andrea_mori
Member level 2
I'm building an emitter coupled oscillator (schematic: OCXO_56448_II.jpg) using an SC-Cut 3rd overtone crystal at 5.6448 MHz that has the following specs:
ESR:100 ohm
C0:3.72pF
Cl:0.122fF
Q:2.3M
While a simple capacitor (C3 in the schematic) is able to suppress the unwanted B-mode oscillation for all the crystals I have tested from 11 up to 49 MHz, with the above crystal the oscillator starts anyway at around 6.13 MHz instead of 5.6448 MHz.
I suspect that the resistance of the crystal at B-mode is lower than the ESR at C-mode.
I've tried several ways to suppress the B-mode oscillation without success (attached). All the attached schematics seems to work correctly in simulation but don't work in the real world (X2 emulates the B-mode of the crystal).
Any idea about a more efficient way to suppress the unwanted oscillation at B-mode?
Thank you in advance
ESR:100 ohm
C0:3.72pF
Cl:0.122fF
Q:2.3M
While a simple capacitor (C3 in the schematic) is able to suppress the unwanted B-mode oscillation for all the crystals I have tested from 11 up to 49 MHz, with the above crystal the oscillator starts anyway at around 6.13 MHz instead of 5.6448 MHz.
I suspect that the resistance of the crystal at B-mode is lower than the ESR at C-mode.
I've tried several ways to suppress the B-mode oscillation without success (attached). All the attached schematics seems to work correctly in simulation but don't work in the real world (X2 emulates the B-mode of the crystal).
Any idea about a more efficient way to suppress the unwanted oscillation at B-mode?
Thank you in advance