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 >> Need of Differential Receiver in Transceiver USB IO...
https://designers-guide.org/forum/YaBB.pl?num=1257139156

Message started by somisetty on Nov 1^st, 2009, 9:19pm

Title: Need of Differential Receiver in Transceiver USB IO...
Post by somisetty on Nov 1^st, 2009, 9:19pm

Hi all,

The basic blocks of Transceiver USB IO attached to the mail...

can anyone say whats the need of Differential Receiver in the Transceiver USB IO?

Thanks

Title: Re: Need of Differential Receiver in Transceiver USB IO...
Post by loose-electron on Nov 5^th, 2009, 10:05am

The USB system exchanges differential data. It might be a better question - what is the need for the single ended receiver in your block diagram?

As for why differential? Look up "LVDS" (Low Voltage Differential Signalling") and read up on that.

Faster data rates, lower current, noise immunity, freedom from good ground connections between RX and TX to name just a few.

THere's a bunch of stuff out there on the LVDS advantadge. Google it.

Title: Re: Need of Differential Receiver in Transceiver USB IO...
Post by somisetty on Nov 8^th, 2009, 8:49pm

thankyou...

Title: Re: Need of Differential Receiver in Transceiver USB IO...
Post by raja.cedt on Nov 9^th, 2009, 12:23am

hi,
generally all drivers will give differential swing through a diffamp kind of structure (as you know single ended data transmission will have lot of impact due to common mode change), so in that case differential RX should be used.

Thanks,
Rajasekhar.

Title: Re: Need of Differential Receiver in Transceiver USB IO...
Post by somisetty on Nov 9^th, 2009, 8:20pm

hi

thanks for the reply...

Why Single ended Receivers in USB Transceiver?

Two single-ended receivers that detect the voltages on D+ and D- with reference to signal ground. The logic states of the receivers’ outputs indicate whether the bus is low or full speed or whether the bus is in the Single-Ended-Zero state.

Thanks

Title: Re: Need of Differential Receiver in Transceiver USB IO...
Post by casual on Dec 15^th, 2009, 6:22pm

Single-ended receiver to support low-speed & full-speed mode whereas differential receiver to support high-speed mode (480Mbps) in USB. If you could differentiate voltage driver & current driver then you got the answer clearly.

Title: Re: Need of Differential Receiver in Transceiver USB IO...
Post by sakthi on Jan 5^th, 2010, 10:16pm

Single ended receiver is for handshake between the host and the device. Single ended signaling is basically used to setup the host and device for the subsequent data transfer. The actual data transfer is done in the differential mode and this is received using the differential receiver.
Since we can have very large ground shifts between the host and the device when using long cables (5m long), differential signaling is used.

also, when a long cable is used for data transfer, the data signal could cause large currents into the ground due to coupling currents (coupling between the data line and gnd). this is reduced by using differential signaling (cancellation of coupling currents). this is the reason why the usb standard has tight cross-over voltage spec and also rise to fall time ratio spec.

sakthi

Title: Re: Need of Differential Receiver in Transceiver USB IO...
Post by loose-electron on Jan 18^th, 2010, 10:21am

somisetty wrote on Nov 9^th, 2009, 8:20pm:

Ah, ok, its a system architecture thing for getting things set up at a low fdata rate before turning things on for differential communication