Objective
Analyze the frequency stability of a TCXO under varying temperature conditions and observe how temperature compensation maintains stable oscillation frequency.
Materials Needed
- TCXO module (e.g., 10MHz TCXO)
- Frequency counter or oscilloscope
- Temperature-controlled chamber or heat source (e.g., heat gun, ice packs)
- Thermometer (to monitor temperature)
- Breadboard or PCB for mounting the TCXO
- Power supply
Theory
A Temperature Compensated Crystal Oscillator (TCXO) is designed to maintain a stable output frequency despite temperature fluctuations. Ordinary crystal oscillators can experience significant frequency drift with changes in temperature, but a TCXO compensates for these fluctuations by using a temperature-sensitive circuit to adjust the oscillation.
In this experiment, we will examine the frequency stability of a TCXO across a range of temperatures and compare the results to the expected performance based on the oscillator’s specifications.
Steps
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Set Up the Circuit
Connect the TCXO module to the power supply (check the datasheet for proper voltage requirements). Use a breadboard or PCB to securely mount the TCXO.
Attach the output of the TCXO to a frequency counter or oscilloscope. This will allow you to monitor the frequency in real-time.
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Record Frequency at Room Temperature
At a stable room temperature (around 25°C), record the output frequency of the TCXO. This value will serve as your baseline.
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Apply Heat to the TCXO
Use a heat source, such as a heat gun, to gently increase the temperature around the TCXO. Monitor the temperature with a thermometer, ensuring you do not exceed the TCXO’s maximum operating temperature (typically around 70°C).
Record the frequency at various temperature points (e.g., 30°C, 40°C, 50°C). Observe if the frequency drifts or remains stable.
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Apply Cold to the TCXO
After returning the TCXO to room temperature, apply a cold source (such as ice packs or a refrigeration chamber) to lower the temperature of the TCXO. Record the frequency at lower temperature points (e.g., 20°C, 10°C, 0°C).
As with the heating test, observe how the TCXO's frequency responds to cooler temperatures.
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Analyze Frequency Stability
After gathering frequency data at various temperatures, plot the frequency versus temperature. Compare the frequency stability to the TCXO’s specifications (often provided in ppm, parts per million, per degree Celsius).
Example Calculation
For a TCXO with a specified stability of ±2.5ppm/°C, the frequency drift for a 10MHz oscillator can be calculated as:
Frequency drift = (±2.5 ppm) × (Temperature change in °C) × (Nominal frequency in MHz)
For a 10MHz TCXO and a 20°C temperature change, the expected frequency drift would be:
Frequency drift = ±2.5 × 20 × 10 = ±500Hz
This gives you an expected drift of ±500Hz over a 20°C change. Compare this to your measured frequency to assess the TCXO’s performance.
Conclusion
This experiment demonstrates how a TCXO maintains frequency stability over a range of temperatures. While standard crystal oscillators exhibit frequency drift with temperature, a TCXO compensates for these fluctuations, keeping the frequency consistent within its specified tolerance. By comparing the experimental results to the expected drift, you can evaluate the effectiveness of the TCXO's temperature compensation.