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I guess the In and Out in your schematic is the analog signal in my schematic that's connected to the driver. Not sure about the Control input in your schematic. Could you please explain about that? I am willing to try anything at this point to get this issue resolved.
thanks
I think something like this is what WTP is talking about.
The 339 comparator turns on the FET when the input voltage goes to about 85mv shorting the input to your driver to ground.
I should ask if you know the input impedance of the driver to make sure the 1k in series with the signal doesn't mess it up.
I think something like this is what WTP is talking about.
The 339 comparator turns on the FET when the input voltage goes to about 85mv shorting the input to your driver to ground.
I should ask if you know the input impedance of the driver to make sure the 1k in series with the signal doesn't mess it up.
I am thinking of a circuit where I can switch the input signal to the driver so that when say from 0.1V and below it will replicate something like unplugging the cable to the driver while it passes through any voltage above 0.1V. Is it even possible or am I thinking about some magic here?
Yes, the ones on the right are the same point and the output from your op amp. The other is just a test point so you can see where the waveform and where it switches.
But I don't think it will work because the voltage drop across the 1k will be to large driving into the 50 ohm load.
A better solution might be to use a switch like a DG2039 to open the signal from your op amp to the laser. I guess I was confused by
We can set the trip point closer to zero, but you will always loose to low counts using this method.
I'm also concerned about your statement that the DAC voltage dropped when hooked to the driver, but maybe that is ok.
Is there any other signal available that says the DAC is at 0?
If your DAC is a parallel one, say 8 bits and external then an 8 input NOR with each input connected to the data inputs (and a chip select if it's not mapped directly to a port) would go high when all inputs are zero.
To improve the noise you might look at figure 21 in the DAC datasheet.
Something like this:
It would open the circuit when the voltage gets close to zero. The only other way I can think of if this won't work would be to try to clean up the noise.
No, since you have 11 mv of noise it would need to be set higher than that or it would go on and off with the noise and you would have the same problem.
Do you have coax from your op amp to the driver? What does the noise look like? What op amp are you using?
I think I have been thinking about this wrong. So what you are saying is the output from the op amp is a 20 Mhz sine wave? So what changes to modulate the laser - the amplitude of the sine wave or the frequency? Is when you want 0 volts when there is no sine wave present?