Tracking servo with closed loop gain correction

Claim 1

A tracking servo circuit for a rotary recording medium reproducing apparatus which picks up and reproduces a recorded signal from a rotary recording medium by a reproducing element, said rotary recording medium being recorded with a main information signal on a spiral information signal recorded track or concentric information signal recorded tracks thereon, said information signal recorded track having a first reference signal for tracking control recorded on one side thereof and having a second reference signal for tracking control recorded on the other side thereof such that the sides on which the first and second reference signals are recorded with respect to said information signal recorded track are interchanged for each track turn of the rotary recording medium, a third reference signal being recorded at positions on the rotary recording medium where the sides on which said first and second reference signals are recorded with respect to said information signal recorded track are interchanged, said tracking servo circuit comprising: control means for controlling said reproducing element to follow and scan over said information signal recorded track; separating means for separating said first, second, and third reference signals from a reproduced RF signal which is reproduced by said reproducing element; detecting means for detecting said first and second reference signals separated in said separating means; circuit means for switching an input transmission path of said first and second reference signals to said detecting means in response to said third reference signal which is separated in said separating means, and for forming and producing a tracking error signal from a differential amplifier based on a detection signal from said detecting means; an cscillator for producing a signal which has a constant amplitude and a constant frequency within a frequency band which is lower than a frequency band in which said main information signal is recorded; signal superimposing means for superimposing the signal from said oscillator on said tracking error signal; signal supplying means for supplying to said control means a superimposed signal from said signal superimposing means; a filter circuit for filtering said signal having the constant frequency from said tracking error signal; and automatic cain control circuit means provided in a stage before said circuit means, for generating a gain control signal which is obtained by detecting an envelope of an output signal of said filter circuit, said automatic gain control circuit means controlling the level of said reproduced RF signal so that said signal which is within the input tracking error signal of said filter circuit and has the constant frequency is kept to an approximately constant level.