for delta modulation, im using a comparator (LM 311) ; its output given to
D flipflop and it is given to a 741 opamp and integrator . this output is given to the comparator as refernce input.
what is the advantage of LM311 ? any advantage over 741

 

An LM311 is a comparator. A 741 is an op amp. Comparators have no internal compensation so generally respond much faster than op amps. The LM311 will also work down to 0V common-mode input with a single supply whereas the 741 can't.

 

The LM311 will also work down to 0V common-mode input with a single supply

Actually, the LM311 inputs can only work down to about 1/2 volt above the negative supply rail. You may be thinking of the LM339.