Cheap and simple analog frontend for DIY oscilloscope, first good results

Some time ago I started a pet project DIY esp8266 oscilloscope, cheap and simple? First experiments showed that the concept is viable, but, to be honest, I didn’t expect so many troubles with my first version of analog frontend (my knowledge in high-speed analog circuits is limited, so now I understand that such result was rather expected). But thanks to free SPICE simulation software (like Tina-TI or LTspice) I was able to analyze my mistakes and fix them. Recently I had time to test the newest version of my schematic for the AFE and it seems very promising. I managed to get 2MOhm ~20pF input amplified enough to feed 2 ADCs on STM32 uC connected in parallel and running at very high speed (in this mode input impedance of the ADC is very low and requires an amplifier to create an input with high impedance). The schematic is based on a very cheap but surprisingly well-performing Chinese OPAMP Gainsil GS8052-SR which is easy to solder rait-to-rail high current output broadband operational amplifier. Here is my test setup with ADALM2000 which I used to get the Bode plot of the amplifier characteristics.IMG_20190915_082346

And here are the measured parameters of the AFE:

Scopy-network-2019-09-15-08-19-50

As you can see the amplification is pretty linear up to ~15Mhz which is perfectly enough for my purposes (max ADC sampling rate in my setup is 18Msps(with adc resolution 6bit), but at practically useful 8bit resolution it is ~13Msps). When I have time I’ll continue my experiments on the creation of the very cheap yet useful oscilloscope. Stay tuned!

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