The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> High-Speed I/O Design >> Gain and Bandwidth of CMFB in LVDS
https://designers-guide.org/forum/YaBB.pl?num=1353592033

Message started by analog_design on Nov 22^nd, 2012, 5:47am

Title: Gain and Bandwidth of CMFB in LVDS
Post by analog_design on Nov 22^nd, 2012, 5:47am

Hi,

How can we decide open loop Gain, Bandwidth as well Loop gain and bandwidth for CMFB circuit in LVDS Transmitter driver .

Please, let me know. I am wondering about it.

Thank You

Title: Re: Gain and Bandwidth of CMFB in LVDS
Post by raja.cedt on Nov 22^nd, 2012, 12:27pm

hello,
please post the schematic. is it an hbridge with current source or any thing else?

Thanks,
Raj.

Title: Re: Gain and Bandwidth of CMFB in LVDS
Post by analog_design on Nov 22^nd, 2012, 10:56pm

Hi Raja,

attached is schematic of LVDS Transmitter from Boni paper. I am trouble to define specs for opamp and CMFB Circuit.

Please let me know.

Warm Regards,
Girish

Title: Re: Gain and Bandwidth of CMFB in LVDS
Post by raja.cedt on Nov 23^rd, 2012, 4:25pm

hello Girish,
i guess it will be tough to define precise gain and BW.

Gain: CMFB gain will decides common mode error, which may impact receiver performance by it's input common mode change. If you have ac coupling at receiver then i guess gain wont impact much. There are few standards which are having tough spec on TX common mode variation, but there will be some min max range.

BW: For example there if common mode disturbs, then loop should restore back in few bits span otherwise you receiver front end may be effected. This will get you the bandwidth limitation.

Thanks,
Raj.