An N-Path Filter Design Methodology With Harmonic Rejection, Power Reduction, Foldback Elimination, and Spectrum Shaping

In this paper, an adaptive design methodology for synthesizing a harmonic free N-path filter with reduced frequency folding is presented. System level analysis of proposed architecture shows that by adding a few extra paths with proper weights to a conventional N-path filter, several characteristics such as harmonic rejection, power reduction, foldback elimination and spectrum shaping can be achieved. The designed filter is reconfigurable to be a band-pass filter (BPF) or a band-reject filter (notch), based on the requirements. By using the n ^th harmonic of Local Oscillator (LO) signal, instead of the fundamental harmonic, the required input clock frequency in N-phase clock generator is reduced by a factor of n. As a proof of concept, a 0.1-5 GHz RF filter with 75 dB and 82 dB harmonic rejection at 3 ^rd and 5 ^th order harmonics respectively is analyzed and simulated using MATLAB and Cadence Spectre-RF. Post-layout simulations are performed using CMOS 180 nm technology with 1.8 V supply voltage. The total power consumption of the chip is less than 8.5 mW while occupying a silicon area of 0.2 mm ² . Furthermore, Noise Figure (NF) of the circuit is shown to be between 3.5 and 4.7 dB and its out-of-band IIP3 is +6 dBm.