Q. The speed of an 8-bit A/D converter is limited by the counter, which has a maximum speed of 4 × 107 counts per second. Estimate the maximum number of A/D conversions per second that can be achieved.
Ans. The rate of the clock will be constant, independent of the analog input. It must be slow enough to allow the counter to count up to the highest possible input voltage. This will require 255(= 27+ 26+ 25+ 24+ 23+ 22+ 21+ 20) counts, which will take 255/(40 × 106) = 6.375 µs.
Thus, the process can be repeated 106 /6.375 = 156,863 times per second.