Device technology identification: which of the following logic families is implemented with bipolar junction transistors (BJTs) as the primary switching devices?

Introduction / Context:
Logic families are categorized by their underlying device technology. Bipolar and MOS technologies exhibit different speed, power, and density characteristics. Knowing which families are bipolar helps in understanding historical performance and interface levels.

Given Data / Assumptions:

• Options include TTL, GaAs, NMOS, and CMOS.
• We identify the family fundamentally based on BJTs.
• No mixed-technology hybrids implied.

Concept / Approach:
Transistor–Transistor Logic (TTL) employs BJTs for both logic and amplification stages. By contrast, NMOS and CMOS use MOSFETs, while GaAs logic uses compound semiconductor FETs, not BJTs.

Step-by-Step Solution:

Verification / Alternative check:
Data sheets and textbooks uniformly classify TTL as a bipolar family; its input/output levels and fan-out characteristics reflect BJT behavior.

Why Other Options Are Wrong:

Common Pitfalls:
Associating “high speed” with “bipolar” automatically; modern CMOS can be extremely fast, but the question is about device type, not speed.

Final Answer:
TTL