How are close loops with resistors biased in this bipolar analog IC?

[xihuwang]

Hi,everyone :
Need your help !
I am analysis an bipolar analog IC's picture . There are many resistor (
they are base diffussion resistor I guess) in one island . The resistor are divided by
diffusion protection closed loops . I mean every resistor is in one closed loops, and
all resistors are in one island . But I can't find how these loops are biased . I mean
these loops are float and not connect to vss or vdd.
So , any body can teach me , what is the problem or what is the structure
of this bipolar process.


Thanks forwads !

Ohh, additionally, I can't find the vdd pad !

 

[keith1200rs]

bipolar analog IC

The resistors are normally in an N well which needs to be biased to the most positive voltage on the chip.

What process are you using?

Keith.

 

[xihuwang]

Re: bipolar analog IC

It is bipolar process with P-sub , n-epi. There is no well .
Yes , the base-diffusion resistors are protected by closed protection loop. What
puzzle me is that the loops seem to be float , I can't see they are connected
with vdd or gnd !

Added after 1 minutes:

What makes me surprise more is that a npn transistor's collecter
is connected with the loop.

 

[keith1200rs]

bipolar analog IC

Could you say the process - manufacturer & process name? It will be a lot easier to comment then. The epitaxial layer will be N type and forms the well wit the base resistors in it, isolated by isolation diffusion would be my guess.

Keith.

 

[dick_freebird]

bipolar analog IC

It might be that the resistor bank is subject to a reversing
voltage, and the only option was to let the isolation float to
the highest / lowest potential (dragged by diode). A hard tie
would make the resistor asymmetric electrically.

 

[xihuwang]

Re: bipolar analog IC

But some transistor's collector is connected with the base resistor's protection closed loop. Can transistor's collector be floated ?

Added after 11 minutes:

When I say base resistor, it means the resistor type that is made up of a strip of base diffusion. I think the n-tank connected usually to power.But why the n+ loop
around the base resistor is float (so the n-tank is also float)?