Please look at the schematic below. This is a very simple resistive adder that works fine with any standard ! (TTL,CMOS,...) or any arbitrary voltage that is fed into it. On the other hand as there is no active component in it, it is extremely fast. It is just made of a few resistors , so it is very cheap. On the other hand there is no limitation for number of input bits ( it can be easily expanded to 32, 64 or hundreds of bits ).
So, Why should we need DAC ICs? I am looking for a 32-bit high frequency DAC. Such devices are not found easily and also if found, they are rather expensive. I mean What is the advantage that I should pay for to find such devices? I think there must be some advantage that they worth to be bought. The only thing that I can think about is their inherent amplification ( for example TTL -> 10V or so), but this goal is simply achievable with any kind of amplification.