R/2R ladder versus binary-weighted DACs What is the major advantage of the R/2R ladder D/A converter compared with a binary-weighted D/A converter?

Introduction / Context:Two common DAC topologies are binary-weighted and R/2R ladder. Understanding why R/2R is preferred in many designs helps explain its ubiquity in mixed-signal systems.

Given Data / Assumptions:

• Binary-weighted DACs require precise resistor ratios spanning many powers of two.
• R/2R ladders use just two resistor values repeated in a ladder network.

Concept / Approach:Manufacturing tolerance and matching dominate DAC accuracy. Using only two nominal resistor values simplifies matching across temperature and process, yielding better practicality for higher resolutions.

Step-by-Step Solution:Identify the key differentiator: resistor value spread.Binary-weighted requires 1R, 2R, 4R, 8R, … which is hard to hold accurately for many bits.R/2R needs only R and 2R repeatedly, easing fabrication and trimming.

Verification / Alternative check:Review of monolithic DAC datasheets shows R/2R networks are standard for medium to high resolutions because of resistor matching benefits.

Why Other Options Are Wrong:Fewer parts: part count is comparable; the main advantage is resistor value uniformity.Easier analysis: both are straightforward; not the primary advantage.Virtual ground eliminated: R/2R DACs typically still use an op-amp with a virtual ground summing node.No op-amp: most implementations still use an op-amp for output buffering/summing.

Common Pitfalls:Believing R/2R inherently has better linearity without considering resistor matching; layout and trimming still matter.

Final Answer:It uses only two different resistor values.