Binary-weighted-input DAC resistor selection In a binary-weighted-input digital-to-analog converter, the values of the input resistors are deliberately chosen to be proportional to the binary weights of the corresponding input bits.

Introduction / Context: Binary-weighted DACs implement digital-to-analog conversion by summing scaled contributions from each bit. The most significant bit contributes half of full-scale, the next contributes one-quarter, and so on, requiring precise weighting in the hardware network.

Given Data / Assumptions:

• Each bit controls a switch that connects a resistor (or current source) weighted by 2^n.
• Resistor values or current magnitudes follow binary ratios: 1, 1/2, 1/4, ... of full-scale.
• Ideal operation assumes perfectly matched components and switches.

Concept / Approach: For a resistor-summing implementation, smaller resistance corresponds to larger contribution (higher conductance). Thus, resistor values are selected so conductance is proportional to the bit weight. Alternatively, current-steering versions use binary-weighted current sources. The common theme is binary proportionality to implement the sum.

Step-by-Step Solution:

Verification / Alternative check: Simulate a ramp across all codes; verify monotonic steps and correct full-scale output based on resistor ratios.

Why Other Options Are Wrong: “Incorrect” contradicts the fundamental structure of binary-weighted DACs. “Only true for R-2R” is wrong—the R-2R ladder is a different approach that avoids wide resistor spreads. “Valid only with current sources” ignores resistor-summing implementations.

Common Pitfalls: Large resistor ratio spreads limit resolution; switch on-resistance and parasitics disturb exact weights; temperature coefficients degrade linearity.

Final Answer: Correct