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MOSCAP (Read 1704 times)
raja.cedt
Senior Fellow
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Posts: 1516
Germany
MOSCAP
Jul 08
th
, 2009, 4:12am
hi,
can any body please tell me why moscap is made in N substrate (i knew that we can connect nmos drain and source and it works well, in that case it will be P substrate)
Thanks,
rajasekhar.N
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solidstate
Junior Member
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Posts: 16
Munich, Germany
Re: MOSCAP
Reply #1 -
Jul 8
th
, 2009, 2:19pm
As far as I know, this allows for the moscap to have a dedicated ground terminal; without the nwell, the bottom plate of the moscap would be the substrate, so substrate noise (e.g. from digital logic) could then be coupled in..
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raja.cedt
Senior Fellow
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Posts: 1516
Germany
Re: MOSCAP
Reply #2 -
Jul 8
th
, 2009, 9:46pm
hi,
thats fine but they could have put pwell right because then it works like nmos then we can connect Drain and Source..
Thanks,
rajasekhar.
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shashi.kiran
New Member
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Posts: 5
india
Re: MOSCAP
Reply #3 -
Jul 9
th
, 2009, 4:39am
if ur using NMOS -CAP it has to be p-sub and PMOS CAP it has to be n-well ..!!..i dont think we use Nmos and n-type substrate ..!!
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Dipankar
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Posts: 59
Re: MOSCAP
Reply #4 -
Jul 9
th
, 2009, 7:01am
Dear All,
N-Moscap in nwell means you need very low gate voltage to send the device into strong inversion. So the C-V does not have accumulation region . With this kind of C-V (monotonic) a VARACTOR is realized. They call it NMOSCAP-VARACTOR.
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With Thanks and Regards,
Dipankar.
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raja.cedt
Senior Fellow
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Posts: 1516
Germany
Re: MOSCAP
Reply #5 -
Jul 9
th
, 2009, 9:24am
hi,
i donno weather i am complicating this question or not, but what i thought is it is like having n diffusion's in nwell,so how inversion will come..i think it will be in accumulation only and works for +ve voltage
Thanks,
Rajasekhar.
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shashi.kiran
New Member
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Posts: 5
india
Re: MOSCAP
Reply #6 -
Jul 9
th
, 2009, 9:40pm
@ raja
if you apply +ve gate voltage ...how can u say its in accumulation ??...infact it will be inverted ....i guess dipankar got it right ...it should be in inversion with less gate voltage.
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raja.cedt
Senior Fellow
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Posts: 1516
Germany
Re: MOSCAP
Reply #7 -
Jul 9
th
, 2009, 10:18pm
if you apply +ve voltage it will attract all electrons from nwell..so this is accumulation..how inversion will come?
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Dipankar
Community Member
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Posts: 59
Re: MOSCAP
Reply #8 -
Jul 10
th
, 2009, 7:00pm
Dear Raja,
The crux is nmoscap in nwell gives a monotonic CV curve. That's the motivation behind the structure - creating a mos-varactor.
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With Thanks and Regards,
Dipankar.
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