Patent ID: 7558351
Filing Date: 2009-07-07
Classification: H03H

Abstract:
1. A harmonic filter for filtering a plurality of frequency components from an input signal, the harmonic filter comprising: a phase shifter having a positive in-phase output, a negative in-phase output, a positive quadrature-phase output, and a negative quadrature-phase output, for generating an in-phase signal and a quadrature-phase signal according to the input signal; and a plurality of polyphase filter networks coupled in series, each having a positive in-phase input, a negative in-phase input, a positive quadrature-phase input, a negative quadrature-phase input, a positive in-phase output, a negative in-phase output, a positive quadrature-phase output, and a negative quadrature-phase output, the first polyphase filter network in the series being coupled to the phase shifter for receiving the in-phase and quadrature-phase signals, each polyphase filter network being for filtering a corresponding one of the frequency components from the input signal; wherein either the positive quadrature-phase input and the negative quadrature-phase input of at least one of the polyphase filter networks are respectively coupled to the negative quadrature-phase output and the positive quadrature-phase output of a preceding polyphase filter network or of the phase shifter, or the positive in-phase input and the negative in-phase input of at least one of the polyphase filter networks are respectively coupled to the negative in-phase output and the positive in-phase output of a preceding polyphase filter network or of the phase shifter; and for each of the polyphase filter networks in the series, either the positive and negative quadrature-phase inputs or the positive and negative in-phase inputs are reversed if the frequency component being filtered by the polyphase filter network is positive and an even number of preceding polyphase filter networks have said reversed inputs.