The paper uses two capacitors that share charge to get the same effect as your code. In effect Cunit (the smaller capacitor) is the increment (i.e., counter++)

The paper uses two capacitors that share charge to get the same effect as your code. In effect Cunit (the smaller capacitor) is the increment (i.e., counter++), while Cmain (the larger capacitor) acts as the count-holding variable (i.e., counter). Another circuit (Schmitt Trigger) acts as the comparator.