Often times DACs will include on-chip references and reference buffers. If a DAC does not include either of these on-chip features, it may be necessary to buffer the input reference pin. The reference is the most important point in any mixed-signal system as any variation in it will affect all other points in the system. Some reference sources will drift if the reference current is not kept constant. Voltage-out R-2R DACs are an example of a technology that is susceptible to variations in reference current. They must therefore be buffered in order to prevent this reference drift.