Signal processing circuit and information recording/reproducing apparatus using the same, and method for optimizing coefficients of equalizer circuit

Abstract

A signal processing circuit for a magnetic recording/reproducing apparatus, including at least an AGC, a PLL, a LPF, an equalizer circuit and a detection circuit, wherein a coefficient compensation circuit is formed by defining a constitution of the equalizer circuit, an error detection circuit is provided which operates by receiving input from the detection circuit, and the LSI is formed by a plurality of analog and digital chips, and the analog and digital chips are connected by current-output type D/A converters connected to at least the AGC and the PLL.

1 . A signal processing circuit comprising: 
 an equalizer circuit;    a coefficient compensation circuit having an input connected to said equalizer circuit, for sequentially compensating tap coefficient values of said equalizer circuit; and    a phase detection circuit, connected to receive an output signal of said equalizer circuit, for sequentially detecting a phase of a signal input to said equalizer circuit, wherein said equalizer circuit includes a transversal type equalizer circuit with five or more taps, and wherein, of tap coefficients of said equalizer circuit, the tap coefficients adjacent on both sides to a center tap are the same value.    
     
     
         2 . A signal processing circuit according to    claim 1   , wherein arrangement is made such that negative coefficient values of said transversal type equalizer circuit are set by positive coefficient values by inverting either output values or coefficient values of tap delay means.  
     
     
         3 . A signal processing circuit according to    claim 1   , wherein the input signal of said equalizer circuit is partial-response-waveform processed and input to said coefficient compensation circuit.  
     
     
         4 . A signal processing circuit according to    claim 1   , wherein said coefficient compensation circuit includes first detection means for detecting said input signal of said equalizer circuit; second detection circuit for detecting said output signal of said equalizer circuit; error calculating means for calculating an error signal from said output signal of said equalizer circuit and a signal of said second detection means; delay means for delaying the output signal of said first detection means; correlation value calculating means for calculating a correlation value between the output signal of said delay means and the output signal of said error calculating means; correlation value adding means for sequentially adding output signals of said correlation value calculating means; coefficient compensation amount calculating means for calculating a coefficient compensation amount from a signal obtained by adding output signals of said correlation value adding means a fixed number of times; and coefficient error compensation means for compensating a coefficient value of said equalizer circuit by an output signal of said coefficient compensation amount calculating means, wherein the sequential addition of correlation values is stopped for more than a delay time after the coefficient compensation has been done in said coefficient compensation circuit.  
     
     
         5 . A signal processing circuit according to    claim 4   , wherein said coefficient compensation circuit further includes delay time control means for controlling a delay time of said delay means; selection means for selecting a tap coefficient to compensate in time with said delay length control means; and coefficient temporary holding means for temporarily holding a tap coefficient compensated by said coefficient error compensation means, wherein said delay time is fixed when tap coefficient compensation amounts are calculated, and when tap coefficient values have been decided by controlling said selection means, all tap coefficients are compensated.  
     
     
         6 . A signal processing circuit according to    claim 5   , wherein the input signal of said equalizer circuit which is concurrently supplied to the equalizer circuit and the output signal of said equalizer circuit are decimated and input to said coefficient compensation circuit and said coefficient compensation circuit is operated at a decimated signal frequency.  
     
     
         7 . A signal processing circuit according to    claim 1   , wherein, of the tap coefficients of the transversal type equalizer circuit, the tap coefficients at positions symmetric with respect to the center tap are the same value.  
     
     
         8 . A signal processing circuit according to    claim 7   , wherein arrangement is made such that negative coefficient values of said transversal type equalizer circuit be set by inverting either output values or coefficient values of tap delay means.  
     
     
         9 . An equalizer coefficient optimizing method for use in an information recording/reproducing apparatus including an equalizer circuit of transversal type with five or more taps in which, of tap coefficients of said equalizer circuit, tap coefficients adjacent on both sides to a center tap are the same value, a coefficient compensation circuit for sequentially compensating coefficient values of said equalizer circuit, and a phase detection circuit for sequentially detecting phases of output signals of said equalizer circuit, the method of optimizing the coefficients of said equalizer circuit comprising the steps of: 
 inputting reproduced waveforms of random, arbitrary data patterns to said signal processing circuit;    operating said coefficient compensation circuit;    reading tap coefficients which have been compensated from said signal processing circuit; and    storing said tap coefficients in a non-volatile storage area in said information recording/reproducing apparatus.    
     
     
         10 . An equalizer coefficient optimizing method for use in an information recording/reproducing apparatus including an equalizer circuit of a transversal type with five or more taps in which, of tap coefficients of said equalizer circuit, tap coefficients at positions symmetric with respect to a center tap are a same value, a coefficient compensation circuit for sequentially compensating coefficient values of said equalizer circuit, and a phase detection circuit for sequentially detecting phases of an output signal of said equalizer circuit, the method of optimizing the coefficients of said equalizer circuit, comprising the steps of: 
 inputting reproduced waveforms of a random, arbitrary data pattern to said signal processing circuit;    operating said coefficient compensation circuit;    reading tap coefficients which have been compensated from said signal processing circuit; and    storing said tap coefficients in a non-volatile storage area in said information recording/reproducing apparatus.    
     
     
         11 . An equalizer coefficient optimizing method for use in an information recording/reproducing apparatus having a signal processing circuit, including an equalizer circuit, a coefficient compensation circuit for sequentially compensating coefficient values of said equalizer circuit, and a phase detection circuit for sequentially detecting phases of the output signal of said equalizer circuit, the method of optimizing coefficients of said equalizer circuit, comprising the steps of: 
 inputting reproduced waveforms of a random, arbitrary data pattern to said signal processing circuit;    operating said coefficient compensation circuit;    reading tap coefficients which have been compensated from said signal processing circuit; and    storing said compensated tap coefficients in a non-volatile storage area in said information recording/reproducing apparatus.    
     
     
         12 . A method of optimizing coefficients in an equalizer circuit according to    claim 11   , wherein said equalizer circuit is a transversal type equalizer circuit with five or more taps, and of tap coefficients of said equalizer circuit, tap coefficients adjacent on both sides to the center tap are a same value.  
     
     
         13 . A method of optimizing tap coefficients of an equalizer circuit according to    claim 11   , wherein said equalizer circuit is a transversal type equalizer circuit with five or more taps, and of tap coefficients of said equalizer circuit, tap coefficients at positions symmetric with respect to a center tap are a same value.  
     
     
         14 . A signal processing circuit comprising: 
 an equalizer circuit;    a coefficient compensation circuit, connected to an output of said equalizer circuit, for sequentially compensating tap coefficient values of said equalizer circuit;    a phase detection circuit, connected to an output of said equalizer circuit, for sequentially detecting phases of the signal input to said equalizer circuit; and    a register for setting the number of taps, wherein said register is arranged to put the coefficient value at “0” at a specific tap position of said equalizer circuit according to contents set in said register, and said signal processing circuit stops the operation of that portion of said coefficient compensation circuit which is related to said tap position.    
     
     
         15 . An information recording/reproducing apparatus, comprising: 
 a head disk assembly;    a signal processing circuit, connected to said head disk assembly, and including an equalizer circuit, a coefficient compensation circuit for sequentially compensating coefficients of said equalizer circuit and a phase detection circuit for sequentially detecting phases of an output signal of said equalizer circuit; and    a training area for coefficient compensation, recorded on a recording medium of said information recording/reproducing apparatus, wherein said training area is erased after a coefficient compensation operation is performed, and is defined as an area for recording and reproducing user data.    
     
     
         16 . An information recording/reproducing apparatus according to    claim 15   , wherein said equalizer circuit is a transversal type equalizer circuit with five or more taps, and of tap coefficients of said equalizer circuit, at least tap coefficients adjacent on both sides to a center tap, and wherein arrangement is made such that negative coefficient values of said equalizer circuit be set by positive coefficient values by inverting either output values or coefficient values of tap delay means.  
     
     
         17 . An information recording/reproducing apparatus according to    claim 15   , wherein, of the tap coefficients of said equalizer circuit, tap coefficients at positions symmetric with respect to the center tap are a same value.  
     
     
         18 . A signal processing circuit comprising: 
 an equalizer circuit;    a phase detection circuit, connected to an output terminal of said equalizer circuit, for sequentially detecting phases of an output signal of said equalizer circuit;    data holding means for holding a signal input to said equalizer circuit at timing of data clock for a length of a data segment twice or longer than a total number of taps of said equalizer circuit; and    clock means for generating a clock signal to output data held in said data holding means, wherein said clock signal is different from the data clock.    
     
     
         19 . An information recording/reproducing apparatus comprising: 
 a head disk assembly;    a signal processing circuit connected to said head disk assembly and including an equalizer circuit, a phase detection circuit, connected to an output of said equalizer circuit, for sequentially detecting phases of an output signal of said equalizer circuit, data holding means for holding a signal input to said equalizer circuit for a length of a data segment twice or longer than a total number of taps of said equalizer circuit at data clock periods, and clock means for generating a clock signal to output data held in said data holding means, wherein said clock signal is different from said data clock;    storage means, provided independently of said signal processing circuit, for storing said held data output from said signal processing circuit;    means for calculating tap coefficient values of said equalizer circuit based on data stored in said storage means; and    non-volatile storage means for storing said tap coefficient values calculated.    
     
     
         20 . An equalizer coefficient optimizing method for use in an information recording/reproducing apparatus having a signal processing circuit including an equalizer circuit, a phase detection circuit for sequentially detecting phases of an output signal of said equalizer circuit, data holding means for holding a signal input to said equalizer circuit for a length of in a data segment twice or longer than a total number of taps of said equalizer circuit at data clock periods, wherein data held in said data holding means is output at a clock signal different from a data clock, the method of optimizing coefficients of said equalizer circuit, comprising the steps of: 
 storing said held data output from said signal processing circuit in storage means provided independently of said signal processing circuit;    calculating tap coefficient values of said equalizer circuit based on data stored in said storage means; and    storing said coefficient values in non-volatile storage means.    
     
     
         21 . A signal processing circuit comprising: 
 an equalizer circuit;    an amplitude detection circuit, connected to an output of said equalizer circuit, for sequentially detecting amplitudes of an output signal of said equalizer circuit;    detection means for receiving, as an input signal, said output signal from said equalizer circuit and detecting said output signal;    error calculating means for calculating an error signal representing an amplitude error occurring at said detection means from said input signal and an output signal of said detection means;    distinction means, having a threshold value set therein, for outputting a count signal when an error signal is larger than the threshold value; and    counting means for counting said count signals.    
     
     
         22 . A signal processing circuit according to    claim 21   , further comprising a register for setting a detection level of said detection means.  
     
     
         23 . A signal processing circuit according to    claim 22   , further comprising a register for setting a number of detection levels of said detection means.  
     
     
         24 . A signal processing circuit according to claim  22 , further comprising target amplitude value setting means including a register for variably setting a target amplitude value of said amplitude detection circuit.  
     
     
         25 . An information recording/reproducing apparatus comprising: 
 a recording head;    a signal processing circuit connected operatively to said recording head, said signal processing circuit including an equalizer circuit, an amplitude detection circuit, connected to an output of said equalizer circuit, for sequentially detecting amplitudes of an output signal of said equalizer circuit, detection means for receiving said output signal as an input signal thereto and detecting said output signal, an error calculating means for calculating an error signal relating to an amplitude error occurring at said detection means from said input signal and an output signal from said detection means, distinction means, having a threshold value set therein, for outputting a count signal when an error signal is larger than said threshold value, counting means for counting said count signals, a register for setting a detection level of said detection means, and a register for setting a number of detection levels of said detection means; and    a write current setting register and a write current output terminal of said recording head, wherein recorded data is so formed as to have a single recording frequency, the number of detection levels of said detection means is set at “1”, each time the write current is changed, count values of said counting means are stored, a write current at which an error distribution is smallest is calculated from said count values, and the write current value of said recording head is taken as the optimum write current.    
     
     
         26 . An information recording/reproducing apparatus comprising: 
 a recording head;    a signal processing circuit connected operatively to said recording head, said signal processing circuit including an equalizer circuit, an amplitude detection circuit, connected to an output of said equalizer circuit, for sequentially detecting amplitudes of an output signal of said equalizer circuit, detection means for receiving said output signal as an input signal thereto and detecting said output signal, an error calculating means for calculating an error signal relating to an amplitude error occurring at said detection means from said input signal and an output signal from said detection means, distinction means, having a threshold value set therein, for outputting a count signal when an error signal is larger than said threshold value, counting means for counting said count signals, a register for setting a detection level of said detection means, and a register for setting a number of detection levels of said detection means; and    a sense current setting register and a sense current output terminal of said recording head, wherein recorded data is recorded such that the magnetization reversal density is smallest, and an output of said detection means is fixed at “0” at all times, and each time a sense current is changed, count values of said counting means, obtained using one or more threshold values in said distinction circuit, are stored, and from said count values, a sense current at which an error distribution is smallest is calculated, and the sense current value of said recording head is taken as the optimum sense current.    
     
     
         27 . An information recording/reproducing apparatus comprising: 
 recording and reproducing heads; and    a signal processing circuit operatively connected to said recording and reproducing heads, said signal processing circuit including an equalizer circuit, an amplitude detection circuit, connected to an output of said equalizer circuit, for sequentially detecting amplitudes of an output signal of said equalizer circuit, detection means for receiving said output signal as an input signal thereto and detecting said output signal, an error calculating means for calculating an error signal relating to an amplitude error occurring at said detection means from said input signal and an output signal from said detection means, distinction means, having a threshold value set therein, for outputting a count signal when an error signal is larger than said threshold value, counting means for counting said count signals, a register for setting a detection level of said detection means, and a register for setting a number of detection levels of said detection means;    offset setting means for d.c. offset compensation;    an offset compensation register; and    counting means for counting count signals generated with reference to one or more threshold values of said distinction means, wherein input to said signal processing circuit is not supplied, output of said detection means is put at “0” at all times, and each time the offset compensation amount setting is changed, the count value is stored, and from said count values, the optimum offset compensation amount is calculated.    
     
     
         28 . An information recording/reproducing apparatus comprising: 
 recording and reproducing heads; and    a signal processing circuit operatively connected to said recording and reproducing heads, said signal processing circuit including an equalizer circuit, an amplitude detection circuit, connected to an output of said equalizer circuit, for sequentially detecting amplitudes of an output signal of said equalizer circuit, detection means for receiving said output signal as an input signal thereto and detecting said output signal, an error calculating means for calculating an error signal relating to an amplitude error occurring at said detection means from said input signal and an output signal from said detection means, distinction means, having a threshold value set therein, for outputting a count signal when an error signal is larger than said threshold value, counting means for counting said count signals, a register for setting a detection level of said detection means, and a register for setting a number of detection levels of said detection means;    offset setting means for d.c. offset compensation; and    an offset compensation register, wherein input to said signal processing circuit is so formed as to have a single frequency, the number of detection levels of said detection means is “1”, and each time the offset compensation amount is changed, said count value of said counting means, obtained using one or more threshold values in said distinction circuit, is stored, and from the count values, the optimum offset compensation amount is calculated.    
     
     
         29 . An information recording/reproducing apparatus comprising: 
 recording and reproducing heads; and    a signal processing circuit operatively connected to said recording and reproducing heads, said signal processing circuit including an equalizer circuit, an amplitude detection circuit, connected to an output of said equalizer circuit, for sequentially detecting amplitudes of an output signal of said equalizer circuit, detection means for receiving said output signal as an input signal thereto and detecting said output signal, an error calculating means for calculating an error signal relating to an amplitude error occurring at said detection means from said input signal and an output signal from said detection means, distinction means, having a threshold value set therein, for outputting a count signal when an error signal is larger than said threshold value, counting means for counting said count signals, a register for setting a detection level of said detection means, and a register for setting a number of detection levels of said detection means; and    a register of coefficient values to give certain characteristics to said equalizer circuit, wherein recorded data is random data, the number of detection levels of said detection means is put at “2”, and each time a coefficient value setting is changed, said count value of said counting means, obtained using one or more threshold values of said distinction circuit, is stored, and from said count values, a coefficient value at which an error distribution is smallest is calculated, and this coefficient value is taken as the optimum coefficient value.    
     
     
         30 . An information recording/reproducing apparatus comprising: 
 recording and reproducing heads; and    a signal processing circuit operatively connected to said recording and reproducing heads, said signal processing circuit including an equalizer circuit, an amplitude detection circuit, connected to an output of said equalizer circuit, for sequentially detecting amplitudes of an output signal of said equalizer circuit, detection means for receiving said output signal as an input signal thereto and detecting said output signal, an error calculating means for calculating an error signal relating to an amplitude error occurring at said detection means from said input signal and an output signal from said detection means, distinction means, having a threshold value set therein, for outputting a count signal when an error signal is larger than said threshold value, counting means for counting said count signals, a register for setting a detection level of said detection means, and a register for setting a number of detection levels of said detection means;    record compensation means for compensating magnetization reversal positions according to a data sequence when recording data; and    a compensation value register for storing compensation values for said compensation means, wherein recorded data is random data, the number of detection levels of said detection means is put at “2”, and each time said compensation value register setting is changed, a count value of said counting means, obtained using one or more threshold values in said distinction circuit, is store, and from said count values, a value in said record compensation value register at which an error distribution is smallest is calculated, and this compensation value is taken as the optimum compensation value.    
     
     
         31 . An information recording/reproducing apparatus comprising: 
 recording and reproducing heads; and    a signal processing circuit operationally connected to said recording and reproducing heads, said signal processing circuit including an equalizer circuit, an amplitude detection circuit, connected to an output of said equalizer circuit, for sequentially detecting amplitudes of an output signal of said equalizer circuit, detection means for receiving said output signal as an input signal thereto and detecting said output signal, an error calculating means for calculating an error signal relating to an amplitude error occurring at said detection means from said input signal and an output signal from said detection means, distinction means, having a threshold value set therein, for outputting a count signal when an error signal is larger than said threshold value, counting means for counting said count signals, a register for setting a detection level of said detection means, and a register for setting a number of detection levels of said detection means;    non-volatile storage means, provided independently of said signal processing circuit, for storing at least any one of a write current setting value, a sense current setting value, a d.c. offset setting value, coefficient values of said equalizer circuit, and a compensation value of record compensation means, which are suitable for recording and reproduction on a recording/reproducing medium; and    means for reading at least any one of said setting values from said non-volatile storage means, and setting said value in said signal processing circuit when supplying power to said information recording/reproducing apparatus or when selecting a recording or reproducing area of said information recording/reproducing apparatus.    
     
     
         32 . A signal processing circuit comprising: 
 an equalizer circuit;    an amplitude detection circuit, operatively connected to an output of said equalizer circuit, for sequentially detecting amplitudes of an output signal of said equalizer circuit; and    error detection means including distinction means for receiving said output signal of said equalizer as an input signal thereto, and outputting a count signal in response to said input signal larger than a threshold value, counting means for counting count signals, and register means for setting said threshold value.    
     
     
         33 . A signal processing circuit comprising: 
 an equalizer circuit;    an amplitude detection circuit, operatively connected to an output of said equalizer circuit, for sequentially detecting amplitudes of an output signal of said equalizer circuit; and    error detection means including first distinction means for receiving said output of said equalizer circuit as an input signal thereto and outputting a first count signal in response to said input signal less than a threshold value, first counting means for counting said first count signals, second distinction means for outputting a second count signal in response to said input signal larger than a threshold value, second counting means for counting said second count signals, count value calculating means for subtracting a count value of said second counting means from a count value of said first counting means, and means for setting said threshold value.    
     
     
         34 . A signal processing circuit according to    claim 33   , wherein, of said output signal of said equalizer circuit, that portion of said output signal which excludes signs is used as an input signal to said error detection means.  
     
     
         35 . A signal processing circuit according to    claim 33   , wherein there are provided two modes, including a first mode that, of said output signal of said equalizer circuit, that portion of said output signal which excludes signs is used as said input signal of said error detection means and a second mode that said output signal including signs is used as said input signal, and a register for switching said two modes is provided.  
     
     
         36 . An information recording/reproducing apparatus, comprising: 
 a head disk assembly;    a signal processing circuit connected to said head disk assembly, said signal processing circuit including an equalizer circuit, an amplitude detection circuit, connected to an output of said equalizer circuit, for sequentially detecting amplitudes of an output signal of said equalizer circuit, and an error detection circuit for receiving said output signal of said equalizer circuit as an input signal thereto, said error detection circuit including first distinction means for outputting a first count signal in response to an input signal less than a threshold value, counting means for counting said first count signals, second distinction circuit for outputting a second count signal in response to said input signal larger than the threshold value, second counting means for counting said second count signals, count value calculating means for subtracting a count value of said second counting means from a count value of said first counting means, and means for setting said threshold value;    a register switchably setting therein a first mode in which, of said output signal of said equalizer circuit, that portion of said output signal which excludes signs is used as an input signal of said error detection means, and a second mode in which said output signal including signs is used said input signal;    a recording medium having a plurality of recording/reproducing areas; and    non-volatile storage means, provided independently of said signal processing circuit, for storing a set of recording/reproducing parameters optimum for each of said recording/reproducing areas, wherein when a recording/reproducing area is selected, a set of recording/reproducing parameters optimum for said recording/reproducing area is set in said signal processing circuit.    
     
     
         37 . An information recording/reproducing apparatus comprising: 
 a head disk assembly;    a recorded signal processing circuit connected to said head disk assembly; and    a reproduced signal processing circuit connected to said head disk assembly,    wherein said recorded signal processing circuit includes a pre-coder for generating a pre-coded data sequence by pre-coding at least a serial recorded code data sequence, and when recording data, said pre-code means is reset or preset just before a sync byte indicating a start of data so that a specific data pattern can be recorded as a pre-coded data sequence.    
     
     
         38 . An information recording/reproducing apparatus according to    claim 37   , wherein a recording method is such that a flux reversal of a write current occurs at data “1” and the ongoing write current direction is maintained at data “0”, and a recorded code data sequence corresponding to a sync byte is set such that data begins with “0” and data “1” does not continue in serial data sequence.  
     
     
         39 . An information recording/reproducing apparatus according to    claim 38   , wherein a sequence of recorded code data “0” and “1” corresponding to said sync byte differs for more than ½ of a byte from a sequence of recorded code data “0” and “1” recorded continuously before a sync byte.  
     
     
         40 . A signal processing circuit having an mixture of an analog signal processing block and a digital signal processing block, comprising: 
 a large scale integrated circuit (LSI) in an at least two-chip structure, including an analog chip which forms at least said analog processing block and a digital chip which forms at least said digital signal processing block; and    an equalizer circuit,    wherein said digital chip includes a phase detection circuit, connected to receive output signal of said equalizer circuit, for sequentially detecting phases of said output signal of said equalizer circuit, a first current-output type D/A converter circuit for D/A converting an output signal of said phase detection circuit, an amplitude detection circuit, connected to receive said output signal of said equalizer circuit, for sequentially detecting amplitudes of said output signal of said equalizer circuit, a second current-output type D/A converter circuit for D/A converting an output signal of said amplitude detection circuit, and pins having outputs of said first and second D/A converter circuits connected thereto, and wherein said analog chip includes a phase control circuit and an amplitude control circuit having output signals of said first and second D/A converter circuits supplied respectively thereto.    
     
     
         41 . A signal processing circuit having a mixture of an analog signal processing block and a digital signal processing block, and also having partial response waveform equalizing and maximum likelihood decoding functions, said signal processing circuit comprising: 
 a large scale integrated circuit (LSI) in an at least two-chip structure, including an analog chip which forms at least said analog processing block and a digital chip which forms at least said digital signal processing block,    wherein said digital chip includes a phase detection circuit and an amplitude detection circuit, first and second current-output type D/A converter circuits for respectively D/A converting output signals of said phase and amplitude detection circuits, and pins having outputs of said first and second D/A converter circuits connected thereto, and wherein said analog chip includes a phase control circuit and an amplitude control circuit having output signals of said phase and amplitude detection circuits supplied respectively thereto.    
     
     
         42 . A signal processing circuit according to    claim 41   , wherein said signal processing circuit has a Trellis code modulation function in addition to said partial response waveform equalizing function and said maximum likelihood decoding function.  
     
     
         43 . An information recording/reproducing apparatus comprising: 
 a head disk assembly; and    a signal processing circuit electrically connected to said head disk assembly, said signal processing circuit having a mixture of an analog signal processing block and a digital signal processing block, including partial response waveform equalizing and maximum likelihood decoding functions, and being formed in a large scale integrated circuit (LSI) of an at least two-chip structure having an analog chip which forms at least said analog signal processing block and a digital chip which forms at least said digital signal processing block, wherein said digital chip includes phase and amplitude detection circuits, first and second current-output type D/A converter circuits for respectively D/A converting output signals of said phase and amplitude detection circuits, and terminals having outputs of said first and second D/A converter circuits connected thereto, wherein said analog chip includes a phase control circuit and an amplitude control circuit having output signals of said phase and amplitude detection circuits supplied respectively thereto, and wherein a reproduced signal of a pre-amplifier for amplifying a signal detected from a recording medium is input to said analog chip, a digital signal after decoding is output from said digital chip, and a digital signal of data to be written on said recording medium is input to said digital chip.