Products > Test Equipment
DG4000 - a firmware investigation
RoGeorge:
By the high Z question, this is probably your first AWG generators. Most probably the generator is calibrated and working fine. The amplitude is constant only when the cable is also 50 ohms, and properly terminated in 50 ohms, otherwise the output can be very different than expected.
You may want to read about terminators, reflections, transmission lines and standing waves.
Blanc:
Thank you for your advice.
As you know, DG4000 has 2ch outputs.
I compared output voltages of ch1 and ch2.
These settings were the same, set to 50 ohm output.
I then connected them to a 2 channel 100Mhz oscilloscope.
Its each channel setting was the same and connected through 50 ohm terminators.
Then, let's try increasing the output power of DG4000.
I found that the voltage on ch2 rises smoothly,
but the voltage on ch1 rises discontinuously.
If the cause of the discontinuity is due to impedance mismatch,
I believe that ch1 and ch2 should have the same discontinuity.
This is the reason I believe Ch1 has some defect.
TurboTom:
You may be onto something here that's actually not a bug but just a performance limitiation. As it appears, you find these inaccuracies only at low output levels. Please verify your findings vs. Rigol's "Performance Verification Guide", pg. 2-4 ff. The PDF is attached.
AWGs aren't meant to be precise low-level sources (like RF signal generators) but rather the "Jack of all Trades". Already the ground-reference (PE) of the outputs on most of the models shows that real low level signals will have to fight ground-coupled noise interference as soon as several instruments are interconnected. There are some AWGs available with outputs that are totally isolated from ground, but those aren't entry-level instruments (which one may argue the DG4000 isn't either, but pricing-wise, there's still a big margin to "professional" grade instruments...). A good signal tansformer to isolate the output may be helpful but probably won't solve the observed inaccuracies.
I just compared my own DG4000 regarding your mentioned inaccuracies, but i don't find anything out of the ordinary. Both channels match pretty well around the "switchover points" of the attenuator chain, though there may be a tiny amount of discontinuity. What worries me more is that my scope has some bad discontinuity at its gain switchover point on its first channel ... more than 4%! And the "autocal" function won't iron it out... >:( The other three channels are okay. The scope is a DHO1000 btw, but that's OT.
Blanc:
Hello everyone.
Thank you very much for your supports and advices.
Last night, I found a USB memory that can refresh the FW of DG4000 among a lot of old USB memories.
After perusing this thread, I managed to get the latest "well tuned" DG4000 :-).
During the FW update, I was frightened by the lights of buttons turning on and off many times.
I made two mistakes along the way.
This morning, I calibrated the DG4000 again.
The attached photos are the conclusion.I set the AWG 50 ohm output, 1kHz.
Then I increased the amplitude in steps starting from -56dBm.
You can see abnormal rises and falls in the amplitude.
This symptom only occurs on ch1. I think this is evidence of a hardware failure in ch1.
I understand that the DG4000 is a hobbyist device, not a professional device,
and the amplitude of the AC frequency is sensitive and affected by various environmental conditions.
I think the photo shows the discontinuous of amplitude exceeds what would be the case in such conditions.
RoGeorge:
DG4000 is a professional AWG, not a hobby one. Its specifications are not a lie. The instrument is expected to have the performance told in its specification/manual. You probably have a defective DG4000.
Please open a new topic about repairing/calibrating your DG4000. People here avoid answering in a hijacked topic. This topic is about the firmware of DG4000, in general, not about repairing a particular DG4000 unit with a defective channel.
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