Diode Transistor Logic Component

In DTL (Diode transistor logic), all the logic is implemented using diodes and transistors. A basic circuit in the DTL logic family is as shown in the figure below. Each input is associated with one diode. The diodes and the 4.7K resistor form an AND gate. If input X, Y or Z is low, the corresponding diode conducts current, through the 4.7K resistor. Thus there is no current through the diodes connected in series to transistor base . Hence the transistor does not conduct, thus remains in cut-off, and output out is High.

If all the inputs X, Y, Z are driven high, the diodes in series conduct, driving the transistor into saturation. Thus output out is Low.
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