I have designed a system which reads optical signals of different wavelenghts (not simultaneosly).
After optical detection by a photosensor, it has different low voltage signals (from 30mV to 100mV - DC values) depending of the wavelenght. I must to convert these voltage signals to a specific range using a AD (24 bits) with different gains and insert the values inside a range from 7.000.000 to 9.000.000. I planned at the beggining to use only a PGA of a AD7190, but it has fixed gains (1, 8, 16, 32, 64 and 128). At this moment, I plan to use a VCA before AD7190 combined with PGA (inside AD). If the value is not inside the range mentioned, the VCA gain will change based on a feedback from a PIC code. I must to use also a DA converter for getting a digital signal from the PIC and input it on VCA for gain selection.
What VCA could I use for this project, considering the low voltage signals? Do you recommend other type of solution?
I understand that the VCA gains must not be high for avoid any problems with resolution of AD and considering that the values from VCA will be amplified by PGA values.
Thank you in advance.