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Here is TTL NAND circuit:

enter image description here

My task is to calculate max. number of circuits of same type it is possible to connect in parallel at output of this circuit. It is known R1=4k, R2=1.4k, R3=1k, Vcc=5V, Vce_satuartion=0.2V, Vbe=VD=0.7V, beta_reverse=0.1, beta_forward=40.

What does parallel connection of TTL circuits look like? Maybe like this?

enter image description here

Igor
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  • Are you questioning how 2 NANDs in parallel are connected? This wouldn't make much sense (as it would be pretty redundant), but they would share the same input signals and the same output signals (as in A connected to A', B connected to B', Y to Y'). I'm really clueless about your second drawing, you are treating A and B as if it were a single differential signal. It's not, they are independent signals referenced to GND. – Vicente Cunha Apr 01 '16 at 16:04
  • Hello, thanks for reply. I will edit my question to clarify what I mean :) – Igor Apr 01 '16 at 16:07
  • Please refresh. – Igor Apr 01 '16 at 16:10

1 Answers1

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Ok, the assignment is not too clear about how the other NANDs should be connected, and it is open for interpretation ("should one input be connected to GND?" like your drawing implies would make perfect sense). If you were to ask me, I would short circuit their inputs like so below.

schematic

simulate this circuit – Schematic created using CircuitLab

This makes more sense to me when thinking about the application of such circuit. When a NAND input is tied to GND, it will always output 1, and therefore it is a "dead" gate - its output will never change. NANDs with both inputs tied together behave as a NOT and are commonly used in NAND only systems.

Vicente Cunha
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