TSMC mimcap pcell question

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Brittoo

Joined: 24 Jan 2007
Posts: 76
Helped: 12

19 Feb 2009 18:46 TSMC mimcap pcell question

Hello all

A mimcap pcell provided by TSMC has the cap in DNW (mimcap_woum). The Nwell and substrate tap guardring structures are tied together. In one of the designs using this mimcap, the guard ring was connected to substrate potential.

As per my understanding, there is no depletion region formed due to the absence of reverse bias . What is the benefit of connecting the DNW to the substrate potential Question

Regards
Brittoo

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erikl

Joined: 09 Sep 2008
Posts: 737
Helped: 139
Location: Germany

21 Feb 2009 17:59 Re: TSMC mimcap pcell question

Brittoo wrote:

As per my understanding, there is no depletion region formed due to the absence of reverse bias .

Due to the built-in voltage, there's still a (small) depletion region.

Brittoo wrote:

What is the benefit of connecting the DNW to the substrate potential Question

One connection less. Actually, I don't know. May be they fear substrate noise coupling if the DNW comes close to the low-ohmic substrate, s. pp. 32, 46 & 50 of the PDF below.

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