IP3 — third order intermodulation product

IP3 is an important quantity in systems analysis of wireless/RF systems. It is a measure of the performance of an amplifier and is related to the 1 dB compression point of an amplifier. To put it simply IP3 can be interpreted as an unwanted signal that comes out of the noise level in an amplifier system ( or a mixer ) and climbs at a rate of 3X the amplifier input – output characteristic. It is, as mentioned above, an unwanted signal and therefore care is taken to calculate it as it sets a boundary on achieveable performance of the circuit. A good paper on this and other related quantities ( such as 1 dB compression point, IP2 ) is presented in the “Engineer’s Corner” in our website located at www.signalpro.biz>Engineering_Pages for interested readers. As young RF engineers it took us a while to completely understand the ramifications of IP3 and associated quantities. To be able to understand intermodulation intuitively is neccessary for good RF/wireless design.

The Harmonic Balance algorithm.

The Harmonic Balance algorithm is now an established technique for CAD programs of various types, specially for RF/MMIC and analog. We felt we needed to understand the algorithm. This would allow us to be better at using it in simulations and more importantly be able to say if we wanted to purchase it in a CAD tool we wanted or not.

The implementation of these algorithms in the circuit simulator are fairly involved. However, luckily, compared to a couple of decades ago we as circuit designers do not really need to know its intricacies. What we want to know is at a higher level of abstraction. The expectation is that, if we do this we can do better at simulation and know when to use it effectively and when to not use it!

As a result of discussions internal to our design and CAD group a better understanding was gained and we decided to write a brief paper on it. This paper is now available on our website at www.signalpro.biz. Interested readers may follow the links www.signalpro.biz>engineering pages>engineer’s corner and read the paper if they wish.