Author Topic: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator  (Read 549224 times)

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Offline DerKammi

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Updated my mistakes indeed, lots of leading zero's missing  :=\
Also updates the formula in the sheet.
 

Offline fremen67

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Suggestion from my side. maybe we can have an automated step function with adjustable step time for these tests? So then we can just write down values and not switching back and forth programs and edit values. I'm half dead right now :)
If ever we build a per value / per device calibration matrix, yes, we should have such auto-set macro function. Does not even have to be in the BP, can be in the PC.

 :) Yes, boring and source of mistakes. If needed, I will do it. I already did this some years ago: automated calibration on a FG with a DMM and and an oscilloscope with SCPI commands from an  excel sheet (do you guess why I was talking of a SCPI interface in the new firmware  ;))
Anyway thank you for your time, both of you. The more values, the more ideas (and you have a lot), the more potential upgrades.

However, I think for now, all we need is some rough guidelines on what autoranges to select, and maybe some coarse global correct. So maybe one or two more person, then we are done for now.
Agreed on that. I will also run tests and that will be enough data at the moment.
It seems now obvious that we have first to deal with some hardware upgrades before finding software workarounds.
For now I will add static calibration only on the 3 ranges on amplitude and offset. This should be enough for low frequencies.
For higher frequencies, it will be time to think about it later on and decide, after fine tuning the opamp part, if this will be done in FPGA via digital filters (zov maybe?) or if something can be done via FP.

Also, I ran the wave all the way down to 0.01Hz, and the shape of the flattened top stayed the same. Meaning it is not a response time thing. Not even a current thing, because if the local capacitor would drain out, surely it would fall off more toward the trailing edge.

I wonder if it is something to do with the fact this OpAmp is described in the datasheet as a "CURRENT-FEEDBACK AMPLIFIER". I do not know what that means, normally when I mess with OpAmp I consider voltages. Need to read up on that.
From the THS3001 datasheet: "The ability to control the amplifier gain independent of the bandwidth constitutes a major advantage of current-feedback amplifiers over conventional voltage-feedback amplifiers"

A test I would suggest would be to use the feedback resistor value recommended in the THS3001 datasheet, that is 560 ohms for a gain around 5 instead of 1.5kohms. Then replacing the gain resistor with a 180 ohms one instead of the 499 ohms one. This would lead to a gain of 4.11 that could be compensated by the software calibration.
I have some THS3095 ready for tests as well as preproduction THS3491 but not time to do it now...

Also, I wonder if it can be resolve by, instead of replacing, *adding* an OpAmp.
Just leave the THS3002 in place, and add a pair of THS3001. They have the same behavior, the PCB traces are in place, de-soldering is harder then soldering.
All we need to do is add to the unpopulated footprint.
Good idea but as DerKammi said, we would have to add shared output resistors. May not be to difficult to modify traces for that... That is a typical design with THS3491.
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Offline DaveR

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I managed to find a new ST-Link locally, so I spent a few hours doing cybermaus's range test, as per the attached spreadsheet.  These were carried out on a factory 1.501 board with linear power supply feeding +/-12.2v (adjustable to 15v when needed).  I've also got a couple of THS3095s on order, in the expectation that another mod will be the order of the day quite soon.
 
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Offline cybermaus

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@DaveR: Please add a leading 0 to F60

For the rest, your data looks similar to mine, including the extra dampening spot around 10V/60MHz
But you have no negative offset in that region?

DerKammi's device with the THS3095 does seem to be less deformed in the higher frequencies.
I mean, the color assignment is manual, so a little subjective, but he did not even paint them yellow.
 

Offline Gandalf_Sr

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DerKammi, I looked at the schematic but U7 (74HC245DW) does not tshpw the power rail connections and I need to know the voltage it's running at to give a recommendation for a replacement.  I'm guessing that it's 5V as it says TTL output and that is actually a limitation on what CMOS family it can be replaced with.
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Offline DerKammi

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Wrong guess :) It's on the 3V3 regulator actually.
 

Offline DaveR

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Well spotted, cybermaus - corrected sheet attached.  Our sets of results are indeed very similar, but I certainly didn't see any extra negative offsets in the places you did - unless the amplitude "flickering" I saw was the same thing?  It occurred in the same parts of the high range you noted it, but what I got was a fleeting extension of the negative half of the wave without a corresponding downward movement of the positive half, so I deemed this to be more amplitude instability than an offset change.  It could have been a combination of both, thinking back to it.
 

Offline DerKammi

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:) Yes, boring and source of mistakes. If needed, I will do it. I already did this some years ago: automated calibration on a FG with a DMM and and an oscilloscope with SCPI commands from an  excel sheet (do you guess why I was talking of a SCPI interface in the new firmware  ;))
Anyway thank you for your time, both of you. The more values, the more ideas (and you have a lot), the more potential upgrades.

NICE!

Also, I ran the wave all the way down to 0.01Hz, and the shape of the flattened top stayed the same. Meaning it is not a response time thing. Not even a current thing, because if the local capacitor would drain out, surely it would fall off more toward the trailing edge.

I wonder if it is something to do with the fact this OpAmp is described in the datasheet as a "CURRENT-FEEDBACK AMPLIFIER". I do not know what that means, normally when I mess with OpAmp I consider voltages. Need to read up on that.
From the THS3001 datasheet: "The ability to control the amplifier gain independent of the bandwidth constitutes a major advantage of current-feedback amplifiers over conventional voltage-feedback amplifiers"

A test I would suggest would be to use the feedback resistor value recommended in the THS3001 datasheet, that is 560 ohms for a gain around 5 instead of 1.5kohms. Then replacing the gain resistor with a 180 ohms one instead of the 499 ohms one. This would lead to a gain of 4.11 that could be compensated by the software calibration.
I have some THS3095 ready for tests as well as preproduction THS3491 but not time to do it now...

As I mentioned I wanted to do some LTspice sims. Had a go with the different feedback resistors, 1k5 as of feeltech. 1k as suggested in the datasheet as all rounder and 560 as per datasheet and fremen76 his suggestion. The 1k version has my preference as the gain is linear in the whole range, gain is 4.0297 in the sim. The 560 shows a bump at the 60..120MHz.

Also did some sims on the max gain vs. voltage. The 12V voltage does not seem to be adequate for 20MHz, 4x gain and 10Vpp out. 15V supply is enough.

I got the Pspice model of the TI site and imported into LTspice, this is working fine normally.
« Last Edit: March 19, 2018, 10:11:44 am by DerKammi »
 

Offline cybermaus

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While your simulation does show a better curve from ~30MHz to 100MHz for the 1K resistor, I am not sure if it explains what we are seeing.
We see the odd flattening (not even calling it clipping, its not sharp enough) at *any* frequency, even at 1Hz, and at both voltages rails of 12V and 15V

So I think we are seeing a different effect.
To be sure, can you run those last two simulations at lower frequencies?


 

Offline DerKammi

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Those are the same questions I'm having, it doesn't explain our findings. I had a huge amount of ringing in the flat spot also, more like oscillations of any sort. Maybe the power supply is acting up because of the low quality capacitors.

I did the sims also at 1k, same effect.

 

Offline rhb

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I finally ordered the JST HX connectors so I can fix my cable and a couple of the "blue pill" STM332F104 boards.  So I should be able to get to work on the FY shortly.  Though I've got a rather large backlog of other projects under way.  My programmers came last week.
 

Offline DaveR

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@Insatman:

Replacement of 50Mhz clock chip with TCXO (1ppm).   

  It has 10 pads of which only 4 are used.  You must connect pads 8 and 9 in this application.

Can I just clarify something with you before I do this mod (I received the D75J and two THS3095s today)?  Did you mean that pads 8 and 9 have to be connected together, ie both to the same solder pad on the board (the one next to L1)?  In other words, you are only using three of the original four solder pads, with the one next to C1 taped off, but still using all four "active" pads on the D75J ?

Thanks,
Dave
 

Offline DerKammi

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I think we're actually pulling too much current out of the THS3001/2. After some searching around the web and triggering by fremen76 his attachment even the new super THS3491 is in need of 2 chips for driving 13Vpp at 50r. And the THS3491 is capable of delivering 380ma instead of the 100ma of the ths3001.

That 13Vpp is delivered at 100r total load and would mean 6.5V/100 = 65mA. That doesn't look like much of a problem for the 380mA super chip. But still they recommend 2 chips. If the THS3491 can't even do 65mA how is the 4 times lower rated THS3001 able to do it then. It doesn't make 100% sense but this is what mind came up with this evening.
 

Offline cybermaus

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So the spice model is rather off at these high currents at high voltage.
Also, it would mean the THS3091/3095 is actually better then the THS3495:

« Last Edit: March 19, 2018, 09:53:30 pm by cybermaus »
 

Offline cybermaus

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Mind you, I think I will pass on modifying the base PCB traces to double up OpAmp. Lots that can go wrong there.
I think I will fix mine by modifying the documentation:

Specs
Output at High-Z load:
  <10MHz         : 20Vpp
  10MHz<f<20MHz  : 10Vpp
  >20MHz         : 5Vpp
Output at 50 Ohm load:
  Any f          : 5Vpp


Modifying with a single 3091/3095 is still a good idea though. Your without load above 20MHz waveform seems better then mine, assuming you colored your XLS correctly.
« Last Edit: March 19, 2018, 09:54:46 pm by cybermaus »
 

Offline Insatman

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@Insatman:

Replacement of 50Mhz clock chip with TCXO (1ppm).   

  It has 10 pads of which only 4 are used.  You must connect pads 8 and 9 in this application.

Can I just clarify something with you before I do this mod (I received the D75J and two THS3095s today)?  Did you mean that pads 8 and 9 have to be connected together, ie both to the same solder pad on the board (the one next to L1)?  In other words, you are only using three of the original four solder pads, with the one next to C1 taped off, but still using all four "active" pads on the D75J ?

Thanks,
Dave

For confusions sake I will call terminals on the D75J "pins" and connections on the PCB "pads".

Yes you must connect pins 8 and 9 together.  Pin 8 is the Enable Pin and must be held High.  I only used three of the original pads and taped off the one closest to C1.  I did this because the datasheet says not to connect to pins 1 and 2 which are facing that pad on the PCB.   Good Luck. 

I should look into the THS3095.  Thus far I have made no mods to the main PCB except the clock chip.   This thread is getting way long.  Can anyone explain quickly benefit of using the THS3095 and which  IC it replaces?
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Offline DaveR

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Thanks for that, Insatman.  I thought that was how you'd done it, looking at your photos, but I just wanted to make doubly sure :)

As for the 3095s, they are to replace the single 30021 opamp under the heatsink on the signal board - see here :  https://www.eevblog.com/forum/testgear/feeltech-fy6600-60mhz-2-ch-vco-function-arbitrary-waveform-signal-generator/150/

As to how well they work, well I'll find out tomorrow after I've put mine in and re-run the high range tests.  I'll do the D75J mod after that, but it will have to be later in the week as I've got some urgent car maintenance to get out of the way as well.
 

Offline Insatman

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Thanks for that, Insatman.  I thought that was how you'd done it, looking at your photos, but I just wanted to make doubly sure :)

As for the 3095s, they are to replace the single 30021 opamp under the heatsink on the signal board - see here :  https://www.eevblog.com/forum/testgear/feeltech-fy6600-60mhz-2-ch-vco-function-arbitrary-waveform-signal-generator/150/

As to how well they work, well I'll find out tomorrow after I've put mine in and re-run the high range tests.  I'll do the D75J mod after that, but it will have to be later in the week as I've got some urgent car maintenance to get out of the way as well.

Please let me know what difference the 3095 chips make using the standard +/-12V power supply rather than the +/- 15V supplies some have retrofitted.  I'm considering ordering them at about $10 each from Digikey on my next order.   I'm reluctant to change out the power supply at this point, other than the mods I've already done to it.

Good Luck with the car maintenance.
Retired Pulsed Power Engineer/Physicist...now I just dabble in electronics
 

Offline DerKammi

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Please order the THS3091, is doesn't have the shutdown pin as the 5 does, we don't need it.

@cybermouse, I'm more than happy with the current output, possibly never use it at these high levels and frequency's together. But a change to the THS3091 I would possibly try out anyway. Just to clarify things whether it helps yes or no.

The white cells in the excel are correct, I checked them yesterday evening. The amplitude goes down by a large amount and therefor the signal stays OK.

The graphs you show are missing in the THS3001/2 datasheet but do show some table values which are running into overload in our use case.
 

Offline cybermaus

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Please order the THS3091, is doesn't have the shutdown pin as the 5 does, we don't need it.
I checked that I while back, when @Vytautas first mentioned the THS3095, but luckily leaving the pins floating is defined in the specs:
"7.2.1 The power-down pin of the amplifier defaults to the positive supply voltage in the absence of an applied voltage,
putting the amplifier in the power-on mode of operation."
 

Offline DerKammi

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Ahh ok, just pick the cheapest then :)
 

Offline paulca

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So mine finally arrived this morning.  Powered it up and measured the BNC shield to Earth. 

96.6V AC (240V supply)
68uA current

Had a play and orientating the 5V reg module, +-12V reg module and the RCore transformer is just about doable, but not if I replace the power socket/switch with a fused/switched IEC 3 pin socket.  The socket protrudes quote a lot.  Might need to get creating like mounting the socket with spaces so it protrudes in less.

I might be able to live without the transformer chassis earth, but I don't think I can live without a fuse.

Question:

If I am going to use this to test basic op-amp circuits, mostly audio.... how much risk is there in using it as is?

Does it matter if I add a ground referenced USB connection into the mix?
"What could possibly go wrong?"
Current Open Projects:  STM32F411RE+ESP32+TFT for home IoT (NoT) projects.  Child's advent xmas countdown toy.  Digital audio routing board.
 

Offline SMB784

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So my supplier actually got me the replacement chip like they said they would. They shipped me the ST microelectronics chip, and the winbond flash chip. I will install them in my working version 3.1 unit and verify that the version has been changed to version 3.2+. At that point I will ship out the 3.1 chips for testing by the community.
« Last Edit: April 04, 2018, 05:35:40 pm by SMB784 »
 

Offline Cliff Matthews

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Hello all, there's a new forum member that posted ( https://www.eevblog.com/forum/beginners/software-feeltech-fy6600/ ) that he received his FY6600 but the CD is not readable. Is there a link anyone can post to help this member download it? - Thanks!
 

Offline DC1MC

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Hello all, there's a new forum member that posted ( https://www.eevblog.com/forum/beginners/software-feeltech-fy6600/ ) that he received his FY6600 but the CD is not readable. Is there a link anyone can post to help this member download it? - Thanks!

Let's have a fresh link here as well:
https://drive.google.com/drive/folders/0B3N_NW8vylrmQVNrbXVERnltSFk
 
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