Editing Analog-to-digital converter (section)

====Aliasing====
{{Main|Aliasing}}
An ADC works by sampling the value of the input at discrete intervals in time. Provided that the input is sampled above the [[Nyquist rate]], defined as twice the highest frequency of interest, then all frequencies in the signal can be reconstructed. If frequencies above half the Nyquist rate are sampled, they are incorrectly detected as lower frequencies, a process referred to as aliasing. Aliasing occurs because instantaneously sampling a function at two or fewer times per cycle results in missed cycles, and therefore the appearance of an incorrectly lower frequency. For example, a 2&nbsp;kHz sine wave being sampled at 1.5&nbsp;kHz would be reconstructed as a 500&nbsp;Hz sine wave.

To avoid aliasing, the input to an ADC must be [[low-pass filter]]ed to remove frequencies above half the sampling rate. This filter is called an ''[[anti-aliasing filter]]'', and is essential for a practical ADC system that is applied to analog signals with higher frequency content. In applications where protection against aliasing is essential, oversampling may be used to greatly reduce or even eliminate it.

Although aliasing in most systems is unwanted, it can be exploited to provide simultaneous down-mixing of a band-limited high-frequency signal (see [[undersampling]] and [[frequency mixer]]). The alias is effectively the lower [[heterodyne]] of the signal frequency and sampling frequency.<ref>{{cite web|title=RF-Sampling and GSPS ADCs – Breakthrough ADCs Revolutionize Radio Architectures|url=http://www.ti.com/lit/sg/snwt001/snwt001.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.ti.com/lit/sg/snwt001/snwt001.pdf |archive-date=2022-10-09 |url-status=live|publisher=Texas Instruments|access-date=4 November 2013}}</ref>