ya agree with jhon,but not completely.As i know Schottkey need 0.3v.But i got other solution that is adding -0.7v battery in series with diode,so i can eliminate it completely(0.7 error)
You won't eliminate errors completely. Look at the data sheet for a 1N914 or any other conventional diode (or BAT54 for Schottkey). You will see that there is a forward voltage drop versus current curve, this will cause errors in your circuit dependent on how big of an input signal you have. With this simple circuit you will still have errors. It is not until you use an opamp rectifer circuit like the one pictured in this link where you will come close to eliminating them.
