Controlling amplitude of Sin and triangle waves...

[777timer]

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.

 

[GreenGiant]

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

 

[KrisBlueNZ]

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.

 

[KJ6EAD]

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.

 

[KrisBlueNZ]

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