# RF Wireless World

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## Second Order Intercept point(IP2) vs Third Order Intercept Point(IP3)

This page on IP2 vs IP3 describes difference between second order intercept point(IP2) and third order intercept point(IP3). These intercept points are observed in saturated amplifier gain response. When amplifier operates in non linear region or when it is over driven it generates intermodulation products of input signals fed at the input. Out of These intermodulation products second order and third order are larger in magnitude and result into interference with the desired signals of interest. Refer intermodulation distortion page which explains IMD types, IMD products and mitigation techniques used to minimize effect of Passive IMD type.

### What are Intermodulation products? As shown any amplifier device/mixing device, produce intermodulation products subjected to two or more signals are fed to the input. Figure shows IMD products of second and third order due to two input signals f1 and f2.

IPn= P + (ΔP/n-1),
Where, IPn is the nth order intercept point
P is the power in the fundamental frequency/tone in dBm
ΔP is the difference between the desired output and undesired nth order output product(dBc).

For Example, if two amplitude tones have a power of about +10dBm and is generating a pair of equal amplitude 3rd order IMD products at -20dBm , calculate 2 tone IP3 of the system.
>>IP3=+10 + ((+10)-(-20)/(3-1))
IP3=25dBm Third Order Intercept Point (IP3):
Figure shows both Third order Input Intercept Point and Third Order Output Intercept point with slope of 3.

OIP3 = Po + 1/2( Po - PIMD)
IIP3= OIP3 -Gain
IIP3= PIN + 1/2( Po-PIMD) Second Order Intercept Point:(IP2)
Figure shows both Second order Input Intercept Point(IIP2) and Second Order Output Intercept point(OIP2) with slope of 2.

IIP2= PIN + Po - PIMD
OIP2= Po - PIMD

### Third order intercept point in cascading stages 1/OIP = (1/(G2 x G3 x OIP1)) + (1/(G3 x OIP2)) + (1/OIP3)

IIP = (OIP/(G1 x G2 x G3))

### Second order intercept point in cascading stages

1/sqrt(OIP) = (1/sqrt(G2 x G3 x OIP1)) + (1/sqrt(G3 x OIP2)) + (1/sqrt(OIP3))

IIP = (OIP/(G1 x G2 x G3))

### Calculator

Refer cascaded IP3 calculator for more.