Products > Test Equipment
RD JDS6600 25MHz 2-Channel DDS AW Function Signal Generator
vk2seb:
--- Quote from: gby on June 24, 2017, 01:27:56 pm ---The JDS6600 generator family has very similar functionality to the Feeltech FY3200 and the MHS-5200 generators. The JDS6600 even uses the exact same plastic case for the enclosure as the FY3200, MHS-5200. For a comparison of those other generators see:
https://www.eevblog.com/forum/testgear/feeltech-fy3224s-24mhz-2-channel-dds-aw-function-signal-generator/msg697718/#msg697718
--- End quote ---
Huh, interesting. Thanks for the link!
--- Quote from: gby ---From testing the FY3200 myself and reading on the MHS5200 they both are both limited in their output voltage range into 50 Ohm load without clipping or high distortion. So the first test I would suggest is:
1. Set 10 KHz sinewave with 20 Vpp/maximum amplitude on an oscilloscope with 1 Meg impedance. Then add the 50 Ohm termination and see if the output drops to 1/2 or if clipping or distortion starts happening.
--- End quote ---
1 meg impedance, max amplitude @ 10KHz:
50 Ohm termination:
--- Quote from: gby ---On these type generators the output buffer is often slew rate limited which in turn means the output amplitude at higher frequencies is limited. So, the second test I recommend is:
2. Set a 10 Vpp 100 kHz sinewave on the output into oscilloscope with 50 Ohm termination. Then increase the frequency until maximum frequency to see if or at what frequency it starts distorting horribly.
--- End quote ---
So I think there are 2 interesting points here, at 10MHz and at 25MHz. Because above 10MHz the amplitude is restricted down from 20Vpp to 10Vpp (probably for slew rate reasons).
At the maximum frequency useable at 20Vpp (into 50 Ohms, so we should be seeing 10Vpp):
Looks pretty distorted. Here's an FFT (didn't use specan because I couldn't find my big attenuator :P)
So that second harmonic is at about -30dBc, which is out of spec (Spec says -40dBc).
At 25MHz, it looks a bit cleaner (but the amplitude is now 10Vpp out, which should look like 5Vpp into 50 Ohms):
And an FFT:
Looks to be about -40dBc, so that's roughly in spec.
--- Quote from: gby ---On the FY3200 generator when you change the frequency the output waveform glitches. Ideally one would expect a change in frequency with a sine wave to step change the slope at the frequency change with no step in the actual voltage. Unfortunately the FY3200 has steps in the output because the phase as well as the frequency changes when you change the frequency. So, the third test I would love to see is:
3. Set the generator to 5 Vpp, 10 kHz sine wave and then step change the frequency to 20 kHz. Try to capture on the oscilloscope the moment when the frequency changes. If you have advanced triggering I set trigger width must be < 20 uSec and then set to capture once.
--- End quote ---
Here's what that looks like:
Slightly zoomed in:
--- Quote from: gby ---When you use two channels both outputting the same frequency sine wave with the phase 90 Deg apart it would be great to repeat test 3 to insure that both channels change frequency at the same time and with no glitches.
4. Repeat test 3 but with two sine wave channels outputting sine waves with 90 Deg relative phase.
--- End quote ---
I couldn't find a way to change the frequency of both channels at once, so I'm not sure if that's possible. Here's what 2 channels at 90 deg phase shift look like when channel 1 is increased in frequency:
--- Quote from: gby ---The last requested test is really just a question of functionality. This generator can do frequency sweeps. But, can it do frequency sweeps while outputting two wave forms? Last requested test is:
5. Can you set the generator to output 2 sine waves with 90 Deg relative phase and then sweep the frequency such that both channels sweep in frequency and stay in phase lock?
In advance I thank you for any of the above tests that you could do and report back results.
--- End quote ---
As far as I can tell it's not possible to do sweeps on 2 channels at once.
Cheers for your suggestions!
vk2seb:
--- Quote from: Kleinstein ---The triangle waveform looks quite good - better than I remember from the MHS5200. However the scope setting is not that good to tell if the little nonlinearity is from the scope of from the generator. If would need a zoom in on details of the slope and maybe an even lower frequency. Usually a simple R2R DAC would show visible errors near the center or 1/4 of the range. There are 2 pots for each channel so these might be for adjusting at least that largest error.
--- End quote ---
All good points, if I get some time later I might try a super-low frequency and use the datalogging feature on my keysight DMM to get some more precise measurments of that.
--- Quote from: Kleinstein ---The picture of the circuit is just to bad in resolution to read the chip numbers. The output amplifiers might be interesting. For the rest I would expect an AD603 or similar for the amplitude adjustment.
--- End quote ---
Strange, I can read most of the chip numbers except a couple on the left - if you go to the raw link it should be a higher resolution than what you're seeing on the forum.
From left-to-right with the front end it looks like a bunch of discretes and then (same for both channels):
1. An AD8056A 300MHz voltage feedback amp.
2. An AD835 250MHz 4-quadrant multiplier.
3. An AD8017 160MHz high output drive op amp
4. All the relays & discretes as well as:
5. A TI part, 3001I. I'm assuming this is the THS3001, which is a 420MHz current-feedback amplifier.
--- Quote from: Kleinstein ---Are the USB and TTL I/Os isolated from the normal outputs ? It does not look like.
--- End quote ---
The chip between the FPGA and TTL I/Os is just a 74HC14 hex inverter, so probably not.
I haven't been able to identify the chip between the FPGA and the USB port, the code looks like CR3400
onlooker:
That is the "well known" WCH CH340G.
gby:
vk2seb,
Thanks for your testing on my questions:
1. Looks like they got the output buffer "strength" right this time. The MHS-5200 had too small a power supply voltage to reach full 10 Vpp across 50 Ohm and the FY3200 buffer had to low a current limit. So, the JDS66000 is definitely improved here and from your photograph it looks like a reasonable heat sink. :-+
2. Looks like some slew limiting on the output at 10 MHz but not too bad. The official specs say 20 Vpp up to 10 MHz, 10 Vpp 10 - 30 MHz, and 5 Vpp > 30 MHz. These specs imply a slew limit of just better than 5V0-p*2*pi*30MHz = 942 V/uSec. Probably around 1000 V/uSec which is pretty good.
3. Changing single channel frequency looks to be smooth which is good. :-+
4. For changing the frequency when both channels are running the same frequency you say:
"I couldn't find a way to change the frequency of both channels at once, so I'm not sure if that's possible"
These generators usually have a channel synchronization mode where you lock them such than changing one channel parameter changes both channels. In the JDS66000 manual I found on line it says under the system setting menu:
4.4.2 Sync: When sync, CH1 is the object of operation. CH2 parameter will be changed with the changes of CH1 parameter. When the sync item is selected, you can press or knob to select the sync item needed, press ON softkey to select and press OFF softkey to cancel.
Could you check for the system setting sync function and try changing the frequency of two channels locked at 90 Deg phase again?
5. Perhaps with the two channels sync'ed you can then sweep two channels with a phase difference simultaneously?? One can only hope....
Again, thanks for your help in evaluating this generator and sharing.
gby
Kleinstein:
The parts used seem to be a little more expensive (e.g. AD835 instead of lower cost AD603) than those in the super cheap versions. The amplifiers also look rather fast. Still strange that there are additional AD8017.
I finally found the higher resolution pictures. So I got a look at the DAC: they seem to use 15 lines in a thermometer style to get the upper about 4 Bits with less errors / glitches. So the DAC is not just an R2R ladder.
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