1. A passive filter circuit for filtering an input signal to attenuate an undesired frequency, comprising: a first stage to receive the input signal, the first stage having a first inductor and a first branch coupled to the output of the first inductor, the first branch having a first capacitor and a second inductor; and a second stage coupled to the first stage, the second stage having a third inductor and a second branch coupled to the output of the third inductor, the second branch having a second capacitor.