| 摘要 |
A lock-in filter that may be used to detect an AC data signal in the presence of high level noise signals that may occur in such systems as those used for acoustical telemetry in boreholes includes a pair of parallel capacitors receptive of the data and noise signals and circuitry operating in response to signals in the capacitors for alternately switching the capacitors to receive the noise and data signals in phase with the data signal.
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