USB oscilloscope projects

[nigelwright7557]

I used the USB project from www.waitingforfriday.com as the basis for a USB low frequency oscilloscope.
It managed 460,000 samples per second and was good for about 20KHz.

My next project was 1,000,000 sampler per second scope but I found the op amps I used struggled with anything over 20KHz.
The op amp gain/bandwidth was 3MHz and input bias current was 1pA so it should have been fine.
The problem turned out to be a 1 meg input resistor in conjunction with the op amp input capacitance giving a loss of 50% at 20KHz.
The input capacitance was 8pf so I put a 10pf in parallel with my 1 meg resistor and this compensated for the losses.