| 摘要 |
A circuit is for reducing the output distortion of the dual tone multiple frequency (DTMF) signal by using the row and column band pass filters (4,6). The circuit comprises a keyboard logic section (2), row and column pulse generators (3,5) for producing the pulse corresponding to the DTMF signal, row and column BPFs (4,6) for producing the sine waves within the bandwidth corresponding to the DTMF signal, and an adder (7) for synthesizing the row and column DTMF signals.
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