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Design >> Analog Design >> Resistor Layouts & IBM process
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Message started by eng on Apr 26^th, 2007, 4:24pm

Title: Resistor Layouts & IBM process
Post by eng on Apr 26^th, 2007, 4:24pm

Hi all,

I'm using IBM .18um process. I need to use some resistors in my design. The first one is compensation resistor that will not draw any DC current, the other one will draw 30 uA. These resistor have big values 30k, 100k. IBM process has a p- polysilicon resistor which gives the biggest resistance per area. It comes W=3u and L=3u by default.
The questions
- In order to minimize the area how far can I reduce W of resistor. (minimum is 1.1u)? It should be dependent on the current flow. Is 30u current big enough to worry about the W of resistor? Is there any equation min W in terms of max current?
- The resistor has two option nwrrpres and nwrrpresx (x means explicit body connection?). Are they different in terms of layout?

P.S. This post should fit in a layout/process forum but I couldn't find any. sorry...

Title: Re: Resistor Layouts & IBM process
Post by ACWWong on Apr 27^th, 2007, 2:38am

IBM have an excellent model guides and design manual which explain things very clearly. These can be found in the process doucmentation as part of the kit.
Anyway
1) A minmum W will exist, as will a maximum DC current density.... 30uA is a small current so you will have no problem with using minimum width. Whilst minimum width will reduce area and parasitic, it will invitably increase variablity.
2) The x allows explicit connection of the bulk connection. Without the x, the component uses netset property to connect the bulk (which i seem to recall is default to sub!). again the kit documentaion should cover this. Layout is the same, although incorrect schematic connect of the x terminal may lead to layout difficulties.
Also nwrrpres sounds like an nwell resistor not a p- poly resistor which should be called oprrpres.

cheers
aw

Title: Re: Resistor Layouts & IBM process
Post by skas20 on Apr 27^th, 2007, 3:21am

IBM process design manual will give you what is the minimum width you can use for the resistor.
However, It is not good to use minimum because the variations on the model parameter will be +-10% or more.
hence you can use may be a 0.5 micron extra than minimum which also brings down the tolerance.

For the maximum side, the process design manuall will give the voltage and current capacity of every device can afford to be operating in normal characteristics.

Appart from oppcres and nwrrpcress, you can also use opndress (diffusion resistor) which has more density compared to poly resistor.

but remember, polyresistor gives you the least tolerance.

Regards,
SK.