| 摘要 |
PURPOSE:To improve the servocontrol performance with a simple and inexpensive circuit by obtaining an error signal from the difference among minimum values of plural data obtained from an approximately equal part of a recording medium where the intensity of signals at the area where an information signal is recorded than that of signals at the area where no information signal is recorded. CONSTITUTION:In a record mode a drive circuit 12 which modulates a light source 1 by an information signal works. Thus the energy density of a condenser spot rises repetitively over a level which changes the reflection factor of a recording medium in a groove of a guide track 6 and falls. In a reproduction mode the energy density is kept under the above-mentioned level. The track 6 is projected or depressed by 1/8 wavelength compared with the peripheral parts, and therefore the reflected beams of the inside and the outside produce an interference. The degree of interference differs between the inside and the outside when the condenser spot has a shift to the guide 6. Then a 2-split detector 11 has different outputs. Peak detecting circuits 14a and 14b detect the minimum value of the signal amplified by amplifiers 13a and 13b i.e., the signal value obtained when the output of the source 1 is set at a reproduction level and at the same time obtained at an area where the condenser spot does not exist in a recording bit. Then an arithmetic circuit 15 delivers an error signal from the minimum signal. |
