PWM modulation in function generators is rare! Siglent anyone?

Hi:

So few seem to have this.

I actually budgeted to buy me an Agilent 33522A for 3 grand a year ago, along with a DSO3000X series scope. I balked at the generator since the ones I have at work have serious bugs. They have fixed them almost, but not perfectly. I know they will fix them fully if I send in new complain-o-grams, but I haven't had time to do that yet.

Anyway, for $3k of my own money, I don't want it to have bugs. That has motivated me to just wait and/or scan the lower cost generator market.

But there are a few features of the Agilent that I really like:

a. 2 channels b. PWM modulation -- why do so few have this? c. Ability to modulate a PWM with noise. This is so cool, because it let me set up a scheme to simulate shot to shot variations in laser performance, then develop the data analysis on my LeCroy scope to plot in real time the relative standard deviation of pulse energy. d. Ability to externally modulate the PWM. Again, very cool. e. Settable noise bandwidth! Only the Agilent does this, from what I've seen.

So now I'm having a look at the TTI model TG2511 25MHz Function, Arbitrary & Pulse Generator:

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Which is at least equipped with PWM modulation including external. Unfortunately, their pulse capabilities don't offer 1ns resolution, which is why I haven't found a suitable TTI to buy at work where I need that.

I don't really want to spend this much though.

This Rigol DG1022 offers two channels for much less money, but no PWM:

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What I really want to do right now is have two synchronized anti-phase PWM channels, that I can adjust duty cycle to drive a half-bridge. Not easy to do this for under $3000 it seems.

Except for Saelig had this Siglent SDG1005 5MHz Waveform Generator on it's site the other day, and now it disappeared. Seems to offer 2 channels and PWM. But the jitter spec on the square wave is terrifying:

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It's getting hard to keep track of all the new Chinese instrument makers. I have ignored them until recently, figuring they just weren't worth the risk. But when you're talking a factor of 10 cheaper, you might as well buy one just for a spare.

Continuing to search for the perfect and cheap signal generator...

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Mr.CRC
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Mr.CRC
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We did a 4-channel arb, in VME and as an oem/embedded box. Once we did the VME version, sticking it in a box was relatively easy.

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It will modulate almost anything onto anything else, and it does have programmable bandwidth noise. It will do noisy PWM. It's mostly just an FPGA with a lot of math, then some DACs and filters.

If you build a DDS and want a square wave, you have a choice of just using the MSB of the phase accumulator (and suffer a full clock of jitter) or use the dac to make a sine and run that through a filter and comparator (and suffer a DAC LSB of jitter at lower frequencies.) What works well is the sine+comparator thing, but keep the DDS frequency in its sweet spot and divide down for lower frequencies.

John

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John Larkin

Yes, I have done a little DDS work and grappled with these choices.

Your box is interesting, but I wish it had a UI.

Have you thought about building a new one with a UI?

I'm sure if you have, your next thought must be, "yeah but the Chinese are making a new one each week, and they are now in the couple $100s range!"

This mustn't be a pleasant thought.

Thank goodness for niche markets!

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Mr.CRC
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Mr.CRC

Exactly!

Double Exactly!

The only thing that seems to be rare in arbs is lots of channels. One is usual, two occasionally, seldom more. We do arbs with dozens of synchronized, phase-shifted, gear-ratioed frequencies for jet engine simulation. It's not a huge market.

John

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John Larkin

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