Volume 4, Chapter 3, Section 2 (The NOT gate)
The picture shows current flowing from the base of Q4, but where is that current coming from, and why would it flow if the output was not at a different potential? <- (I realize that the voltage says "approximately equal to" 0, but if it were approximately zero, how could it overcome the 0.7V to forward bias the base-collector junction of Q4?)
Also, why is Q3 not saturated? The section explains that there wouldn't be enough voltage to forward bias both Q3 and the diode, but isn't that arbitrary based on the values of the resistors? This is a tough chapter for me, thanks in advance.
The picture shows current flowing from the base of Q4, but where is that current coming from, and why would it flow if the output was not at a different potential? <- (I realize that the voltage says "approximately equal to" 0, but if it were approximately zero, how could it overcome the 0.7V to forward bias the base-collector junction of Q4?)
Also, why is Q3 not saturated? The section explains that there wouldn't be enough voltage to forward bias both Q3 and the diode, but isn't that arbitrary based on the values of the resistors? This is a tough chapter for me, thanks in advance.