Author: Thomas Brand, Field Application Engineer, Analog Devices
There are many forms of electrical signal chains.They can be composed of different electrical components, including sensors, actuators, amplifiers, analog-to-digital converters (ADC), digital-to-analog converters (DAC), and evenMicrocontroller. The accuracy of the entire signal chain plays a decisive role. In order to improve accuracy, it is first necessary to identify and minimize individual errors in each signal chain. Due to the complexity of the signal chain, this analysis will be a difficult task. This article introduces a precision digital-to-analog converter (DAC) signal chain error budget calculation tool. This article will describe the individual error effects of the components connected to the DAC. Finally, this article will demonstrate step by step how to use the tool to identify and correct these problems.
The precision digital-to-analog converter (DAC) error budget calculator is accurate, easy to use, and can help developers choose the most suitable component for a specific application. Since the digital-to-analog converter (DAC) usually does not appear in the signal chain alone, but is connected to the reference voltage and operational amplifier (for example, as a reference buffer), it is necessary to pay attention to and summarize these additional components and their individual errors. In order to better understand this concept, we first look at the influence of individual errors of the main components, as shown in Figure 1.
figure 1.The main components of the digital-to-analog converter (DAC) signal chain
The reference voltage has four main error effects. The first one is related to the initial accuracy (initial error), which shows that the output voltage measured in the production test at 25°C (specified temperature) is unstable. In addition, there are errors related to temperature coefficients (temperature coefficient errors), load adjustment errors, and line adjustment errors. The initial accuracy and temperature coefficient error have the greatest influence on the total error.
In an operational amplifier, the input offset voltage error andresistanceThe resistance error has the greatest impact. The input offset voltage error refers to the small voltage difference that is forcibly applied to the input terminal in order to obtain a zero voltage output. The gain error is caused by the resistance error of the corresponding Resistor used to set the closed-loop gain. Other errors are caused by bias current, power supply rejection ratio (PSRR), open loop gain, input offset current, CMRR offset, and input offset voltage drift.
For the digital-to-analog converter (DAC) itself, various types of errors are given in the data sheet, such as integral nonlinearity (INL) error, which is related to the difference between the ideal output voltage and the actual output voltage measured by a given input code. Other error types are gain error, offset error and gain temperature coefficient error. Sometimes they are combined to form a total unadjustable error (TUE). TUE is related to all measurement output DAC errors, namely INL, offset and gain errors, and output drift within the supply voltage and temperature range.
Since different sources of error are usually uncorrelated, the most accurate method for calculating the total error in the signal chain is the statistical squared tolerance method:
Collecting the error of each component is usually a tedious task. Now we can use the error budget calculator to simplify this work and get the same accurate calculation results.
figure 2. Representation of the influence of the error in the ADI error budget calculator
Steps to use precision digital-to-analog converter (DAC) error budget calculator
First, use the error budget calculator to choose from three types of digital-to-analog converters (DAC): voltage output DAC, multiplying DAC, and 4 mA to 20 mA current source DAC. Next, set the temperature range and power supply voltage ripple required for the error calculation, the latter will play a decisive role in the PSRR error. After entering these values, the calculator will generate a graph showing the effect of each error on each component in the signal chain, as shown in Figure 2.
The total error in this example is mainly affected by the reference voltage. This signal chain can be improved by using more accurate reference Modules.
The integrated resistance of the digital-to-analog converter (DAC) is responsible for the comparison of the internal inverting amplifiers, thereby improving the accuracy, and plays a decisive role in the total error of the digital-to-analog converter (DAC). In digital-to-analog converters (DACs) without integrated resistors or internal inverting amplifiers, these parameters can be set individually, as shown in Figure 2.
The error budget calculator is reliable and easy to use, making it easier to create a precision digital-to-analog converter (DAC) signal chain and quickly evaluate design trade-offs.
About the Author
Thomas Brand joined ADI in Munich, Germany in 2015, when he was still studying for a master’s degree. After graduation, he participated in ADI’s trainee program. In 2017, he became a field application engineer. Thomas provides support to large industrial customers in Central Europe and focuses on the industrial Ethernet field. He graduated in electrical engineering from the Union University of Education in Mosbach, Germany, and then obtained a master’s degree in international sales from the Konstanz University of Applied Sciences, Germany.