Video disc reproducing apparatus

Claim 2

A video disc reproducing apparatus comprising: a pickup means for detecting an information recorded on a recording disc as a variation in electrostatic capacity, said pickup means having a pickup needle; a pickup needle pressure control means which controls the needle pressure of said pickup needle; an automatic gain control means which generates a control signal used for maintaining an output signal of said apparatus so as to be constant, wherein said automatic gain control means comprises: a rectifier for rectifying said output signal of said apparatus; a reference voltage source for generating a reference signal; a differential amplifier for generating an error signal between an output signal of said rectifier and said reference signal; an exponential conversion means for converting said error signal to an exponential error signal; and a variable gain amplifier for controlling said output signal of said apparatus according to said exponential error signal, said error signal controlling the needle pressure of said pickup needle.

Claim 3

A video disc reproducing apparatus according to claim 1, wherein said variable gain amplifier is a double balanced modulator circuit, and said exponential conversion means is a transistor, the collector thereof being connected to a control input terminal of said double balanced modulator circuit and the collector current of said transistor varying according to the exponential of a voltage between the base and the emitter of said transistor and being said exponential error signal.

Claim 4

A video disc reproducing apparatus comprising: a pickup means for detecting an information recorded on a recording disc as a variation in electrostatic capacity, said pickup means having a pickup needle; a pickup needle pressure control means for controlling the needle pressure of said pickup needle; a control signal generator which generates a control signal for controlling said pickup needle pressure control means, said control signal being generated in proportion to a logarithm of the amplitude of a signal outputted from said pickup means; wherein said control signal generator comprises: a logarithm converter which generates a voltage signal in proportion to the logarithm of said signal outputted from said pickup needle; a rectifier for rectifying an output signal of said logarithm converter; and a lowpass filter for smoothing an output signal of said rectifier, an output signal of said lowpass filter being applied to said pickup needle pressure control means for controlling the needle pressure of said pickup needle; and wherein: said lowpass filter comprises a first lowpass filter and a second lowpass filter connected in parallel to each other, the time constant of one of said first and second lowpass filters being different from that of the other; and said apparatus further comprises a differential amplifier which generates a differential signal of output signals from said first and second lowpass filters, said differential signal being applied to said pickup needle pressure control means for controlling the needle pressure of said pickup needle.

Claim 5

A video disc reproducing apparatus comprising: a pickup means for detecting an information recorded on a recording disc as a variation in electrostatic capacity, said pickup means having a pickup needle; a pickup needle pressure control means for controlling the needle pressure of said pickup needle; a control signal generator which generates a control signal for controlling said pickup needle pressure control means, said control signal being generated in proportion to a logarithm of the amplitude of a signal outputted from said pickup means; wherein said control signal generator comprises: a logarithm converter which generates a voltage signal in proportion to the logarithm of said signal outputted from said pickup needle; a rectifier for rectifying an output signal of said logarithm converter; and a lowpass filter for smoothing an output signal of said rectifier, an output signal of said lowpass filter being applied to said pickup needle pressure control means for controlling the needle pressure of said pickup needle; and wherein: said lowpass filter comprises a first lowpass filter and a second lowpass filter connected in parallel to each other, the time constant of one of said first and second lowpass filters being different from that of the other; and said apparatus further comprises a differential amplifier which generates a differential signal of output signals from said first and second lowpass filters, said differential signal being applied to said pickup needle pressure control means for controlling the needle pressure of said pickup needle.