why avoid using tri devices?

[lailiya]

too many people tell me don't use tri devices in designs, but i still find
tri buffers in library. since there are tri devices, why we don't use them?

 

[WA]

In the beginning, there was a need for tri-state devices.

These were used mostly for bussing applications. But there was a newer device developed.
The Multiplexer is now the perfered choice for higher speed designs.
Tri state used after logic gates added to delays.
Today the multiplexer is easier to implement, and in the long run cheeper too.

Hope this helps as I'm sure many members will add to your knowledge.
wa

 

[stehenry]

The difficulty concerning tristates on devices is that of contention. If there is a shared bus, it is necessary that all components connected to it do not suffer from contention. If there is any contention on the bus, then the tristates will effectively short circuit the supply rail to ground, causing significant current flow, electromigration and one very dead chip.

Muxes are typically used because they don't have this problem. They do however require more area to implement, and may be slower due to increased loading on the buses themselves. Having said that, the performance penalty required to ensure that contention does not occur with tri-states would probably balance this factor out.

 

[xworld2008]

when you do DFT or test ,it will have error.

 

[sandusty]

Power could be considered as one of the reasons. Tri-state will increase the short circuit current and the switching frequency. Reliability will get worst when the power increased.

The tri-state control can be handle just like the memory reset, gated clock, ... so DFT might be one of the reasons but it's not the main reason.

 

[tom123]

you can use tri for IO cells, but if you use tri for on chip signal,

that will increase chip's power consumption, at the same time,

DFT also will become difficult.

too many people tell me don't use tri devices in designs, but i still find
tri buffers in library. since there are tri devices, why we don't use them?

 

[zyphor]

I doubt that tri-state bus will consume more power than corresponding Mux circuit?
Can someone give more specific analysis?

 

[JesseKing]

but how the tristate gate short the p/g??

 

[jarodz]

Tri-state bus need bus holder to avoid the bus on unknow voltage level when the output of all device are in Z state. This situation will consum very large DC current.
For my point, by the today's process technology, we
don't need to use tri-state bus to save the routing(area) inside the chip. The only chance to use tri-state bus is when the bus is out off chip by pad number limit.

Regards,
Jarod

 

[power-twq]

because TRI may increase DFT's difficulty,

and if TRI are used for internal on chips bus,

if these bus has no bus-hold, The floating

node on chip will increase chip's power consumption.

because tri-state node are prone to noise,

noise can often bias these nodes at VT level,

The power consumption will high.


best regards

too many people tell me don't use tri devices in designs, but i still find
tri buffers in library. since there are tri devices, why we don't use them?