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supermoment Senior Member Offline 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 Community Fellow Offline Posts: 943 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 Senior Member Offline Posts: 167	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 Community Fellow Offline Posts: 943 Shanghai, PRC	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 Senior Member Offline Posts: 167	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 Senior Member Offline Posts: 167	Re: npoly vs ppoly resistor Reply #6 - Feb 28^th, 2010, 8:35pm thank you very much
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