Mainly described that way when it is used to drive. The high collector current of T 1 shifts the stored charge in T 2 and T 3 and hence, T 2 and T 3 go to cut-off and T 1 saturates and then output Y returns to high.įig. Also called totem-pole-or is that reserved for 2 NPNs stacked Can be either 2 NPN or a PNP/NPN totem. The consequent emitter base junction of T 1 starts conducting and T 1 base voltage drops to a low value. Because this current is flowing in the base of T 2, the transistors T 2 and T 3 saturate and then output Y is low.Ĭondition 3: The circuit is operating under II while one of the inputs becomes low. The collector current of T 1 flows in reverse direction. Therefore, T 1 is in reverse active mode. The collector base junction of T 1 is forward biased. The emitter base junctions of T 1 are reverse biased. Output is high (that is Y=1).Ĭondition 2: Each input is high. T 4 functions as an emitter follower and couples a high voltage to load. T 2 is cut off and forces T 3 to cut off. Thus, the base voltage of T 2 is almost zero. The operation can be described briefly by three conditions as specified below:Ĭondition 1: At least one input is low (that is, 0). The voltage drop of diode D remains the base-emitter junction of T 4 reverse biased therefore only T 3 conducts while output is low.

The diode D is added to make sure that T 4 is cut off while output is low. The transistors T 3 and T 4 by the totem pole output, the capacitance CL shows the stray capacitance and so on. The transistor T 2 functions as a phase splitter since the emitter voltage is out of phase along with the collector voltage. In this figure, T 1 has 3 emitters thus there can be three inputs A, B, C. Multiple emitter transistors along with about 60 emitters have been developed. Such transistor can be thought of like a combination of various transistors along with a common collector and base. T 1 is a multiple type emitter transistor. The low output impedance means a short time constant RC therefore the output can change rapidly from one state to the other. The totem pole output implies that transistor T 4 sits atop T 3 in order to give low output impedance. Operation of TTL NAND Gate: Fig.(d) Demonstrates a TTL NAND gate with a totem pole output. Give the circuit of a TTL NAND gate and explain its operation in brief.

Totem pole output configuration