Comparator used to compare (v2-v1) and Ref

[Bin_Wang]

I have met the problem when design the differential receiver used in USB 1.1 Transceiver,according USB 1.1 spec, the differential sensitive is 200mV ,and Common mode range is 0.8 to 2.5V (include dierential range).
So the comparator is needed to compare the (v2-v1) and 200mV, I used the two differential pair to realize (v2-V1)-(ref2-ref1), (ref2-ref1)=200mV, but the common mode is problem.
thanks a lot for advice about it.

 

[uladz55]

Hi,

you can try offset comparator architecture.
See for ex. patent 5,517,134, May14,1996

b/rgds
uladz55

 

[IanP]

The differential architecture ensures common mode rejection.
You should sens ΔV=V(+)-V(-) ≥ 200mV and weatter it is on 0.8 to 2.5V level doesn't matter..
I haven't seen anything like that in RS-485; why USB should be different? The main difference between USB driver and RS-422/485 driver is speed..