Digital information reproducing apparatus

Claim 2

A digital information reproducing apparatus comprising: a waveform shaping means for comparing a level of an input signal with a threshold level so as to thereby obtain a reproduced digital signal; a clock extracting means for extracting a read clock from the reproduced digital signal; and a threshold level control means for controlling the threshold level, comprising a first control means for detecting a threshold level error from the reproduced digital signal and the read clock and for controlling the threshold level so as to cancel the threshold level error, and a second control means for controlling the threshold level so that a DC component of the reproduced digital signal become equal to a predetermined value.

Claim 3

An apparatus as claimed in claim 1, further comprising a selector means for selecting one of the first and second control means.

Claim 4

An apparatus as claimed in claim 2, wherein the selector means selects the second control means in response to a predetermined pattern of a repetitive header area inputted prior to an information-carrying area of the input signal, and selects the first control means after recognizing the predetermined pattern from the reproduced digital signal.

Claim 5

An apparatus as claimed in claim 2, wherein the second control means is faster in response than the first control means.

Claim 6

An apparatus as claimed in claim 1, wherein the first and second control means operate simultaneously and have such characteristics than an open-loop gain of the second control means is higher than that of the first control means for a direct current but is smaller than 1 at a cross-over frequency where the open-loop gain of the first control means is equal to 1.

Claim 7

A digital information reproducing apparatus comprising: a waveform shaping means for comparing a level of an input signal with a threshold level so as to thereby obtain a reproduced digital signal; a clock extracting means for extracting a read clock from the reproduced digital signal; and a threshold level control means for controlling the threshold level, comprising a first control means for detecting a threshold level error from the reproduced digital signal and the read clock and for controlling the threshold level so as to cancel the threshold level error, and a second control means for controlling the threshold level so that a DC component of the reproduced digital signal becomes equal to a predetermined value; wherein the first control means comprises: a means for synchronizing the reproduced digital signal with the read clock to obtain a synchronized digital signal; a gate for selectively passing the synchronized digital signal; a first low-pass filter for passing a low frequency component of the reproduced digital signal; a second low-pass filter for passing a low frequency component of the synchronized digital signal output from said gate; and a differential amplifier for producing a difference, as the threshold level error, between the low frequency components from the first and second low-pass filters; and wherein the second control means comprises: the first low-pass filter, a reference level source coupled to the differential amplifier via the second low-pass filter for generating a reference DC level, and the differential amplifier for producing a difference between the low frequency component from the first low-pass filter and the reference DC level; and wherein an output signal from the differential amplifier is used as the threshold level.

Claim 8

A digital information reproducing apparatus comprising: a waveform shaping means for comparing a level of an input signal with a threshold level so as to thereby obtain a reproduced digital signal; a clock extracting means for extracting a read clock from the reproduced digital signal; and a threshold level control means for controlling the threshold level, comprising a first control means for detecting a threshold level error from the reproduced digital signal and the read clock and for controlling the threshold level so as to cancel the threshold level error, and a second control means for controlling the threshold level so that a DC component of the reproduced digital signal becomes equal to a predetermined value; wherein the first control means comprises: a means for synchronizing the reproduced digital signal with the read clock to obtain a synchronized digital signal; a gate for selectively passing the synchronized digital signal; a first low-pass filter for passing a low frequency component of the reproduced digital signal; a second low-pass filter for passing a low frequency component of the synchronized digital signal output from said gate; and a differential amplifier for producing a difference, as the threshold level error, between the low frequency components from the first and second low-pass filters; and wherein the second control means comprises: the first low-pass filter, a reference level source coupled to the differential amplifier via the second low-pass filter for generating a reference DC level, and the differential amplifier for producing a difference between the low frequency component from the first low-pass filter and the reference DC level; and wherein an output signal from the differential amplifier is used as the threshold level.

Claim 9

An apparatus as claimed in claim 6, further comprising a selector means for producing a mode selection signal for controlling the gate so that the gate does not pass the synchronized digital signal whereby the first control means does not operate.

Claim 10

An apparatus as claimed in claim 7, wherein the selector means produces the mode selection signal in response to a predetermined pattern of a repetitive header area inputted prior to an information-carrying area of the input signal, and terminates the mode selection signal after recognizing the predetermined pattern from the reproduced digital signal.

Claim 11

An apparatus as claimed in claim 7, further comprising a variable gain amplifier for amplifying the output signal from the differential amplifier, the variable gain amplifier being responsive to the mode selection signal for decreasing its gain to reduce a response of the threshold level control means.

Claim 12

A digital information reproducing apparatus comprising: a waveform shaping means for comparing a level of an input signal with a threshold level so as to thereby obtain a reproduced digital signal; a clock extracting means for extracting a read clock from the reproduced digital signal; a threshold level control means for controlling the threshold level, comprising a first control means for detecting a threshold level error from the reproduced digital signal and the read clock and for controlling the threshold level so as to cancel the threshold level error, and a second control means for controlling the threshold level so that a DC component of the reproduced digital signal becomes equal to a predetermined value; and a selector means for producing a mode selection signal in response to a predetermined pattern of a repetitive header area inputted prior to an information-carrying area of the input signal, and for terminating the mode selection signal after recognizing the predetermined pattern from the reproduced digital signal; and a switch means for normally selecting the first control means and being responsive to the mode selection signal for selecting the second control means during a duration of the mode selection signal; wherein the first control means comprises: a first phase comparator for comparing the phase of a leading edge of the reproduced digital signal with the phase of the read clock; a second phase comparator for comparing the phase of a trailing edge of the reproduced digital signal with the phase of the read clock; a first differential amplifier for producing a difference signal between output signals from the first and second phase comparators; and a low-pass filter coupled through a switch means to the first differential amplifier for passing a low frequency component of the difference signal as the threshold level error; and wherein the second control means comprises: a second differential amplifier for producing a difference signal between the reproduced digital signal and a reference DC level; and the low-pass filter coupled through the switch means to the second differential amplifier for passing a low frequency component of the difference signal produced by the second differential amplifier; and wherein an output signal from the low-pass filter is used as the threshold level.

Claim 13

A digital information reproducing apparatus comprising: a waveform shaping means for comparing a level of an input signal with a threshold level so as to thereby obtain a reproduced digital signal; a clock extracting means for extracting a read clock from the reproduced digital signal; a threshold level control means for controlling the threshold level, comprising a first control means for detecting a threshold level error from the reproduced digital signal and the read clock and for controlling the threshold level so as to cancel the threshold level error, and a second control means for controlling the threshold level so that a DC component of the reproduced digital signal becomes equal to a predetermined value; and a selector means for producing a mode selection signal in response to a predetermined pattern of a repetitive header area inputted prior to an information-carrying area of the input signal, and for terminating the mode selection signal after recognizing the predetermined pattern from the reproduced digital signal; and a switch means for normally selecting the first control means and being responsive to the mode selection signal for selecting the second control means during a duration of the mode selection signal; wherein the first control means comprises: a first phase comparator for comparing the phase of a leading edge of the reproduced digital signal with the phase of the read clock; a second phase comparator for comparing the phase of a trailing edge of the reproduced digital signal with the phase of the read clock; a first differential amplifier for producing a difference signal between output signals from the first and second phase comparators; and a low-pass filter coupled through a switch means to the first differential amplifier for passing a low frequency component of the difference signal as the threshold level error; and wherein the second control means comprises: a second differential amplifier for producing a difference signal between the reproduced digital signal and a reference DC level; and the low-pass filter coupled through the switch means to the second differential amplifier for passing a low frequency component of the difference signal produced by the second differential amplifier; and wherein an output signal from the low-pass filter is used as the threshold level.

Claim 14

A digital information reproducing apparatus comprising: a waveform shaping means for comparing a level of an input signal with a threshold level so as to thereby obtain a reproduced digital signal; a clock extracting means for extracting a read clock from the reproduced digital signal; and a threshold level control means for controlling the threshold level, comprising a first control means for detecting a threshold level error from the reproduced digital signal and the read clock and for controlling the threshold level so as to cancel the threshold level error, and a second control means for controlling the threshold level so that a DC component of the reproduced digital signal becomes equal to a predetermined value; wherein said first control means comprises: a means for synchronizing the reproduced digital signal with the read clock to obtain a synchronized digital signal; a first low-pass filter for passing a low frequency component of the reproduced digital signal; a second low-pass filter for passing a low frequency component of the synchronized digital signal; and a first differential amplifier for producing a difference signal, as the threshold level error, between the low-frequency components from said first and second low-pass filters, where said second control means comprises: said first low-pass filter, a second differential amplifier for producing a difference signal between the low-frequency component from said first low-pass filter and a reference DC level; and an integrator for integrating the difference signal from said second differential amplifier; and wherein the difference signal from said first differential amplifier and an output signal from said integrator are added by an adder to obtain the threshold level.

Claim 15

A digital information reproducing apparatus comprising: a waveform shaping means for comparing a level of an input signal with a threshold level so as to thereby obtain a reproduced digital signal; a clock extracting means for extracting a read clock from the reproduced digital signal; and a threshold level control means for controlling the threshold level, comprising a first control means for detecting a threshold level error from the reproduced digital signal and the read clock and for controlling the threshold level so as to cancel the threshold level error, and a second control means for controlling the threshold level so that a DC component of the reproduced digital signal becomes equal to a predetermined value; wherein said first control means comprises: a means for synchronizing the reproduced digital signal with the read clock to obtain a synchronized digital signal; a first low-pass filter for passing a low frequency component of the reproduced digital signal; a second low-pass filter for passing a low frequency component of the synchronized digital signal; and a first differential amplifier for producing a difference signal, as the threshold level error, between the low-frequency components from said first and second low-pass filters, where said second control means comprises: said first low-pass filter, a second differential amplifier for producing a difference signal between the low-frequency component from said first low-pass filter and a reference DC level; and an integrator for integrating the difference signal from said second differential amplifier; and wherein the difference signal from said first differential amplifier and an output signal from said integrator are added by an adder to obtain the threshold level.

Claim 16

An apparatus as claimed in claim 11, wherein the input signal is a DC free signal.

Claim 17

An apparatus as claimed in claim 11, wherein an open-loop gain of the second control means is higher than that of the first control means but is smaller than 1 at a cross-over frequency where the open-loop gain of the first control means is equal to 1.