N or P substrate, how to know ?

Nov 18, 2008 1 Replies
R

Hello,



I have several hex inverters (actually, they are on a pcb but can be removed), and I would like to know if they are P-substrate or N- substrate based. I assume they are CMOS. Is there a testing configuration in which I can test the inverters, that would tell me if they are N-sub or P-sub? Datasheets are unavailable.



One reason for my wanting to know is that I would like to (re)use the nmos of one the inverters as a stand alone pull-down on a signal. As such, I would like to leave the vdd pin floating and the gnd pin @ 0V. This way the substrate would be polarized at 0V and all the nwells would be left floating. Sounds safer this way (as opposed to having pwells @ 0V and an N-substrate floating).



Any help would be welcome. Roger


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A

There's a clever design for a zero-frequency IF (direct conversion) receiver with gain-matched I and Q channels in the RSGB Microwave Projects book where they use 4049 CMOS hex inverters to make matched voltage-controlled attenuators. The agc voltage goes to all 6 inputs and the Vdd pin. Only the NMOS transistors can conduct. The outputs are paralleled in two groups of 3 for I and Q. It's important to have exactly equal gains in the I and Q channels.

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