| 摘要 |
A frequency selection circuit which is equivalent to an LCR series resonant circuit, though not provided with inductance and which can adjust resonant frequency, selectivity or quality factor Q and circuit impedance at resonance independently of one another, merely by adjusting resistance. The circuit comprises an operational amplifier connected to receive an input signal at its noninverting input, a band rejection filter connected to an output of the operational amplifier, a positive feedback resistor connected between an output of the band rejection filter and the noninverting input of the operational amplifier, and a voltage divider connected between the output of the band rejection filter and the output of the operational amplifier and connected at its output to an inverting input of the operational amplifier. The band rejection filter comprises a series combination of a first resistor and a first capacitor and a parallel combination of a second resistor and a second capacitor. The first and second resistors have the same resistance, and the first and second capacitors have the same capacitance. The resonant frequency of the frequency selection circuit depends solely on the resistance of the first and second resistors and the capacitance of the first and second capacitors in the band rejection filter. The circuit impedance at resonance depends solely on the feedback resistor, and the selectivity solely on a dividing factor of the voltage divider.
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