replacing AN6878 led driver IC
If you wanted to replicate this with monolitic IC's then the datasheet would be a good place to start. Instead of a regular op amp the first amplifier is probably a log amp, and then followed by comparators. The resistors set a range of voltages for the comparators from lowest to highest, the external resistor between 6 &amp; 7 sets the range for all. The comparators need enough current to drive whatever LED's are selected.