Which of the following logic families is well suited for high-speed operation?
2012
Which of the following logic families is well suited for high-speed operation?
Answer: B. ECL — ConceptA digital logic family is judged by electrical characteristics such as propagation delay, power dissipation, noise margin, and fan-out. Propagation…
- A.
TTL
- B.
ECL
- C.
MOS
- D.
CMOS
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Show answer & explanation
Correct answer: B
Concept
A digital logic family is judged by electrical characteristics such as propagation delay, power dissipation, noise margin, and fan-out. Propagation delay measures how quickly an output responds to an input transition; a smaller delay supports faster operation.
Switching speed depends strongly on whether transistors enter saturation. Avoiding saturation removes storage delay, although this design choice can increase steady power consumption.
Application
Compare the switching mechanism and delay implication of each offered family.
Logic family | Switching characteristic | Speed implication |
|---|---|---|
TTL | Bipolar stages commonly use saturated switching | Moderate propagation delay |
ECL | Differential current steering keeps transistors out of saturation | Very small propagation delay |
MOS | MOSFET switching with high input impedance | Speed varies with the NMOS or PMOS implementation |
CMOS | Complementary nMOS and pMOS networks charge and discharge capacitances | Low static power, with switching delay set by capacitance and drive strength |
Contrast
TTL provides robust bipolar logic with moderate speed and power consumption.
MOS is a broad family name; its speed depends on the particular process and circuit style.
CMOS emphasizes very low static power and high noise margins, while its transition time depends on capacitive loading.
Result
ECL is the best-suited offered family for high-speed operation because its non-saturating current-steering design minimizes propagation delay.
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