WK>> There are even some canned oscillators with LVDS  outputs. But
 WK>> those, of course, are never in the 4-lead dip packages. 

 GM> What is LVDS?

Low voltage differential signaling. It's used for high speed data in the 
hundreds of megabits/s to a couple of gigabits/s range.

The voltage swing at the driver is only a few hundred millivolts, which 
provides several advantages. Lower power because you don't have to dump as much
energy into the transmission line as you would if you wanted it to swing near 
the supply rails. Better noise tolerance because most induced noise will be 
common mode. Higher speed because you don't have to wait for the outputs to 
slew very far before changing them again.

It requires two outputs that are differentially driven. It also requires 
controlled impedance differential routing on the PCB. The two outputs need to 
be close together and preferably with small smt pads to have minimal impact on 
the transmission line impedance. That's why you'll never find these in the DIP 
style cans. Any connectors in the path have to be chosen for minimal disruption
of the line impedance. Cables and PCB routing must have the same differential 
impedance, typically 100ohms.

Probably the most common application is interfacing to flat panel displays. 
Four LVDS pairs for data and one for clock is a common arrangement.

There are some descriptions of LVDS floating around on the web that incorrectly
state or imply that the "LV" refers to operation at low supply
voltages like 
3.3, 2.5, 1.8, etc. It does have the advantage of working well with low voltage
systems, but that isn't the point at all. The point is that the signal swing is
significantly lower than the supply voltage, whatever that may be.



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