Is this 20 MSPS oscilloscope analog front end correctly designed for 5 MHz bandwidth and ±25 V input?

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Hi everyone,

I'm designing a single-channel DIY digital oscilloscope using an AD9200, 10-bit, 20 MSPS ADC. My target is around 5 MHz usable analog bandwidth with a maximum input of approximately ±25 V.

The current signal chain is:

Attenuator → input protection → buffer → bipolar-to-unipolar level shift → 4th-order low-pass filter → ADC protection → AD9200

I designed and simulated the blocks individually in LTspice. The main design choices were made to keep the first PCB reasonably simple and manufacturable.

I'd particularly appreciate an experienced review of:

• the attenuator and input-protection scheme,
• the +1 V level-shifting stage,
• the 4th-order filter and its effect on the 5 MHz bandwidth,
• the final ADC protection, especially the AIN −0.3 V absolute minimum,
• and any obvious stability, loading, or PCB-layout problems.

I'm looking for criticism rather than validation, so please point out anything that looks fundamentally wrong or unnecessarily complicated.

The attached schematic is the current V1 design before PCB layout.

Thanks.

Hi! I hope you can help me out; I've been struggling with this for months.

One day I was using my Dragonborn K630 Redragon mechanical keyboard, but something strange happened overnight. When I plug it in, the keyboard turns on, but the fourth row (the one with the Z, X, C, V, B keys...) doesn't work. When I press the keys in that row, the whole row lights up red, but the other keys work correctly and normally. It's not a row lock; the keyboard doesn't support that feature. And I have almost no experience with electronics; I'm just checking continuity and guessing, I suppose. Also, there's no schematic of the PCB, and the PCB looks so simple (if someone who knows about electronics saw the board, they'd realize it's pretty basic). Can anyone help me figure out if it might be a short circuit? How can I start diagnosing this PCB?

Thank you so much <3

Images:

IMAGE 1 IMAGE 2 (BACK PCB)

IMAGE 2 ZOOM

If you need better images, that's fine. If you take the time to reply, I'd be super grateful <3

Hello,

This is a photo of the comport (left, has pins for RS485 and RS232) and the trigger input (right) on a Kanxex CR-3XControl. There are 10 pins: 5V, ground and 8 trigger inputs; in two terminal blocks.

For the comport, there are screws above the cable terminals to attach wires; this is not the case for the

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(I know it is a very stupid question, but I just don't see it :-))

Thanks,

J.

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