AnsweredAssumed Answered

Reduce voltage from 5V to 3.3V 10MHz TTL for HSE in STM32L1

Question asked by bubakovsky.richard on Jun 9, 2015
Latest reply on Jun 9, 2015 by Clive One
Hello, 
I would like to clock RTC with external clocking signal. The problem is, I have 10MHz TTL 0-5V signal at disposal but pins OSC_IN and OSC_OUT have TC pin structure (standart 3.3V I/O). 

I cannot simply reduce voltage by a resistor divider. While the diviter works fine with a direct current, it does not give expected result with 10MHz TTL signal (I am reading noise on oscilloscope). I read somewhere that parasitic capacitance on resistors can spoil high frequency signals.

My question is either: 1) cannot I simply use the 0-5 TTL signal ?  2) how do I reduce voltage of high frequency signal without spoiling its shape significantly ? 

Outcomes