Logic with microwave devices – Gunn diode and GaAs MESFET usage Consider these statements: A Gunn diode can be used in combinational logic circuits. A Gunn diode can be used in sequential logic circuits. Both a Gunn diode and a GaAs MESFET can be used in logic circuits. Which statements are correct in the context of specialized high-speed logic families and device capabilities?

Introduction:
Logic implementation at microwave and very high speeds has explored various device physics beyond mainstream silicon CMOS, including transferred-electron devices (TEDs, e.g., Gunn diodes) and GaAs field-effect transistors (MESFETs). Understanding which devices have been used for practical logic is important in the history of high-speed digital design and specialized RF control logic.

Given Data / Assumptions:

• Gunn diodes exhibit negative differential mobility and are commonly used as oscillators.
• GaAs MESFETs are three-terminal transistors widely used in GaAs logic (e.g., direct-coupled FET logic).
• “Logic circuits” means circuits with bistability or Boolean operations at high speed, not just simple RF switching.

Concept / Approach:

Although two-terminal Gunn diodes lack gain in the conventional sense, their negative differential resistance and domain dynamics have been used to realize sequential logic such as bistable elements, frequency dividers, and triggered circuits where hysteresis or oscillation-to-lock behavior is exploited. Meanwhile, GaAs MESFETs underpin entire logic families (combinational and sequential), so the statement that both Gunn and GaAs MESFET can be used in logic is broadly accurate when considering specialized, non-mainstream logic implementations.

Step-by-Step Solution:

Verification / Alternative check:

Publications on TED-based logic demonstrate flip-flops and dividers using Gunn-effect dynamics; commercial digital IC families are GaAs MESFET-based, not Gunn-based, corroborating the conclusions.

Why Other Options Are Wrong:

Options A, B, and D rely on statement 1, which overstates Gunn applicability to combinational logic. Option E ignores the well-established role of GaAs MESFETs in logic.

Common Pitfalls:

Assuming “oscillator-only” means “no logic”; sequential logic can be built from oscillatory or hysteretic elements. Conversely, mistaking this for mainstream digital logic—Gunn-based logic is niche.

Final Answer:

2 and 3 only.