Double speed playback mode judgment circuit of video cassette recorder

摘要

The present invention is a circuit for detecting a double speed mode in a special playback mode in a general 8mm VCR that can be loaded with 8mm and Hi-8mm magnetic tapes. A detection circuit (1) for detecting an envelope waveform of the video signal detected by the head (H); A level converting circuit (2) for driving in accordance with an input switching signal to vary and output a voltage level of an envelope waveform of the detecting circuit; A mode judging circuit (3) for judging a double speed mode according to the voltage level applied from said level converting circuit (2) and outputting a mode signal; A switching signal is output when the magnetic tape of the Hi-8mm is mounted, and the control mode determines the double speed mode according to the mode signal applied from the mode determining circuit 3 and outputs a rotation signal corresponding to the double speed mode. Circuit 4; The capstan motor 5 which drives a tape at the double speed corresponding to the rotation signal of the said control circuit 4 is provided. Therefore, when the signal of the Hi-8mm tape is specially reproduced in the 8mm VCR, the present invention has the effect of accurately determining the double speed mode by determining the double speed mode after compensating the DC level of the envelope waveform. have.