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question about BJT simulation in Cadence

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EMfox

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I try migrating to BJT by reading the textbook by Gray & Meyer. Simulations should be the best way to get an insight into the methodologies.

But I need advice on the starting point, say, on how to run simulations in Cadence. I don't know what Vcc I should choose for the supply, how to size the transistors, etc...

I have experience with CMOS, but I need some guide to get a simply circuit up and running so that I can build up atop.

I tried to google for online manuals/tutorials, but it turned out that CMOS is the dominant player.


So please let me know about anything I can start up with... Thank you!
 

willyboy19

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There is nothing magic about BJT, if you already know how to analyze/design a MOS cicuit. Always starting from DC operating point, which will determine the current level of the BJT and associated biasing resistor values. Once you have the DC operating point set, you can then play around with AC simulation for BW and noise, and then transient analysis for all other specs (such as slew rate, THD, etc). Of course, you need to remember one single most important difference: the BJT base current is non-zero and has finite input impedance from base input -- a big difference from MOS transistors. You will appreciate this difference when you get to know more and more of the BJT based analog circuit -- more than 80% of the difference from the MOS counterpart originates from the difference I quoted above.
 

sankudey

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The above post gives most answear of the original topic. I would like to add some points to that.

1. For Vcc selection, u may need to look for the Bvceo (C-E break down voltage) which is, infact, some times limit the powersupply. This u could thought of like Gate oxide breakdown voltage of MOS. But not exactly same.
--> for newer technologies (hetero junction, HBT) the Bvceo is really very low (even ~2V). For discreate component it is much much higher (~10V to ~200V).

2.After defining the Vcc, most of the mathematics u could find from the book (gray meyer as u mentioned) to bias it and to meet the spec.

Good Luck...
sankudey
 

EMfox

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Thank you guys! I appreciate your help!
 

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