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The difference between N substrate and P substrate

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Bin_Wang

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I hope someone can give some information about N substrate and P substrate process. I found a dual -slope adc design ,which used N substrate process and I do not know the reason.thanks
 

the main is the substrate is difference voltage.
For n, the max voltage
for p, the min voltage
 

for p sub(n well), circuit is more sensitive to ground noise.
for n , it is sensitive to power noise.
 

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    Bin_Wang

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I think two points:
1.Using N sub. The PMOS and NMOS are matching better.The NMOS's mobility is about 2-3 times PMOS's in P sub process.But using N sub process, we can decrease the difference
2.Yout circuit need special NMOS,such as large current NMOS.Using N sub,we can isolate the NMOS and decrease the noise,and so on.
 

Hi,
The first point is correct about better matching but can you elaborate on the second point a little more?
 

there is another reason that if your circuit will produce a negative output voltage, from a single power supply let say +5V, then a N type is preferred like 7660. because u donot want to have trouble to bias the substrate with different voltage level.
 

Psub has higher resistance -> better for isolation of structures.
 

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