| 摘要 |
An apparatus and method for improving the signal-to-noise ratio of a composite input signal having a desired signal and one or more undesired, noise signals mixed therewith. In a preferred embodiment, the present invention comprises a phase coherence filter which improves the signal-to-noise ratio of a composite input signal having a periodic signal and an aperiodic signal by interfering a sample of the composite input signal taken at a current time during a current cycle of the periodic signal with one or more previous samples of the composite input signal taken at one or more respective previous times during one or more respective previous cycles of the periodic signal, where the periodic signal at the respective previous time(s) of the respective previous cycle(s) is substantially in-phase with the periodic signal at the current time during the current cycle. The phase coherence filter includes a memory, an adder, and an attenuator. The memory connects to a source of digital data samples of the composite input signal and stores digital data samples of the composite input signal taken during one or more previous cycles of the periodic signal. The adder receives digital data samples from the memory which are substantially in-phase with a current digital data sample. The adder constructively interferes the periodic portion of the digital data samples and destructively interferes the aperiodic portion of the digital data samples to generate an intermediate resultant. The attenuator receives the intermediate resultant and adjusts its amplitude to at least substantially match the amplitude of the composite input signal, thereby creating an output data sample. By processing successive digital data samples, the phase coherence filter produces an output signal having an improved signal-to-noise ratio when compared to the composite input signal due to the destructive interference and attenuation of the aperiodic signal.
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