Q1Digital Electronics
Question
4 marks
Describe Schottky TTL and CMOS logic.
Answer
Schottky TTL uses Schottky diodes to prevent transistor saturation for higher speed; CMOS uses complementary MOSFETs for very low power consumption.
- Propagation delay: ~3 ns (74S series) vs ~10 ns standard TTL
- Higher power: ~20 mW per gate
- Advanced Schottky (74AS) and Advanced Low-power Schottky (74ALS) offer better speed-power product
- Supply voltage: 3V to 15V (standard); 1.8V-3.3V for modern sub-families
- Static power: nearly zero (only leakage current)
- Dynamic power: proportional to frequency (CV^2 f)
- Noise margin: ~30-45% of supply voltage (excellent)
- Fan-out: very high (50+ in static CMOS)