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| BIRD CHART |
The bird chart plots the spurious signals, through the 9th order, that appear at the output of all mixers. The heavy lines indicate that spurious products may be present of the 5th order or less. The lighter lines are 6th order or higher.
The first step in plotting your mixer application is to look at the frequency range of the input signal and the higher level carrier signal. Determine the highest frequency that either attains. Using this frequency, determine and label a scale for the graph, which will go from zero to at least this highest frequency. Determine which is the larger frequency, the Input signal or the switching Carrier, and label the axis appropriately. Plot the coordinates of the lowest Signal and Carrier signal frequency that corresponds to it. Then plot the coordinates of the highest Signal frequency and its Carrier frequency. Draw a line connecting these two coordinates. At each point that this line crosses a spurious line, a potential spurious product exists. To find if a product exists, and if so what the product is, you must determine if the desired mixer output is the result of the Sum or Difference of the Input and Carrier signal. If it is the Sum, then the spurious will be found above the line in the table to the right. If it is the Difference, it will be found below the line. The first of the two numbers representing the spurious is the smaller frequency multiplier and the second is the larger frequency multiplier. To determine the approximate level of any spurious signal, enter the Typical Mixer Spurious Level chart in the upper left at the appropriate multipliers. Make sure you are using the proper multipliers on the Carrier and Signal components for it will make a great deal of difference. The shaded values on the chart are for input levels of –10dBm; the unshaded are for 0 dBm input signals. The data is shown for three different mixer recommended drive level designs. This data is only approximate and may vary depending on the application and circuit configuration. For more accurate data in a particular application, or for a particular mixer, contact the Signal Processing Component Application Engineers at Emhiser Tele-Tech, Inc.
NOTICE:
The following two files are in Adobe Acrobat (.PDF) format and are quite large (over 1.2 Mb).
They will print well on legal size paper, in landscape format, on a color inkjet printer.