In Digital Electronics (DE), logic families and IC technology are very important topics. ECET exams usually ask direct questions about TTL, CMOS, ECL, fan-out, power dissipation, and IC classifications.
📘 Concept Notes
🌐 Logic Families
A logic family defines the implementation technology used for digital circuits.
Major logic families:
- Diode Logic (DL) – primitive, obsolete.
- RTL (Resistor-Transistor Logic).
- DTL (Diode-Transistor Logic).
- TTL (Transistor-Transistor Logic).
- ECL (Emitter Coupled Logic).
- MOS & CMOS (Complementary MOS).
⚙️ Parameters of Logic Families
- Fan-in: Number of inputs a gate can handle.
- Fan-out: Maximum number of gates a gate output can drive.
- Noise Margin (NM): Ability to tolerate noise.
- Propagation Delay (
): Time taken for input change → output change. - Power Dissipation (P):
- Speed-Power Product (SPP):
- Fan-out Calculation:
🔋 Comparison of Families
| Parameter | TTL | CMOS | ECL |
|---|---|---|---|
| Power Dissipation | High | Very Low | Very High |
| Speed | Medium | Medium–High | Highest |
| Fan-out | 10–20 | >50 | 20–30 |
| Noise Margin | Moderate | High | Low |
🏭 IC Technology
IC Classification by Scale of Integration:
- SSI: Small Scale Integration (<100 gates/chip).
- MSI: Medium Scale Integration (100–1000 gates/chip).
- LSI: Large Scale Integration (1k–10k gates/chip).
- VLSI: Very Large Scale Integration (10k–1M gates/chip).
- ULSI: Ultra Large Scale Integration (>1M gates/chip).
📐 Example
If:
Then Power Dissipation =
🔟 10 Expected MCQs – ECET 2026
Q1. Which is the fastest logic family?
A) TTL
B) CMOS
C) ECL
D) RTL
Q2. In CMOS, power dissipation is:
A) Very high
B) Very low
C) Same as TTL
D) Same as ECL
Q3. Fan-out is defined as:
A) No. of inputs a gate can accept
B) No. of gates an output can drive
C) No. of logic levels in a system
D) None
Q4. Formula for power dissipation is:
A) 
B) 
C) 
D) 
Q5. Which family has the best noise margin?
A) TTL
B) CMOS
C) ECL
D) RTL
Q6. The speed-power product (SPP) is given by:
A) 
B)
C) 
D) 
Q7. Which IC technology refers to >1M gates/chip?
A) MSI
B) VLSI
C) LSI
D) ULSI
Q8. Typical TTL fan-out is:
A) 1–2
B) 5
C) 10–20
D) >50
Q9. In IC technology, SSI means:
A) <100 gates
B) 100–1000 gates
C) 1k–10k gates
D) >10k gates
Q10. Which logic family is least affected by noise?
A) TTL
B) CMOS
C) ECL
D) RTL
✅ Answer Key
| Q.No | Answer |
|---|---|
| Q1 | C |
| Q2 | B |
| Q3 | B |
| Q4 | B |
| Q5 | B |
| Q6 | B |
| Q7 | D |
| Q8 | C |
| Q9 | A |
| Q10 | B |
🧠 Explanations
- Q1 → C: ECL is fastest.
- Q2 → B: CMOS has very low static power dissipation.
- Q3 → B: Fan-out is no. of gates driven by one output.
- Q4 → B: Power = Voltage × Current.
- Q5 → B: CMOS has highest noise margin.
- Q6 → B: SPP = Delay × Power.
- Q7 → D: Ultra Large Scale Integration = >1M gates.
- Q8 → C: TTL fan-out = 10–20.
- Q9 → A: SSI = <100 gates/chip.
- Q10 → B: CMOS least affected by noise.
🎯 Why Practice Matters
- Logic Families questions are straightforward and formula-based.
- With a few formulas and comparisons, students can score quick marks.
- IC classification is a repeated concept in ECET exams.
