NASR-M board bring-up, TCXO adventures II
Yesterday’s TCXO drama was resolved in a more elegant way than surgery. I have always been a fan of conservative treatment, and decided to try one last option before attempting rework. That option was an AC termination of the TCXO’s signal. The datasheet doesn’t explicitly mention single-ended AC termination of the reference input, so it’s kind of a gray area, but it’s perfectly fine for bootstrapping the board. Long story short, I replaced the termination resistor R127 with a 1uF capacitor, and LMK03328 magically passed my reference signal to the output. This might not be the optimal solution in terms of stability, phase noise, e.t.c, but it kind of works for now. In the next board revision, I’ll reserve another footprint for a TCXO with a CMOS output and then compare which one performs better. I’m rooting for an existing clipped sine wave TCXO because of fast rise and fall times, but let’s see. Now I have to work on the Zephyr driver for LMK03328 to correctly configure all the dividers and multipliers for proper PLL operation. This may take some time... Schema with correction is under the cut.
