Schottky Ttl 1970s Confront the Storage Time Problem Ttl Inherited
# Schottky TTL (early 1970s): Step 1 — Confront the Storage-Time Problem TTL Inherited
Confront the Storage-Time Problem TTL Inherited. Standard TTL (the 5400/7400 series, commercial from the mid-1960s) replaced the diode-transistor logic of its predecessors with a multi-emitter input transistor and a totem-pole output stage, and in doing so delivered a far better power-delay product than RTL or DTL.
## 1. The Saturation Legacy TTL Did Not Escape
Standard TTL (the 5400/7400 series, commercial from the mid-1960s) replaced the diode-transistor logic of its predecessors with a multi-emitter input transistor and a totem-pole output stage, and in doing so delivered a far better power-delay product than RTL or DTL. But standard TTL's output transistor still drove into hard saturation on a logic-low output, exactly the failure mode the Bipolar ECL Logic (1960s) series' Step 1 identified as the dominant speed ceiling for saturating bipolar logic: once a transistor's base-collector junction is forward-biased and excess minority carriers flood the base region, turning the transistor back off means first sweeping out that stored charge before collector current can fall, and storage time (t_s) routinely added several nanoseconds to standard TTL's roughly 10 ns typical gate delay.
## 2. Real Diagram: Storage-Time Delay Breakdown in Standard TTL
## 3. Why This Series Picks Up Where ECL Left a Fork in the Road
Both ECL and Schottky TTL are answers to the identical storage-time problem, discovered and solved in roughly the same half-decade, but they take opposite strategies. ECL (covered in the companion Bipolar ECL Logic (1960s) series) sidesteps saturation entirely: its differential-pair current switch is designed so neither transistor ever approaches the base-collector forward-biased region, at the cost of a non-standard negative supply, continuous current draw, and a specialized logic-level convention. Schottky TTL, arriving commercially in the early 1970s, takes the cheaper, more TTL-compatible route: keep the same saturating bipolar topology and standard 5 V supply, multi-emitter input, and totem-pole output that the entire TTL ecosystem already depended on, but add a small clamping diode across each base-collector junction that prevents the junction from ever fully forward-biasing in the first place. This step frames that fork; the next step develops the clamp itself.
## 4. Companion Diagram: Stage Sequence and Trend Summary
## Confront the Storage-Time Problem TTL Inherited's Place in the Process Lineage
This is step 1 of 20 in the Schottky TTL (early 1970s) series, establishing the storage-time problem that every subsequent step's engineering choice answers.