Servo control circuit for optical disk apparatus

Claim 2

In a servo loop for positional adjustment of an optical head relative to an optical disk, an automatic servo gain control system comprising: first means provided in the servo loop for receiving a first signal (a) indicative of a positional relationship be­tween the optical head and the optical disk and being derived from a light beam reflected from the optical disk into the optical head, and receiving a second signal (b) indicative of a light intensity of said light beam, for varying a gain for said first signal based on said second signal so that a signal level of said second signal is controlled to be con­stant and producing a third signal (e, f); oscillator means (11) oscillating at a predetermined fre­quency selected to be within a servo frequency band; second means (7) provided in the servo loop for introducing an output of said oscillator means (11) into the servo loop; third means (13 - 18) for comparing signal values of said third signal at an input side (e) of said second means (7) and an output side (f) of said second means in the servo loop and for varying said gain for the first signal (a) based on a compared difference between said input side and output side signal (e, f) values, so as to control said input side and output side signal (e, f) values to be at a predetermined constant ratio, thereby causing an open loop gain of the servo loop to be constant.

Claim 3

In a servo loop for controlling positional adjustment of an optical head that produces and receives a reflected light beam from an optical disk, an automatic servo gain control system comprising: first means in the servo loop connected to receive a first signal (a) indicating a positional relationship between the optical head and the optical disk, said first signal (a) being derived from the light beam reflected from the optical disk back to the optical head, and connected to receive a second signal (b) indicating intensity of said reflected light beam, for varying a gain for said first signal (a) based on said second signal (b) so that a signal level of said second signal is controlled to be constant and thereby producing a third signal (e) at an output of said first means; an oscillator (11) having an output that oscillates at a predetermined frequency selected to be within a servo fre­quency band; second means (7) receiving said third signal (e) and said output of said osciliator (11) in the servo loop for selectively connecting an output of said oscillator (11) into the servo loop; third means (13-18) for comparing signal values of said third signal at an input side (e) of said second means (7) and an output side (f) of said second means (7) in the servo loop and for varying said gain for the first signal (a) based on a compared difference between said input side and output side signal (e, f) values, so as to control said input side and output side signal (e, f) values to be at a predetermined constant ratio, thereby causing an open loop gain of the servo loop to be constant.

Claim 4

In a servo loop for controlling positional adjustment of an optical head that produces and receives a reflected light beam from an optical disk, an automatic servo gain control system comprising: first means in the servo loop connected to receive a first signal (a) indicating a positional relationship between the optical head and the optical disk, said first signal (a) being derived from the light beam reflected from the optical disk back to the optical head, and connected to receive a second signal (b) indicating intensity of said reflected light beam, for varying a gain for said first signal (a) based on said second signal (b) so that a signal level of said second signal is controlled to be constant and thereby producing a third signal (e) at an output of said first means; an oscillator (11) having an output that oscillates at a predetermined frequency selected to be within a servo fre­quency band; second means (7) receiving said third signal (e) and said output of said osciliator (11) in the servo loop for selectively connecting an output of said oscillator (11) into the servo loop; third means (13-18) for comparing signal values of said third signal at an input side (e) of said second means (7) and an output side (f) of said second means (7) in the servo loop and for varying said gain for the first signal (a) based on a compared difference between said input side and output side signal (e, f) values, so as to control said input side and output side signal (e, f) values to be at a predetermined constant ratio, thereby causing an open loop gain of the servo loop to be constant.

Claim 5

The automatic servo gain control system as set forth in claim 1 or 2, wherein said first means controls said signal level of the second signal (b) to be equal to a reference voltage, and said third means (13-18) controls said reference voltage based on said difference between the input side and output side signal values of said second means.

Claim 6

The automatic servo gain control system as set forth in anyone of claims 1 to 3, wherein said third means (13-18) compares said input side and output side signal (e, f) values by deriving a fourth signal from said third signal at said input side and a fifth signal from said third signal at said output side, each of said fourth and fifth signals having its center frequency the same as the frequency of said oscillator means (11), and by obtaining an absolute signal (g, h) value for each of the fourth and fifth signals, said reference voltage (d) being controlled based on a difference between said obtained absolute signal (g, h) values of the fourth and fifth signals.

Claim 7

The automatic servo gain control system as set forth in anyone of claims 1 to 4, wherein said third signal (e) at said input side of said second means is fed through a bandpass filter (13) having its center frequency the same as the fre­quency of said osciliator means (11) output to a full-wave rectification circuit (14) to obtain an absolute signal (g) value thereof, and said third signal (f) at said output side is fed through a bandpass filter (15) having its center fre­quency the same as the frequency of said oscillator means (11) otuput to a full-wave rectification circuit (16) to ob­tain an absolute signal (h) value thereof, said reference voltage (d) being controlled based on a difference between said absolute signal values.

Claim 8

The automatic servo gain control system as set forth in anyone of claims 1 to 5, wherein said second means is an operational amplifier (7) having a negative feedback resistor (27), said operational amplifier (7) receiving said third signal (e) at its non-inverting input terminal and said oscillator means (11) output at its inverting input terminal.

Claim 9

The automatic servo gain control system as set forth in claim 6, wherein said oscillator means (11) output is fed to said inverting input terminal through a capacitor (28) and a resistor (29), said osciliator (11) means, said capa­citor (28), and said resistor (29) being connected in series between said inverting input terminal and ground.

Claim 10

The automatic servo gain control system as set forth in claim 7, wherein a value of said resistor (29) is much greater than a value of said negative feedback resistor (27).

Claim 11

The automatic servo gain control system as set forth in anyone of claims 1 to 8, wherein said predetermined constant ratio is 1:1.

Claim 12

The automatic servo gain control system as set forth in anyone of claims 5 to 9, wherein said bandpass filters (13, 15) are switched capacitor filters using a clock common to said oscillator means (11).