Get modulus and plot complex function


I have the following function:

freq[a_, b_, t0_, tr_, s_] := -((b E^(-s (b + t0)) (b E^(s (b + t0)) (-1 +             b s) UnitStep[-b] - b E^(s t0) UnitStep[b] +          E^(s (b - tr)) (E^(s (t0 + tr)) (-1 + b s) UnitStep[-t0] +             E^(s tr) (-1 + b s - s t0) UnitStep[t0] -             E^(s (t0 + tr)) (-1 + b s) UnitStep[-t0 - tr] + (1 +                s (-b + t0 + tr)) UnitStep[t0 + tr])))/(s^2 tr)) 

Now I want to plot the function as follows:

Plot[ComplexExpand@Abs@ExpToTrig@freq[0, 1, 0, 10^-6, Iw], {w,0,10^9}] 

However that doesn’t work. I couldn’t exact the absolute value of the complex function to plot it.
(w is a real positive number)

Does anyone know how to plot that?