nRF52840 with 32.768kHz MEMS oscillator - AC or DC coupled signal path?

[guidoT]

Hello everyone,

according to the device specification, the nRF52840 can be operated with a MEMS oscillator as LFCLK input, which we intend to do. We plan to use a SiT1552 device with the low-swing option (swing 300mV +- 55mV, which meets the electrical requirements listed in chapter 5.4.4.3 Low frequency crystal oscillator (LFXO) of nRF52840 devspec)

What confuses me: This device can be ordered to serve an AC- or DC- coupled signal path. I cannot find anything in the nRF52840 specification or in any Q&A about the internal signal path. From the SiT1552 datasheet:

Output Voltage Setting
NanoDrive Reduced Swing Output
Refer to Table 5 for output setting options
“A”: AC-coupled signal path
“D”: DC-coupled signal path

Any valuable advice is highly appreciated.

Thanks

gT

[ketiljo]

As long as the signal is between the rails (GND and VDD), it doesn't matter what the DC bias is. It's probably best to use a DC coupled output here.

[guidoT]

Thank you ketiljo, for replying so fast