Optimizing IP3 and ACPR Measurements

As wireless communication becomes widespread, the increased complexity of the devices and wireless protocols create an unrelenting demand for linear RF components and systems. These ubiquitous wireless devices require high performance test systems to characterize linearity. Linearity performance, particularly third order intercept point (IP3 or TOI), has become a defining characteristic as it affects power efficiency, channel density, signal coverage, and adjacent channel power ratio (ACPR).

IP3 performance is a figure of merit used to describe the linearity of components including power amplifiers, frequency mixers, switches, ADCs, DACs, and others. This measurement involves the use of a two-tone stimulus and requires the comparison of the power of two fundamental tones with the power of third order distortion products.

ACPR, also known as Adjacent Channel Leakage Ratio (ACLR), is an important metric for components designed for use in wireless standards such as UMTS or 3GPP LTE. This measurement describes the ratio of power in a modulated signal versus power emitted into an adjacent channel. In order to measure ACPR, one must provide the device under test (DUT) with a modulated stimulus – or in the case of a DAC – internally generate a modulated signal on the DUT itself.