2nd order sigma delta ADC:

ADC filter section: updown counter and accumulator
the filter stage1 after comparator 1 uses  x = x + xx * (n - i +1)
where xx is comp1 output and x is output of filter and  1<i <n

the filter stage2 after comparator 2 uses  y = y + yy*1
where yy is comp2 output and y is output of filter2 and  from summation 1 to n

Now as far as i understood, (n+1-i) in the filter1 is triangular window function which comprises of two stage rectangular window function. if i need one more stage of rectangular window function ie cascading three rectangular window shud gimme quadratic window.

what is the fucntion for quadratic window and how it will be implmented in filter 1 if i want use it?

according to attached file, (page 738), the term (n-i+1) with  0<i<n+1 is for triangular window function which is a cascade of two rectangular window function.This term is used in filter section

in case we want to use higher order filter, we can use quadratic window function which consists of three rectangular windows. what is the weight expression used for quadratic (parabolic) window function (as for triangular it is Ci=(n-i+1) and for rectangular it is Ci =1)?

thanks