AN-691 errata ???


I am a little confused about the low frequency description of the AD8302 in AN-691.
Figure 47 make sense, but in figures 50, 51, 54 and 56 the x axis is labeled PIN (dBm).
Should it not be dB ? (INPB fixed at -30dBm and INPA varying from -30dB to 30dB as in AD8302 datasheet)

Moreover, I have a question concerning the LF behavior of the AD8302.
I want to measure down to a few Hz if possible, and in order to optimize the Gain Conformance (minimizing the error...)
I'd like to adjust PINA and/or PINB.

So here my question: can we consider that both channels behaves as shown in figures 50 to 57 and
each input signals should have between 0 and 10 dB (not dBm) in order to minimize
the overal error or must it be the sum of both inputs.

Tks a lot for any reply

  • +1
    •  Analog Employees 
    on Feb 12, 2020 2:29 AM

    Hello ATu,

    1. You are correct. Figures 50, 51, 54, and 56 have the horizontal axis labeled incorrectly. Thanks for pointing this out. We will correct it ASAP.

    2. To operate AD8302 at relatively low frequency, there are altogether SIX capacitors that must be increased in value: two input coupling capacitors, two input offset cancellation capacitors, and the two output filter capacitors MFLT and PFLT. You might refer to the AD8302 datasheet which is more descriptive, compared to AN-691. Be sure to check output AC ripple at the desired output, VMAG or VPHS. If significant AC ripple is observed at 2x the input frequency, this indicates a larger value of capacitor is needed at MFLT or PFLT respectively. Note that AN-691 test results use 1uF capacitor for MFLT. Your results should be better at very low frequency if the capacitor at MFLT is somewhat larger than 1uF.