Vertical PNP in circuit simulation

[bhl777]

Hi All, I saw a vpnp model in a circuit, but have some questions about its parasitic pn junction. Could anyone advise how can we connect this pn junction in a circuit? Thank you!

 

[erikl]

The only way for a diode as drawn in your schematic I can imagine would be a second (separate) n-well guardRing with n+ diff contacts surrounding the VPNP's n-well - and, possibly, also the VPNP's collector p+ substrate contacts. In this case its cathode pin (n+ diff) should be connected to the highest positive potential (probably VDD). But of course its anode connection shouldn't point to the base but to the collector of the VPNP = substrate connection.

This construction also would implicate a parasitic lateral NPN, which is totally off, however. Would be nice to see the layout.

 

[bhl777]

Hi erikl, thank you very much for so detailed explanation. I also saw another kind of vpnp from Cadence, like attached. The parasitic diode symbol has different direction. Is this one will be connected exactly the same as the one I showed at the beginning? Thank you very much!

The only way for a diode as drawn in your schematic I can imagine would be a second (separate) n-well guardRing with n+ diff contacts surrounding the VPNP's n-well - and, possibly, also the VPNP's collector p+ substrate contacts. In this case its cathode pin (n+ diff) should be connected to the highest positive potential (probably VDD). But of course its anode connection shouldn't point to the base but to the collector of the VPNP = substrate connection.

This construction also would implicate a parasitic lateral NPN, which is totally off, however. Would be nice to see the layout.

 

[erikl]

I also saw another kind of vpnp from Cadence, like attached. The parasitic diode symbol has different direction. Is this one will be connected exactly the same as the one I showed at the beginning? Thank you very much! View attachment 89910

Yes, I think it's also an n-well guardRing diode surrounding the VPNP. Same connections as above, then. But as the pins are crossed out, I think the connections are handled automatically. Could you provide a layout image?

 

[bhl777]

Hi erikl, I do not have the layout image of any of them. This vpnp is from Cadence Virtuoso ibm 8hp library, and the first one is from internet. Is there any way to search for their layout?

Yes, I think it's also an n-well guardRing diode surrounding the VPNP. Same connections as above, then. But as the pins are crossed out, I think the connections are handled automatically. Could you provide a layout image?

 

[erikl]

Is there any way to search for their layout?

Not easily, because they are confidential in most cases. Some foundries use to include them into their PDKs, but most of them provide only the layout abstracts. You could try and find a full chip layout which contains, e.g., a band gap reference, which very often contains VPNPs - not necessarily with a guardRing, however.