Welcome to the lecture on diode transistor logic, this is the circuit diagram here given. So in this diagram you can see we have 4 diodes, this is diode D1, this is D2 and this is diode D3 and this is diode D4 and we have 3 resistors, this is star R1 which is connected to the power supply and this is R2 that is also connected to the power supply, this is R3 which is connected to the base of this transistor, transistor T, this is the base of the transistor, this is the collector of the transistor and this is the emitter. So since we have diodes and transistors in the circuit we call it diode transistor logic so you can see the figure of a diode, this is how diode looks like, so this part of the diode is nothing but the cathode and this is the anode, if the diode wants to conduct in the power direction the anode should be high and the cathode should be low, kept at low voltage. So if you keep the cathode at low voltage the diode would conduct in reverse direction, the low voltage will be propagated, so you can see we have 2 input leads for the diode transistor logic circuit, so let us name them A and we will draw a table here and it can be B and the output can be taken from B0, where is B0, here is B0, so just above the collector of the transistor, so since we have 2 variables we can have input A and this can be input B, that is what 0 for A and 0 for B, so the cathode of the 2 diodes D1 and D2 are kept at low voltage, here in the first condition, low voltage will be propagating 2 diode D3 like this, so you can see the diodes D3 and D4, so the low voltage is propagated from diode D1 and D2, 2 diode D3 and D4, now the diode D3 will not conduct because the anode of the diode D3 is at low voltage, if the anode is kept at low voltage, that will not be any power flow, so the diode will be cutting off, D3 will be cutting off and D4 will be cutting off and the transistor will be cutting off, the power will be since 1 layer B0, so D3, D4 and transistor T are not going to conduct and the power will be since 1 layer B0, next condition is 01, let us see what happens if 01 is applied to the input leads A and B, now we will see, I will just erase the previous points, 01, now you can see for diode D2, the cathode is kept high, if the cathode is kept high, diode is not going to conduct, it will be cut off from the circuit itself, now here you can see the cathode is kept at low voltage, the diode will start conducting and the low voltage will be propagating to again diode D3, it will be reaching the anode of the diode D3, since the anode of diode D3 is kept at low voltage, so what happens, you can see the truth, what happens in the first part of the input 0, the same thing is going to happen now, anode is kept at low voltage, the plus 5 from the BC will be sent to B0, since diode D3 is not conducting, D4 will not conduct and T is not going to conduct and B0 is going to get 1, next input will be 1 0, so 1 0 is the next combination we have, I will just change it, erase all the points we discussed, now what happens if you are giving 1 0, I am sorry this here also, this 1 0, now you can see 1 0 is given to this, diode D1, the cathode of diode D1 is connected to the high voltage, it is not going to conduct, it will be cut off from the circuit itself, diode D2 will be conducting, low voltage from diode D2 will be propagating to D3, now the anode of D3 will be getting the low voltage, if anode is getting the low voltage, the D3 is not going to conduct and hence what diode D4 is not going to conduct and the transistor T is not going to conduct because the base of the transistor is low, now the transistor if it is not conducting, it is going to cut off region, it is not conducting, naturally the power will be flowing to B0, so B0 will be showing high voltage, the last one is 1 1, if you keep 1 1, I will just erase this extra points, so that we will be confused, and there is this also, just a minute, ok, so I think it is done, now 1 1 is applied, so 1 1, I will be applied to the cathodes of both the diodes, if both diodes are kept at high and the cathodes side that means what happens, they are cut off from the circuit itself, right, so both the diodes are not conducting anymore, so what happens, the voltage at the top you can see, so these two are disconnected, I am just showing you, yeah, so the voltage at the top will be driving, right, the current to flow through the diodes, right, now the voltage, you know power will be traveling in this way, now the anode is kept at high, anode of D3 will be getting high, high voltage, right, this is anode cathode of D3, right, the anode will be transferring power, and now the D4 will be conducting, right, the high voltage will be given to the base of the transistor T, now the T will be in the conduction state, right, previously it was in the cutoff region, now, most of the voltage power will be traveling to the transistor, right, so only low voltage is avoidable at V0, so V0 is getting lower voltage, right, so this resembles the truth table of a nan gate, right, so this is the truth table of a nan gate, and this is how you create a nan gate from diode transistor logic, right, so this is how you create, in the next video, we will design a circuit with resisted transistor logic, right, if you have any doubts, please put it in the comments section, and thanks for watching.