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Controlling amplitude of Sin and triangle waves...

Discussion in 'General Electronics Discussion' started by 777timer, Sep 19, 2012.

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  1. 777timer


    Sep 4, 2012
    I am trying to control the output amplitude of a triangle or sin wave from an exar chip. I was originally going to try a transresistance amplifier, but the output kept getting messed up and it was only stable for about 1/4 of the pot range. I am guessing that I need to convert the exar chip signal to a current signal as opposed to voltage? What other ways can I do this? In the end, this has to be automatable, so I was thinking adjustments with a digit pot or incorporating a a DAC somehow (which is probably just a digit pot to begin with).

    Frequency I am running at is 100 kHz to 350 kHz.

    Also, how about a transconductance amp? I wanted to try that, but I am not really sure what to do with the diode inputs on the LM13700.
  2. GreenGiant


    Feb 9, 2012
    what voltages are we talking about here? like min and max you will need on the output and what is the input voltage?

    Why not try a simple op-amp? (LM741)

    using a set resistor and a pot in series with another on the gain side you can adjust the gain as needed, and you could even get a digital pot (expensive yes but fun to use) so you can make the gain adjustments automatically too
  3. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    Nov 28, 2011
    That frequency range is probably going to be a problem. The LM13700 has a gain-bandwidth product of only 2 MHz.

    I doubt I'll be able to help, but if you want to describe your project in detail, I or someone else here may be able to suggest something.
  4. KJ6EAD


    Aug 13, 2011
    I had thought of trying to tame the amplitude flatness of an XR-2206 in a crude way by using a dual deck rotary switch so that changes in waveform selection or frequency range would make a corresponding amplitude adjustment. I lost interest in the project when I realized I could probably go farther with DDS and a μC.

    I don't know if this will help but many commercial function generators have traditionally used amplification followed by thick film resistor network attenuation stages switched through relays.
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    Nov 28, 2011
    KJ6EAD's post reminded me. Analog Devices ( make a range of direct digital synthesis devices that might be applicable, depending on exactly what your needs are.
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