Intergrator circuit

Passive integrator circuit is a simple quadripole consisting of two passive elements. It is also the simplest (first-order) low-pass filter. A passive integrator circuit is often used in cheap digital audio systems (i.e. cheap soundcards) as a reconstruction filter. It is also one of the basic electronic circuits, being widely used in circuit analysis based on the equivalent circuit method. see more details here : http://en.wikipedia.org/wiki/Integrator_circuit