In which of the below-mentioned logic families, the transistors operate between cut-off and active (non-saturation) states? (i) Transistor-Transistor Logic (TTL) (ii) Schottky TTL (iii) Diode Transistor Logic (DTL) (iv) Emitter Coupled Logic (ECL) Choose the correct answer from the code given below: Code:
In which of the below-mentioned logic families, the transistors operate between cut-off and active (non-saturation) states? (i) Transistor-Transistor Logic (TTL) (ii) Schottky TTL (iii) Diode Transistor Logic (DTL) (iv) Emitter Coupled Logic (ECL) Choose the correct answer from the code given below: Code: Correct Answer (ii) and (iv) are correct
Explanation:
Logic families are the logic circuits having identical electrical parameters.
- It is a group of compatible ICs with the same logic levels and supply voltages for performing various logic functions.
- They are fabricated using a specific circuit configuration which is referred to as a Logic family.
- The logic family is designed by considering the basic electronic components such as resistors, diodes, transistors, and MOSFET; or combinations of any of these components.
Different logic families of digital ICs that have been introduced commercially are listed in the table.
|
Name of the logic family |
Components used |
|
DL (Diode Logic) |
Diodes |
|
RTL (Resistor Transistor Logic) |
Resistors and Transistors |
|
DTL (Diode Transistor Logic) |
Diodes, Transistors, and Resistors |
|
TTL (Transistor-Transistor Logic) |
Transistors and Resistors |
|
ECL (Emitter Coupled Logic) |
Transistors and Diodes |
|
PMOS (P Channel Metal Oxide Semiconductor Logic) |
P – MOSFETs |
|
NMOS (N Channel Metal Oxide Semiconductor Logic) |
N – MOSFETs |
|
CMOS (Complementary Metal Oxide Semiconductor Logic) |
P – MOSFET & N – MOSFET |
Logic families are classified according to the principle type of electronic components used in their circuitry as shown in Figure.
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Conclusion:
Schottky TTL and ECL are non – saturated logic.
Extra concept:
The main characteristics of the Logic families are:
- Speed
- Fan-in
- Fan – out
- Noise immunity
- Power dissipation
Emitter Coupled Logic
This logic family also referred to as “Current Mode Logic families”
- ECL is a high-speed integrated circuit bipolar transistor logic family.
- ECL uses an overdriven BJT differential amplifier with single-ended input and limited emitter current to avoid the saturated (fully on) region of operation and its slow turn-off behavior.
- Transistors are not allowed to go into deep saturation thus, eliminating storage delays like in TTL logic families.
The input/output voltages have a small swing (0.8 V), the input impedance is high and the output impedance is low. So, as a result, the transistors change states quickly, gate delays are low, and the fan-out capability is high.
Advantages
- The essentially constant current draw of the differential amplifiers minimizes delays and glitches due to supply-line inductance and capacitance.
- The complementary outputs decrease the propagation time of the whole circuit by reducing the inverter count.
Disadvantages
The major disadvantage is that each gate continuously draws current, which means that it requires (and dissipates) significantly more power than those of other logic families, especially when quiescent.
