Op-amp applications — A digital-to-analog converter (DAC) can be implemented using which classic operational-amplifier building block, where weighted digital inputs are summed to produce a proportional analog output voltage?

Introduction:
A digital-to-analog converter (DAC) transforms an N-bit digital word into a proportional analog quantity. One of the most common analog circuit realizations for a voltage-output DAC is based on the op-amp summing amplifier, often called a scaling adder, where each digital bit drives a weighted branch whose contribution is summed at the op-amp input.

Given Data / Assumptions:

• Goal: convert a digital word into an analog voltage.
• Available op-amp topologies: summing (scaling) adder, noninverting amplifier, voltage-to-current converter, etc.
• Binary weighting can be implemented by resistor networks (R-2R ladder or binary-weighted resistors).

Concept / Approach:

A scaling adder sums currents from multiple input resistors into the op-amp’s inverting node (virtual ground). Each input branch is weighted so that its contribution is proportional to the digital bit’s significance. With an R-2R ladder or binary-weighted resistors, the summed current becomes an output voltage via the op-amp’s feedback resistor, creating a precise, linear mapping from code to voltage.

Step-by-Step Solution:

Verification / Alternative check:

R-2R ladders are industry-standard DAC cores. Their front end is exactly a current summing (scaling) network terminated at an op-amp that performs I-to-V conversion, i.e., a scaling adder behaviorally.

Why Other Options Are Wrong:

• voltage-to-current converter: Often part of DACs but alone does not implement code-weighted summation.
• noninverting amplifier: Provides gain to a single analog input, not code-weighted summation.
• adjustable bandwidth circuit: A filter concept, not a DAC core.
• instrumentation amplifier: Precision differential gain, unrelated to code summation.

Common Pitfalls:

• Confusing the op-amp I-to-V stage with the entire DAC function; the essential feature is weighted summation.
• Ignoring resistor matching and reference stability, which set DAC linearity and accuracy.

Final Answer:

scaling adder