| 摘要 |
A key operated signal generator comprising a pair of interconnected transistor oscillators having twin-T notch-filter feedback networks in which one resistance in each filter is variable and consists of a plurality of resistive elements arranged in a series parallel configuration. The series parallel configuration is such that when a single button of the key is actuated, at least two resistive elements are connected in series in each filter and when two buttons are actuated simultaneously, at least one resistive element is connected in series with two or more parallel resistive elements in at least one filter.
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