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Design >> High-Speed I/O Design >> Pull-up circuit in USB IO transceiver...
https://designers-guide.org/forum/YaBB.pl?num=1257828095

Message started by somisetty on Nov 9^th, 2009, 8:41pm

Title: Pull-up circuit in USB IO transceiver...
Post by somisetty on Nov 9^th, 2009, 8:41pm

Hi All,

Is there any particular reason why most of the USB IO Transceivers,prefer Pull-up circuit at the output?

Thanks

Title: Re: Pull-up circuit in USB IO transceiver...
Post by raja.cedt on Nov 9^th, 2009, 9:26pm

hi,
i guess it's 50 ohms termination...

Thanks,
rajasekhar.

Title: Re: Pull-up circuit in USB IO transceiver...
Post by casual on Dec 15^th, 2009, 6:11pm

Most of the time, USB will be in idle mode, then the driver can be in tristate mode (not consuming power) and let the weak pull up resistor pull the signal to a known voltage instead of tristate/floating. Beside this, receiver also need to sense the speed mode based on the pull-up resistor setting.