Many digital devices incorporate analog circuits. For instance, microprocessors, application specific integrated circuits (ASICs), and field-programmable gate arrays (FPGAs) may have internal voltage references, analog-to-digital converters (ADCs) or digital-to-analog converters (DACs). However, there are challenges when you integrate more analog onto a digital design. As with all things in life, in electronics we must always trade one parameter for another, with the application dictating the proper trade-off of analog function. This application note examines how the demand for economy of space and cost pushes analog circuits onto digital substrates, and what design challenges emerge.