I'm designing a 6-channel amplifier which requires one LPF, one HPF, and one gain stage for each channel. I use 4*1 multiplexers for LPF and HPF, and 8*1 multiplexer for gain to control these multiplexers. So I have 7 selection pins for each channel. Now for 6 channels, I need 42 selection pins.
This is simply too much for me. My controller has at most 20 digital outputs. So I think I might need to use something like multiplexing. But the problem is that I can't do sweeping because none of these filters can be left floating. I can't even think of any solution to google for answers. Can anyone suggest a way?