Im trying to get a VCO to work at very low frequencies and I stumbled upon this short paragraph:
"For low-frequency VCOs, other methods of varying the frequency (such as altering the charging rate of a capacitor by means of a voltage controlled current source) are used"
unfortunately theres was no further elaboration. Does anybody have any expierience with this technique? What is probably the lowest frequency achievable and what might be the problems?
best possible result would be something like 1Hz to 50Hz
When you say "not easily" do you acutally mean "no" or "not unless you find a 5MH coil" or do you have anything in mind how it might work?
Yes there is. You just need a wave shaper. You can make a pretty good one with an emitter coupled pair. I have one, but it uses alot of transistors. And it doesn't work down to your frequency.
Yes there is. You just need a wave shaper. You can make a pretty good one with an emitter coupled pair. I have one, but it uses alot of transistors. And it doesn't work down to your frequency.
It's a triangle wave to sine wave shaper. You can generate a triangle wave by integrating a square wave. Alternatively, if you're using a timer to generate your signal, you can get a pretty good triangle wave from the timing capacitor. I'll try to cobble up a schematic when I get home....
okay I guess I can figure out how to get a triangle output. How does a waveshaper work? Is it some sort of filter? Do you maybe have a link to a data sheet or something?
You can generate low frequency sine-waves with a function generator IC, such as the XR-2206, which use wave shaping techniques. It has a small amount of distortion, so may not be usable if you need a very pure sine-wave.
okay I guess I can figure out how to get a triangle output. How does a waveshaper work? Is it some sort of filter? Do you maybe have a link to a data sheet or something?
Look at THIS LINK. Go to page 8 and look at figure 10a. See the logarithmic waveshaper made from the LM394 at the bottom of the diagram? The input to the left most device is a triangle wave, and the output from the right device is a shaped sine wave. The author claims the distortion can be kept low at .35%.
Now say thank-you. It took me for freeking ever to find this app note again.
Look at THIS LINK. Go to page 8 and look at figure 10a. See the logarithmic waveshaper made from the LM394 at the bottom of the diagram? The input to the left most device is a triangle wave, and the output from the right device is a shaped sine wave. The author claims the distortion can be kept low at .35%.
Now say thank-you. It took me for freeking ever to find this app note again.