Current mirror amplifier for use in an optical data medium driving apparatus and servo-circuit

Abstract

An optical data medium driving apparatus which constitutes amplifiers for an output current signal of a photosensor including a plurality of current mirror circuits having different amplification factors in order to switch, in a wide range, the output current signal of the photosensor. The photosensor detects a quantity of the reflected light corresponding to a variation of the quantity of reflected light from an optical data medium having various characteristics. The output is obtained with high accuracy and in a wide band. A servo-circuit is used for an AGC circuit and normalizes a difference signal from each light receiving surface at a photosensor having a plurality of light receiving surfaces. An A/D converter is given the difference signal as an analog input signal and the sum signal as the reference input signal. The A/D converter outputs an offset binary type digital signal, thereby being inexpensive to produce, easy to be integrated having high function, and high in reliability.

What is claimed is: 
     
       1. An optical data medium driving apparatus and a servo circuit, comprising: a photosensor which outputs a current signal corresponding to a quantity of transmitted light or reflected light from an optical data medium;   an amplification means intercoupled to and receiving said photosensor output current signal including a current mirror circuit having a plurality of switching elements, each switching element providing a current signal equal to said photosensor output current signal; and   means for combining selected ones of said current signals thereby amplifying said output current signal from said photosensor by said current mirror circuit.   
     
     
       2. An optical data medium driving apparatus and a servo circuit as set forth in claim 1, wherein said amplification means includes a plurality of current mirror circuits each current mirror circuit having a different amplification factor, and wherein the combining means includes switching means for selecting an output of at least one of said current mirror circuits, so that the photosensor output current signal is amplified by .[.the plurality of.]. said .Iadd.at least one .Iaddend.current mirror .[.circuits, the output signal of at least one of said current mirror circuits is selected by said switching means,.]. .Iadd.circuit .Iaddend.thereby providing variable amplification of the photosensor output current signal. 
     
     
       3. An optical data medium driving apparatus and a servo circuit as set forth in claim 2, wherein the amplification factor of each of said current mirror circuit in the plurality of current mirror circuits is described by 2 n+1 , 2 n+2 , . . . 2 n+m  (n:integer, m:number of current mirror circuits) and the respective amplification factors of each of said current mirror circuits are stepwise variable from ##EQU8## 
     
     
       4. An optical data medium driving apparatus and a servo circuit as set forth in claim 1, wherein said amplification means includes a preconverter having an input and an output and means coupling the photosensor output current signal to the input of the preconverter and means coupling the output of the preconverter to the current mirror circuit, said preconverter comprising a first means for converting the photosensor output current signal to a voltage signal and a second means for converting the voltage to a current signal to be input to the current mirror circuit, and thereafter said current mirror circuits amplify said current signal. 
     
     
       5. An optical data medium driving apparatus and a servo circuit as set forth in claim 1, further comprising: at least one additional photosensor which outputs a current signal corresponding to a quantity of transmitted light or reflected light from an optical data medium;   at least one additional amplification means intercoupled to and receiving said additional photosensor output current signal including a current mirror circuit having a plurality of switching elements, each switching element producing a current signal equal to said at least one additional photosensor output current signal;   at least one additional means for combining selected ones of said additional current signals, thereby amplifying said additional output of current signal from said additional photosensor by said additional current mirror circuit; and   means, intercoupled to the combining means and the at least one additional combining means, for adding and subtracting said amplified current signals.   
     
     
       6. An optical data medium driving apparatus and a servo circuit as set forth in claim 2, wherein the .[.current mirror circuits include.]. switching elements .[.comprising.]. .Iadd.comprise .Iaddend.transistors having different resistances connected to respective emitters of the .[.transistor.]. .Iadd.transistors.Iaddend.. 
     
     
       7. An optical data medium driving apparatus and a servo circuit according to claim 2, wherein the .[.current mirror circuits include.]. switching elements .[.comprising.]. .Iadd.comprise at least some .Iaddend.transistors having multiple emitters. 
     
     
       8. An optical data medium driving apparatus and a servo circuit, comprising a photosensor which outputs a current signal corresponding to a quantity of transmitted light or reflected light from an optical data medium, an amplification means, means coupling the output current signal from said photosensor to said amplification means, said amplification means comprising a current mirror circuit including a plurality of switching elements, and means for intercoupling the switching elements so as to provide respective element current signals that are equal to the photosensor output current signal while combining selected ones of said element current signals to thereby provide amplification of said photosensor output current signal. 
     
     
       9. An optical data medium driving apparatus as set forth in claim 8 wherein said means for intercoupling includes means for intercoupling the switching elements directly in a parallel array. 
     
     
       10. An optical data medium driving apparatus and a servo circuit, comprising: a photosensor which outputs a current signal corresponding to a quantity of transmitted light or reflected light from an optical data medium;   an amplification means for amplifying the photosensor output current signal, the amplification means including a current mirror circuit having a plurality of switching elements, each switching element providing a current signal being one of a current signal equal to the photosensor output current signal and a current signal equal to a multiple of the photosensor output current signal;   means for connecting the photosensor output current signal to each switching element in the plurality of switching elements in the amplification means; and   means for combining selected ones of the current signals thereby amplifying the photosensor output current signals thereby amplifying the photosensor output current signal from the photosensor by the current mirror circuit.   
     
     
       11. An optical data medium driving apparatus and a servo circuit as set forth in claim 10, wherein each switching element includes a control electrode and the coupling means couples the photosensor output current signal to the control electrode of each switching element. 
     
     
       12. An optical data medium driving apparatus and a servo circuit as set forth in claim 11, wherein each switching element includes a transistor having a base and wherein the control electrode is coupled to the base. 
     
     
       13. An optical data medium driving apparatus and a servo circuit, comprising: a photosensor which outputs a current signal corresponding to a quantity of transmitted light or reflected light from an optical data medium;   an amplification means for amplifying the photosensor output current signal, the amplification means including a current mirror circuit having a plurality of switching elements and at least one current determining means associated with each switching element and each providing a current signal substantially equal to the photosensor output current signal;   means for connecting the photosensor output current signal to each switching element in the plurality of switching elements; and   means for combining selected ones of the current signals thereby amplifying the photosensor output current signal from the photosensor by the current mirror circuit.