I want to sample an analog signal of around 300 KHz . So which arduino board should i use for it?? I have tried it using arduino uno but it gives proper readings only upto 400 Hz. I was also reading about arduino due. Will it be useful for this??
What is the nature of signal? Amplitude, bandwidth, modulation? Precision of reconstruction in mV or %?
Signal is from function generator,sine wave.Amplitude is 3v,with no modulation,and i want to reconstruct it exactly. reply asap. 
You'll need an ADC with a sampling rate of at least twice the signal frequency. Eventually a fast buffer memory should be added, for independent and slower read-out of the values by the Arduino. Exact reconstruction of the signal requires an fast DAC for playback, with a multitude of the signal frequency. Depending on the allowed harmonic distortion of the output signal, a much higher sampling frequency will be required.
Perhaps you better explain why you don't want to use an amplifier for the exact reconstruction of the signal.
and i want to reconstruct it exactly.
Buy another signal generator. In real world you can have only approximation, and question is how close replica have too be to origin.
Thanks DrDiettrich for your kind reply.For faster data acquisition we are using port manipulation using PINC.but still we are not getting above 300 hz signal when the sampling rate is 9.6 khz.
pls find the attachment of the code we are using.
sketch_jun05a.ino (5.22 KB)
Please use code tags </> to present your code.