JP2926743B2 - Magnetic recording / reproducing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing apparatus capable of setting a high band mode and a normal mode.

[Summary of the Invention]

According to the present invention, in a magnetic recording / reproducing apparatus in which a high-band mode and a normal mode can be set, the operation of a mode discriminating circuit for discriminating a mode based on the presence or absence of a predetermined frequency component in a reproduced signal is determined. , It is possible to prevent erroneous determination of the mode, especially during variable speed reproduction.

[Conventional technology]

In a rotary head VTR that converts the luminance signal to FM and converts the chroma signal to a low-frequency band for recording, the horizontal resolution is increased by raising the carrier frequency when FM-modulating the luminance signal and widening its frequency shift. And the image quality can be improved. Therefore, in such a VTR,
It is recommended to improve the image quality by setting a recording mode in which the carrier frequency at the time of FM modulation of the luminance signal is set higher than the conventionally used frequency.

As described above, in a VTR in which a high band mode can be set in addition to the normal mode, according to the recording mode,
It is necessary to switch between various setting states. It is very troublesome to set such a mode manually. Therefore, there has been proposed a mode discriminating circuit that detects a signal level of a predetermined frequency component in a reproduced signal and discriminates a mode.

FIG. 7 shows an example of a conventional mode discriminating circuit. In FIG. 7, a reproduced FM modulated luminance signal is supplied to an input terminal 101. This signal is transmitted via the limiter 102 to, for example, a frequency 4.2
The signal is supplied to a bandpass filter 104 having a frequency of 9.8 MHz, for example, while being supplied to a bandpass filter 103 of MHz.

The output of the bandpass filter 103 is supplied to the detection circuit 105. The detection circuit 105 detects the level of the 4.2 MHz frequency component in the reproduced FM modulated luminance signal. Detection circuit 105
Is supplied to the determination circuit 107 via the integration circuit 106.

The output of the bandpass filter 104 is supplied to the detection circuit 108. The detection circuit 108 detects the level of a component having a frequency of 9.8 MHz in the reproduced FM modulated luminance signal. Detection circuit 108
Is supplied to the determination circuit 107 via the integration circuit 109.

In the discriminating circuit 107, the bell of the component of the frequency of 4.2 MHz and the frequency
From the level of the 9.8 MHz component, it is determined whether the mode is the high band mode or the normal mode. This judgment output is output terminal 11
Taken from 0.

This mode discrimination circuit detects the level of the component of the frequency 4.2 MHz corresponding to the carrier frequency when recording in the normal mode by the band-pass filter 103, the detection circuit 105, and the integration circuit 106, and when recording in the high band mode. Assuming that the lower sideband is at a frequency of 4.2 MHz, the mode is determined by detecting the level of a component at a frequency of 9.8 MHz where the upper sideband should be.

That is, when recording is performed in the normal mode, the eighth
As shown in the figure, the carrier CAR frequency becomes 4.2 MHz, and the sideband components USB and LSB spread up and down around the carrier frequency. Therefore, if a component having a frequency of 4.2 MHz can be detected, the normal mode can be determined, and if a component having a frequency of 4.2 MHz cannot be detected, the high band mode can be determined.

However, as shown in FIG. 9, when performing high-band recording, the lower side bud component LSB has a frequency of 4.2 MHz.
May be matched. If the 4.2 MHz frequency component can be detected, the normal mode is determined.If the 4.2 MHz frequency component cannot be detected, the high band mode is determined.In such a case, recording is performed in the high band mode. Despite the operation, it is erroneously determined that the mode is the normal mode.

Therefore, while detecting the component of the frequency of 4.2MHz,
The level of a signal component having a frequency of 9.8 MHz is detected. If the lower sideband component LSB of the recording signal in the high band mode has a frequency of 4.2 MHz, its upper sideband component US
This is because B is at the frequency of 9.8 MHz.

Therefore, the mode determination circuit 17 outputs a determination signal as follows.

That is, a component having a frequency of 4.2 MHz is detected, and a frequency of 9.
If the 8 MHz component is not detected, it is determined that the mode is the normal mode. If a component with a frequency of 4.2 MHz is not detected,
Alternatively, if a component having a frequency of 4.2 MHz is detected and a component having a frequency of 9.8 MHz is detected, it is determined that the mode is the high band mode.

[Problems to be solved by the invention]

With the above-described mode determination circuit, the mode of the reproduced signal can be reliably determined during normal reproduction.

However, the mode discrimination circuit described above may erroneously discriminate the mode when performing reproduction in which noise is generated, such as during variable speed reproduction or reverse track reproduction.

That is, for example, assume that a normal mode signal is reproduced at variable speed. When performing variable-speed reproduction, a noise component spreads in the reproduction signal. This noise component is detected via a band-pass filter 103 having a frequency of 4.2 MHz and also detected via a band-pass filter 104 having a frequency of 9.8 MHz. For this reason, a component of a frequency of 4.2 MHz and a component of a frequency of 9.8 MHz are detected in spite of the normal mode, and it is determined that the mode is the high band mode.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a magnetic recording / reproducing apparatus capable of avoiding erroneous mode determination due to noise during variable speed reproduction or the like.

[Means for solving the problem]

According to the present invention, in a magnetic recording / reproducing apparatus capable of setting first and second modes having different carrier frequencies when a luminance signal is FM-modulated, the mode is determined based on the presence or absence of a predetermined frequency component in the reproduced signal. This is a magnetic recording / reproducing apparatus having a mode discriminating circuit for controlling the operation of the mode discriminating circuit depending on the presence or absence of a reproduction signal.

[Action]

The portion where noise is generated is detected by the dropout detection circuit 44. In the portion where noise is generated, the mode determination operation is stopped and the previous determination state is maintained. For this reason, the mode is not erroneously determined even when performing reproduction in which noise is generated, such as during variable speed reproduction or reverse track reproduction.

〔Example〕

Embodiments of the present invention will be described in the following order.

a. Configuration of recording system b. Description of high-band mode and normal mode c. Description of tape cassette d. Configuration of playback system e. Description of mode discriminating circuit in one embodiment a. Configuration of recording system 1 shows an overall configuration of an embodiment of the present invention. In one embodiment of the present invention, in addition to the normal mode, a high-band mode in which a carrier frequency for FM modulation of a luminance signal is set can be set.

First, the configuration of the recording system will be described. At the time of recording,
The switch circuit 16 is switched to the a side.

In FIG. 1, an imaging output of a CCD imaging device 1 is supplied to a process circuit 3 via a preamplifier 2. In the process circuit 3, the luminance signal Y is obtained from the imaging output of the CCD imaging device 1.
And the color difference signals (RY) and (BY) are formed. The luminance signal Y from the process circuit 3 is supplied to the FM modulation circuit 5 via the pre-emphasis circuit 4. Process circuit 3
Are supplied to the chroma modulation circuit 6 from the color difference signals (RY) and (BY).

In the FM modulation circuit 5, the luminance signal Y is FM-modulated. The carrier frequency at this time is switched according to when the normal mode is set and when the high band mode is set. When set to normal mode, the carrier frequency is
The frequency is 4.2 MHz, for example, the frequency is 5.4 MHz at the white peak level. When the high-band mode is set, the carrier frequency is, for example, 5.7 MHz at the sync chip level, and is, for example, 7.7 MHz at the white peak level.

The output of the FM modulation circuit 5 is supplied to the half trap circuit 7. The half trap circuit 7 has a sideband component whose FM-modulated audio signal A _FM and low-frequency-converted chroma signal C _A
It is provided to prevent interference.
The characteristics of the half trap circuit 7 include the normal mode / high band mode from the controller 25 and the tape type.
The switching signal S ₂ of the MP / ME, is set according to the tape type and recording mode. The output of the half trap circuit 7 is supplied to the addition circuit 8.

In the chroma modulation circuit 6, a color difference signal from the process circuit 3 (R-Y) and from (B-Y), the low-band converting chrominance signal C _A
Is formed. The center frequency of the low-band converting chrominance signal C _A is, for example, a 743KHz. Downconverted chrominance signal C _A from chroma modulation circuit 6 is supplied to the adding circuit 8.

An audio signal from the microphone 11 is supplied to the pre-emphasis circuit 13 via the amplifier 12. The output of the pre-emphasis circuit 13 is supplied to the audio FM modulation circuit 14. The audio signal is FM
Modulated. The center frequency of the FM-modulated audio signal A _FM is, for example, 1.5 MHz. This audio FM modulation circuit
The output of 14 is supplied to the adding circuit 8.

In addition circuit 8, and an FM modulated luminance signal Y _FM and the low frequency converted chroma signal C _A and FM-modulated audio signal A _FM is frequency division multiplexed. The multiplexed signal is supplied to the a-side input terminal of the switch circuit 16 via the recording amplifier 15.

The switch circuit 16 is switched to the a side during recording. The output of the switch circuit 16 is supplied to a switch circuit 17 for switching the head. The switch circuit 17 has a terminal 19
Supplies a head switching signal RFSW. The switch circuit 17 is switched for each field by the head switching signal RFSW. The output of the switch circuit 17 is supplied to rotating heads 18A and 18B arranged on the rotating drum 20.

The rotating drum 20 is provided with rotating heads 18A and 18B and a flying erase head 21. An erasing current is supplied to the flying erase head 21 from a flying erase signal oscillation circuit 28. The frequency of the erase current, the normal mode / high band mode switching signals S ₁ from the controller 25,
Switching is performed according to the normal mode and the high band mode.

A tape 22 drawn from a tape cassette is wound around the rotating drum 20. The operation mode is set by operating the key switch 27. The capstan motor 23 is driven according to this operation mode.

b. Description of High Band Mode and Normal Mode As described above, in one embodiment of the present invention, the high band mode and the normal mode can be set.

FIG. 2A is a spectrum of a recording signal when recorded in a normal mode on an 8 mm VTR, and FIG. 2B is a spectrum of a recording signal when recorded in a high band mode on an 8 mm VTR. . In Figure 2, Y _FM is the spectrum of the FM modulated luminance signal, C _A low-pass converted chroma signal, A _FM modulated audio signal, P is a pilot signal for ATF tracking.

As shown in FIG. 2A, in the normal mode, the carrier frequency of the FM modulated luminance signal Y _FM has a sync tip level of 4.2 MHz and a white peak level of 5.
4 MHz. In the high band mode, FIG.
As shown in the figure, the sync tip level is 5.7 MHz and the white peak level is 7.7 MHz.

The center frequency of the low frequency converted chroma signal C _A is a 743KHz,
The center frequency of the FM-modulated audio signal A _FM is a 1.5 MHz.

c. Description of Tape Cassette Here, a tape cassette used in an embodiment of the present invention will be described.

FIG. 3 shows an example of a tape cassette used in one embodiment of the present invention. The tape types include a normal mode MP tape tape cassette (hereinafter abbreviated as a normal MP tape cassette), a high band MP tape tape cassette (hereinafter abbreviated as a high MP tape cassette), and a high mode MP tape tape cassette. There are three types of band ME tape tape cassettes (hereinafter abbreviated as high ME tape cassettes).

The MP tape (coating type metal tape) is obtained by applying ultrafine particles of an alloy in which nickel and cobalt are mixed with iron to a base material together with a binder. MP tape has excellent quality stability and mass productivity. The ME tape (evaporated tape) is obtained by evaporating an alloy containing nickel in cobalt in a vacuum and attaching the alloy to a base material. ME tapes have higher performance than coated metal tapes, but mass production is difficult.

These three types of tape cassettes (normal MP tape cassette, high MP tape cassette, high ME tape cassette) can be identified from the state of the detection hole 64 and the tape type detection hole 66.

That is, in FIG. 3, the positioning holes 63, the detection holes 64, the erroneous erasure prevention detection holes 65, the tape type detection holes 66, the positioning holes 67, the preliminary detection holes 68, the tape thickness detection holes 69, 70 are formed.

The tape type detection hole 66 is provided to identify whether the tape uses the ME tape or the MP tape.
If this tape cassette is a tape cassette using an ME tape, that is, a high ME tape cassette, the tape type detection hole 66 is opened. If this tape cassette is a tape cassette using an MP tape, that is, a normal MP tape cassette or a high MP tape cassette, the tape type detection hole 66 is closed.

The detection hole 64 is provided for distinguishing between a high MP tape cassette and a normal MP tape cassette. If this tape cassette is a high MP tape cassette, the detection hole
64 are open. This tape cassette is normal
In the case of an MP tape cassette, the detection hole 64 is closed. Note that the detection hole 64 is also closed when the tape cassette is a high ME tape cassette.

Therefore, as shown in FIG. 4, three types of tape cassettes can be detected from the state of the detection holes 64 and the tape type detection holes 66.

The states of the detection hole 64 and the tape type detection hole 66 are detected by the tape hole detection means 24 in FIG. 1, and the detection output is supplied to the controller 25.

In one embodiment of the present invention, a high-band automatic recording mode can be set. This mode setting is performed by the key switch 26.

If the high-band automatic recording mode is set, the recording mode is automatically set according to the detected tape type. That is, the tape type detection hole 66 is opened, and the detection hole
If 64 is closed, it is determined that the mounted tape cassette is a high ME tape cassette. In this case, recording is performed in the high band mode. If the tape type detection hole 66 is closed and the detection hole 64 is open, it is determined that the mounted tape cassette is a high MP tape cassette. In this case, recording is performed in the high band mode. If the tape type detection hole 66 is closed and the detection hole 64 is closed, it is determined that the mounted tape is a normal MP tape cassette. In this case, recording is performed in the normal mode.

When the high-band automatic recording mode is set to off, the normal mode is set regardless of the type of the tape cassette mounted. This makes it possible to set a recording state in which recording is performed in the normal mode using the high ME tape cassette and a state in which recording is performed in the normal mode using the high MP tape cassette.

From the controller 25, is output switching signals S ₁ normal mode / high band mode, the switching signals S ₁ of the normal mode / high band mode is switched the characteristics of the pre-emphasis circuit 4, FM modulation circuit 5. Further, the switching signal S ₂ in the normal mode / high band mode and the tape type MP / ME from the controller 25 is outputted, the switching signal S ₂ in the normal mode / high band mode and the tape type MP / ME, half trap circuit 7 Are switched.

d. Configuration of Reproduction System Next, the configuration of the reproduction system will be described.

The recording signals on the tape 22 are reproduced by the rotary heads 18A and 18B. The outputs of the rotary heads 18A and 18B are supplied to the switch circuit 16 via the switch circuit 17. During reproduction, the switch circuit 16 is switched to the b side. The output of the switch circuit 16 is supplied to the reproduction amplifier 31. The output of the reproduction amplifier 31 is supplied to a trap-peaking circuit 32 and also to a band-pass filter 33 and a band-pass filter.

A band-pass filter 33, the low-band converting chrominance signal C _A being reproduced signal is extracted. Downconverted chrominance signal C _A from the band pass filter 33 is supplied to the converter 35. In the converter 35, while being the time axis variation of the removal during the reproduction signal, the reproduced low range converted chroma signal C _A frequency
It is converted to a 3.58 MHz chroma signal C. The chroma signal C is extracted from the output terminal 38.

A band-pass filter 34, FM-modulated audio signal A _FM being reproduced signal is extracted. Bandpass filter 3
FM-modulated audio signal A _FM from 4 is supplied to an audio FM demodulation circuit 36. Audio FM demodulation circuit 36
The modulated audio signal A _FM is FM-modulated. The demodulated audio signal A is extracted from the output terminal 39 via the de-emphasis circuit 37.

The FM modulated luminance signal Y _FM in the reproduction signal is supplied to the trap peaking circuit 32. Trap peaking circuit
Numeral 32 removes unnecessary components and compensates for insufficient frequency components. Frequency characteristics of the trap peaking circuit 32 (peak frequency and Q) is by switching signal S ₄ of the normal mode / high band mode and the tape type MP / ME from the controller 25, the high-band mode / normal mode and tape type MP Can be switched according to / ME.

The output of the trap peaking circuit 32 is the RFAGC circuit 40,
The signal is supplied to the FM demodulation circuit 42 via the soft limiter 41.
At the same time, the output of the RFAGC circuit 40 is
And supplied to the dropout detection circuit 44. The characteristics of the soft limiter 41 and the FM demodulation circuit 42 are switched according to the high band mode and the normal mode.

The mode determination circuit 43 detects the level of a predetermined frequency component in the reproduced FM modulated luminance signal Y _FM and determines whether the signal reproduced from the tape 22 is a high band mode signal or a normal mode signal. is there. In this example, the mode discriminating circuit 43 detects a component having a frequency of 4.2 MHz and a component having a frequency of 9.8 MHz, whereby a mode discrimination between a high band mode and a normal mode is performed.

That is, the carrier frequency when the luminance signal is FM-modulated is different between the high band mode and the normal mode. Therefore, if the level of the frequency component concentrated on the recording signal in the high band mode or the frequency component concentrated on the recording signal in the normal mode is detected and it is determined whether or not the level of this frequency component is equal to or higher than a predetermined value, the high band mode is determined. It can be determined whether the mode is the normal mode.

However, when the mode discrimination is performed by detecting the level of the frequency component concentrated on the recording signal in the high band mode or the level of the frequency component concentrated on the recording signal in the normal mode, the mode is affected by the side band component. May be erroneously determined. For example, when recording in the normal mode, a component having a frequency of 4.2 MHz, which is a frequency component concentrated in a recording signal, is detected. If the component having the frequency of 4.2 MHz is detected, the normal mode, if the component having the frequency of 4.2 MHz is not detected. If it is determined that the mode is the high band mode, the signal of the high band mode is reproduced,
If the sideband component in this signal is 4.2 MHz, it is erroneously determined that the mode is the normal mode.

Therefore, in one embodiment of the present invention, the component of the frequency 4.2 MHz, which is the frequency component concentrated on the recording signal when recording in the normal mode, and the lower sideband becomes the frequency 4.2 MHz when recording in the high band mode. If so, the upper side band detects a frequency component of 9.8 MHz, which is a frequency that should be present, and performs mode discrimination. This prevents erroneous mode determination due to the influence of the sideband component.

However, such a mode discrimination circuit may erroneously discriminate the mode when noise is generated, such as during variable speed reproduction or reverse track reproduction.

In other words, if the recording signal is in the normal mode and noise is generated, such as during variable speed reproduction or reverse track reproduction, a frequency component having a frequency of 9.8 MHz is detected by the noise. Therefore, in such a case, the frequency
A frequency component of 4.2 MHz and a frequency component of 9.8 MHz are detected. When a frequency component of a frequency of 4.2 MHz and a frequency component of a frequency of 9.8 MHz are detected, it is erroneously determined that the recording signal is in the high band mode even though the recording signal is in the normal mode.

Therefore, in one embodiment of the present invention, a dropout detection circuit 44 is provided, and the state of the mode determination circuit 43 is controlled by the output of the dropout detection circuit 44. That is, when the dropout is detected by the dropout detection circuit 44, the state of the mode determination circuit 43 is held. Thereby, erroneous determination of the mode at the time of variable speed reproduction or reverse track reproduction can be avoided.

The output of the mode determination circuit 43 is supplied to the controller 25. The controller 25 determines the mode of the recording signal of the tape 22 from the output of the mode determination circuit 43. Based on this mode determination result, the switching signal S ₃ of the normal mode / high-band mode is formed. The switching signal S ₃ of the normal mode / high-band mode, soft limiter 41, FM demodulator 42, de-emphasis circuit 45
Are switched.

In the FM demodulation circuit 42, the reproduced FM modulated luminance signal Y _FM is FM demodulated. The reproduced luminance signal from the FM demodulation circuit 42 is supplied to the b-side input terminal of the switch circuit 46 via the de-emphasis circuit generator 45. A gray signal of a predetermined luminance level is supplied from a gray back generation circuit 47 to the a-side input terminal of the switch circuit 46. A synchronization signal is added to the gray signal output from the gray back generation circuit 47.

The output of the de-emphasis circuit 45 is supplied to a signal detection circuit 48 shown by a broken line. In the signal detection circuit 48,
The presence or absence of a reproduction signal is detected. The switching of the switch circuit 46 is controlled in accordance with the detection output of the signal detection circuit 48.

When the reproduction signal is detected by the signal detection circuit 48, the switch circuit 46 is switched to the b side, and the demodulated reproduction signal is output from the switch circuit 46. When the reproduction signal is not detected by the signal detection circuit 48, the switch circuit 46 is switched to the side a, and the reproduction signal is switched to a gray signal having a synchronization signal.

As described above, by replacing the reproduced signal with the gray signal having the synchronization signal, the synchronous deflection circuit of the monitor does not go into a free-run state, and it is possible to prevent the display character from flowing or the display character from being out of position. .

The signal detection circuit 48 includes a sync separation circuit 50, a level detection circuit
51, a comparator 52, and a time constant circuit 53.
The sync signal in the reproduced signal is detected by the sync separation circuit 50, and the sync signal level is detected by the level detection circuit 51. The output of the level detection circuit 51 is supplied to the comparator 52. Two large and small threshold levels V _thH and V _thL are set in the comparator 52.

In the comparator 52, the synchronization signal level detected by the level detection circuit 51 is set to a predetermined threshold level V _{thH or} V _thL.
Is detected. The output of the comparator 52 is supplied to the switch circuit 46 as a switch control signal via the time constant circuit 53.

If there is a reproduction signal, the synchronization signal in the reproduction signal can be separated by the sync separation circuit 50. Therefore, the level detection circuit
The level of the synchronizing signal in the reproduction signal output from 51 is within the two threshold levels V _thH and V _thL set in comparator 52.

If there is no playback signal, the synchronization signal in the playback signal cannot be separated by the sync separation circuit 50. Therefore, the level of the synchronizing signal in the reproduction signal output from the level detection circuit 51 _{does not fall} within the two threshold levels V _thH and V _thL set in the comparator 52.

When the output of the level detection circuit 51 is within the two threshold levels V _thH and V _thL set in the comparator 52 and it is determined that there is a reproduced signal, the switch circuit 46 is switched to the b side. If the output of the level detection circuit 51 is not within the two threshold levels V _thH and V _thL set in the comparator 52 and it is determined that there is no reproduced signal, the switch circuit 46 is switched to the a side. .

The time constant circuit 53 is a switch circuit at the time of mode transition.
This is to prevent the screen from being discontinued due to the switching of 46. That is, for example, when switching from normal reproduction to high-speed reproduction, a synchronization signal in the reproduction signal cannot be obtained at the time of the mode transition. for that reason,
If the output of the level detection circuit 52 is supplied as it is to the comparator 53, a gray screen is momentarily displayed at the time of mode transition, and then a reproduced screen is displayed, and the continuity of the screen is interrupted.

The time constant circuit 53 is supplied with the variable speed reproduction identification signal JOG from the controller 25. The time constant circuit 53 operates according to the variable speed reproduction identification signal JOG, and the output of the comparator 52 is delayed. Thereby, the detection sensitivity of the signal detection circuit 48 is reduced at the time of mode transition. Thus, by providing the time constant circuit 53, it is possible to prevent the continuity of the reproduced signal from being interrupted at the time of mode transition.

The output of the switch circuit 46 is output via an adder circuit 54 to an output terminal.
Retrieved from 55. The display signal from the character generator 56 is supplied to the addition circuit 54. The character generator 56 generates display signals according to the setting mode and various operation modes. This display signal is superimposed on Y in the reproduced luminance signal by the addition circuit 54. This reproduced signal Y
Is taken out from the output terminal 55.

e. Description of Mode Discrimination Circuit in One Embodiment The mode discrimination circuit 43 described above will be described in detail. FIG. 5 shows the configuration of the mode determination circuit 43 described above.
In FIG. 5, a reproduced FM modulated luminance signal is supplied to an input terminal 71. The signal from the input terminal 71 is supplied to a band-pass filter 73 having a frequency of, for example, 4.2 MHz via a limiter 72, and is also supplied to a band-pass filter 74 having a frequency of, for example, 9.8 MHz. The limiter 72 reproduces the sideband component. Further, a signal from the input terminal 71 is supplied to the dropout detection circuit 44.

The output of the band pass filter 73 is supplied to the detection circuit 75. The frequency in the reproduced FM modulated luminance signal is detected by the detection circuit 75.
The level of the 4.2 MHz component is detected. The output of the detection circuit 75 is supplied to the determination circuit 77 via the integration circuit 76.

The output of the band pass filter 74 is supplied to the detection circuit 78. The frequency in the reproduced FM modulated luminance signal is detected by the detection circuit 78.
The level of the 9.8 MHz component is detected. The output of the detection circuit 78 is supplied to the determination circuit 77 via the integration circuit 79.

In the discriminating circuit 77, the bell of the frequency component of 4.2 MHz and the frequency 9.
From the level of the 8 MHz component, it is determined whether the high band mode is the normal mode. This judgment output is taken out from the output terminal 80.

That is, a component having a frequency of 4.2 MHz is detected, and a frequency of 9.
If the 8 MHz component is not detected, it is determined that the mode is the normal mode. If a component with a frequency of 4.2 MHz is not detected,
Alternatively, if a component having a frequency of 4.2 MHz is detected and a component having a frequency of 9.8 MHz is detected, it is determined that the mode is the high band mode.

At the time of variable speed reproduction or reverse track reproduction, a noise bar is generated. The period of this noise is the dropout detection circuit 44
Is detected by

When noise is detected by the dropout detection circuit 44,
The control signal is supplied to the limiter 72, the operation of the limiter 72 is stopped, and the previous determination result is held. That is, the limiter 72 includes diodes 91 and 92 as shown in FIG.
And a capacitor 93. A transistor 94 is provided in parallel with the diodes 91 and 92. The dropout detection signal from the dropout detection circuit 44 is supplied from the terminal 95 to the base of the transistor 94. When the dropout detection signal from the dropout detection circuit 44 is supplied from the terminal 95, the transistor 94 turns on,
The operation of the limiter 72 is stopped. While the operation of the limiter 72 is stopped, the signals held in the integration circuits 76 and 79 are supplied to the determination circuit 77. Therefore, during this time, the operation mode is maintained at the previous state.

As described above, in one embodiment of the present invention, while the noise is detected from the output of the dropout detection circuit 44, the operation of the limiter 72 is stopped, and the operation mode is maintained in the previous determination state. Therefore, it is possible to prevent the mode from being erroneously determined due to noise.

〔The invention's effect〕

According to the present invention, in the portion where noise occurs, the mode determination operation is stopped, and the previous determination state is maintained. For this reason, the mode is not erroneously determined even when performing reproduction in which noise occurs, such as during variable speed reproduction or reverse track reproduction.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, FIG. 2 is a spectrum diagram used to explain a normal mode and a high band mode, FIG. 3 is a bottom view of an example of a tape cassette in one embodiment of the present invention, FIG. 4 is a schematic diagram for explaining an example of a tape cassette according to an embodiment of the present invention, FIG. 5 is a block diagram of an example of a mode discriminating circuit according to an embodiment of the present invention, and FIG. FIG. 7 is a block diagram showing an example of a conventional mode discriminating circuit, and FIGS. 8 and 9 are spectrum diagrams used for explaining an example of a conventional mode discriminating circuit. FIG. Description of main reference numerals in the drawings 43: mode discriminating circuit, 44: dropout detecting circuit, 73, 74: band pass filter, 77: discriminating circuit.

Claims (1)

(57) [Claims] 1. A magnetic recording / reproducing apparatus in which first and second modes having different carrier frequencies for FM modulation of a luminance signal can be set, a reproduction FM modulation signal is supplied to an input terminal, and the input terminal is And a mode discriminating circuit for discriminating a mode based on the presence or absence of a predetermined frequency component in the reproduced signal, which is supplied to a bandpass filter via a limiter including a diode and a capacitor for reproducing a sideband component. The output of the dropout detection circuit for detecting the dropout of the reproduced FM modulation signal is supplied to a switching element provided in parallel with the diode of the limiter, and when the dropout is detected, the operation of the limiter is stopped, A magnetic recording / reproducing apparatus wherein the operation of the discriminating circuit is controlled by the dropout detecting circuit.