JPH0266775A - Digital data reproducing circuit - Google Patents

Abstract

PURPOSE:To suppress the fluctuation of an error rate by reproducing a carrier signal from a reading phase modulating PSK signal and executing the level adjustment for a reproducing carrier and a PSK signal in accordance with the recording frequency characteristic of a recording medium. CONSTITUTION:A reading phase modulating PSK signal obtained from a recording medium is inputted to a carrier reproducing part 43 and carrier signals C1' and C2' are reproduced. The reproducing carriers C1' and C2', when a magnetic tape is an oxide tape, has a level larger than the time of the metal tape and supplied to a PSK demodulating part 42. The PSK signal is supplied through an equalizer 40 to the demodulating part 42, and in phase detecting parts 68 and 69, the level adjustment for the signal is executed in accordance with the recording frequency characteristic of a recording medium. Thus, the fluctiation of the error rate in reproducing digital data is suppressed and faithful reproducing digital data are obtained.

Description

[Detailed description of the invention] The present invention will be explained in the following order.

Industrial application field Overview of the invention Conventional technology Problems to be solved by the invention Means for solving the problems Embodiment G-1 VTR to which the embodiment is applied (Figures 2 to 4) 2 Recording system (Fig. 2) 3. Reproduction system (Fig. 2) 4. Main parts of the embodiment (Fig. 1) 5. Modification H Effect of the invention A. Industrial application field The present invention relates to a digital data reproducing circuit that demodulates a read phase modulated signal obtained through a signal reading means from a recording medium on which a modulated phase modulated signal is recorded, and obtains reproduced digital data.

B. Summary of the Invention The present invention provides read phase modulation that is obtained through signal reading means such as a magnetic head from a recording medium such as a magnetic tape on which a phase modulation signal obtained by phase modulating a predetermined carrier wave signal with digital data is recorded. In a digital data reproducing circuit that extracts a signal, reproduces a general transmission signal based on the extracted read phase modulation signal, demodulates the read phase modulated signal using the reproduced carrier signal, and obtains reproduced digital data. By adjusting the level of the reproduced carrier wave signal or the read phase modulation signal used for demodulation according to the recording frequency characteristics of the recording medium, when the reproduced digital data is digitally processed, the recording frequency characteristics of the recording medium are adjusted. This suppresses fluctuations in the error rate due to differences in the numbers, and enables faithful reproduction of digital data.

C. Prior Art A video tape recorder (VTR) is used to record video signals such as color video signals and audio signals on magnetic tape, and to reproduce each signal from the magnetic tape on which the video signals and audio signals are recorded. ), video signals are recorded and played back on magnetic tape as low frequency converted color signals and frequency modulated luminance signals, and audio signals are digitized in the recording system and recorded on magnetic tape in order to improve the quality of reproduced audio. In recording and reproducing systems, it has been proposed to reproduce an audio signal digitized from a magnetic tape and perform digital/analog conversion to obtain a reproduced audio signal. In such a case, when the audio signal is digitized and recorded on a magnetic tape, the Fr voice signal is converted into digital data based on pulse code modulation (PCM), that is, audio PCM digital data, and the audio signal is converted into digital data based on pulse code modulation (PCM), that is, audio PCM digital data. PC
Four-phase phase modulation (1-PS) is applied to a carrier signal (carrier) having a predetermined frequency using M digital data.
K) modulation according to the system is performed to form an audio 1-PSK signal. At that time, the audio 4PSK signal is, for example, A in the frequency spectrum shown in FIG.
As shown by P, it is arranged in a band between the frequency band C of the low frequency conversion color signal and the frequency band Y of the frequency modulated luminance signal, and its carrier frequency is set to 2 MHz. Then, the audio 4-PSK signal is recorded on the magnetic tape with a common recording track with the video signal, for example, by a rotating magnetic head separate from the rotating magnetic head used for recording the video signal, and is then recorded on the magnetic tape. It is assumed that each of the formed recording tracks has a video signal recorded on its surface layer and an audio 4-PSK signal recorded on its deeper layer.

When a magnetic tape on which a video signal and an audio 4-PSK signal are recorded on a common recording track is used for signal reproduction, the recorded video signal and audio 4-PSK signal are
The K signal is read by a separately provided rotating magnetic head for video signals and a rotating magnetic head for audio signals. The read video signal from the rotary magnetic head for video signals is supplied to a video signal reproduction processing system and undergoes necessary processing, and the read audio and IPsK signals from the rotary magnetic head for audio signals are supplied to the video signal reproduction processing system. is supplied to the audio signal reproduction processing system.

In the audio signal reproduction processing system, a carrier is reproduced based on the read audio 4-PSK signal to form a reproduced carrier, and the read audio 4-PSK signal is demodulated using the reproduced carrier to reproduce the reproduced signal. audio PC
M digital data is obtained, and the obtained reproduced audio PCM digital data is subjected to processing such as error correction, and then subjected to digital/analog conversion to obtain a reproduced audio signal.

D. Problem to be Solved by the Invention As mentioned above, the video signal and the audio 1PsK signal are each
A magnetic recording medium that is recorded on a common recording track by a rotating magnetic head, and the recorded video signal and audio 4-PSK signal are read by a rotating magnetic head for video signals and a rotating magnetic head for audio signals, respectively. Tapes are broadly divided into oxide tapes, which have a structure in which a base member is provided with an iron oxide magnetic layer, and metal tapes, which have a structure in which a metal magnetic layer is provided in a base member.
Oxide tapes and metal tapes have different recording frequency characteristics. For example, in Figure 4, where the horizontal axis shows the frequency f and the vertical axis shows the level L, the curve MT As a result, the recording level on the metal tape is higher than the recording level on the oxide tape over the entire recording frequency, as shown by the curve ◯ in the case of the oxide tape. Therefore, when recording on magnetic tape, the recording signal level supplied to the rotating magnetic head is controlled to be constant, depending on whether oxide tape or metal tape is used. , resulting in significant differences in the recorded signal levels on the magnetic tape.

In this way, the recorded signal levels are different between oxide tape and metal tape, so when the audio 4-PSK signal is read from the oxide tape and when the audio 1-PSK signal is read from the metal tape in the playback system. In this case, the obtained read audio 4-PSK signals have a level difference, and as a result, they are
When the carrier having a certain level obtained from the carrier forming section that reproduces the carrier based on the read audio 4-PSK signal is used and demodulated to obtain the reproduced audio PCM digital data, the oxide tape The error rate in the reproduced audio PcM digital data will be different depending on whether the metal tape is used for reproduction or the metal tape, and there is a possibility that faithful audio signal reproduction will not be possible.

In view of the above, the present invention provides a method for recording a phase modulated signal (PSK signal) obtained by phase modulating a predetermined carrier with digital data such as audio PCM digital data from a recording medium such as a magnetic tape. PSK
A read PSK signal obtained by reading the signal is supplied, and a carrier is regenerated based on the supplied read PSK signal to obtain a reproduced carrier, and the supplied read PSK
When obtaining reproduced digital data by demodulating the K signal using a reproduced carrier, even when the read PSK signal is obtained from any one of a plurality of recording media having different recording frequency characteristics, It is an object of the present invention to provide a digital data reproducing circuit in which fluctuations in error rays 1 to 1 in reproduced digital data due to differences in recording frequency characteristics of respective recording media are suppressed.

E. Means for Solving the Problems In order to achieve the above-mentioned object, the digital data reproducing circuit according to the present invention reproduces a signal from a recording medium on which a PSK signal obtained by phase-modulating a predetermined carrier signal with digital data is recorded. a signal extraction unit that extracts a read PSK signal read and obtained by the signal reading unit; a carrier forming unit that reproduces a carrier based on the read PSK signal obtained from the signal extraction unit to obtain a reproduced carrier; a demodulating unit that demodulates using the reproducing gear obtained from the forming unit to obtain reproduced digital data, and a PSK
a level control section that operates according to the physical characteristics of a recording medium on which the signal is recorded; Read PS supplied to demodulator
It is configured to perform level adjustment for the K signal.

F-action In the digital data reproducing circuit according to the present invention, when the read PSK signal obtained from the recording medium is demodulated in the demodulator using the reproduced carrier reproduced based on the read PSK signal, the read PSK signal is The level of the reproduced carrier used for signal demodulation or the read PSK signal supplied to the demodulator is adjusted according to the recording frequency characteristics of the recording medium on which the PSK signal is recorded, so that, for example, the read PSK Even if the recording frequency characteristics of the recording medium from which the signal is obtained are different, in the demodulation section, a read PSK signal of a constant level is demodulated using a reproduced carrier of a constant level.

Therefore, fluctuations in the error rate in reproduced digital data due to differences in recording frequency characteristics of each recording medium are suppressed, and faithful reproduced digital data can be obtained.

G Embodiment G-1 VTR to which the embodiment is applied (FIGS. 2 to 4) FIG. 2 shows the configuration of a VTR to which an example of the digital data reproducing circuit according to the present invention is applied.

This VTR converts the color video signal into a low frequency conversion color signal and frequency modulation luminance signal, and converts the audio signal into an audio PCM.
A recording system that records digital data on a magnetic tape in the form of an audio 4-PSK signal, and a magnetic tape on which a low frequency conversion color signal 1 frequency modulation luminance signal and an audio 1-PSK signal are recorded. , a reproduction system that operates to reproduce color video signals and audio signals, and low frequency conversion color signals recorded on magnetic tape.

The frequency bands of the frequency modulated luminance signal and the audio 4-PSK signal are set as shown by C1Y and AP in FIG. 3. As the magnetic tape, an oxide tape or a metal tape, whose recording frequency characteristics are shown in FIG. 4, is used.

In such a VTR, a pair of rotating magnetic healds Ha and Hb for video signals are arranged with a mutual angular interval of 180 degrees, and a pair of rotating magnetic healds Ha and Hb are arranged with a mutual angular interval of 90 degrees between them. A pair of rotating magnetic heads Hc for audio signals
A rotary cylinder SLD to which a rotary magnetic head Ha and a rotary magnetic head Ha are fixed is arranged as common to the recording system and the reproducing system.

Hb, Hc, and Hd have different azimuth angles, and rotate as the rotary cylinder SLD is rotated at a constant rotational speed by the head drive unit 1.

Then, while being guided by the guide pin GP, the magnetic tape TP is placed on the outer peripheral surface of the rotary cylinder SLD by approximately 18 mm.
The rotating magnetic head H is arranged to form a traveling path including a contact portion over a predetermined angular range defined as 0 degrees, and is in contact with the outer peripheral surface of the rotating cylinder SLD.
a, Hb, Hc and Hd. The magnetic tape TP is driven by a capstan 3 and a pinch roller 5 provided in relation to its running path, and the capstan 3 is rotationally driven by a capstan drive section 7 to generate magnetic The tape TP is run at a predetermined running speed. A tape guide portion formed by the outer circumferential surface of such a rotating cylinder SLD and the guide bin CP,
and capstan 3. A tape drive unit formed by the pinch roller 5 and the capstan drive unit 7 is also provided as a common unit for the recording system and the reproduction system.

In addition, the system and
A controller 50 is provided, and the system controller 50 receives a tape identification signal St indicating whether the magnetic tape TP is an oxide tape or a metal tape through a terminal 51 and a recording operation mode through a terminal 52. An operation mode designation signal Sm that designates one of the reproduction operation modes is supplied. The system controller 50 then takes a high level when the tape identification signal St indicates that the magnetic tape TP is an oxide tape, for example, and a low level when it indicates that the magnetic tape TP is a metal tape. It sends out a level control signal Qv that takes the level, and also sends out an operation mote designation signal Sm.
When specifying the recording operation mode, for example, it takes a high level, and when specifying the playback operation mode, it sends out a switch control signal Qs that takes, for example, a low level, and furthermore, the operation mode designation signal Sm takes the recording operation mode. , the switching control signal Qhr alternately takes a high level and a low level every half rotation of the rotary cylinder SLD, and the operation mode designation signal Sm specifies the regeneration operation mode. A switching control signal Qhp that alternates between a high level and a low level is sent out every half rotation of the SLD.

G-2 Recording System (Figure 2) In the recording system of the VTR shown in Figure 2, the video signal input terminal 10 is supplied with, for example, a color video signal Sn based on the normal NTSC system. . This color video signal Sn is supplied to a video signal recording processing system 11, where it is separated into a color signal component and a luminance signal component, and subjected to predetermined processing. The video signal recording processing system 11 outputs a low frequency converted color signal formed based on the color signal component of the color video signal Sn and a frequency modulated brightness signal formed based on the brightness signal component of the color video signal Sn. A combined recorded video signal R3n is obtained and supplied to the movable contact 12a of the switching section 12.

Further, an audio signal Sa is supplied to the audio signal input terminal 13, and this audio signal Sa is guided to the A/D converter 14 through the audio signal input terminal 13.

The A/D converter 14 converts the audio signal Sa into audio PCM digital data Da and sends the error correction code adder 15 to the audio PCM digital data Da.
The error correction code addition section 15 adds a predetermined error correction code to the audio PCM digital data Da from the A/D conversion section 14, and outputs the audio PCM digital data Da' to which the error correction code has been added. The signal is supplied to the audio data recording modulation system 16. The audio data recording modulation system 16 includes a pair of PSK modulators 17 to which the audio PCM digital data Da' from the error correction code adding section 15 is supplied, both having frequencies of 2 MHz and having a mutual phase difference of 90 degrees. and a carrier generating section 18 that supplies the gear rears C1 and C2.

In the PSK modulation modulator 17, phase modulation is performed on the pair of carriers C1 and C2 from the carrier generation section 18 according to the 1-PSK method using the audio PCM digital data Da. , the audio and IPsK signals Pa are obtained and supplied to the movable contact 19a of the switching section 19.

The switching units 12 and 19 are designed to be interlocked, and are activated by a switching control signal Ghr from the system controller 50 supplied through the control terminal 20, and the movable contact 12a of the switching unit 12
However, every half rotation of the rotating cylinder SLD, the selection contact 12b
and 12c alternately, and the switching unit 1
Nine movable contacts 19a are alternately connected to selection contacts 19b and 19c every half rotation of the rotary cylinder SLD. Thereby, the recorded video signal R3n from the video signal recording processing system 11 is alternately supplied to the recording amplification units 21 and 22 through the switching unit 12 every half rotation of the rotary cylinder SLD, and the PSK modulation modulator 17 Audio 4-PS
The K signal Pa is alternately supplied to the recording amplification sections 23 and 24 through the switching section 19 every half rotation of the rotary cylinder SLD.

Then, the recording video signal R3n that has passed through the recording amplifying section 21 or the recording amplifying section 22 is switched to the recording contact R by a switch control signal Qs that takes a high level from the system controller 50 and is supplied through the control terminal 25. Recording/playback selection switch 2 shall be connected to
6, the audio 4-PSK signal Pa is alternately supplied to the rotating magnetic heads Ha and Hb, and has also passed through the recording amplification section 23 or the recording amplification section 24.
The movable contact is alternately supplied to the rotating magnetic heads Hc and Hd through the recording/reproducing selection switch 26, which is connected to the recording contact R. Thereby,
For example, an audio 4-PSK signal Pa is recorded on the magnetic tape TP by a rotating magnetic head Hc to form a first recording track, and then a recorded video signal R3n is recorded as a first recording track by a rotating magnetic head Ha. The sound is recorded over the track, and then the audio 4-PS is recorded by the rotating magnetic head Hd.
The K signal Pa is recorded to form a second recording track adjacent to the first recording track, and then the recording video signal R3n is recorded overlappingly on the second recording track by the rotating magnetic head Hb. Ru. Thereafter, an operation in which the first recording track and the second recording track are alternately formed is performed.
This is repeated +li times to form a plurality of recording tracks on the magnetic tape TP, each of which has the audio 4-PSK signal Pa recorded in the deep layer and the recorded video signal R3n recorded in the surface layer.

G-3 Reproduction System (Figure 2) In the reproduction system of the VTR shown in Figure 2, a rotating cylinder SLD has rotating magnetic heads Ha and Hb for video signals and rotating magnetic heads Hc and Hc for audio signals. The recorded video signal R3n is sequentially read from each recording track by the rotating magnetic heads Ha and Hb from the magnetic tape TP, which is rotated with the magnetic tape Hd and on which the recorded video signal R3n and the audio 4PSK signal Pa are recorded as described above. At the same time, the audio 1-PSK signal Pa is sequentially read from each recording track by the rotating magnetic heads Hc and Hd, and the color video signal Sn and the audio signal Sa are reproduced based on them.

The recorded video signal R3n alternately read by the rotating magnetic heads Ha and Hb is changed from a movable contact to a reproducing contact P by a switch control signal Qs which takes a low level from the system controller 50 and is supplied through the control terminal 25. Recording/playback selection switch 2 to be connected
6 to the regenerative amplification sections 31 and 32, respectively,
Also, the audio 4-PSK signal Pa read alternately by the rotating magnetic heads Hc and Hd is transmitted to the switch control signal Q.
The signal is supplied to the reproduction amplification sections 33 and 34 through the recording/reproduction selection switch 26 whose movable contact is connected to the reproduction contact P by s.

Then, the recorded video signal R passes through the reproduction amplification sections 31 and 32.
3n are selection contacts 35b and 35 of the switching section 35;
Furthermore, the audio 4-PSK signal Pa that has passed through the regenerative amplification sections 33 and 34 is supplied to the selection contacts 36b and 36C of the switching section 36, respectively. The switching units 35 and 3G are interlocked, and ff1
The movable contact 35a of the switching unit 35 is activated in response to the switching control signal Qhp from the system controller 50 supplied through the IJ control terminal 37, and the movable contact 35a of the switching unit 35 is alternately connected to the selection contacts 35b and 35c every half rotation of the rotary cylinder SLD. , and also connected to the switching section 36
The movable contacts 36a are alternately connected to the selection contacts 36b and 36c every half rotation of the rotary cylinder SLD. As a result, the recorded video signal R that has passed through the reproduction amplification sections 31 and 32
3n is alternately taken out to the movable contact 35a of the switching section 35, and the audio 4-PSK signal Pa that has passed through the regenerative amplification sections 33 and 34 is alternately taken out to the movable contact 36a of the switching section 36.

The recorded video signal R3n obtained at the movable contact 35a of the switching section 35 is supplied to the video signal reproduction processing system 38,
In the video signal reproduction processing system 38, the signal is separated into a low frequency conversion color signal and a frequency modulated luminance signal and subjected to predetermined processing.

Then, from the video signal reproduction processing system 38, a color video signal Sn consisting of a color signal component reproduced based on the low-pass converted color signal and a luminance signal component reproduced based on the frequency modulated luminance signal is obtained, The signal is outputted to the video signal output terminal 39 as a reproduced color video signal.

Further, the audio 4-PSK signal Pa obtained at the movable contact 36a of the switching section 36 is transmitted through the equalizer 40 to
The signal is then directly supplied to the audio data reproduction and demodulation system 41.

The audio data reproduction demodulation system 41 includes a PSK demodulation section 42 to which the audio 4-PSK signal Pa from the equalizer 40 is supplied, and an audio 1-PSK signal Pa from the movable contact 36a of the switching section 36.
Carrier regeneration is performed based on the PSK signal Pa, and each carrier has a frequency of 2M) corresponding to carriers C1 and C2, respectively.
PSKS.
In the S side demodulation 2, the audio 4- from the equalizer 40
For the PsK signal Pa, the reproduced carriers CI' and C2'
is used, phase demodulation is performed according to the 4-PSK demodulation method, and from the PSKS side demodulation 2, the audio PC
M digital data Da'' is obtained.

At this time, the carrier reproducing section 43 is supplied with the level control signal Qv from the system controller 50, and the carrier reproducing section 43 determines whether the magnetic tape TP is an oxide tape or not according to the level control signal Qv. In this case, level adjustment is performed so that the levels of the reproduced carriers CI and C2' are higher than in the case where the magnetic tape TP is a metal tape.

The audio PCM digital data Da" obtained from the PSKS side demodulation 2 is supplied to the error correction section 44, where it is subjected to error correction. Audio P
Obtained as CM digital data. Then, the error-corrected audio PCM digital data Da is
The audio PCM digital data D is supplied to the /A converter 45 and subjected to error correction in the D/A converter 45.
a is converted into an audio signal Sa, which is output to the audio signal output terminal 46 as a reproduced audio signal.

In the VTR playback system shown in FIG. 2,
Reproduction amplification sections 31 to 34. Switching sections 35 and 36.
The portion including the equalizer 40 and the audio data reproducing demodulation system 41 consisting of the PSKS side demodulator 2 and the carrier reproducing section 43 is constituted by an example of the digital data reproducing circuit according to the present invention.

Main Parts of Embodiment G-4 (FIG. 1) As described above, it is applied to the reproduction system of the VTR shown in FIG. Switching sections 35 and 36. An audio data reproduction demodulation system 41 consisting of an equalizer 40, a PSKS side demodulation 2, and a carrier reproduction section 43
The main part of an example of the digital data reproducing circuit according to the present invention, which is configured to include a part including the following, is as shown in FIG. 1, for example.

In the main part shown in FIG.
The audio 4-PSK signal Pa from the movable contact 36a is supplied to the 4-multiplying section 61 forming the carrier reproducing section 43,
A multiplied signal 4Pa having a fundamental frequency of 8 MHz is obtained from the quadruple multiplier 61 and is supplied to one input terminal of the phase comparator 62. The phase comparator 62, together with a low pass filter (LPF) 63 connected to its output terminal and a voltage controlled oscillator (VCO) 64 whose oscillation range center frequency is 8 M° to which the output of the LPF 63 is supplied, is a phase comparator. A locked loop (PLL) is configured, and the oscillation output Co of the VCO 64 is supplied to the other input terminal of the phase comparator 62. In the phase comparator 62, the multiplied signal 4Pa and VC
The phase of the oscillation output Co of the O64 is compared, and the comparison output is supplied to the VCO 64 as an oscillation frequency control voltage through the LPF 63. As a result, the oscillation output C of VCO64
o is a signal with a frequency of 8 MHz and a phase fluctuation that follows the phase fluctuation of the multiplied signal 4Pa.

Oscillation output C with a frequency of 8 MHz from VCO64
o is supplied to the 1/4 step-down section 65 and its frequency is reduced to 1/4, and a signal (C1'') with a frequency of 2 MHz is obtained from the 1/4 step-down section 65. That is, the switching section 3
A carrier having a frequency of 2 MHz is reproduced based on the audio 4PSK signal Pa from the movable contact 36a of the level adjustment unit 6.
6.

The level 811 unit 66 includes the system controller 50
The level control signal Qv is supplied from the level adjusting section 6.
6 is the level of the reproduction carrier C1' and the level of the magnetic tape T.
When P is an oxide tape and the level control signal Qv takes a high level, the adjustment is made larger than when the magnetic tape TP is a metal tape and the level control signal Qv takes a low level. The reproduced carrier C1'' whose level has been adjusted in the level adjustment section 66 is further phase-shifted by π/2 in the phase shift section 67, and the reproduced carrier C1'
Regenerated carrier C2' having a phase difference of π/2 with respect to
It is said that In this way, the carrier regeneration unit 4
When the magnetic tape TP is an oxide tape, the reproduced carriers C1' and C2' obtained from 3 have a higher level than when the magnetic tape TP is a metal tape. 42.

The PSK demodulation unit 42 receives the audio 4-PSK signal Pa from the movable contact 36a of the switching unit 36 and outputs it to the equalizer 4.
0 are provided, and these phase detectors 68 and 69 receive reproduced carriers C1' and 02'' having a mutual phase difference of 90 degrees from the carrier reproducing unit 43. Then, in the phase detection section 68, the phase of the audio 4-PSK signal Pa is detected by the reproduced carrier C1', and the detected output E1
is derived through the LPF 70. The detection output E1 from the LPF 70 is supplied to the comparison input terminal of the comparator 71 and also to the DC level detection section 72. DEL is obtained and supplied to the reference input terminal of comparator 71. In the comparator 71, the detection output E1 is compared in level with the voltage DEL, and the comparison output signal E2 obtained from the comparator 71 is supplied to the data terminal (D) of a D-type flip-flop (D-FF) 73. , PLL74. From PLL 74, the comparison output signal E
A clock signal CB2 synchronized with I)-FF is obtained.
It is supplied to the clock terminal (C) of 73. As a result, D
-The comparison output signal E2 is output from the output terminal (Q) of FF73.
A digital signal sequence E3 formed by waveform shaping is obtained and supplied to the synthesizing section 75.

Further, in the phase detection section 69, the audio 4-PSK signal Pa is phase detected by the reproduced carrier C2', and the detected output F1 is derived through the LPF 76. The detection output F1 from the LPF 76 is supplied to a comparison input terminal of a comparator 77 and also to a DC level detection section 78. A voltage DPI is obtained from the DC level detection section 78, which is equal to the average level of the detection output F1, and is supplied to the reference input terminal of the comparator 77. The comparator 77 compares the level of the detection output F1 with the voltage DFI, and the comparison output signal F2 obtained from the comparator 77 is supplied to the data terminal (D) of the D-FF 79 and also to the PLL 80. A clock signal CF2 synchronized with the comparison output signal F2 is obtained from the PLL 80 and is supplied to the clock terminal (C) of the D-F79.

As a result, a digital signal string F3 formed by waveform shaping the comparison output signal F2 is obtained from the output terminal (Q) of the I)-FF 79 and is supplied to the synthesis section 75.

Then, the digital signal string E3 from the output terminal (Q) of the D-FF 73 and the digital signal string F3 from the output terminal (Q) of the D-FF 79 are supplied to a combining section 7 where they are combined.
5, audio PCM digital data Da' containing an error correction code is reproduced.

In such a case, the reproduced carriers Cl' and C2 from the carrier regenerator 43 are supplied to the phase detectors 68 and 69, respectively.
”, if the magnetic tape TP is an oxide tape,
That is, when the level of the audio 4-PSK signal Pa supplied to each of the phase detection sections 68 and 69 is lower than that in the case where the magnetic tape TP is a metal tape, the magnetic tape Since the level of the detection outputs E1 and Fl obtained from the phase detection sections 68 and 69, respectively, is higher than that when the magnetic tape TP is a metal tape, the levels of the detection outputs E1 and Fl obtained from the phase detection sections 68 and 69, respectively, are higher than when the magnetic tape TP is an oxide tape. The case where the magnetic tape TP is a metal tape is equivalent to the case where the magnetic tape TP is a metal tape. As a result, the audio PCM digital data Da” obtained from the synthesis unit 75
In this case, fluctuations in the error rate due to the difference between the recording frequency characteristics when the magnetic tape TP is an oxide tape and the recording frequency characteristics when the magnetic tape TP is a metal tape are suppressed.

G-5 Modified Example In the above example, the level control signal Qv obtained from the system controller 50 is supplied to the level adjustment section 66 constituting the carrier reproduction section 43, and the level adjustment section 6
6, the respective levels of the reproduction carriers CI and C2' are adjusted to be higher when the magnetic tape TP is an oxide tape than when the magnetic tape TP is a metal tape. However, unlike that, the level control signal Qv obtained from the system controller 50 is sent to the switching unit 3 instead of the level adjusting unit 66, as shown by the dashed line in FIG.
The audio 4-PSK signal Pa from the movable contact 36a of No. 6 is supplied to the equalizer 40, whereby the level of the audio 4-PSK signal Pa supplied to the phase detection units 68 and 69 is adjusted to the magnetic tape. T.P.
If is an oxide tape, then equalizer 4
When the level of the audio 4-PSK signal Pa supplied to 0 is assumed to have a lower level than when the magnetic tape TP is a metal tape, the level of the audio 4-PSK signal Pa supplied to the It may also be made larger.

Further, in the above example, the audio 1-PSK signal obtained by reading from the magnetic tape is demodulated to reproduce audio digital data, but the digital data reproducing circuit according to the present invention Without being limited to this example, other PSK signals obtained by reading from a magnetic tape, for example, 2PSK signals, may be demodulated to reproduce digital data.

Furthermore, the tape identification signal St supplied to the system controller 50 is obtained based on a manual operation performed depending on whether the magnetic tape used for signal reproduction is an oxide tape or a metal tape. Alternatively, the magnetic tape used for signal reproduction may be detected as an oxide tape or a metal tape, and the information may be obtained according to the result.

H. Effects of the Invention As is clear from the above explanation, according to the digital data reproducing circuit according to the present invention, a PSK signal obtained by phase modulating a predetermined carrier with digital data such as audio PCM digital data is recorded. A read PSK signal obtained by reading a recorded PSK signal from a recording medium such as a magnetic tape is supplied, and a carrier is reproduced based on the supplied read PSK signal to obtain a reproduced carrier, and the supplied read PSK signal is supplied. When obtaining reproduced digital data by demodulating a PSK signal using a reproduced carrier, even when the read PSK signal is obtained from any one of a plurality of recording media having different recording frequency characteristics, Fluctuations in error rate in reproduced digital data due to differences in recording frequency characteristics of each recording medium can be effectively suppressed, and as a result, faithful digital data can be reproduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a main part of an example of a digital data reproducing circuit according to the present invention, and FIG. 2 is a block diagram showing an example of a digital data reproducing circuit according to the present invention together with a VTR to which it is applied. FIG. 3 is a characteristic diagram showing the recording signal frequency spectrum in a VTR, and FIG. 4 is a characteristic diagram showing the recording frequency characteristic of a magnetic tape. In the figure, 31, 32, 33 and 34 are reproduction amplification units, 35 and 36 are switching units, 40 is an equalizer, 41 is an audio data reproduction demodulation system, 42 is a PSK demodulation unit, 43 is a carrier reproduction unit, and 44 is an error correction unit. 45 is a D/A converter, Ha and Hb are rotating magnetic heads for video signals, Hc and Hd are rotating magnetic heads for audio signals, and TP is a magnetic tape.

Claims (1)

[Claims] From a recording medium on which a phase modulated signal obtained by phase modulating a predetermined carrier wave signal with digital data is recorded,
a signal extraction unit that extracts a read phase modulation signal read and obtained by the signal reading unit; a carrier signal forming unit that reproduces a carrier signal based on the read phase modulation signal obtained from the signal extraction unit to obtain a reproduced carrier signal; , a demodulation unit that demodulates the read phase modulation signal using the reproduced carrier signal obtained from the carrier wave signal forming unit to obtain reproduced digital data; A digital data reproducing circuit comprising: a level control section that adjusts the level of the reproduced carrier wave signal used for demodulation or the read phase modulation signal supplied to the demodulating section;