Consider the following statements:A Darlington emitter-follower circuit is sometimes used in output stage of TTL gate in order to:1. Increase its IOL2. Reduce its IOH3. Increase speed of operation4. Reduce power dissipationWhich of these statement(s) is/are correct?

When the active pull up resistor is replaced by the Darlington pair the following will occur:High current (IOH) flows through the OUTPUT SIDE since the output impedance of the Darlington pair is low. This prevents the high output current IOH from flowing.Capacitor charges within no time due to this high current.The time constant is high and propagation delay is very less.As the capacitor charging very fast, the transition from one level to another level will be fast.It has higher current GAIN and smaller resistances. The smaller resistances cause the logic level transition faster and it increases the SPEED of operation.Totem pole TTL: When the output is at a low level, the transistor Q3 must be ON and Q4 must be OFF.When the output is at a high level, the transistor Q4 must be ON and Q3 must be OFF.A diode is RESPONSIBLE for this compliment operation of the transistors.The addition of the diode at the output also increases the noise margin.The pull-up resistor in Open collector TTL is replaced by the active pull up resistor in the Totem pole TTL.