Question

An ADC using op-amp summing amplifier with binary weighted resistors

Answer 1

Hoot! You just asked your first question! Hang tight while I find people to answer it for you. You can thank people who give you good answers by clicking the 'Good Answer' button on the right!

Answer 2

Are you sure you mean an ADC (analog-to-digital) and not DAC (digital-to-analog converter)?

For DAC, here is a good tutorial:
http://www.electronics-tutorials.ws/opamp/opamp_4.html

See especially the last schematic, but the whole page is well-written and worth reading.