| 摘要 |
A mode changing circuit includes a noise bar detection circuit (10), a latch circuit (20) and a logic control circuit (30). The noise bar detection circuit has a drop-out detecter (2) for detecting a drop- out pulse, an AGC circuit (1), 1-H delay session (3) and a switch (SW). Some part of the drop-out pulse is provided to a smoothing circuit (5) and converted to a rectangular wave by a schmitt trigger (6). A counter counts the drop-out pulse for one period of a head switching pulse and provides the output to the latch circuit. A F/F provides the regular or long-time mode control signals.
|
