| 摘要 |
<p>PURPOSE:To obtain a high-quality picture, by installing a resonance circuit in the negative feedback loop of an amplifier containing the positive and negative feedback loops and reducing the impedance when the leadrer tape of a VTR comes close to a coil of the resonance circuit. CONSTITUTION:When a leader tape of a VTR does not reach its termination, the leader tape is not close to coils L1 and L2 of a resonance circuit. Thus the Q of the resonance circuit is high with a large impedance. As a result, the positive feedback is applied to an amplifier A3 through an amplifier A1 and a resistance R1, and at the same time the negative feedback is also applied through an amplifier A2 and a resistance R2. In this case, the gain of the amplifier A2 is larger than that of the amplifier A1 if a switch S1 is connected to F. As a result, O is delivered to a terminal T1 of a wave detecting circuit D1. When the leader tape comes close to the coil L2, the impedance of a resonance circuit including the coil L2 and a capacitor C2 is reduced. Thus the negative feedback quantity is reduced to deliver 1 to the terminal T1. In such a way, a high-quality picture can be obtained.</p> |
