upconvert

Upconvert is the process of increasing the frequency of an electrical signal from a lower to a higher frequency. In RF engineering, it is typically accomplished by mixing the input signal with a local oscillator (LO) signal in a nonlinear device such as a mixer. The nonlinear mix produces sum and difference frequencies, and the desired output is selected by filtering to reject unwanted components. Upconversion is the opposite of downconversion and is a key step in many heterodyne systems.

In receivers, upconversion translates signals from an RF front end to a higher intermediate frequency or to baseband, allowing fixed hardware to operate at a convenient frequency while preserving the information content. It is also used in transmitters to shift baseband or IF signals to a carrier frequency for transmission. Common considerations include conversion gain or loss, noise figure, LO phase noise, spurious emissions, and image frequencies. Filtering and image-rejection techniques are used to suppress unwanted products. Design choices may include using single-sideband upconversion or using multiple stages to improve selectivity and image suppression.

Other uses of the term appear in digital video and image processing, where upconversion can refer to upscaling the sampling rate or the display resolution of a signal, rather than RF band translation. In detector physics, upconversion can describe certain photon-energy conversion processes, but this usage is context dependent.