reference will now be made in detail to the present embodiments of the present invention , examples of which are illustrated in the accompanying drawings , wherein like reference numerals refer to the like elements throughout . the embodiments are described below in order to explain the present invention by referring to the figures . fig2 is a block diagram showing the circuit configuration of an interface device for an optical recording and / or reproducing apparatus according to an embodiment of the present invention . as shown in fig2 , the interface device for the optical recording and / or reproducing apparatus mainly includes a pickup 100 and a main pcb 200 . the pickup 100 and the main pcb 200 are connected to each other via a cable 400 through connectors 300 . the pickup 100 is a device to read and write information from / on discs 110 , each of which may be a bd , hd - dvd , dvd , and / or cd or another format . the pickup 100 includes laser diode driver units ( hereinafter referred to as ld units ) 112 to drive laser diodes ( lds ) for the respective discs 110 , respectively , photo diode ( pd ) units ( hereinafter referred to as pd units ) 114 to receive laser signals reflected from the associated discs 110 , respectively , and an mux ic 120 including a plurality of mux channels ch 1 to ch 9 , each of which selects an output signal from a pd unit ( pd signal ) corresponding to an associated one of the discs 100 from among output signals from the pd units 114 ( pd signals ) corresponding respectively to the discs 100 . each of the mux channels ch 1 to ch 9 in the mux ic 120 is also adapted to multiplex output signals from monitor photo diodes ( hereinafter referred to as mpds ) attached to the respective lds for the discs 110 to select an output signal from an mpd ( mpd signal ) corresponding to the associated disc from among the output signals from the mpds ( mpd signals ). the main pcb 200 includes an rf ic 210 for rf signal processing , and a microcomputer 220 which outputs a switch control signal bd / hd - dvd / dvd / cd to the pickup 100 and the rf ic 210 to select a desired one of the types of the discs 110 . the rf ic 210 includes an auto laser diode power control unit ( hereinafter referred to as an apc unit ) 230 which optimally controls outputs of the lds for all the types of discs 110 including at least one of a bd , hd - dvd , dvd , and / or cd . the rf ic 210 also includes an rf signal processor 240 which converts a pd signal from the mux ic 120 into a servo control signal and an rf signal necessary to a particular disc 110 corresponding to the pd signal and performs a servo control operation and an rf data processing operation for the particular disc , respectively , according to the converted servo control signal and rf signal . the rf ic 210 further includes a demultiplexer ( demux ) 250 which receives an mpd signal corresponding to the particular disc 110 from the mux ic 120 , selects one of a plurality of output terminals thereof corresponding to the particular disc 110 in response to the switch control signal bd / hd - dvd / dvd / cd from the microcomputer 220 , and outputs the mpd signal to a corresponding apc of the apc unit 230 through the selected output terminal . the apc unit 230 optimally controls outputs ( amounts of light ) of the respective lds for the discs 110 , each of which is at least one of a bd , hd - dvd , dvd , and / or cd . that is , the apc unit 230 keeps the outputs of the lds constant by feeding variations in the outputs of the lds back thereto , respectively . to this end , the apc unit 230 includes at least one of a bd apc , hd apc , dvd apc , and cd apc . the rf signal processor 240 includes an rf controller 242 to generate the rf signal for the rf data processing operation , and a servo controller 244 to generate the servo control signal for the servo control operation . fig3 is a block diagram showing the circuit configuration of an interface device for an optical recording and / or reproducing apparatus according to another embodiment of the present invention . some parts in fig3 are the same as those in fig2 . therefore , the same elements are denoted by the same reference numerals and names , and a repeated description thereof will be omitted . as shown in fig3 , the main pcb 200 includes the rf ic 210 , the microcomputer 220 , and a demux 260 . it is noted that the demux 260 is provided on the main pcb 200 rather than in the rf ic 210 in a different manner from that of the demux 250 in fig2 . the demux 260 receives the mpd signal of the particular disc 110 from the mux ic 120 , selects one of a plurality of output terminals thereof for selection of the particular disc 110 , and outputs the mpd signal to a corresponding apc of the apc unit 230 . the demux 260 also receives the outputs of the respective pd units 114 for the discs 110 , selects the pd signal corresponding to the particular disc 110 , and outputs the pd signal to a mux 270 provided in the rf ic 210 . in addition , the rf ic 210 includes the mux 270 which selects the pd signal of the particular disc 110 among the pd signals outputted from the demux 260 in a different manner from the demux 250 in fig2 . this pd signal selected by the mux 270 is inputted to the rf signal processor 240 and is used for the servo control operation and the rf data processing operation of the particular disc 110 . a description will hereinafter be given of the operation of the interface device for the optical recording and / or reproducing apparatus with the above - stated configuration according to the present invention . an aspect of the present invention aims to simplify the configuration of the interface circuit between the pickup 100 to read and write disc information and the rf ic 210 for rf signal processing in a universal optical recording and / or reproducing apparatus which is capable of reading and writing information from / on all kinds of optical discs including at least one of a bd , hd - dvd , dvd , and cd . the operation of this interface configuration will hereinafter be described with reference to fig2 . first , the user opens a disc tray , inserts a disc 110 of at least one of a bd , hd - dvd , dvd , or cd type into the disc tray , and closes the disc tray . then , the microcomputer 220 loads the inserted disc 110 , identifies the type thereof , and drives an ld corresponding to the inserted disc 110 of the identified type . as the ld is driven , a corresponding pd unit 114 receives a laser signal reflected from the inserted disc 110 and generates a pd signal corresponding to at least one of a bd , hd - dvd , dvd , or cd , depending upon the determination of the type of the inserted disc 110 . the mux ic 120 provided in the pickup 100 selects the pd signal of the inserted disc 110 from among respective outputs of the bd , hd - dvd , dvd , and cd pd units 114 in response to a switch control signal from the microcomputer 220 . the pd signal selected by the mux ic 120 is outputted through the connectors 300 to the rf ic 210 placed in the main pcb 200 . accordingly , reduction of a number of pins of the connectors 300 from the pickup 100 to the main pcb 200 is possible by placing the mux ic 120 , which selects input / output signals of the pickup 100 and rf ic 210 , in the pickup 100 . also a reduction of a size of the rf ic 210 for rf signal processing is possible by reducing the number of input / output pins thereof . in addition , a simplification of an assembly between the pickup 100 and the main pcb 200 is possible . afterwards , an mpd signal inputted from the pickup 100 to the rf ic 210 is switched through the demux 250 according to the type of the inserted disc 110 , and fed to a corresponding apc of the apc unit 230 , which then performs an apc operation to control the amount of output light from the ld corresponding to the inserted disc 110 . in the apc operation , if the amount of the output light of the ld , set to a predetermined value , is altered with a change in voltage or temperature of the ld , the apc unit 230 in the rf ic 210 detects a variation in output current of the associated mpd of the pickup 100 to maintain an amount of the output light of the ld . the pd signal , inputted to the rf ic 210 from the pickup 100 , is converted by the rf signal processor 240 in the rf ic 210 into a servo control signal and an rf signal necessary to be used in accordance with the determined type of the inserted disc 110 , and is then used for a servo control operation and an rf data processing operation for the inserted disc 100 . the second embodiment of fig3 has the same configuration as that of the first embodiment of fig2 , except that the demux 260 is placed on the main pcb 200 not in the rf ic 210 and the mux 270 is disposed between the demux 260 and the rf signal processor 240 . this arrangement may be changed by the designer . with the configuration of fig3 in which the mux ic 120 , which selects input / output signals of the pickup 100 and the rf ic 210 , is placed within the pickup 100 , a reduction of a number of pins of the connectors 300 from the pickup 100 to the main pcb 200 is also possible . as is apparent from the above description , the present invention provides an interface device for an optical recording and / or reproducing apparatus , wherein a multiplexer mux is provided in a pickup and adapted to multiplex input / output signals of the pickup and an rf ic . thus , the number of pins of connectors from the pickup to the rf ic may be reduced so as to lead to advantages in that pcb layout is relatively simplified and signal quality is relatively preserved . in addition , the interface device according to the present invention has another advantage of reducing the size and cost of the optical recording and / or reproducing apparatus by decreasing the number of input / output pins of the rf ic . although a few embodiments of the present invention have been shown and described , it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention , the scope of which is defined in the claims and their equivalents .