I've built a simple pc oscilloscope using pic18f4550 and a 20 MHz crystal.
I've made a simple application using vb2010 which is able to show the frequency oscillation on pc. The problem that I have right now is, when I apply a sine wave to my pic project, the sine wave is properly displayed on my pc. But when a sine wave is applied to pic with a frequency of 40 kHz and above the displayed amplitude will decrease, and it will continue to decrease with higher frequencies.
Why is the amplitude decreasing ? How to maintain the amplitude at freq 1 MHz ?
I did not put any buffer opamp before input signal to pic.