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Clipped sine TCXO for SX1262 usable?

Semtech Transceivers SX126x family
#1

For a stable and reliable operation we consider the use of a clipped sine TCXO, as mentioned in some SEMTEC docs.
Datasheets of most manufacturers show the following characteristics:
Load R ca. 10kOhm / Load C ca. 10pF. That should match the reference circuit from semtech. (10pF/220R in series of the SX1262 input)
But an input level of min 0.4Vpp at the XTA (oscillator-input) of the SX1262 will defenetly not be reached. Even with a 100pF Load (series) Cap, 0.4Vpp is not sure. --> real measurements were done!
I want to meet the requirements of the SEMTECH SX1262 datasheet to guarantee a safe operation.

What is your opinion, what is SEMTECHs answer?

#2

The 10 pF + 220R network attenuates reference products which appear at n*+/-32 MHz about the carrier as a function of PLL reference frequency spurious. Wrt you comment, are you measuring using an active probe or passive probe? If the latter, the probe capacitance most probably loading the XTA port.

Semtech Support

#3

Thank you Support for answering!
Its not about the load of the (passive) probe because:

  1. In you doc is written, that the internal capacity in TCXO mode is 33.4pF. The clipped sine TCXOs supply min. 0.8Vpp at 10pF/10kOhm. That makes 200mVss at the XTA input.
  2. I changed the external cap from 10pF to 100pF. Without the XTA connected, I measured ca. 1Vss directly at the output of the TCXO. (min 0.8Vss) with the XTA connected, the signal directly at the TCXO dropped below 0.8Vss.
  3. With some interpolation I measured at XTA with the 100pF-external cap a voltage of ca. 380mVss @ room temperature.
    In practice the transmission works, but its outside of the specs, at least with the 10pF external resistor.
    What are Semtechs measurements, investigations, certifications?
    What is the right circuit to assure a safe operation?

Tahnk you very much for your help!