In-Series current source equation solving
If you look at it closely, you can see that one cell made of a current source and a capacitor acts as an integrator, with its Laplace expression \$\dfrac{1}{sC}\$. And you have three such cells on top of each other, which means they add up to one integrator with three times its magnitude, or \$\dfrac{3}{sC}\$. Adding one shunt resistor means the usual parallel operation:
$$\dfrac{1}{\dfrac{1}{\dfrac{3}{sC}}+\dfrac{1}{R}}=\dfrac{3R}{sRC+3}=\dfrac{1}{C}\dfrac{3}{s+\dfrac{3}{RC}}$$
And testing this shows identical traces -- here the magnitudes are slightly shifted, so that they don't completely overlap (their phases do):