Author Topic: Function generator booster for MSO5000  (Read 849 times)

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Offline thmjpr

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Function generator booster for MSO5000
« on: March 11, 2020, 07:10:23 am »
As mentioned in other threads, often the output voltage of built in waveform generators is lacking. In this case, MSO5000 output is +/-2.5V.
This circuit is a simple plug-in board to provide a fixed output gain of 2x for both generator channels. So +/-5V output.

The voltage rails are created from 5V USB by TPS65130.
I've went with +/-7.5V for 3201 but up to +/-15V should be possible. The positive rail in that IC was rock solid, the negative rail however gives me some problems. With cf- removed it became stable, so far.

USB output on the MSO5000 should be capable of at least 1A, could be up to 1.5A. But I did not test it with a load tester.

Files: https://gitlab.com/thmjpr/fg_boost/
Schematic: https://gitlab.com/thmjpr/fg_boost/-/raw/master/Rev1/rigol_fg_boost.pdf


Opamp selection options:
THS3091:
- +/-15V
- 210 MHz (G=2)
- 250mA

THS3095:
- Same as 3091 with added power down pin and ref pin ( 8, 1)

THS3061:
- +/- 15V
- 275MHz (G=2 MSOP)
- 140mA

THS3001:
- +/- 16V
- 350 MHz, 300MHz (G=2)
- 120mA

THS3201
- +/- 7.5V supply
- 850MHz at G=2 (Rf 768R)
- 176mA

THS3491:
- +/- 15V
- 900 MHz (G=5)
- 420mA

Most will have a thermal pad package for a slight increase in cost, it shouldn't be necessary when driving 50R load. But if you plan on abusing the output it would be good to have. Since the output bandwidth is not that high (25MHz), Rin could be some larger value to protect the AWG output should anything backfeed. Rt1 and Rt2 should be replaced with 1M, just to pull the input to Gnd when generator output is off.
So far I have tried with THS3201, and will be getting MSOP THS3061 which may fit in the SOIC footprint..

A few spare Rev1 boards will be available for sale at some point with THS3061.





 
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Offline schmitt trigger

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Re: Function generator booster for MSO5000
« Reply #1 on: March 11, 2020, 02:11:49 pm »
This is an interesting thread because I've an old HP sinewave generator which I cherish. However, it only has an output impedance of 600 ohm, and there have been instances where I require a lower impedance, at least 50 ohm.

Of course in a sinewave generator, the THD levels are very important.
Do you have an idea on the performance of your proposed circuit?
 

Offline thmjpr

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Re: Function generator booster for MSO5000
« Reply #2 on: March 12, 2020, 06:33:47 am »
SMA can be fitted as well for outputs:


This is an interesting thread because I've an old HP sinewave generator which I cherish. However, it only has an output impedance of 600 ohm, and there have been instances where I require a lower impedance, at least 50 ohm.

Of course in a sinewave generator, the THD levels are very important.
Do you have an idea on the performance of your proposed circuit?

In terms of bandwidth of the onboard generator, response is a flat from 0-25MHz.
For higher frequencies.. its not terribly flat, I had a lot of peaking at ~450MHz. Could be excess capacitance on the PCB. But I think I'd need spec-an or similar for good HF measurements.



For distortion, 2nd harmonic datasheet spec:
THS3201 is -64 dBc at 10MHz RL=100R.
THS3061 is -78 dBc at 10MHz RL=150R.

Measuring on the scope I'm getting (THS3201):
- 2nd harmonic -48dBc
- 3rd harmonic -40dBc

Compared to direct from the internal generator:
- 2nd harmonic not visible
- 3rd harmonic -58dBc

So there is a lot of distortion added, but I don't know specifically from where. I will compare to the THS3061 when I receive it.
 
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Offline schmitt trigger

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Re: Function generator booster for MSO5000
« Reply #3 on: March 12, 2020, 04:27:45 pm »
Thanks for sharing your findings.

My generator only goes to 2 Mhz, so I should be ok.
 


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