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npoly vs ppoly resistor (Read 4412 times)
supermoment
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Posts: 167
npoly vs ppoly resistor
Feb 25
th
, 2010, 11:23pm
For a nmos CML logic eg: typical CML latch, should I pick up npoly or ppoly as a resistor loads? The voltage swing is from Vdd to Vdd-swing, Does it have any difference to use npoly or ppoly if Rsheet is about the same
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ywguo
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Shanghai, PRC
Re: npoly vs ppoly resistor
Reply #1 -
Feb 26
th
, 2010, 12:53am
Hi Casual,
If Rsheet is different, I suggest that you choose the resistor with larger Rsheet. Because it means smaller area and parasitic cap. If Rsheet is about equal to each other, I don't know what is the difference between the two.
Yawei
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supermoment
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Re: npoly vs ppoly resistor
Reply #2 -
Feb 26
th
, 2010, 10:52pm
I think npoly is much better than ppoly because npoly sit at p-substrate, thus has larger reverse bias voltage (nmos is reference to vdd swing) results in smaller parasitic cap. is it correct?
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ywguo
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Re: npoly vs ppoly resistor
Reply #3 -
Feb 27
th
, 2010, 5:56am
supermoment wrote
on Feb 26
th
, 2010, 10:52pm:
I think npoly is much better than ppoly because npoly sit at p-substrate, thus has larger reverse bias voltage (nmos is reference to vdd swing) results in smaller parasitic cap. is it correct?
Casual,
I am sorry that I don't understand what you said. -- Yawei
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supermoment
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Re: npoly vs ppoly resistor
Reply #4 -
Feb 27
th
, 2010, 9:39pm
sorry i think i had made a mistake in previous statement.
npoly is sitting at tox and not on the diffusion, so there is no diffusion cap as in nplus resistor
So is there any big difference between npoly or ppoly resistor? I use it as a load in nmos CML latch.
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HdrChopper
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Re: npoly vs ppoly resistor
Reply #5 -
Feb 28
th
, 2010, 11:34am
Hi
Since both resistors have different type of implants, they will also have different temperature coefficients.
If TC is not an issue I agre with Yawei: use the one with highest sheet rho.
If they are similar and TC is something you care about for your circuit you might want to select the one that gives behavior over temp suited for your application.
Tosei
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Keep it simple
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supermoment
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Re: npoly vs ppoly resistor
Reply #6 -
Feb 28
th
, 2010, 8:35pm
thank you very much
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