CMX631A Low-Power SPM Detector

Using the graph supplied in the FX631 datasheet, section 4.3 and following the steps 1, 2 and 3, the required ‘gain-range’ of -4.75dB to -6.80dB is obtained.
Note: This graph is produced using a VDD of 3.0V.

For 5.0V, VDD operation the graph provided in Figure 5 of the datasheet should be used. This will provide a ‘gain-range’ of -0.50dB to -2.50dB.

Using the ‘gain-range’ for 5.0V, VDD, the mid-point gives a gain requirement of -1.5dB.