EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: JoeN on August 10, 2016, 05:45:40 am
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By digital circuits, I mean transistor circuits working as digital circuits where the circuit is modeled up from transistors up to gates, more complex subcircuits, and finally state machines. Right now I modeled a RS flip flop and built a test circuit to use it as a frequency divider, just as a test. I think it is quite interesting how as an analog simulation it shows you the slew of the transistors (especially when it is run at a faster clock), voltage excursions, etc. Is this the way to do it? Or is this insane? How well is this going to perform if there are a few thousand transistors in the simulation?
Comments or advice would be appreciated.
Basic gates:
Inverter
(https://www.eevblog.com/forum/beginners/is-ltspice-an-appropirate-tool-to-use-to-model-digital-circuits/?action=dlattach;attach=246772;image)
2-NAND
(https://www.eevblog.com/forum/beginners/is-ltspice-an-appropirate-tool-to-use-to-model-digital-circuits/?action=dlattach;attach=246776;image)
3-NAND
(https://www.eevblog.com/forum/beginners/is-ltspice-an-appropirate-tool-to-use-to-model-digital-circuits/?action=dlattach;attach=246774;image)
The RS flip flop:
(https://www.eevblog.com/forum/beginners/is-ltspice-an-appropirate-tool-to-use-to-model-digital-circuits/?action=dlattach;attach=246770;image)
The testbench circuit:
(https://www.eevblog.com/forum/beginners/is-ltspice-an-appropirate-tool-to-use-to-model-digital-circuits/?action=dlattach;attach=246768;image)
The results:
(https://www.eevblog.com/forum/beginners/is-ltspice-an-appropirate-tool-to-use-to-model-digital-circuits/?action=dlattach;attach=246766;image)
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Looks good and if it works for you, why not!
Simulations will start to slow down the more components and signal paths you have.
Also, there are a few digital gate components built into LTSpice's shipped library.
I just wonder though, if you are going to design something using thousands of transistor, it might be time to look at something like CPLD/FPGA.
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Or at least use the toolchain for the CPLD/FPGAs. Most have schematic entry and many have simulators. There's a bit of a learning curve to using the toolchain and describing circuits but they can be described at the gate level.
Try the free version of Xilinx Vivado.