I posted a question about a week ago about impedance and have a follow up if you will indulge me.
I'm comparing input and output impedance from TTL and CMOS ICs, specifically 7401 and 4011 NAND gate ICs.
I know that the frequency plays a part but generally I am led to believe that Vcc-Voh/Ioh gives me the high logic output impedance and Vcc-Vol/Iol gives me the low logic output impedance. Right?
For the 4011, the datasheet gives a min Voh of 4.95 at Vcc 5V. So 5-4.95/Ioh(0.88) = 0.05/0.00088 = 56 ohms. Sounds about right. Right?
For the low logic, Vol is max 0.05V @ Vcc 5V. so 5-0.05/Iol(0.88) = 4.95/0.00088 = 5625 ohms. From my internet research, the output impedance from CMOS ICs is low in either logic state so the value of 5625 can't be right. Right?
Also taking the input impedance I'm using Vcc-Vih/Iin and Vcc-Vil/Iin which gives me a high logic impedance of 13Mohm and 36Mohm @Vcc15V (15V as that's all that's provided for Iin) Is this about right? I can't help but think that I should be doing something with Vo as it's specified in the conditions for Vih and Vil.
If you've read this far perhaps you'll do me another solid. Why does the output impedance matter? I understand that the high input impedance is important for driving other logic gates but what about the low output impedance?
Thank you so much. Appreciate the help I receive here