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Automatic Gain Control Chip Selection


I'm looking for help in selecting a chip for an Automatic Gain Control circuit. My requirements are

Input signal: 0.1Hz-100Hz, random waveform, 50mV-4Vpk

Output needs to be an exact replica of the input but normalized to always have a 4.8V peak.

I've run into a few chips that have AGC, like the AD8367 and AD8336, but I'm not sure if they are right for my application.

much thanks!

  • Hi,

    Thanks for the email, I'm familiar with both of these parts. For such a low frequency application you'll need a VGA designed for dc operation. These are generally lower BW, with specified Vos numbers and dual supply. Your input range is only 80:1 (38dB) so you could use the AD600, AD602, AD603, AD8336 or AD8338. Avoid single supply parts if possible. There are a few agc circuits for guidance, one of them is AN-1341, which I've attached for your convenience.

    Good luck!!


  • Hi,

    Thanks for the response, and recommendations. I'm trying to decide between the AD8336, and AD8338.  Could you help me decide between the two? (I think the AD60x do not have enough gain).

    The AD8338 has some kind of built in AGC circuitry which might work for me.

    There's an AGC app note for the AD8336  AN-934 (which maybe you wrote?), it shows a steady output over a range of frequencies. I don't want a steady DC output, I'd like my output to follow my input, just at a normalized gain setting that keeps my output at a specific amplitude over a range of different input amplitudes while keeping my waveform intact. Do you think the AN-934 circuit could do that?

    much thanks!

  • Hi Monse,

    Yes I did write that one. The output isn't dc it does follow the input. I assume you're referring to fig. 6, the output is actually a measurement of mV peak-to-peak, not dc. The curve shows us that the output level remains constant over a wide range of input voltages.

    I hope this helps.


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