The Wave Form of STM32F429 osc_out pin have a DC level, Is it correct?

helixwmonkey · ‎2014-04-26

Posted on April 27, 2014 at 03:25

The picture is the wave form of STM32F429 osc_out pin,The low level is not 0V, but is 1.24V, Why the sine wave's value of peak to peak is 1.04V. Is it correct?

Danish1 · ‎2014-04-28

Posted on April 28, 2014 at 11:54

Yes that is correct.

That voltage is needed to bias the osc_in pin so it operates as an amplifier rather than a digital inverter.

Inside the stm32 there is a resistor that goes between osc_out and osc_in, perhaps 10 Megohms. So there is no DC voltage across the crystal.

As well as this resistor to set the bias, there is also a mechanism to control the gain of this amplifier and thereby the amplitude of oscillations. This is so that you should be able to get reliable oscillations without consuming excessive power or damaging the crystal.

Hope this helps,

Danish

helixwmonkey · ‎2014-04-29

Posted on April 29, 2014 at 12:03

Thank you for help.