I need to compare and contrast a CMOS IC with a TTL IC. I've chosen a quad 2 input NAND gate IC, 7400 for the ttl version and 4011 for the CMOS. I'm having a bit of trouble with 2 of the requirements.

I need to: compare the power consumption compare the input and output impedance

I've got all other required comparisons but these 2 are upsetting me.

I'm using the following datasheets http://web.mit.edu/6.131/www/document/7400.pdf and https://www.futurlec.com/4000Series/CD4011.shtml 7400 (TTL)

4011 CMOS

Can I calculate the power consumption and input/output impedance from these data sheets? If so, can someone please explain how? I've tried datasheets from other manufacturers but it's the same information. I know it's probably a bit of a hand holdy question but I've been reading up on this for 2 days now and really need some help


  • 5
    \$\begingroup\$ Combine "supply current" with "supply voltage" for your first question. Likewise, input voltage (or VCC - input voltage for high inputs) with input current, etc. \$\endgroup\$
    – user16324
    Commented Jan 4, 2021 at 20:14
  • \$\begingroup\$ what do you understand by the term impedance, if anything, when used with input or output? \$\endgroup\$
    – Neil_UK
    Commented Jan 4, 2021 at 20:31
  • 1
    \$\begingroup\$ I'm sure your instructor talked about how to do this. Go through your notes. It will be important to use the assumptions and methods that you were given in class. \$\endgroup\$ Commented Jan 4, 2021 at 21:52
  • 1
    \$\begingroup\$ I've been through all of the material and it's not there. What I've found with other modules is that some of the required info is in another module which will be covered later which is annoying. As for the impedance, I understand that it is the total resistance of a circuit at a given frequency. I can calculate the average reactance of the CMOS input I suppose using Cin from the data sheet, but what of the output and the ttl device? \$\endgroup\$
    – Barryd
    Commented Jan 4, 2021 at 22:28
  • 1
    \$\begingroup\$ See these TI FAQs: How do I Calculate Power Consumption or Current Consumption for my CMOS Logic Device?, What is the impedance of the device's pin? \$\endgroup\$
    – CL.
    Commented Jan 6, 2021 at 14:01

1 Answer 1


I will answer the output impedance since that seems to be the case that you have the most problems with.

Imagine a perfect source, either ground or Vcc with a series impedance (resistor). The current and voltage is given in the spec sheet for one test case. Use this to calculate the equivalent output impedance. The value of the load resistor doesn't matter, in fact it would be an electronic load for the vendor testing.

Since min and max values are given in the spec, the impedance will have a range.

Note that for TTL, the equivalent output impedance is much different for logic high and logic low.

Note that the output impedance is an estimate, it will vary somewhat depending on the load condition.

And I agree with what Elliot commented, look at your class notes, your instructor may want you to do this a different way.


simulate this circuit – Schematic created using CircuitLab


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.