Binary Weighted Resistor DAC

A DAC or Digital to Analog Converter is an electronic circuit that converts a digital input signal into an analog output signal. DACs are essential devices widely used in signal processing and communication systems. A digital to analog converter accepts signal input in the form of binary digits, i.e. 0 and 1 and generates output in the form of a continuous signal.

Types of Digital-to-Analog Converters

Based on construction and working principle, DACs are mainly classified into the following two types:

• Binary Weighted Resistor DAC

• R-2R Ladder DAC

A binary weighted resistor DAC consists of a network of resistor which are binary weighted. Whereas the R-2R ladder DAC has a ladder network of resistors of values R and 2R.

In this article, we are going to study the binary weighted resistor DAC. Here, we will cover various concepts, such as definition, construction, working, advantages, disadvantages, and applications. So, let's start with the basic definition of binary weighted resistor digital to analog converter.

What is a Binary Weighted Resistor DAC?

A binary weighted resistor digital to analog converter (DAC) is a type of digital to analog converter that converts a digital input signal into an equivalent analog output signal by using a network of binary weighted resistors.

In simple words, a binary weighted resistor DAC uses a network of precision resistors with binary-weighted values to produce an analog output signal corresponding to the digital input signal.

The binary weighted resistor DAC utilizes a resistive ladder network connected to a summing amplifier to generate an analog output. In the ladder network, each resistor has a resistance value which is in a binary proportion to previous resistor.

This type of DAC ensures that the digital input signal is properly weighted and converted into the analog output signal.

Circuit Diagram of Binary Weighted Resistor DAC

The circuit diagram of a binary weighted resistor digital to analog converter is shown in the following figure.

As we can see, it is a 3-bit binary weighted resistor digital to analog converter. It consists of a ladder network of binary weighted resistors connected to a summing amplifier (Op-Amp). Each resistor of the ladder network has a value weighted in binary proportion to the value of the preceding resistor. For example, if the value of first resistor is 20 R, i.e. R, then the value of the second resistor will be 21 R or 2R, similarly the value of third resistor is 22 R or 4R, and so on.

The summing amplifier provided at the end of the ladder network sum up all the intermediate output values to generate an appropriate analog output signal.

Working of Binary Weighted Resistor DAC

We can understand the operation of the binary weighted resistor DAC by splitting it in multiple stages. The working of a binary weighted resistor DAC is explained below:

Step 1 - Taking Digital Input

At this stage, the binary weighted resistor DAC takes a digital input signal specified in the form of a group of bits. Each bit of the input signal has a binary weight, where the highest weight is associated with the MSB (Most Significant Bit) of the digital signal, while the lowest weight is associated with the LSB (Least Significant Bit).

Step 2 - Switching of Resistive Network

The digital input signal switches (connect or disconnect) resistors in the ladder network based on the bits of the signal. For example, a bit of the input signal has a binary weight of 21, i.e. 2 will connect the resistor with a value 2R in the ladder network.

Step 3 - Summing Amplifier & Analog Output

The summing or operational amplifier is connected at the summing node of the circuit. It combines different outputs of resistors together to produce a final analog signal at output.

Advantages of Binary Weighted Resistor DAC

The following are some important benefits of a binary weighted resistor DAC over other types of digital to analog converters:

• Binary weighted resistor DACs are simple to design and implement due to its simple architecture.

• Binary weighted resistor DACs have good linearity that can be easily achieved by proper matching of resistor values.

• Binary weighted resistor DACs provide relatively higher accuracy in digital to analog conversion.

• Binary weighted resistor DACs offer high speed conversion of digital signal into analog signal.

• Binary weighted resistor DACs provide higher resolution and wide range of analog output.

• Binary weighted resistor DACs consume less power as compared to other types of DACs.

Disadvantages of Binary Weighted Resistor DAC

Though a binary weight resistor DAC has several advantages over other types of DACs. But it also suffers from various disadvantages. Some key disadvantages of binary weighted resistor DACs are listed below:

• Binary weighted resistor DACs are uneconomical at higher bit resolutions. This is due to increased complexity of the circuit with the increase in number of bits.

• At higher resolutions, binary weighted resistor DACs consume high power.

• The implementation of binary weighted resistor DACs become a challenge at higher number of bits due to some physical limitations like reduced precision and performance, decreased accuracy, etc.

• Binary weighted resistor DACs can face issues related to switching transients and settling time. It may cause errors in the case of fast switching signals.

Applications of Binary Weighted Resistor DACs

The following are some key applications of binary weighted resistor digital to analog converters:

• Binary weighted resistor DACs are widely used for audio signal processing in various audio systems like audio players, audio mixers, sound cards, etc.

• Binary weighted resistor DACs are also used in communication systems to converter digital signals into analog signal for modulation and transmission of data over communication channels.

• Binary weighted resistor DACs are also employed in control systems in various fields like robotics, motor drive control, process control, industrial automation, etc.

• Binary weighted resistor DACs are used in various measuring instruments like digital voltmeters/ammeters, oscilloscopes, multimeters, signal generators, etc.

Conclusion

In conclusion, the binary weighted resistor DAC is a type of digital to analog converter which is known for its high performance, high resolution, and high energy efficiency. It is mainly used in applications where simplicity, speed and accuracy are crucial, such as in communication systems, control systems, audio signal processing, etc. However, binary weighted resistor DACs have some limitations, such as circuit complexity and limited resolution for higher bits.