I need a clock fanout buffer to drive 3 components with same clock, and I have found this reference design but could not understand the reason of using the inverter in the middle.

Can I directly connect the tcxo clock to fanout buffer?

enter image description here


1 Answer 1


The square wave generator is running of 1.8V while the rest of the circuit is 3.3V. The datasheet for the NB3N551 states that a high level clock input requires at least (VDD / 2) + 1V, which makes 2.65V, so it won't recognize the square wave generator's 1.8V output as logic high. The Schmitt trigger inverter is acting as a level translator of sorts.

R8 and C16 form your classic Schmitt trigger inverter oscillator. When the output is high C16 charges and when the input trigger level is reached the output will go low and the same thing will happen in reverse.

The square wave generator's 1.8V output is capacitively fed into this to push the Schmitt trigger's input up and down so it oscillates in sync with the square wave generator.

  • \$\begingroup\$ Thank you for your answer. If i use a 3.3v clock generator(by using 3.3v regulator to tcxo's VDD), can i directly connect it to the buffer fanout. \$\endgroup\$
    – Cenk
    Mar 30, 2023 at 11:04
  • \$\begingroup\$ Yes, that should work. \$\endgroup\$ Mar 30, 2023 at 11:58

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.