bandgap & BJTs in TSMC18

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heng155

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Hi,
I'm designing a Bandgap in TSMC18 process.
Simulation shows "beta" of vpnp is quite small, about 2.5; "beta" of npn is about 23.
It seems I must use npn instead of vpnp? Why "beta" of vpnp is so small?(I've heard that "beta" of vpnp is bigger than lpnp, which is no bigger than 5) Why so many designs use vpnp? When we use npn, we must have deep n-well. Does TSMC18 have n-well? Is it vnpn?
v-vertical l-lateral

Thanks!
 

generic 180nm process of TSMC is double well process that's mean there is no vertical pnp., L-pnp is the parasitic pnp at all. so the beta is not larger than vpnp. also l-pnp the collection is p-substrate. Base is nwell. no npn provide at all. because there is no isolated pwell unless use tri-well process.

BTW i don't think beta have effect with bandgap design. but Resistor and structre type do.
 

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    heng155

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I don't think so.
In double well process. Pplus(in n-well)-Nwell-Psub is a vertical pnp, so it's collection must be connected to gnd. L-pnp can put in a single n-well. plus-nplus-plus is a lpnp.
When we have triple-well, a p-well in the deep-nwell, we can use npn, either vnpn or lnpn.
Thanks!
 


you are right
 

ramberwang said:
BTW i don't think beta have effect with bandgap design. but Resistor and structre type do.
Click to expand...

You're right. Thanks!
 

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