An Alternative Approach to the Realization of Network Transfer Functions: The N-Path Filter

The application of conventional design techniques to network problems in systems operating at relatively low frequencies often leads to impractical circuits. In addition, designs based on active RC techniques are frequently very sensitive to small changes in element values. Alternatively, a time-varying network approach to the solution of a wide class of such problems appears to be particularly promising. The time-varying network described and analyzed in this paper consists of a parallel combination of N identical linear time-invariant networks, each operating between input and output modulators. Attention is focused upon several properties of this configuration that are of theoretical as well as practical importance. In particular, these properties include: i. Periodic filtering characteristics can be obtained over a limited frequency band without employing distributed elements. The practical uses for this property include the realization of low-frequency comb filters. 1321 1322 T H E BELL SYSTEM TECHNICAL J O U R N A L , S E P T E M B E R 1 9 6 0