Third-order intercept point

In telecommunications, a third-order intercept point (IP₃ or TOI) is a measure for weakly nonlinear systems and devices, for example receivers, linear amplifiers and mixers. It is based on the idea that the device nonlinearity can be modeled using a low-order polynomial, derived by means of Taylor series expansion. The third-order intercept point relates nonlinear products caused by the third-order nonlinear term to the linearly amplified signal, in contrast to the second-order intercept point that uses second order terms.

The intercept point is a purely mathematical concept, and does not correspond to a practically occurring physical power level. In many cases, it lies far beyond the damage threshold of the device.

Definitions

Two different definitions for intercept points are in use:

Second-order intercept point

The Second Order Intercept Point, also known as the SOI, IP2, or IIP2 (Input Intercept Point), is a measure of linearity that quantifies the second-order distortion generated by nonlinear systems and devices. Examples of frequently used devices that are concerned with this measure are amplifiers and mixers. It is related to the third-order intercept point, which is generally used for quantifying degree of nonlinearity of a nonlinear system or it can also be used to estimate the nonlinear products present at the output of such a system.

Definition

At low power levels, the fundamental output power rises in a one-to-one ratio (in terms of dB) of the input power, while the second-order output power rises in a two-to-one ratio. If the input power is high enough for the device to reach saturation, the output power flattens out in both the first- and second-order cases.

The second order intercept point is the output power point at which the extrapolated first- and second-order lines intersect on a plot, since the actual power levels will flatten off due to saturation at much lower power level typically. In other words, the response is assumed to be perfect all the way to infinity. There are actually values for both the input and output SOI (known as the ISOI & OSOI or IIP2 & OIP2) of a device or system, being related by the small signal gain of the device or system. The OSOI in dB is simply the ISOI in dB plus the small signal gain of the device or system.

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Investors in People provides a best practice people management standard, offering accreditation to organisations that adhere to the Investors in People framework. Investors in People is owned by the UK government, managed nationally by the UK Commission for Employment and Skills and supported by the Department for Business, Innovation and Skills (BIS). Investors in People assessments are conducted locally through seven local Delivery Centres. It was launched in 1991.

History

Investors in People UK was formed in 1991 to protect the integrity of the Investors in People framework. It was a non-departmental public body and received funding from the UK Department for Business, Innovation and Skills (BIS). The organisation was based in London, United Kingdom and managed the development, policy, promotion and quality assurance of the Investors in People framework.

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