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How's going dear engineers. I hope your everything's going well.

I've made a sawtooth waveform oscillator aim for about few hundread kHz.

I didn't see any problems on simulation results, everything was so fine, so i bought every same components as shown in Image 1. and I put them on breadboard and did the experiments on same condition.

However,unlike simulation results, experiment results show that an oscillator needs few seconds to be stablized. (Image 3. shows that oscillator's frequency goes up incrementally and then its frequency is stablized).

I want them make it right, fast and stable.

If you don't mind, I would like know how to get it right.

  1. What do you think that I should fix for stable and fast circuit like simulation.

  2. What other analysis needs to be take for stable circuit?, (TBH, I forgot everything about pole and zero stuffs, not good at those works though. But If I need it, I'm willing to study it again.)

  3. Any other comments If you like to say?

Thanks so much for reading this. Sincerely

Image 1. Sawtooth oscillator circuit diagram for simulation and experiment Image 2. Simulation Results from LTSpice GIF 3. Experiment Results

(One more thing! I refrenced this page! http://www.piclist.com/images/www/hobby_elec/e_ckt17.htm.)

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    \$\begingroup\$ Experiment results show that an oscillator needs few seconds to be stablized I'm not sure. You don't seem to have proper sync on the signal, and many scopes use the sync pulses to measure signal frequency. You can only expect valid frequency values when the waveform is not gliding horizontally across the screen. But it's hard to tell what's going on. The video is barely usable for anything. \$\endgroup\$ Aug 12, 2022 at 0:33
  • \$\begingroup\$ Note that the supply voltage range is 12.6V max or +/-5V specified. \$\endgroup\$
    – Antonio51
    Aug 12, 2022 at 6:41
  • \$\begingroup\$ Tested until 500 kHz with LM6164 and "some" little adjustment components value. \$\endgroup\$
    – Antonio51
    Aug 12, 2022 at 8:32

1 Answer 1

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LT1809 allows maximum of 1.4V across the inputs - there are two series diodes in an antiparallel configuration across the input pins. The absolute maximum input current is 10mA.

In your circuit, U1 is working like a comparator, and LT1809 cannot be used for this purpose - at least not the way you're using it.

I guess that you're driving enough current into the clamping diodes in U1 to warm them up. The clamp voltage grows with temperature. And that may well cause at least some of the drift.

This concern doesn't apply to U2.

schematic

simulate this circuit – Schematic created using CircuitLab

But, in order to diagnose anything else, we need to see your circuit. If you have not properly placed decoupling capacitors for the op-amp supplies, nothing will work, since you're using very fast op-amps. They are not docile like a 741 or even TL07x/08x would be. Their default behavior in unskilled hands is to oscillate, unless the circuit is constructed specifically to prevent that.

I suggest you replace U1 with an actual comparator. It can even be an LM339/393 - should be fast enough for this application. Do mind that some comparators have open collector outputs and need a pull-up resistor on the output.

For a precision sawtooth generator action, you'll need to use a comparator for U1, and use its output to drive a CMOS switch that connects the current sources (R2 and R3) alternately to the summing node and to ground. Ideally, R2 and R3 would be actual current sources then - LM334 for example. You'd be now close to what could be called precision oscillator territory, for such circuit architecture can be made quite good with just slightly better parts.

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