Hi everyone. Sorry for my english. Please try understand me:) I have a problem with AD8330. I'm designing a DIY digital oscilloscope. I want to use a typical double j-fet circuit in input. The j-fet are powered by +/-5V. Next AD8131 (+/-5V) are driving VGA AD8330(+5V). On all schematics I have seen that the AD8131 has a two resistors: 24.9 and 49.9 ohm. My question is...can I connect theinverting input to global ground and non inverting input trought the output j-fet without those resistors? In my circut I can't connect the 49.9ohm resistior to ground, it's too big load for J-FET.
I recommend the AD8129/AD8130 amplifiers for the box marked ???.
Take a look at the AD830 data sheet (the AD830 was an earlier part with the same architecture as the AD8129/AD8130) -- it has a bit more theory.
1. Check the slew rate of each part to ensure you can meet your full power bandwidth requirement
2. Anti-aliasing filter
3. Noise calculations and noise bandwidth
4. Enough system gain to drive ADC to full scale (V_FS) at desired oscilloscope scale (V/DIV)