input output characteristics

hi there,

i was studying this lab sheet for almost 2 days, and i still dont understand whats going on over here in this circuit. we were supposed to find out the input and output characteristics, but i just don understand how do you do so by applying a triangular wave at the output of the gate (TI's 74LS00 NAND Gate) through a resistor.

please help me.. any help is greatly appreciated. I have attached my lab sheet here.

Thanks

The series resistor is the key. The output of the gate is high. The voltage and current characteristic of that logic "high" depend on the "load". The "load" consists of the series resistor and the signal generator output which is a very low impedance. As the trigangular wave form sweeps from -4V to +8V the gate output will see an ever changing load, and will adjust it's output current and voltage according to its chracteristics. You will certainly notice a big difference when you do the same thing with the CMOS gate.

Here is the key feature. You can connect two outputs together as long as you put a resistor in between them. The source with the lowest impedance will drag the other one where ever it can go.

I can't for the life of me figure why you're doing any head scratching. Just do the experiment first and contemplate the results afterwords.