I am really sorry about my tone.As you can see i can't speak good english.I am sorry Berkeman and other the users and thank you for helping me.I will try try to wright more kindly.
Berkeman: You are true about the use of RC but i must make the project only with FPGA and th SENSOR of 16x16...
OK.Listen if you make an R.O. with 11 stages of inverters you will have a 3.4GHz oscillation! Not possible in FPGA... more inverters less frequency oscillation.Understand it?
Ok look.I have create a 100 stages inverters and one AND gate with two inputs ,so i have a 101 stage R.O with on/off from an external input on a pin of the fpga.For example 23 pin. If i put a capacitor in this pin 200nF between this pin and GND the oscillation of R.O. it wil be slower... true...
Guys i need help about ring oscillator.One use of R.O. is to measure capacitors.I have build an R.O. in one FPGA knows anyone what is the range of capacitance measure? I must measure 4-5pF with 0.1pF at least resolution!