JPH04221404A - Apparatus for reproducing information signal - Google Patents

Abstract

PURPOSE:To provide a magnetic reproducing apparatus by which an image signal having no waveform distortion and a stable and excellent SN ratio can be obtained. CONSTITUTION:In a reproducing apparatus which reproduces an information signal which is modulated and recorded magnetically, a resonance correction circuit 6 is provided as the post stage of a reproducing amplifier 3. Further, if the information signal is recorded by frequency modulation, an FM carrier component extracted by a square sine wave filter 13, etc., in an equalizer circuit 7 which equalizes side band waves is subjected to a limiter process and an FM side band wave component extracted by a square cosine filter 14 is added to it. With this constitution, a reproducing apparatus by which the CN ratio of a reproducing modulation signal is improved and a reproduced information signal having no distortion and a high SN ratio is obtained can be realized. Moreover, if frequency modulation is employed, an inversion phenomenon caused by the level fluctuation and deterioration of the frequency characteristics of the reproduced FM signal can be avoided and a reproducing apparatus by which a stable and high quality reproduced information signal can be obtained can be realized.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is applicable to FM modulation or PC
The present invention relates to a reproducing device that reproduces an information signal that has been modulated and recorded using M modulation or the like.

0002

2. Description of the Related Art In rotary head type magnetic recording and reproducing devices such as VTRs that record and reproduce video signals, a method is generally used for recording and reproducing video signals by FM modulating them. FM modulation converts the video level to the frequency of the modulation signal, so in order to reproduce a good video signal, the FM transmission system for recording and playback must convert the FM within the band occupied by the modulation signal.
It is necessary to faithfully transmit the amplitude and phase of the modulated signal without distortion. However, the FM modulated signal reproduced by a magnetic reproducing apparatus that reproduces a video signal magnetically recorded using FM modulation becomes a distorted signal due to amplitude changes in magnetic recording and reproduction and amplitude and phase distortion in the reproduction system. In other words,
The transmission characteristics in the reproducing circuit of a rotating head type magnetic reproducing device such as a VTR are based on the primary (rotor) of the rotary transformer.
It exhibits complex resonance characteristics due to the inductance of the magnetic head connected to the side and the input capacitance of the regenerative amplifier connected to the secondary (stator) side of the rotary transformer, and due to this resonance characteristic, amplitude distortion and phase distortion occur at the resonant frequency. arise. In conventional magnetic reproducing devices, in order to prevent the demodulated video signal from being distorted by amplitude distortion and phase distortion due to this resonance characteristic, a method described in "Introduction to Home VTR" co-authored by Katsuya Yokoyama et al. (Corona Publishing, October 1988), p. As described in 158-159, a variable capacitor and a variable resistor are connected to the input of the regenerative amplifier on the secondary side of the rotary transformer, and by adjusting these, the resonance characteristics are corrected (resonant frequency and resonance Q (adjusting the quality factor).

Next, the reproduced FM output from the regenerative amplifier
The signal is corrected in an equalizer circuit for amplitude changes caused by magnetic recording and reproduction, that is, emphasis on the lower sideband and suppression of the upper sideband. This equalizer circuit is described in "VTR Technology" edited by Japan Broadcasting Corporation (Japan Broadcasting Publishing Association, October 20, 1981), p. 47-50, a cosine equalization circuit whose phase characteristic is linear and whose amplitude characteristic cancels out amplitude changes during recording and reproduction is generally known. However, this cosine equalization circuit emphasizes the upper sideband having a small CN ratio, which causes deterioration of the SN ratio of the demodulated video signal. As an equalizer circuit that prevents this deterioration of the SN ratio, "NHK Technical Research" Vol. 38 No. 2 (Japan Broadcasting Corporation,
1986) p. There is a sine equalization method described in 36-39.

0004

SUMMARY OF THE INVENTION The magnetic reproducing apparatus using the above-mentioned prior art has the following problems.

Conventionally, correction of resonance characteristics is done by damping the Q of resonance by adjusting a variable resistor connected to the input of a regenerative amplifier, and this is done by adjusting the frequency characteristics of the signal input to the regenerative amplifier. The goal is to reduce the ripple at the resonant frequency. FIG. 12 shows how this frequency characteristic is corrected. In FIG. 12, 200a is a state in which the resonance characteristics are not corrected, and 200b is a state in which the resonance characteristics are corrected. Furthermore, a dotted line 200c is input noise (amplifier noise) possessed by the regenerative amplifier. As shown in Figure 12, in the conventional resonance correction method, the ripple at the resonant frequency of the frequency characteristics of the signal input to the regenerative amplifier is only reduced, and the input noise of the regenerative amplifier does not change. Therefore, near the resonant frequency, correction (damping) of the resonant characteristics causes a problem in that the CN ratio deteriorates due to a reduction in the signal level. In addition, playback FM, such as a magnetic playback device that plays back high-definition video signals, is also used.
In a device that reproduces high-quality video signals using both upper and lower band waves of a signal, due to the problem of CN ratio deterioration mentioned above, the resonant frequency must be set to a frequency higher than the occupied band of the FM modulation signal (for example, twice the frequency of the FM carrier wave). Therefore, it was necessary to reduce the inductance of the magnetic head, that is, reduce the number of windings. Generally, the output of a magnetic head is proportional to the number of its windings, so if the number of windings decreases, sufficient reproduction output cannot be obtained from the magnetic head.C
There was a problem in that the N ratio deteriorated and a sufficient S/N ratio could not be obtained even in the demodulated video signal. Furthermore, when the regenerative amplifier is provided on the rotary cylinder, there is a problem that the number of parts increases in the narrow space of the rotary cylinder, making mounting difficult and adjustment difficult.

Next, in the equalizer circuit, when using the above-mentioned sine equalization method, noise in not only the lower side band but also the upper side band of the reproduced FM signal is suppressed to improve the S/N ratio of the demodulated video signal. However, since the signal components in the upper sideband are also suppressed, if the level of the reproduced FM signal decreases or the frequency characteristics deteriorate due to dropouts, etc.
There has been a problem in that the difference in level between the upper side band wave and the lower side band wave becomes large, making it easy for an inversion phenomenon to occur. In conventional magnetic reproducing devices, this reversal phenomenon has been prevented by reducing the amount of resonance correction (damping) described above to emphasize the upper sideband. However, when inversion is prevented in this way, sufficient correction (damping) of the resonance characteristics is not performed in the resonance correction circuit, and amplitude and phase distortion remains in the reproduced FM signal at the resonance frequency. Waveform distortion occurs in the demodulated video signal,
Moreover, there was a problem that the SN ratio also deteriorated.

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic reproducing apparatus which eliminates the drawbacks of the prior art described above and obtains a stable video signal with a good signal-to-noise ratio without waveform distortion.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present invention has a first feature in that a resonance correction circuit is provided at a subsequent stage of a regenerative amplifier, and also includes a resonance correction circuit that forms a resonance circuit with a magnetic head. The regenerative amplifier is connected to the primary (
The second feature is that it is placed on the rotor side. The third feature of the present invention is that the reproduced FM signal inputted to the equalizer circuit is separated by two types of filters having amplitude characteristics approximating squared sine characteristics and squared cosine characteristics, and the separated signals are added at a predetermined addition ratio. After that, the added signal is passed through a limiter and added again to the signal separated by the squared cosine filter at a predetermined addition ratio, and the added signal is outputted via a band-limiting filter. .

A fourth feature of the present invention is that the equalizer circuit adds the time-delayed signals of the output of the band-limiting filter and the output of the squared sine filter at a predetermined addition ratio, and the added signal is applied to the limiter and the band-limiter. Repeating output through the filter n times (n is an integer greater than or equal to 1),
The reason is that the output is used as the output of the equalizer circuit.

0010

[Operation] According to the present invention, since the resonance characteristics generated at the input stage of the regenerative amplifier are corrected at the subsequent stage of the regenerative amplifier, there is no deterioration of the CN ratio at the resonant frequency due to input damping, and the SN ratio of the demodulated video signal is also corrected. A good video signal can be obtained. Furthermore, according to the present invention, since the regenerative amplifier is placed on the primary (rotor) side of the rotary transformer, the resonant circuit formed by the magnetic head and this regenerative amplifier is connected to the secondary (stator) side via the rotary transformer. Since the model is theoretically much simpler than the side configuration, resonance correction can be achieved with a simple circuit configuration and with high accuracy, resulting in high fidelity with low amplitude distortion and phase distortion. transmission characteristics can be obtained. Further, since there is no deterioration of the CN ratio at the resonant frequency, the resonant frequency, which was conventionally set outside the FM occupied band, can be set within the band of the FM modulation signal (for example, within the upper side band). In other words, the number of windings of the magnetic head can be increased accordingly, sufficient reproduction output can be obtained, and the CN ratio can be improved relative to amplifier noise.
Further improvement in the SN ratio of the demodulated video signal can be realized. Further, even if a regenerative amplifier is provided within the rotary cylinder, the number of parts within the rotary cylinder can be reduced, and secondary effects such as the ability to downsize the cylinder can also be obtained.

Next, since the equalizer circuit of the present invention uses a limiter, it is possible to reproduce the upper sideband of the FM modulation signal, and the upper sideband is emphasized in the equalizer circuit output compared to the conventional sine equalization method. has been done. Therefore, inversion of the demodulated video signal can be prevented,
Furthermore, desired equalization characteristics can be obtained. In addition, because the equalization characteristics change according to the level of the reproduced FM signal due to the amplitude limiting action of the limiter, the reversal phenomenon is prevented even when the level of the reproduced FM signal decreases and the frequency characteristics deteriorate due to dropouts etc. be able to. Furthermore, since the inversion phenomenon is prevented as described above, the resonance characteristics can be sufficiently corrected synergistically in the resonance correction circuit of the present invention, and this synergistic effect produces a good video signal without distortion even in the demodulated output. can be obtained.

0012

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing an embodiment in which the present invention is applied to a reproducing circuit of a VTR. In FIG. 1, 1 is a magnetic tape, 2 is a magnetic head, 3 is a regenerative amplifier, 4 is a rotary transformer, 5 is a buffer amplifier, 6 is a resonance correction circuit, 7 is an equalizer circuit, 8 is a limiter circuit, and 9 is an FM
In the demodulation circuit, 10 is an output terminal for a demodulated video signal. Further, 30 indicates a rotating cylinder. The FM modulation signal recorded on the magnetic tape 1 is reproduced by a magnetic head 2 installed inside a rotating cylinder 30 and amplified by a reproducing amplifier 3 also installed inside the rotating cylinder 30. Regenerative amplifier 3
The output signal is subjected to amplitude changes due to magnetic recording and reproduction, and amplitude and phase distortion due to resonance characteristics. Here, the resonance characteristics will be explained using FIG. 2. FIG. 2 shows an equivalent circuit of the magnetic head 2 and the reproducing amplifier 3, where 101 is a voltage source indicating the reproducing voltage of the magnetic head, 102 is an inductor having an inductance LH of the magnetic head, and 103 has a resistance RH of the magnetic head. A resistor, 104 is a capacitor representing the input capacitance Cin of the regenerative amplifier, 105 is a resistor representing the input resistance value Rin of the regenerative amplifier, 106 is a voltage source representing the input equivalent noise NA of the regenerative amplifier, 107 is a gain G and a frequency characteristic. The flat amplifier 108 is the output terminal of the regenerative amplifier. In FIG. 2, the voltage E1 obtained at the output terminal 108 is the voltage E0, ω
is the angular frequency, and S is the complex angular frequency (S=jω), which is expressed by the following equation.

[0014]

[Math 1]

Here, since RH is generally several Ω and Rin is several tens of kΩ, Equation 1 can be simplified as follows.

[0016]

[Math 2]

The output E1 expressed by Equation 2 exhibits resonance characteristics, and amplitude and phase distortion occur at the resonance frequency. On the other hand, noise 10
6 is amplified by the amplifier 107, so the output terminal 10
8 becomes G/NA. Next, in FIG. 1, the FM signal output from the regenerative amplifier 3 is supplied to a low input impedance buffer amplifier 5 via a rotary transformer 4, and then to a resonance correction circuit 6. The resonance correction circuit 6 corrects the resonance characteristics. One embodiment of this resonance correction circuit 6 is shown in FIG. In FIG. 3, 110
is an input terminal, 111 is an output terminal, 11, 12a, 12b
are circuit blocks, respectively, 112, 114, 11
8a, 118b, 119a, and 119b are resistors whose resistance values are R2, R1, R3, R3, R4, and R4, respectively;
13 is an inductor whose inductance is L1, 115
, 117a, 117b have capacitances C1, C2,
Capacitors C2, 116a, 116b, 116c
is a buffer amplifier. A signal input to the input terminal 110 is supplied to the circuit block 11. The transfer function H0(S) of this circuit block 11 is given by the following equation,

[0018]

[Math 3]

[0019] Here, L1=LH, C1=Cin, R1
=RH, R1+R2=2√(L1/C1), the output voltage E2 of this circuit block 11 is given by the following equation.

[0020]

[Math 4]

In Equation 4, the first term on the right side is a signal component and the second term is a noise component, and it can be seen that the resonance characteristics are corrected in this circuit block 11. The signals whose resonance characteristics have been corrected in this way are then input to the circuit blocks 12a and 12b. This circuit block 12a
, 12b, respectively, the transfer functions H1(S) and H2(S)
is given by the formula shown below.

[0022]

[Math 5]

[0023] Here, C2・R3=√(L1・C1)
If you set it like this, R3>R3・R4/(R3+R4)
Therefore, the signal transmission band can be expanded in the circuit blocks 12a and 12b, and the voltage E3 output from the resonance correction circuit 6 is equal to the voltage E0 reproduced by the magnetic head 2 from equations 2 and 5. Using this, we get the following equation.

[0024]

[Math 6]

As can be seen from Equation 6, the noise component has a suppressed characteristic at the output of the resonance correction circuit 6 with a characteristic opposite to the resonance characteristic. This is shown in FIG. In Figure 4, A, B
are the frequency characteristics of the signal before correction, that is, the signal component of E1 and the noise component, A' is the frequency characteristic of the signal after only the resonance characteristics have been corrected, that is, the signal component of E2, and C, D is the frequency characteristic of the signal component and noise component of the output signal of the resonance correction circuit 6, that is, E3. Figure 4
From this, it can be seen that in the resonance correction circuit 6, the resonance characteristics of the signal component are corrected, the band is expanded, and the noise component is efficiently suppressed. As described above, according to the present invention, without deteriorating the CN ratio at the resonant frequency,
It is possible to realize transmission characteristics with flat amplitude without phase distortion. Furthermore, in order to suppress noise, the band of sideband waves that can be reproduced in FIG. 4 has conventionally been a band up to near the resonant frequency f0, but it can be widened to a higher frequency f1. In other words, if the FM modulation frequency is limited, the resonant frequency f0 can be set within the band, more specifically within the upper sideband, which means that the winding of the magnetic head 2 This means that by increasing the number of wires, the inductance component may be increased accordingly. Since the output of the magnetic head 2 is generally proportional to the number of windings thereof, by using the present invention, a higher output can be obtained from the head, and the CN ratio can be further improved. In addition, the regenerative amplifier 3 is connected to the rotary transformer 4.
When installed on the primary (rotor) side, that is, inside the rotating cylinder 30, as in this embodiment, the resonance correction circuit 6
By providing the rotary cylinder 30 outside the rotary cylinder 30, the number of parts inside the rotary cylinder 30 can be reduced. Moreover, this suppresses the imbalance of the rotary cylinder 30 and improves productivity. Furthermore, according to the present invention, since the regenerative amplifier 3 is placed on the primary (rotor) side of the rotary transformer 4, the resonant circuit formed by the magnetic head 2 and the regenerative amplifier 3 is connected via the rotary transformer 4. Because this model is theoretically simpler than placing it on the secondary (stator) side, this resonance correction can be achieved with a simple circuit configuration and with high accuracy, and the high Faithful transmission characteristics can be obtained. In this embodiment, the inductance LH and resistance value RH of the magnetic head 2 are constant regardless of the frequency, but if this had the frequency characteristics as shown in FIG. Inductance L1 of inductor 113 and resistance 114 in circuit block 11 of resonance correction circuit 6
It is sufficient that the resistance value R1 has the same characteristics as in FIG.
More specifically, instead of the series components 113 and 114, a head component having the same characteristics as the magnetic head 2 may be used, and this case also falls within the gist of the present invention. Further, in the resonance correction circuit 6 shown in FIG. 3, the circuit block 12a and the circuit block 12b are not necessarily necessary, and if there is no need to expand the reproduction band, only one of the circuit blocks 12a and 12b is used. Alternatively, these may be omitted, and even in this case, the gist of the present invention is met.

Next, in FIG. 1, the reproduction F whose resonance characteristics have been corrected by the resonance correction circuit 6 and whose amplitude distortion and phase distortion have been removed is
The M signal is input to an equalizer circuit 7, where sideband waves changed due to recording and reproduction are equalized. This equalizer circuit 7
An example of this is shown in FIG. In FIG. 6, 19 is an input terminal of the equalizer circuit, 20 is an output terminal, 13 is a filter whose amplitude characteristic has a squared sine characteristic and whose phase characteristic is linear;
4 is a filter whose amplitude characteristic has a squared cosine characteristic and whose phase characteristic is linear; 15a and 15b each have a coefficient of K0 (K
0≧0), K1 (K1≧0), 16a, 1
6b is an adder, 17 is a limiter, and 18 is a band-limiting filter having a delay time τ and passing only the fundamental wave component including the first-order sideband of the FM modulation signal. The reproduced FM signal output from the resonance correction circuit 6 is input to an input terminal 19 and supplied to a squared sine filter 13 and a raised cosine filter 14 . Here, the squared sine filter 13 and the squared cosine filter 14 are constituted by an LC ladder circuit network, as is known from Japanese Patent Publication No. 60-53483, for example.
For example, as shown in FIG. 7, the center frequency is set to fc at or near the center of the carrier frequency of the FM modulation signal, and the squared sine filter 13 is a filter for extracting the carrier wave component, and the squared cosine filter 14 is for extracting sideband components. It becomes a filter. This operation is shown in the spectrum diagram of FIG. FIG. 8 shows a reproduced FM modulation signal of a signal whose frequency is fp, where the carrier wave (frequency fc) is J0, the first lower sideband (frequency fc-fp) is J-1, and the first upper sideband (frequency fc
+fp) is shown as J+1. FIG. 8A shows the spectrum of the signal input to the equalizer circuit 7, in which the level of the lower sideband is emphasized and the level of the upper sideband is suppressed by magnetic recording and reproduction. The input signal shown in FIG. 8(a) has the spectrum shown in FIG. 8(b) in which the carrier component is emphasized by the squared sine filter 13, and
As a result, the spectrum shown in FIG. 6(c) is obtained, with the sideband components emphasized. In FIG. 6, the signal output from the squared sine filter 13 is supplied to an adder 16a, and the signal outputted from the squared cosine filter 14 is amplitude-adjusted by K0 times by a coefficient unit 15a to the other side of the adder 16a. Supplied and added. The output of the adder 16a is supplied to a limiter 17, subjected to amplitude limitation, and output. The signal output from the limiter 17 is supplied to the adder 16b, and added to the output of the squared cosine filter 14 whose amplitude has been adjusted by a factor of K1 by the coefficient multiplier 15b. The result added by the adder 16b is supplied to the band-limiting filter 18 and subjected to band-limiting. This operation is shown in FIG. In FIG. 9, the carrier wave (
frequency fc) is J0, the first lower sideband wave (frequency fc-fp
) is J−1, and the first upper sideband wave (frequency fc+fp) is J+
It is shown as 1. The spectrum of the output of the adder 16a is as shown in FIG. 9(a), and the signal of this spectrum is input to the limiter 17 and subjected to amplitude limitation. Due to this amplitude limitation, the upper and lower sidebands become equal, and are output to the band-limiting filter 18 as a signal having the spectrum shown in FIG. 9(b). Generally, a signal whose amplitude has been limited by a limiter has a fundamental wave component and odd harmonic components, but for convenience, FIG. 9(b) shows the fundamental wave component and the third harmonic component, and The next harmonic is 3J0 (frequency 3fc),
The third harmonic of the first lower sideband is 3J-1 (frequency 3fc-
fp), and the third harmonic of the first upper sideband is indicated by 3J+1 (frequency 3fc+fp). The band-limiting filter 18 removes odd harmonic components of the FM modulation signal generated by the limiter 17, and is a low-pass filter whose cutoff frequency is, for example, 2fc. The spectrum shown in FIG. 9(c) is a state in which unnecessary harmonic components have been removed by the band-limiting filter 18, and this signal is output to the output terminal 20 in FIG. 6, and changes in sidebands are equalized. This becomes the output signal of the equalizer circuit 7. In FIG. 1, the signal output from the equalizer circuit 7 is transmitted to the limiter circuit 8.
is input, and the upper and lower sidebands are completely restored, subject to amplitude limitation again. The spectrum at this time is shown in FIG. 9(d). Note that harmonic components are not shown in FIG. 9(d). The FM modulation signal whose sidebands have been restored by the limiter circuit 8 is input to the FM demodulation circuit 9, where it is FM demodulated and becomes a reproduced video signal, which is output to the output terminal 10. In the above embodiment, the equalization characteristic of the equalizer circuit 7 is equivalent to the characteristic shown in FIG. 10 when viewed from the output of the limiter circuit 8. Furthermore, as shown in FIG. 9(c), in the FM modulated signal input to the limiter circuit 8, the upper sideband is enhanced and the lower sideband is enhanced, compared to the conventional sine equalization method that does not use the limiter 17. Because of the suppression, according to this embodiment, an inversion phenomenon due to imbalance between the upper and lower side band waves does not occur in the reproduced video signal, and the optimum equalization characteristic can always be set. In addition, playback F due to dropout etc.
When the level of the M signal decreases and the frequency characteristics deteriorate, the equalization characteristics change according to the amplitude level of the reproduced FM signal as shown in FIG. 10 due to the amplitude limiting action of the limiter 17 in the equalizer circuit 7. This is equivalent to the coefficient value K1 of the coefficient multiplier 15b apparently becoming smaller in accordance with the amplitude of the input signal, and since this has a characteristic that suppresses sidebands, the reproduced FM signal due to dropout etc. It is possible to expand the margin against the reversal phenomenon when a level drop and frequency characteristic deterioration occur. In the equalizer circuit of FIG. 6, a band-limiting filter 18 is used to remove unnecessary harmonic components, but this band-limiting filter 18 is not necessarily necessary. The transmission line and limiter circuit 8 can transmit harmonic components without distortion,
In the case where the equalizer circuit 7 compensates for the loss during sideband wave restoration that occurs in the limiter circuit 8 due to an imbalance between the relationship between the carrier wave and sideband waves in the fundamental wave component and the relationship between the carrier wave and sideband waves in the harmonic component. In this case, the band-limiting filter 18 may be omitted, and this case also follows the gist of the present invention.

As described above, by using the equalizer circuit 7 of the present invention in a VTR, optimum equalization characteristics can be obtained without causing an inversion phenomenon. Therefore, the resonance characteristics can be sufficiently corrected in the resonance correction circuit 6 as well, and thereby a reproduced video signal with no waveform distortion and a good S/N ratio can be obtained.

Next, another embodiment of the equalizer circuit 7 according to the present invention will be described with reference to FIG. The circuit in FIG. 11 has a new circuit block 22 added to the circuit in FIG.
The delay device 18b having the same delay time τ is a band-limiting filter having the same characteristics as the band-limiting filter 18. Description of the same circuit parts as in FIG. 6 will be omitted. The signal output from the band-limiting filter 18 is supplied to a limiter 17b, subjected to amplitude limitation, and then supplied to an adder 16c. The output of the squared cosine filter 14 is delayed by a time τ by a delay device 21 and is connected to the other end of the adder 16c by a limiter 17b.
It has the same phase as the output of , and is input after being amplitude-adjusted by K2 times by the coefficient multiplier 15c. Adder 16c adds these signals and outputs the result to band-limiting filter 18b. Like the band-limiting filter 18, the band-limiting filter 18b removes unnecessary harmonic components and outputs a signal to the terminal 20. In this embodiment, in the circuit block 22, the limiter 17b
Since the sidebands are regenerated by , it is possible to output a signal with enhanced upper sidebands compared to the embodiment of FIG. 6, resulting in an equalizer circuit that is even less likely to cause an inversion phenomenon. Further, in this embodiment, the circuit block that assists in enhancing the upper sideband is provided in one stage, the circuit block 22, but the present invention is not limited to this, and a plurality of circuit blocks similar to the circuit block 22 may be connected in cascade. Good too. Further, as described above, the band-limiting filters 18, 18b are not necessarily necessary, and may be omitted if the transmission band can be secured and the loss in the limiter can be compensated for. Moreover, when the band-limiting filter 18 is removed,
The delay device 21 for performing phase matching is also not required. Even in these cases, it is clear that effects equivalent to those of this embodiment can be obtained, and this is in accordance with the gist of the present invention.

In the embodiments shown in FIGS. 6 and 11, the center frequencies of the squared sine filter 13 and the raised cosine filter 14 are set to fc, which is the carrier frequency, but the present invention is not limited to this, and the above-mentioned The center frequency may be set to the optimal frequency for magnetic recording and reproduction, such as the upper sideband or an even higher frequency, specifically, nearly twice the carrier frequency, and it is clear that similar effects can be obtained in this case as well. It is.

Although the present invention has been described above with reference to embodiments in which it is applied to a reproducing circuit of a VTR, the present invention is not limited to magnetic recording and reproducing apparatuses, and is not limited to magnetic recording and reproducing apparatuses, for example, video disc players that record using FM modulation. The equalizer circuit of the present invention can also be applied to a device that optically reproduces information signals, and the equalizer circuit of the present invention can obtain similar effects.
It can be applied not only to M modulation recording but also to playback devices in which information signals are digitally recorded by PCM modulation. This also applies to the gist of the present invention.

[0031]

[Effects of the Invention] As described above, according to the present invention, the resonance characteristics caused by the magnetic head and the regenerative amplifier can be corrected without deteriorating the CN ratio, thereby making it possible to freely set the resonance frequency. The number of windings of the magnetic head can be optimized, and the CN ratio can be further improved. Further, since the equalizer circuit reproduces the sideband waves and prevents the inversion phenomenon, it is possible to optimize the equalization characteristics, and it is possible to obtain a reproduced video with no distortion and a good signal-to-noise ratio.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a diagram showing an equivalent circuit of a magnetic head and a regenerative amplifier.

FIG. 3 is a circuit diagram of a resonance correction circuit according to the present invention.

FIG. 4 is a characteristic diagram showing the operation of the resonance correction circuit.

FIG. 5 is a characteristic diagram showing impedance characteristics of a magnetic head.

FIG. 6 is a block diagram showing an embodiment of an equalizer circuit according to the present invention.

FIG. 7 is a characteristic diagram showing the characteristics of a squared sine filter and a raised cosine filter.

FIG. 8 is a spectrum diagram showing the operation of a squared sine filter and a raised cosine filter.

FIG. 9 is a spectrum diagram showing the operation of the equalizer circuit.

FIG. 10 is a characteristic diagram showing equalization characteristics of an equalizer circuit.

FIG. 11 is a block diagram showing another embodiment of the equalizer circuit according to the present invention.

FIG. 12 is a characteristic diagram showing the operation of a conventional resonance correction circuit.

[Explanation of symbols]

2... Magnetic head, 3... Regenerative amplifier, 4... Rotary transformer, 6... Resonance correction circuit, 7... Equalizer circuit, 8... Limiter circuit, 9... FM demodulation circuit, 30... Rotating cylinder, 112, 114, 118a
, 118b, 119a, 119b...Resistor, 113...
Inductor, 115, 117a, 117b... Capacitor, 116a, 116b, 116c... Buffer amplifier, 13... Squared sine filter, 14... Squared cosine filter, 15a, 15b, 15c... Coefficient unit, 16a, 1
6b, 16c...Adder, 17, 17b...Limiter,
18, 18b...Band limit filter.

Claims (8)

[Claims] 1. A magnetic recording and reproducing device for reproducing a modulated information signal recorded on a magnetic recording medium (1) by a magnetic head (2), in which a reproducing output from the magnetic head (2) is transmitted to a reproducing amplifier (3). ), the inductance (LH) and resistance (RH) of the magnetic head, and the resonant circuit formed by the input capacitance (C) of the regenerative amplifier. Resonance correction circuit (6) having a transfer function and the above-mentioned resonance correction circuit (6)
and a means for connecting the regenerative amplifier (3) to a subsequent stage of the regenerative amplifier (3), the modulated information signal regeneratively amplified and outputted from the regenerative amplifier (3) to the resonance correction circuit (6).
An information signal reproducing device characterized in that the information signal reproducing device is configured to demodulate after correcting the resonance characteristics of the resonance circuit. 2. The resonance correction circuit (6) comprises at least:
An inductor (113) having an inductance value (LH) that is approximately the same as the inductance of the magnetic head (2).
And the resistance value (RH) is almost the same as the resistance of the above magnetic head.
and a capacitor (115) having a capacitance value (C) that is approximately the same as the input capacitance of the regenerative amplifier.
, the transfer function is represented by a rational function, and the numerator term of the rational function is at least 1+S・C
2. The information signal reproducing apparatus according to claim 1, wherein the information signal reproducing apparatus is configured to have: -RH+S2·LH·C. 3. A magnetic recording and reproducing apparatus for reproducing an information signal modulated and recorded on a magnetic recording medium (1) by a magnetic head (2) installed in a rotating cylinder (30), wherein the magnetic head (2) ) for supplying the regenerative output from the rotary cylinder (30) to a regenerative amplifier (3) installed in the rotary cylinder (30); ), the inductance (LH) and resistance (RH) of the magnetic head, and the resonant characteristic of the resonant circuit formed by the input capacitance (C) of the regenerative amplifier. a resonance correction circuit (6) having a transfer function with opposite characteristics; and means for supplying the stator side output of the rotary transformer (4) to the resonance correction circuit (6);
, the modulated information signal regeneratively amplified and output from the regenerative amplifier (3) is supplied to the resonance correction circuit (6) via the rotary transformer (4), and the resonance correction circuit ( 6) An information signal reproducing device characterized in that the resonant characteristic of the resonant circuit is corrected before demodulation is performed. 4. A recording and reproducing apparatus that reproduces an information signal that has been FM modulated and recorded on a recording medium, wherein the reproduced signal reproduced from the recording medium has an amplitude characteristic that is approximated by a linear phase characteristic and a squared sine characteristic. a first filter (13
); means for supplying the reproduced signal to a second filter (14) having an amplitude characteristic approximated by a linear phase characteristic and a squared cosine characteristic; a first adder (16a) that adds the outputs of the second filter (14) at a predetermined addition ratio; and a limiter (17) that has an amplitude limiting effect on the output of the first adder.
and a second adder (16b) for adding the output of the limiter (17) and the output of the second filter (14) at a predetermined addition ratio, An information signal reproducing device characterized in that an adder (16b) obtains an output equalizing amplitude changes of sideband waves of the reproduced signal. 5. The squared sine characteristic, which is the amplitude characteristic of the first filter (13), is expressed as Sin2(2·π·f·T), where f is the frequency of the input signal and T is a constant having a unit of time. The squared cosine characteristic, which is the amplitude characteristic of the second filter (14), is given by Cos2(2・π・f・T), and the amplitude of the first filter (13) and the second filter ( 5. The information signal reproducing apparatus according to claim 4, wherein the center frequency f=1/(4·T) of the amplitude characteristic of step 14) is approximately equal to the frequency of the FM carrier wave of the reproduced signal. . 6. A recording and reproducing apparatus that reproduces an information signal that has been FM modulated and recorded on a recording medium, wherein the reproduced signal reproduced from the recording medium has an amplitude characteristic that is approximated by a linear phase characteristic and a squared sine characteristic. a first filter (13
); means for supplying the reproduced signal to a second filter (14) having an amplitude characteristic approximated by a linear phase characteristic and a squared cosine characteristic; a first adder (16a) that adds the outputs of the second filter (14) at a predetermined addition ratio; and a limiter (17) that has an amplitude limiting effect on the output of the first adder.
a second adder (16b) for adding the output of the limiter (17) and the output of the second filter (14) at a predetermined addition ratio;
a third filter (18) that performs band limitation on the output of b);
An information signal reproducing device, characterized in that the third filter (18) produces an output in which amplitude changes of sideband waves of the reproduced signal are equalized. 7. A recording and reproducing apparatus that reproduces an information signal that has been FM modulated and recorded on a recording medium, wherein the reproduced signal reproduced from the recording medium has an amplitude characteristic that is approximated by a linear phase characteristic and a squared sine characteristic. a first filter (13
); means for supplying the reproduced signal to a second filter (14) having an amplitude characteristic approximated by a linear phase characteristic and a squared cosine characteristic; A first adder (16a) that adds the outputs of the second filter (14) at a predetermined addition ratio, and a first limiter (16a) that has an amplitude limiting effect on the output of the first adder.
means for supplying the first limiter (17) to the first limiter (17);
a second adder (16b) that adds the output of the second filter (14) and the output of the second filter (14) at a predetermined addition ratio; and a third adder (16c) for adding the output of the second limiter (17b) and the output of the second filter (14) at a predetermined addition ratio.
An information signal reproducing device, characterized in that the third adder (16c) obtains an output equalizing amplitude changes of sidebands of the reproduced signal. 8. A magnetic recording and reproducing apparatus for reproducing an information signal that has been FM modulated and recorded on a magnetic recording medium (1) using a magnetic head (2), in which the output from the magnetic head (2) is transmitted to a reproducing amplifier (3). ), the inductance (LH) and resistance (RH) of the magnetic head, and the resonant circuit formed by the input capacitance (C) of the regenerative amplifier. Resonance correction circuit (6) having a transfer function and the above-mentioned resonance correction circuit (6)
a first filter (13) having an amplitude characteristic approximated by a linear phase characteristic and a squared sine characteristic for the reproduction signal from the resonance correction circuit (6); means for supplying the reproduced signal to a second filter (14) having an amplitude characteristic approximated by a linear phase characteristic and a squared cosine characteristic; a first adder (16a) for adding the outputs of the filters (14) at a predetermined addition ratio; means for supplying the output of the first adder to a limiter (17) having an amplitude limiting action; Limiter (17)
a second adder (16b) that adds the output of the second filter (14) and the output of the second filter (14) at a predetermined addition ratio; and an FM demodulator (9) that adds the output from the second adder (16b). 1. An information signal reproducing device comprising: means for supplying an information signal.