Circuit Question (Purpose of the Resistors)

[yUNeeC2]

Hey everybody,

I’m taking a class in switching theory, and am having a little trouble with a theoretical review question. There is a schematic, but I feel it’s unnecessary (and I don’t know how to post it.)

We have 2 inputs to a circuit, A and B. 3 combinations stem from this. A’B, A’B’, AB’ …these three combinations are each sent to an NAND gate. The outputs of these 3 NAND gates are each connected to a fuse and then run through an OR gate (which gives the final output).
Between each fuse and the OR gate, there is a connection that leads to a resistor which is connected to a ground.

We are supposed to be able to tell the function of the resistors/grounds, as well as what would happen if they were removed.

There is no DC labeled (assumed to be there though) and 3 resistors/grounds.
We do all of our work in TINA, and when I removed the resistors, nothing changed. (NOTE: the resistors aren’t in series with the output of the NANDS…they stem off of the NANDS output and would only be encountered (I guess) if the current chose to flow through that path)

If it makes any difference, we simulated destroying 1 or 2 of the fuses leaving no connection between the output of the NANDS and the input to the final OR gate. Don’t know if this would change the effect of the resistors.

Thanks so much for any help,
yUNeeC

 

[Ele38]

Maybe they are just pull-down resistors.

It's purpose is to force a zero (low) value when no other component is driving the input (no load) by providing a current limited path to negative power source through the resistor, while allowing the voltage to swing high if a load is present.
(from WikiAnswer)

 

[berkeman]

Hey everybody,

I’m taking a class in switching theory, and am having a little trouble with a theoretical review question. There is a schematic, but I feel it’s unnecessary (and I don’t know how to post it.)

We have 2 inputs to a circuit, A and B. 3 combinations stem from this. A’B, A’B’, AB’ …these three combinations are each sent to an NAND gate. The outputs of these 3 NAND gates are each connected to a fuse and then run through an OR gate (which gives the final output).
Between each fuse and the OR gate, there is a connection that leads to a resistor which is connected to a ground.

We are supposed to be able to tell the function of the resistors/grounds, as well as what would happen if they were removed.

There is no DC labeled (assumed to be there though) and 3 resistors/grounds.
We do all of our work in TINA, and when I removed the resistors, nothing changed. (NOTE: the resistors aren’t in series with the output of the NANDS…they stem off of the NANDS output and would only be encountered (I guess) if the current chose to flow through that path)

If it makes any difference, we simulated destroying 1 or 2 of the fuses leaving no connection between the output of the NANDS and the input to the final OR gate. Don’t know if this would change the effect of the resistors.

Thanks so much for any help,
yUNeeC

They are addressing the issue of floating inputs to CMOS gates. Try a google search on this to see if you can find the answer. It's an important concept in logic design.