what is the purpose of these transostors..?

[savithru]

hi..

These are the two inverters used at the output of the S-R latch..

Can you pls tell me what is the purpose of these additional transistors( I11, I9, I51, I49).

Yours
SavithRu

 

[xuel]

for esd protection? But their size are a little small, i think.

 

[Btrend]

it must be options for pull high or pull low function.
In this way, u can have option (chance) to set it default to 1 or 0.

 

[Humungus]

Just another idea: could not they be intended to reduce overshoots and undershoots produced by the large capacitance of the output transistors so not to overstress the input transistors of the following stages?

 

[mswug]

if it is the option device, it should be dummy with all nodes tieing to VDD or VSS. So Humungus' idea is more sensible.

 

[hyy95120]

if the VDD and GND were mistakenly connected, the I49,I51 will turn on and protect the circuit inside?

 

[niezimei]

for ESD protection

 

[hung_wai_ming@hotmail.com]

There are 2 reasons behind, maybe
(1) Dummy transistors in layout to provide better matching, put the dummy aside the working transistors
(2) An metal option to increase driving by just changing the gate connection

However, I am afraid (1) is not very true as the m factor is not even so putting such dummy does not help matching. (2) is possible.

Also, it is NOT for ESD protection as this must be an internal logic instead of connecting to PADs, as you can see the device size, not large especially the poly gate length, which is only 0.25, not acceptable for typical ESD protection. If this guy really uses it as ESD protection, it means he doesn't know much about ESD, a wrong design, definitely.

To be honest, I really think adding such dummy transistors are rather useless in practical design as logic is seldom necessary to add such transistors. If the design require such stringent option, then the design got to have some problems already in the mind

 

[jinnose]

Definitely, Dummies!

The connection is right. If the drains are not tied together, it is very difficult to use dummy devices later on. It's not for matching! Who cares about the matching for inverter? Definitely not for ESD, either. ESD only for PADs and it doesn't look like good ESD, either.

 

[ambreesh]

I have seen them being used more from ESD protection perspective.
If you get pads that are provided by foundry good, but lots of product company design their own pads and pad ESD. This is mainly due to their application and system requirment. A pad ESD is decided after lots of testing and lots of redesign.
No harm for us designers in adding certain devices for just in case