Transistor-Transistor Logic OR gate with Open Collector Output: Several emitters on T1 are connected as inputs to create a NAND gate function. When both inputs “A” and “B” are at a logic HIGH level (1), the input transistor T1 turns OFF and the primary switching transistor T2 turns HIGH, making the Q output LOW due to the switching function of the transistor. Therefore, T2 will be in the “OFF” state and the output at Q will be HIGH. This causes the base of T2 to be grounded (0V). When one or both emitter inputs A and B of T1 are connected to the logic LOW level (0), T1’s base current flows via the base or emitter junction to GND (0V), T1 saturated and is followed by the collector terminal. Here, T1 with 2 input emitter terminals acts as an input transistor, and T2 acts as a single-stage NPN inverting switching transistor. The above circuit shows a simplified Transistor-Transistor Logic which functions as v a 2-input NAND gate. So, the TTL (transistor-transistor logic) is formed when the input diodes of the DTL (Diode-Transistor Logic) are replaced with a single NPN transistor with multiple emitter inputs as shown in the above circuit. Therefore, a bipolar junction transistor uses 2 junction diodes, which represent either NPN Or PNP transistors. The basic diode-resistor logic formed with AND gate uses separate diodes for the inputs. To understand this, consider a basic transistor-Transistor logic circuit diagram as shown in the figure below. The operation principle of TTL is based on the switching function of logic gates and amplification performed by the transistors in the circuit. Transistor-Transistor Logic (TTL) is one of the digital circuits designed from BJT (Bipolar Junction Transistor) and resistors. Transistor-Transistor Logic Operation Principle The whole operation is the same as described above. When any one of the inputs A and B is low, then the diode gets forward biased due to the low input. The output is HIGH, which represents logic 1. The transistor T3 turns ON (HIGH) and acts as an emitter follower. Therefore, the transistor T4 also turns OFF due to T2 being OFF. The voltage supply drops in R1 and the transistor T2 turns OFF because it has not had enough voltage to turn ON. The current goes to the ground via the D1&D2 and the resistor R1 due to the supply voltage VCC of 5V. When both the inputs are LOW, diodes D1 and D2 get forward biased. The output is LOW, which represents logic 0. The transistor T4 and the diodes at the emitter are forward biased and a negligible amount of current flows. When the inputs A and B are HIGH, the transistors T2 and T3 turn ON and act as common-emitter amplifiers. The circuit is designed as a high-performance TTL NAND gate where NAND elements are four-pair inputs of type 74H00 or 54H00. The operating speed and power dissipation are higher than low-power TTL. The high power TTL is the high-speed version of standard TTL. This TTL Schottky is further subdivided into many types such as Low Power Schottky, Low Power Schottky, and Extended Schottky TTLs. The Schottky transistor used in this type of TTL is nothing more than a bipolar transistor, the base, and collector of which are connected by a Schottky diode. The circuit design is very similar to high-power TTL. The power dissipation is the same for both TTLs and there is no additional power consumption. The speed offered by this type of TTL is twice that of high-power TTL. It is used in various applications in a combination with speed and dissipation. These are used as glue logic, which can connect more complex devices in digital systems. This is the first TTL IC developed in the year 1965 to perform basic logic functions. The most important feature of the TTL device is that the inputs of the gate will be logic high (1) if they are not connected. Transistor-transistor logic (TTL) is an integrated circuit that performs a logic function to provide a switching function by using bipolar transistors. What is Transistor-Transistor Logic Or TTL? This article gives a brief description of the internal structure and working of a transistor-transistor logic circuit with a 2-input NAND gate function. It is widely used in various applications such as electronic devices, computer control systems, industrial controlling systems, the design and fabrication of integrated circuits, and many more. It belongs to the digital logic family and is designed with bipolar transistors, resistors, and diodes. The concept of TTL was developed to achieve high speed, low power dissipation that allows optimization of the design. In 1963, Sylvania as Sylvania Universal High-Level Logic (SUHL) introduced the first Transistor- Transistor Logic circuits.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |