If there are means to process all signals after they have been captured and digitilized, why are we still designing ICs to do analog signal processing? For any giving case, can not we just digitilize the signal and then perform what ever processing we want?
Try digitizing a 17GHz signal..
You will quickly find it difficult to procure a fast enough adc that does not cost a fortune and you will also need memory bandwidth of tens of Gb/s (depending on adc bit count) not to mention the processing power to process such amount of data in realtime. Analog circuits do not suffer from data storage problems and realtime is the norm rather than exception because signal does not need to be measured first in order to be processed. Electrons just flow through the circuit and no special intelligence is needed besides a correctly designed circuit to make that happen.
There are valid reasons to use digital circuits as well. When signal bandwith is low and more advanced processing needs to be done such as software based control of something then it does make sense to sacrifice signal content for ease of implementation. In such cases the lost data due to sample rate does not matter because it will be lost anyway since software would not be able to keep up with faster rate. Also all software always does discrete processing rather than continuous time (continuous flow of electrons) as in analog circuits. So in order to use the signal in a discrete time software the signal must be digitized first.
There aren’t means to capture “all signals” and it takes analog to convert analog to digital.
A lot of what we “want” is analog in nature.
Fundamentally, why does anyone do anything. Usually, there is some sort of reason specific to a problem.
Analog HDL https://en.m.wikipedia.org/wiki/VHDL-AMS has probably helped keeping analog economically competitive in many applications.
Then there is going to be new things, like Quantum Computers that some people will argue is digital because of discrete quanta and others will argue about the wave nature.