Op-amp function blocks: An exponential (anti-log) amplifier configuration uses which component placement relative to the operational amplifier?

Introduction / Context:Log and antilog (exponential) amplifier building blocks are classic op-amp applications that exploit the exponential I–V characteristic of a diode or transistor junction. Distinguishing between the two is frequently tested in analog electronics.

Given Data / Assumptions:

• Ideal op-amp behavior around its linear region.
• Use of a diode (or BJT junction) obeying i = I_s * exp(v/(nV_T)).

Concept / Approach:

Log amplifier: place the diode/junction in the feedback path and drive the input through a resistor; output is proportional to ln of the input magnitude. Antilog (exponential) amplifier: place the junction at the input (in series from source to the summing node) and keep a resistor in the feedback path; the output then becomes proportional to the exponential of the input voltage.

Step-by-Step Solution:

Verification / Alternative check:

Standard analog design texts show: log amplifier → diode in feedback; antilog amplifier → diode at input. This matches option (b).

Why Other Options Are Wrong:

• (a) describes a log amplifier, not exponential.
• (c), (d), and (e) do not produce exponential transfer characteristics.

Common Pitfalls:

• Confusing log and antilog configurations.
• Ignoring temperature compensation requirements for precision designs.

Final Answer:

A diode at the input and a resistor in feedback.