Monotonicity is a property of certain types of digital-to-analog converter ( DAC ) circuits. In a monotonic DAC, the analog output always increases or remains constant as the digital input increases. The analog output never decreases during the input sequence. If the analog output decreases at any point during the input sequence, a DAC is said to be non-monotonic.
Monotonicity is an important characteristic in many communications applications in which DACs are used. Such applications can function in the presence of nonlinearity , but not in the presence of non-monotonicity. The term derives from monotonic mathematical functions, also known as non-decreasing functions, in which the value of the dependent variable never decreases as the value of the independent variable increases.