Bipolar Ecl 1960s Compare Ecl Delay Against Contemporary Ttl
# Bipolar ECL Logic (1960s): Step 10 — Comparing ECL Delay Against Contemporary TTL
Putting a number on why ECL, not TTL, was the choice for the fastest 1960s digital logic. TTL (transistor-transistor logic), introduced commercially in the mid-1960s, became the dominant general-purpose bipolar logic family because of its favorable power-delay product and single positive 5 V supply. But standard TTL still switched its output transistors between saturation and cutoff, inheriting the storage-time delay problem Step 1 identified in RTL/DTL, just with a faster, better-controlled version of it. This step quantifies the resulting gap.
## 1. Delay Numbers, Side by Side
Standard 1960s TTL (the 5400/7400-series baseline) specified typical gate propagation delays around 10 nanoseconds, dominated by the storage-time recovery of its saturating output transistor even with Schottky-diode clamping not yet widely deployed (Schottky TTL arrives commercially only in the early 1970s). Contemporary first-generation MECL parts specified typical gate delays around 2-4 nanoseconds, and MECL II (Step 16) pushed to roughly 1-2 nanoseconds by the late 1960s — a three-to-five-fold speed advantage over standard TTL using transistors from a broadly comparable process generation. The gap was not primarily about having better transistors; it was almost entirely about avoiding the saturation-recovery delay that Step 1 and Step 3 identified as the dominant TTL/DTL/RTL bottleneck.
## 2. Real Diagram: ECL vs. TTL Delay Comparison Chart
## 3. Why TTL Still Won the Volume Market Anyway
ECL's speed advantage came bundled with the tradeoffs this series covers in later steps: continuous (state-independent) power draw that was typically five to ten times TTL's average power per gate (Step 11), a non-standard negative supply and logic-level convention that complicated interfacing with the rest of a mostly-TTL system (Step 5), and a transmission-line interconnect discipline (Step 12) that most 1960s board designers did not need for the bulk of their logic. TTL's lower cost per gate, single 5 V supply, and comfortable noise margins made it the right choice for the overwhelming majority of digital logic, while ECL was reserved for the specific subsystems — processor arithmetic units, high-speed memory interfaces, and clock/control paths — where the extra speed justified the extra power and design discipline, a pattern that becomes explicit in the mainframe case studies of Step 19.
## 4. Companion Diagram: Stage Sequence and Trend Summary
## Comparing ECL Delay Against Contemporary TTL's Place in the Process Lineage
This is step 10 of 20 in the Bipolar ECL Logic (1960s) series, quantifying ECL's speed advantage over contemporary TTL and setting up the power/complexity tradeoffs examined in the steps that follow.