R2R

R2R, short for R-2R ladder, is a type of digital-to-analog converter (DAC) that uses a repeating network of resistors with only two values, R and 2R, to convert binary digital signals into an analog voltage. The input bits control switches that connect nodes to a reference voltage or to ground. The ladder network sums currents in a way that produces a voltage proportional to the binary value, typically fed into an amplifier to produce the final output.

The standard implementation places the ladder at a summing node and uses a precision amplifier, such as a transimpedance or op-amp configuration, to convert the ladder’s current to a voltage with low output impedance. Because only two resistor values are required, the R-2R ladder is easy to manufacture and scales well with word length, making it a popular choice in integrated circuits and discrete designs.

Advantages of the R2R ladder include simplicity, ease of production due to using only two resistor values, good linearity, and predictable performance as the number of stages grows. It also provides monotonic output, assuming matched components, and is relatively tolerant to some resistor-value variations.

Limitations include sensitivity to resistor mismatches, which can degrade accuracy, and potential glitch energy during code transitions at higher speeds. The output impedance can be high without buffering, requiring a surrounding amplifier stage. Careful layout and matching are important in high-precision or high-speed applications.

Applications span consumer electronics, instrumentation, and embedded systems where a compact, low-cost DAC is suitable. Variants include current-output configurations and different reference schemes, but the core principle remains the same: a two-value resistor ladder implementing binary-weighted conversion.