substrate terminal - RF Cafe Forums

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dipak

Post subject: substrate terminal Posted: Mon Dec 18, 2006 8:10 am

Captain

Joined: Tue Nov 14, 2006 7:21 pm

Posts: 9

Location: Nagpur(M.S)

what should be the effects if we dont connect substrate terminal to the ground in CMOS process?

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fred47

Post subject: SubstratePosted: Mon Dec 18, 2006 12:33 pm

General

Joined: Wed Feb 22, 2006 3:51 pm

Posts: 104

Hi Dipak!

Not connecting the substrate to ground in a CMOS process would have differing results, depending on what it is connected to:

1. Nothing. A floating substrate will cause roughly one-half of the mosfets to operate improperly. Which half would depend on whether your process was N-well or P-well. (As an aside: when I covered for a professor during a sabbatical, I was able to watch the students try to find out why their labs weren't working - a lot of very strange effects showed up due to an open substrate connection.

2. Negative voltage (for a normally-powered chip): Unless Vdd(max) is exceeded, you'll only encounter problems if the substrate is inadequately bypassed.

3. Positive voltage: depending on the voltage, as you increase from 0 volts, you'll increasingly move away from proper operation until your design doesn't work.

Good Luck!

Fred

Posted  11/12/2012