This is nonsense.
Please state what you are measuring .
Your analog signal does NOT need to "reach" 5V . 5V is simply the FULL SCALE voltage. The ADC can measure anything from 5 mV to 5V. Obviously you have a misunderstanding about ADCs and how to use them. Start by explaining
I am measure the sensor signal and I just amplify the siganl and through the low pass filter, I'm thinking is there any possible about impedance matching..........I'm not sure
First of all, the only way to AMPLIFY a sensor signal is add an AMPLIFIER. The fact that you are not aware of that means you need to start at ground zero. An LPF (Low Pass Filter ) does NOT amplify. It Filters (out) (duh) high frequencies. If it was a high pass filter it would filter (out) low frequecies.
1- what is the sensor ?
2- do you have a clue how to make an amplifier ?
3-how much electronics experience do you have ?
Do you have a DMM (Digital Multi-Meter) (NOT VOM) ?