H7RS HSE Analog Bypass Oscillators

[MWisBest]

Hi there, I am designing a product using an STM32H7RS-series MCU, and am looking for some clarification about the operation of the HSE oscillator. I see the H7RS has the option of an "analog" external oscillator in HSE bypass, in addition to the usual "digital" HSE bypass of previous products, and I am very interested in using that analog mode to use a lower voltage clipped sinewave output external oscillator, such as an NDK NT2016SE.

My question is do I need anything in series between the STM32H7RS OSC_IN pin and the output pin of the analog (clipped-sine in this case) TCXO? I would assume I'm not supposed to use a series capacitor like the datasheets of these oscillators tend to show, because the STM32H7RS appears to be looking for a DC-biased signal, but before I make a board with no provision for such an inline passive and find out it doesn't work I figured I should double check here.

Thanks!

[Peter BENSCH · Accepted solution]

Welcome @MWisBest, to the community!

A TCXO such as the NT2016SE, which is only supplied with a positive voltage, can only output a positive output voltage, i.e. a signal with DC offset. The data sheets of those oscillators usually add a series capacitor to remove this DC offset for applications that require a zero-balanced signal.

However, for the analogue HSE of the STM32R/S, you can connect such TCXOs directly without a series capacitor.

Hope that helps?

Regards
/Peter

[MWisBest]

Thanks Peter! That's what I needed to know.