| 摘要 |
<p>This disclosure depicts a single frequency detector for detecting a tone having a given frequency first comprising first a circuit input terminal. A band-pass filter means for filtering a pre-determined band of frequencies has an input operatively connected to the circuit input terminal and has an output. A notch filter means for filtering a pre-determined single frequency has an input operatively connected to the circuit input terminal and also has an output. A first negative half-wave rectifier means for converting a first AC signal to a first DC voltage level is provided and has an input operatively connected to the output of the band-pass filter means and also has an output. A second negative half-wave rectifier means for converting a second AC signal to a second DC voltage level is provided and has an input operatively connected to the output of the notch filter means and also has an output. A comparator means for comparing the first DC voltage level with the second DC voltage level is provided and has first and second inputs operatively connected to the outputs of the first and second negative half-wave rectifier means and produces an output signal on a circuit output terminal when the tone having the given frequency is received at the circuit input terminal.</p> |
