Making variable-width pulses with an EOM
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Posted by matt-5589 on March 15, 2007, 8:05 pm
Please log in for more thread options like to get pulses in the 0.5 ns to 2 ns range, but I am finding that most benchtop function generators or pulse generators usually die out in the 5-10 ns range. RF function generators that I have seen are over my budget. Since the optical signal mirrors the electrical signal, it needs to be straight up and down - not a switch turning on an RF source, as is shown in a "microwaves101.com" tutorial. Meanwhile, everyday people do optical communications at 2.5Gb/s and 10 Gb/s, among other rates. Surely there must be some relatively inexpensive electrical sources. I've found various links for XFP and SFP modules. Though these have lasers built in, does anyone know of demo boards or evaluation kits for these types of things that will generate the pulses? Do these modules actually generate the pulses, or just have the drive amplifier and receiver circuitry? I can amplify them after with an RF amp we already have, so output voltage is not important. OEM modules would be fine, as I can supply them with regulated DC voltage if necessary. If anyone knows of a cheap pulse source, I would really appreciate it. Thanks | |||||||||||||
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Posted by John_H on March 16, 2007, 11:43 am
Please log in for more thread options If your budget want to keep you in small k$ range, you might not have much luck. As an electrical engineer, I'm left wondering about your specific requirements. Do you want continuously variable pulse widths? Do you need 15 ps transition times or is 500 ps rise/fall fine for pulses down to 500 ps? Do you need to generate the pulses through extenal electrical control or are you looking for pushbutton operation? How fast do you need to generate a second pulse of the same width? ...of a different width? Do you want the width on a dial where you don't necessarily know the actual width as you turn the dial but get "longer" and "shorter" pulses as expected or do you want to specify the width with digits? I've seen arbitrary waveform/pulse generators that can deliver narrow pulses but I'm worried they're out of your budget as well. The Tektronix Data Timing Generators, for instance, http://www.tek.com/site/ps/0,,86-16679-SPECS_EN,00.html have a pulse width minimum of 290 ps with 5 ps resolution. The ~$25k price tag is a bit harsh if all you want is pulse shaping from another data (trigger) source. A quick google search for "pulse generator" came up with hits from places like Avtech (avtechpulse.com) that have specs along the lines of what you need at more moderate pricing (I clicked on one instrument, $5k). So. What do you really need? | |||||||||||||
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Posted by matt-5589 on March 16, 2007, 5:39 pm
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>
> If your budget want to keep you in small k$ range, you might not have much > luck. As an electrical engineer, I'm left wondering about your specific > requirements. > > Do you want continuously variable pulse widths? > > Do you need 15 ps transition times or is 500 ps rise/fall fine for pulses > down to 500 ps? > > Do you need to generate the pulses through extenal electrical control or are > you looking for pushbutton operation? > > How fast do you need to generate a second pulse of the same width? > ...of a different width? > > Do you want the width on a dial where you don't necessarily know the actual > width as you turn the dial but get "longer" and "shorter" pulses as expected > or do you want to specify the width with digits? > > I've seen arbitrary waveform/pulse generators that can deliver narrow pulses > but I'm worried they're out of your budget as well. The Tektronix Data > Timing Generators, for instance, > > http://www.tek.com/site/ps/0,,86-16679-SPECS_EN,00.html > > have a pulse width minimum of 290 ps with 5 ps resolution. The ~$25k price > tag is a bit harsh if all you want is pulse shaping from another data > (trigger) source. A quick google search for "pulse generator" came up with > hits from places like Avtech (avtechpulse.com) that have specs along the > lines of what you need at more moderate pricing (I clicked on one > instrument, $5k). > > So. What do you really need? Thanks for your response. I'm a grad student, and so the budget is under $1K. Thanks for the link to Avtech. They do have OEM modules in the $2K range which would work, and there is currently one on an E- Bay auction. I also found a demonstration board for an Analog Devices PLL that operates at 1.2 GHz. That would give ~1 ns pulses, though I would want to drop the rep rate to somewhere in the range of 10KHz-1MHz. I anticipate taking whatever signal I get and putting it in the RF amp we already have, so anything above 100mV (into 50 Ohms) would probably work. I am thinking there should be a number of devices that work out there. Gigabit ethernet seems to be fairly common these days. While I havn't studied ethernet, I would imagine they would have to supply pulses around 1 ns in width. There is a great deal of optical equipment built for 10 Gb/s and 2.5 Gb/s. These have to use some kind of electrical-to-optical modulation. It seems to me there should be some way to stick an SMA connector on one of these, and adjust the bit pattern to send a single 1 every few microseconds, or change pulse widths by sending a succession of NRZ 1's. Unfortunately, I come from the optical side, and I'm just trying to pick up the electronics on the fly. Thanks. | |||||||||||||
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Posted by John_H on March 16, 2007, 6:10 pm
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> Thanks for your response. I'm a grad student, and so the budget is > under $1K. Thanks for the link to Avtech. They do have OEM modules > in the $2K range which would work, and there is currently one on an E- > Bay auction. I also found a demonstration board for an Analog Devices > PLL that operates at 1.2 GHz. That would give ~1 ns pulses, though I > would want to drop the rep rate to somewhere in the range of > 10KHz-1MHz. I anticipate taking whatever signal I get and putting it > in the RF amp we already have, so anything above 100mV (into 50 Ohms) > would probably work. > > I am thinking there should be a number of devices that work out > there. Gigabit ethernet seems to be fairly common these days. While > I havn't studied ethernet, I would imagine they would have to supply > pulses around 1 ns in width. There is a great deal of optical > equipment built for 10 Gb/s and 2.5 Gb/s. These have to use some kind > of electrical-to-optical modulation. It seems to me there should be > some way to stick an SMA connector on one of these, and adjust the bit > pattern to send a single 1 every few microseconds, or change pulse > widths by sending a succession of NRZ 1's. Unfortunately, I come from > the optical side, and I'm just trying to pick up the electronics on > the fly. > > Thanks. The comm systems you mention don't communicate with pulses but with coded NRZ data. You drive the laser (or EOM) until you get a transition to not drive (or to drive less). If you want pulses to occur on demand with specific widths and low overall duty cycle, you're no longer working in the communications modes. | |||||||||||||
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Posted by Matt-5589 on March 19, 2007, 4:10 pm
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> > Thanks for your response. I'm a grad student, and so the budget is
> > under $1K. Thanks for the link to Avtech. They do have OEM modules > > in the $2K range which would work, and there is currently one on an E- > > Bay auction. I also found a demonstration board for an Analog Devices > > PLL that operates at 1.2 GHz. That would give ~1 ns pulses, though I > > would want to drop the rep rate to somewhere in the range of > > 10KHz-1MHz. I anticipate taking whatever signal I get and putting it > > in the RF amp we already have, so anything above 100mV (into 50 Ohms) > > would probably work. >
> > I am thinking there should be a number of devices that work out
> > there. Gigabit ethernet seems to be fairly common these days. While > > I havn't studied ethernet, I would imagine they would have to supply > > pulses around 1 ns in width. There is a great deal of optical > > equipment built for 10 Gb/s and 2.5 Gb/s. These have to use some kind > > of electrical-to-optical modulation. It seems to me there should be > > some way to stick an SMA connector on one of these, and adjust the bit > > pattern to send a single 1 every few microseconds, or change pulse > > widths by sending a succession of NRZ 1's. Unfortunately, I come from > > the optical side, and I'm just trying to pick up the electronics on > > the fly. > The comm systems you mention don't communicate with pulses but with coded
> NRZ data. You drive the laser (or EOM) until you get a transition to not > drive (or to drive less). > > If you want pulses to occur on demand with specific widths and low overall > duty cycle, you're no longer working in the communications modes. For anyone still interested in the topic, I did find a circuit that will do ns pulses. Even better, you can probably get the IC's as free samples if you are aligned with a company. It uses the LT1721 Comparator from Linear. Here is a link: http://www.edn.com/article/CA476913.html So, the good news is that it is cheap and readily available. The bad news is that it would require soldering. RF speed (for the ns transitions) scares me when it comes to my soldering ability, as does surface mount components. I think this circuit, despite it's simplicity in components and acquisition, may be too difficult for me to construct without ringing like a tuning fork. S o, I am still looking for an evaluation board-type kit, but at least there is hope. And, I hope anyone else that might struggle with ns generation now has another option they can look at. | |||||||||||||
| Similar Threads | Posted |
| Making variable-width pulses with an EOM | March 15, 2007, 8:05 pm |
> like to get pulses in the 0.5 ns to 2 ns range, but I am finding that
> most benchtop function generators or pulse generators usually die out
> in the 5-10 ns range. RF function generators that I have seen are
> over my budget. Since the optical signal mirrors the electrical
> signal, it needs to be straight up and down - not a switch turning on
> an RF source, as is shown in a "microwaves101.com" tutorial.
>
> Meanwhile, everyday people do optical communications at 2.5Gb/s and 10
> Gb/s, among other rates. Surely there must be some relatively
> inexpensive electrical sources. I've found various links for XFP and
> SFP modules. Though these have lasers built in, does anyone know of
> demo boards or evaluation kits for these types of things that will
> generate the pulses? Do these modules actually generate the pulses,
> or just have the drive amplifier and receiver circuitry?
>
> I can amplify them after with an RF amp we already have, so output
> voltage is not important. OEM modules would be fine, as I can supply
> them with regulated DC voltage if necessary. If anyone knows of a
> cheap pulse source, I would really appreciate it.
>
> Thanks