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This short video shows you how to create a simple resistor ladder in DEX.

 

What is a Resistor Ladder

A resistor ladder is a type of electrical circuit made up of repeating units of resistors. Two common types of resistor ladders are the "R-2R" ladder and the "string" type, and they're used primarily in digital-to-analog converters, or DACs, and sometimes in analog-to-digital converters (ADCs).

R-2R Ladder

The R-2R ladder is designed using resistors of two different values: R and 2R. The configuration is called a ladder because of the way the resistors are organized in the circuit, resembling the steps of a ladder when drawn schematically.

Structure

•It consists of resistors valued at R and 2R, organized in a way where each "rung" of the ladder forms a repeating unit with a consistent structure.

•The ladder is connected to the digital input, usually consisting of bits that are either in a state of 0 (usually ground) or 1 (usually a positive voltage).

Function

•The R-2R ladder allows the conversion of a digital binary code (usually Binary Coded Decimal) into an analog output voltage.

•It operates on the principle of voltage division and current division to generate the necessary analog voltage corresponding to the digital input.

Advantages

•Requires only two resistor values, simplifying manufacturing and ensuring consistency.

•The resistance seen by each digital input (the "bit" inputs) is the same, making it relatively insensitive to the resistance tolerance and ensuring uniform performance.

String Resistor Ladder

The string resistor ladder, often used in DACs, uses a series of resistors in a direct chain. Each resistor in the chain has the same resistance value, and the taps between resistors go to different comparator circuits or switches, depending on the specific application.

Function

•The string resistor ladder divides the voltage across the entire chain into smaller segments.

•In a DAC, switches (like transistors) are used to connect or disconnect the taps to the output, effectively controlling the output voltage based on which sections of the ladder are included.

Advantages

•Simplicity in structure, making it easy to understand and design.

•In specific cases, especially with fewer bits, it might require fewer total resistors than an R-2R ladder.

Disadvantages

•As the desired resolution increases (more bits), the number of resistors needed increases, making high-resolution designs bulky and expensive.

•More sensitive to resistor tolerance, meaning precision resistors are often necessary for high accuracy.

 

Both types of resistor ladders are integral in modern electronics, enabling digital systems to interface effectively with their analog counterparts. They are fundamental in audio processing, telecommunications, and any technology requiring precise digital-to-analog conversion. The choice between R-2R and string resistor ladders depends on the specific application, cost, space, and required resolution.