ADC Monotonicity

An Analog-to-Digital Converter (ADC) is monotonic if, for increasing analog voltage input, the digital output code increases and vice versa. Monotonic behavior does not guarantee that there will be no missing codes.

Monotonic behavior is an especially important characteristic for ADCs used in feedback control loops since non-monotonic response can cause oscillations in the system. Monotonicity is a critical specification with automatic control applications. It does not, however, mean no missing codes.

A monotonic ADC can still have a Differential Non-Linearity (DNL) greater than 1 Least Significant Bit (LSB) which would result in a missing code(s) at some point in the transfer function.

Non-Monotonic ADC with Missing Code

A non-monotonic ADC transfer function will miss a lower code until after the higher code is converted (assuming linearly increasing input voltage). The figure below shows a 3-bit ADC with a missing code:

© 2024 Microchip Technology, Inc.
Notice: ARM and Cortex are the registered trademarks of ARM Limited in the EU and other countries.
Information contained on this site regarding device applications and the like is provided only for your convenience and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. MICROCHIP MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WHETHER EXPRESS OR IMPLIED, WRITTEN OR ORAL, STATUTORY OR OTHERWISE, RELATED TO THE INFORMATION, INCLUDING BUT NOT LIMITED TO ITS CONDITION, QUALITY, PERFORMANCE, MERCHANTABILITY OR FITNESS FOR PURPOSE. Microchip disclaims all liability arising from this information and its use. Use of Microchip devices in life support and/or safety applications is entirely at the buyer's risk, and the buyer agrees to defend, indemnify and hold harmless Microchip from any and all damages, claims, suits, or expenses resulting from such use. No licenses are conveyed, implicitly or otherwise, under any Microchip intellectual property rights.