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How do I know the gain of the AD8338 in AGC mode

Category: Hardware

I wanna use AGC of AD8338 to amplify the signal from ADXL1005, then via the ADC and displayed on the PC. So, How do I know the gain of the AD8338 in AGC mode via "deto" pin or other pins, it will help me to draw the signal on PC. What i know is "deto" can only output +-10uA for AGC. But i wanna know the gainin the form of voltage, is there any way to do it?

below is my schematic:

  • Hi  ,

    I will look into this and update you once I have information.

    Thank you!

    Best regards,


  • Hi Kurao,


    Yes, there is a way to measure gain in terms of voltage in AD8338 board which is by using the gain/deto pin. I was able to confirm it by setting up the board based on the AGC mode that can be found in the AD8338 User Guide and you could check the picture below as your reference for my setup.



    In my setup, I set the VAGC to 0.7V so the output would be 0.6Vrms based on the Output RMS Voltage vs VAGC plot. Hence, if I want to have a gain of 0.6V, I should input 0.008Vrms in Low Mode based on the Two Gain Control Modes of the AD8338 plot.


    With this, I was able to measure the gain which is 0.666V to the Gain pin that is shorted to the Deto Pin, and the differential output which is 886mVrms. Hence, the measured gain and differential output is approximately equal to the expected values.



    Then, with the same VAGC, I changed the input to 0.009V so the expected gain would be 0.61V and differential output would remain which is 0.8Vrms. Measuring the two parameters shows that the measured values are approximately equal to the expected values.


    Therefore, you could measure the gain in Gain Pin that is shorted to the Deto pin when in AGC Mode.


    Best regards,


  • Thanks for your experiment and reply,  i measured this pin before, but i used a Handheld multimeter. when i  plugged it into the circuit to measure Gain Pin that is shorted to the Deto pin when in AGC Mode. The following behavior occured:measurement result is 0 and the gain will be inginy, so output signal will be distorted.

    just now, The same experiment was conducted, but the handheld multimeter was replaced with a digital multimeter. the voltage of Gain Pin can be measured. and output signal(blue) is normal:

    it's my mistake, but wasted your time. i am really sorry.

    At last, I appreciate you. 

    Best wishes~

  • Hi  ,

    You didn't waste my time so you don't need to worry about that and I am glad that I could help you. Thank you too! 

    If you have more questions of the board, please feel free to post another question.

    Best regards,