver
·OCXO frequency: 10 MHz (external reference)
· Role: Generate 1575.42 MHz (L1 band) local oscillating signals via PLL, while providing accurate timing for baseband.
(2) LEO Satellite Communication Terminal (e.g. Starlink)
·OCXO Frequency: 100 MHz
· Role: Drive high-speed ADC (e.g., 1 GSPS) and multi-channel PLL to support fast capture and tracking of Ku-band (12-18 GHz) signals.

9. Hangjing provides rapid delivery of standard packaging products (1-2 weeks) and customized requirements for temperature-controlled crystal oscillators.

For further details, please contact the sales or technical engineer at Hang Jing.

Summary

Constant temperature crystals are the core clock source for terrestrial satellite receivers through extreme frequency stability and low phase noise, and are especially suitable for demanding environments with high dynamics and low signal-to-noise ratio (SNR). Despite power consumption and size limitations, OCXO remains an irreplaceable choice in critical areas such as navigation, communications, and remote sensing.