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VGA with AGC real time.

Pradeep kadela
Prodigy 10 points

Hi,

We are working on a project that requires a Variable gain amplifier with automatic gain adjustment. We have found several articles from TI which convey different solutions, but we are still figuring out the best possible way and require your assistance for the same.
Requirement : We have a sinusoidal wave as an input of amplitude 1 Vpeak-peak. The gain for the amplifier in default has to be 2. Hence the output wave of the amplifier is 2 Vpeak-peak. The amplitude of the input wave keeps changing. We want to adjust the gain such that the output is in sync with the input wave with constant amplitude of 2 Vpeak-peak. For example, if the input sine wave amplitude increases, the gain reduces linearly such that the output wave is 2 Vpeak-peak. 

The input wave amplitude changes in the range of 0.25 Vpeak-peak to 1.5 Vpeak-peak. The input wave frequency is under 100Hz.
If you have any IC solutions, please let us know. Else, if there is any other ic that can serve as a smaller block in the whole circuit, please let us know.
If you have any other questions please contact us. 
Thanks,
Anirudh Garg
  • 0
    TI__Genius 13245 points

    Hi Anirudh,

    I can't say I am familiar with any device that does this.  I know some of our Ultrasound Front End devices have integrated VGAs and PGAs, for example:

    https://www.ti.com/lit/ds/symlink/afe5812.pdf

    But, I imagine unless you need an ultrasound front end this does not help.

    It may be that you are able to do this with some sort of discrete peak-detect circuit, feeding some sort of inverted signal into a VGA.  However, there would be a lot of design details that would need to be taken into account, and we do not actually have any VGA on our team, I'd have to connect with another team to get their opinion.  I would approximate this may take a quad amplifier (2 amps for peak detect, another amp for a difference amp. from a reference voltage to the VGA, and a buffer), a suitable VGA, and possibly a reference.  The peak detect would potentially have some decay, I'm not sure how tolerant the circuit can be to gain changes, we can filter the peak detect but that may add delay.

    Are there limitations on size/complexity?

    Regards,
    Mike