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Design >> Analog Design >> effect of pnp in CMOS bandgap
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Message started by love_analog on Jul 20^th, 2014, 8:38am

Title: effect of pnp in CMOS bandgap
Post by love_analog on Jul 20^th, 2014, 8:38am

What is the effect of poor pnp in CMOS bandgap in very fine geometry.

I believe CMOS pnp have poorer base resistance. Also the Ie is not equal to Ic since base is wide.

How does this translate into overall bandgap performance? Does it lead to more tempco. Can it be trimmed out so not an issue?

thanks

Title: Re: effect of pnp in CMOS bandgap
Post by RobG on Jul 29^th, 2014, 4:15pm

I don't think there is anything drastically different. The main effect of high base resistance is that you have to run the device at lower currents so the Ib*Rb drop is negligible. otherwise this IR drop will add curvature to the design which may not be modeled accurately. It also adds a non-ptat error that cannot be easily trimmed out.

I don't know why smaller geometries would necessarily make the base "wide." Quite the opposite in fact.