Mixer Spur Analysis
The well known equation found behind all mixer-spurious analysis programs is given by (after the paper by Bert Henderson)
in which n and m are (positive and negative) integers. Even though this equation is quite simple, its ramifications in RF design are significant. This same equation can be applied to A/D converters and D/A converters, but this usage will not be discussed here at this time.
There are many mixer spur analysis programs on the internet along with a host of other retail packages – so why yet another program?
The analysis program described here is tailored more closely to the different perspectives involved with receiver versus transmitter related design. The receiver design mode is choreographed using the main screen to the left and provides two types of output results. The first output type is the traditional spurious plot shown below where a specific receive (and consequently specific LO) frequency is used. The receive frequency of interest is easily changed using the “Adjust LO Frequency” slider in the main screen. Provisions to facilitate easy labeling of each spurious track are provided as shown.
A Second Output Perspective
A second analysis output result is particularly useful, referred to here as the “TRW style” since it was originated by M.Y. Huang et al while he was at TRW to the best of our knowledge. This graphical representation makes it possible to see the role of the complete frequency tuning range along with different bandwidths all in one single graphic. In any mixer analysis, there are three different frequencies involved at any one time (RF, LO, IF), but if the associated equations are normalized (to the larger of the RF and LO frequencies), the results can be viewed in 2-dimensions rather than requiring three dimensions. This analysis formulation later appeared in an issue of Ham Radio Magazine as well.
Transmit Design Perspective
The main screen for the transmit related design activity is very similar to the main screen for receive design, but a careful inspection will reveal differences. Two analysis output types are provided for transmitter design as well. The first type considers a single output frequency at a time with the output frequency adjustable using a slider. In the second type, the “frequency sliding” is automatically provided and the resultant spur levels are traced out in a “maximum hold” type presentation.
