| 摘要 |
PURPOSE:To facilitate externally the adjustment of the on/off sensitivity by connecting a current mirror circuit forming a DC bias impressed circuit. CONSTITUTION:An output current of a transistor (TR) of emitter follower connection is fed back to a parallel resonance circuit comprising a detection coil L and a capacitor C via TR3, TR2 forming a current mirror, the Q of the coil 1 is changed by a metallic proximity object, which is detected by the attenuation of the oscillation amplitude or the oscillation stop. The DC bias application circuit of the current mirror circuit formed by TR5, TR4 is provided to the collector of the TR3 and an external DC bias is fed freely to the input terminal of the circuit. Even when the Q differs depending on the approach or parting of the proximity object by the adjustment of the DC bias, the detection sensitivity is adjusted externally easily so that the sensitivity at both the states is made identical. |
