| 摘要 |
A constant amplitude, variable-bandwidth filter is provided having a variable resistor and a high-Q passive filter cascaded between a pair of amplifiers. The input amplifier having a low output impedance and the output amplifier having a low input impedance. As the resistance of the variable resistor is varied, the Q of the system varies and thus its bandwidth. The gain of the system also varies as the variable resistor is varied. To compensate for the gain variation, a current, equivalent to the value of the output voltage of the input amplifier divided by the value of the equivalent series resistance of the high-Q passive filter, is inserted at the node where the variable resistor and the high-Q passive filter are coupled one to the other. This results in a constant current at resonance being conducted by the high-Q passive filter, independent of the selected overall bandwidth of the filter.
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