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P1dB vs TOI-1dB compression point vs Third Order Intercept Point

This page describes difference between P1dB(1dB compression point) and TOI(Third Order Intercept Point). It also describes IIP3,OIP3 etc.

TOI Point

As mentioned TOI refers to Third Order Intercept Point. As we know from our discussion in intermodulation distortion page, saturated or overdriven amplifier produces unwanted products of input signals. This is known as IMD (Intermodulation Distortion). There are many combinations of input signals produced at the output. Out of these IMD products only third order products are vulnerable to interference due to its higher amplitude and close proximity with the desired signals. For f1 and f2 input signals, output third order products namely 2f1-f2 as well as 2f2-f1 lead to IMD interference.

TOI Third Order Intercept Point

TOI Point= OIP3
Each P1dB increase results in 3dB increase in 3rd order IM(Intermodulation) power. TOI point is a figure of merit, which characterizes a RF receiver's tolerance subjected to multiple RF signals outside passband of interest.

P1dB Gain compression point

P1dB-1dB compression point

P1dB point is the output point where 2dB increase in input power fed to the amplifier(RF circuit) results in 1dB change in the output power. In reality, Intercept point is usually about 10 to 15 dB higher value compare to P1dB point(1dB gain compression point).

Hence RF circuit does not function correctly or amplify the input signal properly at the IIP3 input level.

IIP3 mentioned above is the 3rd order intercept point at the input of the amplifier for OIP3(Output third Order Intercept point). Remember that,
Gain + IIP3 = OIP3

It is useful to characterize linearity of a RF receiver for signals below the saturation level.

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