This may be too advanced to include in the e-book. In the section on TTL internal circuitry, the following statement is made:
I have attached a simulation of the TTL vs "DTL" circuits. I used 2N2369 for the transistors. 2N2369 is a fast saturating switch with low storage times.
From a DC point of view, this is true. However, if that were all there is to it, DTL would have been just fine, and TTL might never have been invented. In fact, Q1 in the inverter acts to speed up switching when the input goes low. When the input is high, Q2 is saturated. When the input goes low, excess base charge must be removed from Q2 before it can turn off. If Q1 were simply two diodes, this charge would have to leak off through its base-emitter junction, which would be very slow. A resistor from base to ground would help, but is not needed here. This is because Q1 briefly acts as a common-base transistor when the input goes low, and the excess charge is rapidly dumped to ground through Q1 C-E and the collector of the driving stage. Once the charge is dumped, Q2 turns off, and current ceases to flow in the Q1 collector.transistor Q1 is not being used as is customary for a transistor. In reality, Q1 is being used in this circuit as nothing more than a back-to-back pair of diodes.
I have attached a simulation of the TTL vs "DTL" circuits. I used 2N2369 for the transistors. 2N2369 is a fast saturating switch with low storage times.
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