8/2/2023 0 Comments Totem pole ttl output![]() In essence, these two transistors are acting as paralleled switches, allowing current through resistors R 3 and R 4 according to the logic levels of inputs A and B. Notice how transistors Q 3 and Q 4 are paralleled at their collector and emitter terminals. The same can be said for input B and transistor Q 4: the logic level of input B determines Q 4‘s conduction: either saturated or cutoff. ![]() If input A is grounded, that current is diverted away from Q 3‘s base through the left steering diode of “Q 1,” thus forcing Q 3 into cutoff. If input A is left floating (or connected to V cc), current will go through the base of transistor Q 3, saturating it. We may replace Q 1 and Q 2 with diode sets to help illustrate: Rather than functioning as amplifiers, Q 1 and Q 2 are both being used as two-diode “steering” networks. Transistors Q 1 and Q 2 are both arranged in the same manner that we’ve seen for transistor Q 1 in all the other TTL circuits. Let’s examine the following TTL circuit and analyze its operation:
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