AD8338 AGC Discontinuous GAIN

Hi,

In AGC mode, I apply a slowly-AM modulated Input signal (CH1 below).

As the input amplitude increases, the output (SENSOR_OUT = CH2 below), reaches the VOUT_RMS target value of ~250mV, the AGC (attenuation) engages suddenly accompanied by a large spike in SENSOR_OUT level.

As the input amplitude falls, the SENSOR_OUT fails to track the Input (time  = 0-1.8sec below).  In this interval the observed SNR falls rapidly.  That is, the AD8338 output contains in-band noise amplified to 250mVrms.

The Schematic:

I welcome any suggestions as to what causes this behavior and how to correct.

Thanks.

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  • 0
    •  Analog Employees 
    on Aug 19, 2019 8:00 AM

    Hi PeterM,

    I haven't noticed anything wrong with the circuit.
    Though, may I ask the details regarding the AM input signal,
    What's the modulation and carrier frequency?
    Are you using the AD8338 evaluation board on your setup?

    I'll still check if I missed something on the circuit.
    Apologies for the delayed response.

    Best Regards,
    Dann

Reply
  • 0
    •  Analog Employees 
    on Aug 19, 2019 8:00 AM

    Hi PeterM,

    I haven't noticed anything wrong with the circuit.
    Though, may I ask the details regarding the AM input signal,
    What's the modulation and carrier frequency?
    Are you using the AD8338 evaluation board on your setup?

    I'll still check if I missed something on the circuit.
    Apologies for the delayed response.

    Best Regards,
    Dann

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