Dropout detecting circuit with one-half wavelength delay

Claim 2

A circuit for detecting dropout from playback signals reproduced from an optical recording medium, said playback signals having a carrier wave with a center frequency corresponding to a given wavelength and said circuit comprising: a delay circuit for effecting in said playback signals a delay corresponding in time to one half of said given wavelength of said center frequency of said carrier and thereby producing delayed output signals; a summation circuit for summing said playback signals and said delayed output signals and thereby producing a sum signal having amplitude substantially equal to two times an amplitude of said playback signal; and a level detection circuit for detecting when said sum signal has a level that exceeds predetermined offsets levels and thereby producing a detection output signal; said detection output signal being indicative of a dropout in said playback signals.

Claim 3

A dropout detection circuit according to claim 1 further comprising control means for controlling the signal level of at least one of said playback signals and said delayed output signals.

Claim 4

A dropout detection circuit according to claim 2 wherein said control means includes a variable resistor for changing the signal level of said playback signals.

Claim 5

A dropout detection circuit according to claim 1 wherein a hysteresis effect for level discrimination is imparted to the level detection circuit.

Claim 6

An optical device for reproducing video signals from an optical disk on which said video signals are optically recorded in successive horizontal scanning periods with frequency modulation of a carrier signal having a center frequency corresponding to a given wavelength, said device comprising: pickup means for picking up said frequency modulated video signals from said optical disk and producing playback signals; demodulation means for frequency demodulating said playback signals formed of said frequency modulated video signals picked up by said pickup means; horizontal scanning period delay means for delaying said frequency demodulated video signals by one horizontal scanning period of said video signals; a dropout detecting circuit; an output terminal; switching means responsive to said dropout detecting circuit and connected to said demodulation means, said horizontal scanning period delay means, and said output terminal; and said dropout detecting circuit including a delay circuit for effecting in said playback signals produced by said pickup means a delay corresponding to one half of said wavelength of said center frequency of said carrier signal and thereby producing delayed output signal, a summation circuit for summing playback signals produced by said pickup means and said delayed output signals and thereby producing a sum signal having an amplitude twice that of said playback signals, and a level detection circuit for detecting when said sum signal has a level that exceeds predetermined offset levels and thereby producing a detection output signal said detection output signal being supplied to said switching means as a control signal for selectively connecting said demodulation means or said horizontal scanning period delay means to said output terminal.

Claim 7

An optical device for reproducing video signals from an optical disk on which said video signals are optically recorded in successive horizontal scanning periods with frequency modulation of a carrier signal having a center frequency corresponding to a given wavelength, said device comprising: pickup means for picking up said frequency modulated video signals from said optical disk and producing playback signals; demodulation means for frequency demodulating said playback signals formed of said frequency modulated video signals picked up by said pickup means; horizontal scanning period delay means for delaying said frequency demodulated video signals by one horizontal scanning period of said video signals; a dropout detecting circuit; an output terminal; switching means responsive to said dropout detecting circuit and connected to said demodulation means, said horizontal scanning period delay means, and said output terminal; and said dropout detecting circuit including a delay circuit for effecting in said playback signals produced by said pickup means a delay corresponding to one half of said wavelength of said center frequency of said carrier signal and thereby producing delayed output signal, a summation circuit for summing playback signals produced by said pickup means and said delayed output signals and thereby producing a sum signal having an amplitude twice that of said playback signals, and a level detection circuit for detecting when said sum signal has a level that exceeds predetermined offset levels and thereby producing a detection output signal said detection output signal being supplied to said switching means as a control signal for selectively connecting said demodulation means or said horizontal scanning period delay means to said output terminal.

Claim 8

An optical device according to claim 5 wherein said switching means normally connects said demodulation means to said output terminal and connects said horizontal scanning period delay means to said output terminal in response to a determination that said sum signal has a level that exceeds said predetermined level.