Suppose I have a pair of 12-bit ADC's, I can imagine that they can be cascaded to get <= 24-bit output.
I can think of simply using one for the positive range and the other for the negative range, though there probably will be some distortion in the cross-over
region. (suppose we can ignore are a few error bits or, perhaps, place a 3rd ADC to measure the value around 0 volts).
Another option I had been thinking of is using a single hi-speed ADC and switching the reference voltages to get a higher resolution at lower speed.
Also there should be a way of getting a real-valued result with using one fixed-ref ADC and then switching the aref's of the secondary converter to get more precise value in between.
Any comments and suggestions are welcome.
I am presuming that a quad 8-bit (or dual 12-bit) chip is less expensive then a single 24-bit chip.