Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
I am glad that you guys are coming up with some good suggestions to resolve this issue. It would be great if you guys can provide with some sample circuits that I can try them out to see which one works better.
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.
+5Volts on the Control input switches the FET on, thus grounding any signal present at the output. The 1K resistor prevents excess loading of the driving signal during the grounding.
Thanks for your suggestion, I will definitely try your setup and see how it performs.
The manufacturer specs states that the input impedance as 50Ω. But I have ot mention that the lower limit for the FET to turn on must be very low (lower than 85mV), this is because the resolution of the driver is pretty good that we drive it with DAC resolution of 10bit from 0-1V.
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
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?
The voltage of the DAC output drops to half when I connect the output from DAC directly to any driver (we have drivers from two manufacturers and they all does the same), this is where we started using gain amplifiers.
Unfortunately, there is no other signal that says if the DAC output is at 0.
The TTL option that the manufacturer is providing is just like a digital ON/OFF switch which is not what we want though, so that's not an option to try.
To be clear, our analog signal form DAC is a continuous wave from 0-1V at 20MHz and the DAC resolution is 10bit which is about 0.9mV per step.
I will look at DG2039, looks like something I used in my other project to electronically switch between two modes using a 5V signal. Not sure how I can incorporate that into this setup
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.
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.
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.
That's an option, but we don't use differential output rather we modified it to be single ended output. The reason is that the offset for the differential output is 1V rather than 0V.
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?
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 am not sure which op-amp I used back then when I put together that gain amp. I guess I need to measure few things about the signal before I proceed with building something like you suggested. Looks like I need to compromise on the lower limit at which the switch goes off. I will get back with the findings tomorrow.
Maybe a bit more info if you can. Are you trying to modulate the laser at 20Mhz or is this signal to keep it steady? If the response doesn't have to be to fast some filtering might help.
What does the system do?
The DAC output drives the driver at 20MHz which in turn produces an RF signal to drive a crystal that modulates the laser power by diffracting the beam depending on the power of RF signal which is derived based on the input modulation signal from the DAC. The response time of the modulator itself is ~100MHz. The system is used for precise stimulus delivery at 20MHz in a research based system.
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?
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?
The output from the Op-Amp which is basically amplified output of DAC is an arbitrary continuous waveform. The amplitude of the waveform is anywhere from 0-1V with an offset of 0.5V. The waveform resembles to a pulse waveform at 20MHz at its highest frequency to a square wave of 15KHz at its lowest (imagine a square wave in both instances with different duty cycles). So, when the waveform is at low level (zero), I want it to be a true zero. The extinction ratio of the modulator that the manufacturer specified/measured is higher (which is what we would like to have) than what we can measure in our setup and the only reason they can think of is the 'Zero' level not being a real 'Zero'.
OK. so the output is a digital signal between ground and 1 volt with a varying duty cycle. The problem being that it may not get all the way to ground.
Since you have +/- 15 volts to the op amp why not just increase the gain a bit so the output swings below ground?
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.
