While we all went through intensive course work in engineering school studying analog-to-digital converters (ADC), operational amplifiers (Op Amp), digital-to-analog converters (DAC) and other electronic architectures, you would think the basic function of those circuits would be understood. Most of us have a good understanding of how an ADC works, but are less familiar with its counter part, the DAC, and how it really functions. Still, for most of us, a DAC is mainly a black box where digital data goes in and a representative analog signal comes out. Only a few know the differences in architecture and what advantages and disadvantages a string architecture has over an R2R ladder, and vice versa. Knowing the differences and how those general purpose DACs work enables the designer to choose the best DAC for their application.
This article will shed some light on the basic operation of DACs and will give some answers to questions you always wanted to know.
As the DAC is seen mainly as a black box where digital data goes in and a representative analog signal comes out, there is much more to it. The digital data can be either in a serial or parallel data format. Serial interfaces, for example SPI or I2C which transmit the digital data stream serially, are like a necklace or chain into the "black box," whereas the parallel interface loads all necessary bits in one clock cycle into the device. On the other side of the device, the analog output signal is either a voltage or a current. See Figure 1.
Figure 1: Principal function of a Digital-to-Analog Converter
The different input interfaces offer variation in the form of the data format and, therefore, in speed, pin count, chip area, device size and flexibility. However, both interfaces, serial or parallel, will get the digital data into the device.