JPH01231579A - Reproduced signal processor - Google Patents

Abstract

PURPOSE:To obtain the reproduced information signal of high quality at reproduction regardless of the level of the information signal by using a nonlinear compression processing circuit which has the large dynamic value compared with that of a nonlinear amplifying process carried out to a recording medium. CONSTITUTION:The same characteristics are not secured between the dynamic value of a nonlinear compression processing circuit set at the reproduction side and that of a nonlinear amplifying process carried out at recording. That is, the former dynamic value is increased compared with the latter one. As a result, the dynamic value of a compression circuit of a nonlinear de-emphasizing circuit 30 is set larger than that of a compression circuit of a nonlinear emphasizing circuit 25. Thus it is possible to compensate the S/N deterioration which is caused by the difference of loss values of the side band spectra at the input of a signal of a low level. In such a way, the reproduced information signal of high quality is obtained at reproduction regardless of the level of the information signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a reproduced signal processing device that reproduces an information signal recorded on a recording medium and processes the reproduced signal.

[Prior Art] Conventionally, there has been an apparatus that records, for example, a video signal on a recording medium and reproduces the video signal from the recording medium on which the video signal is recorded. FIG. 2 is a diagram showing an example of the configuration of a conventional video signal recording and reproducing device.

A luminance signal is input to the input terminal 1, and the luminance signal is outputted by the luminance signal recording process circuit 2, as shown in FIG.
For example, FM modulation is performed so that the frequency of the sync tip portion is 7°7 MHz and the frequency of the white peak portion is 9.7 MIIz. The configuration of this luminance signal recording process circuit 2 is as follows.
The configuration is as shown in the figure. First, the input luminance signal is fixed to a predetermined level by the clamp circuit 24, which fixes the potential of the sync chip included in the luminance signal, and then by the non-linear emphasis circuit 25 and the linear emphasis circuit 26. After applying emphasis processing, F
The signal is FM modulated by the M modulation circuit 27 and input to the adder 10 as a luminance FM signal.

On the other hand, color difference signals R-Y and B-Y are input to the input terminal 3 as color information in a line-homogeneous form.

First, the color difference line sequentialization circuit converts the R-Y signal and the B-Y signal.
The signal is converted into a color difference line sequential signal, which is then manually inputted to the color difference signal recording process circuit 5, and this circuit records F.
M modulated. The configuration of this color difference signal recording process circuit 5 is almost the same as the luminance signal recording process circuit 2 shown in FIG. , and a non-linear emphasis circuit 25. The characteristics of the linear emphasis circuit 26 and the FM modulation circuit 27 are also adapted to the color difference signal.

The output of the color difference signal recording process circuit 5 is R in the figure.
The signal passes through a switch 6 connected to the side, and is input to a frequency conversion circuit 7 that performs frequency conversion based on a frequency conversion carrier signal input manually from an input terminal 8, and is modulated in a high frequency band to reduce overmodulation. The color difference line sequential signal is converted to a lower frequency band, and an LPF (low pass filter) 9 removes signals of extra frequency components, and then output as a low frequency converted color difference FM signal. Then, as shown in FIG. 3, the adder 10 multiplexes the luminance FM signal onto the lower frequency band side. The output of the adder 10 is amplified as a recording signal in the recording amplifier 11, then passes through the switch 12 connected to the R side in the figure, and is sent to the magnetic head 13.
is recorded on the magnetic recording medium 14 by.

On the other hand, during reproduction, the minute level reproduction signal reproduced by the magnetic head 13 passes through the switch 12 connected to the P side in the figure, is amplified to a sufficient level by the preamplifier 15, and is first amplified by the 1-IPF. Only the luminance FM signal is separated by a bypass filter 21 and input to a luminance signal reproduction process circuit 22 . The luminance signal reproduction processing circuit 22 then performs processing during reproduction as described later, and outputs the reproduced luminance signal from the output terminal 23.

The luminance signal regeneration process circuit 22 has a configuration as shown in FIG. In FIG. 5, the linear de-emphasis circuit 29 has a transfer function opposite to that of the linear emphasis circuit 26, and the non-linear de-emphasis circuit 30 has a transfer function opposite to that of the non-linear emphasis circuit 25.
The reproduced luminance signal demodulated by the FM demodulation circuit 28 is sent to the linear de-emphasis circuit 29. The non-linear de-emphasis circuit 30 restores the original luminance signal and outputs it.

On the other hand, the output of the preamplifier 15 is also supplied to the LPFI 6, and only the color difference FM signal is separated in the PF16, passes through the switch 6 connected to the P side in the figure, and is converted to the high frequency side by the frequency converter 7. The signal is frequency-converted into a frequency band, and after excess frequency component signals are removed by a BPF (band pass filter) 17, the signal is supplied to a color difference signal reproduction process circuit 18. The color difference A3 reproduction process circuit 1B performs reproduction processing on the signal output from the BPFI 7 as described later, and outputs the signal as a color difference line sequential signal. Then, the color difference line uniformization circuit 19 converts the supplied color difference line sequential signal into a table of contents, and outputs it from the color difference signal output terminal 20 as R-Y and B-Y signals. The configuration of the color difference signal reproduction process circuit 18 may be the same as that of the luminance signal reproduction process circuit 22 as shown in FIG. 5, or the configuration of the FM demodulation circuit 28. The characteristics of the linear de-emphasis circuit 29 and the non-linear emphasis circuit 30 are adapted to color difference signals.

Here, the nonlinear emphasis circuit 25 (fourth
(see figure) is shown in detail in FIG. 6. In this figure,
The signal input to the input terminal (luminance signal or color difference line sequential signal) is separated by II P F 31 into only the band in which non-linear characteristics are desired, and then the voltage V-
A compression circuit 32 having current characteristics performs non-linear processing, and a coefficient circuit 33 multiplies the coefficient by 1 to appropriately weight the signal, and an adder 34 adds the signal to the original signal.

Therefore, the transfer function G of the nonlinear emphasis circuit shown in FIG. 6 is expressed by the following equation (1).

G, = 1 +G, -Kl...(1)
However, Gf is a transfer function including the HPF 31 and the compression circuit 32, and l is a coefficient multiplied by the coefficient circuit 33.

FIG. 8 is a diagram showing an example of an actual circuit configuration of the nonlinear emphasis circuit shown in FIG. 6.

The portion surrounded by a broken line in this figure constitutes the HPF 31 and the compression circuit 32 (see FIG. 6). That is, the capacitor C1 and the resistor R1 constitute an IPF3], which is further amplified by the transistor q1, and a nonlinear processing output is obtained from the collector.

FIG. 9 is a diagram showing the vr characteristics of the compression circuit. °'Ra'' shown in this figure represents the equivalent resistance exhibited by the compression circuit when a small level signal is input (in other words, the equivalent resistance when almost no compression is performed). "Rh" represents the equivalent resistance exhibited by the compression circuit when a high-level signal is applied manually (in other words, the equivalent resistance when a limiter is applied).

Therefore, when these Ra and Rb are applied to the circuit shown in FIG. 8, they are expressed by the following equation.

Ra press R+/ (R5/2) -(
2) Rb: R6+ r −(3
) However, when R5, R3>>R, r represents the dynamic resistance of the diode.

If the biases V and -V2 shown in Fig. 8 are increased, the characteristics shown by ■ in Fig. 9 will be exhibited;
When V2 is made smaller, the characteristics shift to those shown by ■.

The transistor Q3 in FIG. 8 is an summing amplifier, and the weighting of the nonlinear characteristic is determined to be 1 by the resistors R8 and R7.

X1=R8/R7 (4) On the other hand, the nonlinear de-emphasis circuit 30 (see FIG. 5) has the configuration shown in FIG. 7, but the compression circuit 32'
Assuming that the characteristics of are exactly the same as those of the compression circuit 32 (see FIG. 6), the transfer function 62 of the nonlinear de-emphasis circuit 30 is expressed by the following equation.

Here, if the coefficient multiplied in the coefficient circuit 36 is set to 2 and the amplification factor A of the differential amplifier 35 is set so as to obtain Kl・A−Kl, then the characteristic of the linear emphasis circuit 25 shown in equation (1) is completely opposite to that of the linear emphasis circuit 25. This shows the characteristics of However, the amplification factor A of the differential amplifier 35 is selected so that the output signal level of the nonlinear de-emphasis circuit 30 is equal to the human input signal level of the nonlinear emphasis circuit 25.

In this way, in the conventional device, the nonlinear emphasis circuit 25 and the nonlinear de-emphasis circuit 3
The characteristics of each compression circuit within 0 were set to be equal.

[Problems to be Solved by the Invention] However, by setting the characteristics of the compression circuits in the emphasis circuit and de-emphasis circuit to be equal as in the past, the characteristics of the non-linear de-emphasis circuit can be made completely opposite to the characteristics of the linear emphasis circuit. In this case, a sufficient SN ratio could not be obtained. In other words, if the adjustment is made so that sufficient characteristics are obtained when a high-level signal is input (which is generally done), the frequency characteristics when a low-level signal or input is input will increase as the frequency range increases. However, the drawback was that a sufficient signal-to-noise ratio could not be obtained.

This drawback is particularly seen when FM modulation with a large modulation index is performed.

That is, the FM modulated signal rM(t) is generally expressed by the following equation (6).

÷2nπfj t+ (-1) 0・cos (2πf
c-2nπf,)・t])...(6) Here, fc Carrier frequency f□ Modulation frequency m (Modulation index (mr-Δf/f, Δf is the maximum frequency deviation of the carrier frequency) (6) J.(mf) in the formula is a Heracel function of the first kind, and is expressed by the following formula (7).

...(7) In formula (7), "(S) is a comma function, and when S is an integer, r (S) - (S-1)! ...
・(8) Therefore, equation (6) becomes the following equation (9).

(9) Figure 1O (8) and Figure 10 (B) show the brightness 1'M signal deviation in the video signal recording and reproducing apparatus described above]-
FIG. 12 is a diagram showing the results of calculation of the signal from equations (6) and (9) for a large level signal when human power is applied (068 human power) and a small level signal when human power is applied (-20 dB human power). In addition, 11PF21 (
(See Figure 2) h) The amount of loss of the lower wave when the 2 MHz spectrum is not passed is shown in the upper right of each graph.

As is clear from FIG. 10(A) and FIG. 1θ(B), the amount of loss is large when a high-level signal is input, and becomes larger as the modulation frequency becomes higher. This loss in the lower side wave spectrum causes a drop in the level after demodulation, so if the frequency characteristics after demodulation are matched when a high-level signal is input, the frequency characteristics will be the same as the frequency characteristics of a low-level signal when input by hand. If you want to do it, you'll end up paying twice.

In addition, the amount of loss in the upper side wave spectrum due to the deterioration of high-frequency characteristics caused by the electromagnetic conversion operation in the magnetic head is greater than when inputting large-level signals manually or when inputting small-level signals. This also causes deterioration of frequency characteristics after demodulation.

SUMMARY OF THE INVENTION In view of the above-mentioned points, an object of the present invention is to provide a reproduced signal processing device configured to obtain a high-quality reproduced information signal during reproduction regardless of the level of the information signal.

[Means for Solving the Problems] In order to achieve the above object, the reproduced signal processing circuit according to the present invention performs nonlinear compression processing when reproducing an information signal recorded by performing nonlinear amplification processing on a recording medium. This apparatus is equipped with a nonlinear compression processing circuit having a larger dynamic value than the dynamic value of the nonlinear amplification processing performed when recording on the recording medium.

[Function] With the above-described configuration, the present invention achieves a nonlinear compression processing circuit on the reproduction side that makes the dynamic value of the nonlinear compression processing circuit on the reproduction side have the same characteristics as the dynamic value of the nonlinear amplification processing performed during recording. By making the dynamic value of the pressure 191 processing circuit larger than the dynamic value of the nonlinear compression processing during recording, the frequency characteristics of the reproduced information (2) of the parent signal are improved.

[Example] Below, the present invention will be described in detail based on examples.

Here, the SN ratio of the restored signal is improved by making the dynamic value of the compression circuit in the nonlinear de-emphasis circuit larger than the dynamic value of the compression circuit in the nonlinear emphasis circuit applied during recording.

Number +121 is a diagram showing an embodiment of a nonlinear de-emphasis circuit to which the present invention is applied. In addition, the part surrounded by a broken line in this figure constitutes 11 P F 31 and a compression circuit 32' (see Fig. 7) Transfer function Gr'
).

Transistor 05 functions as a summing amplifier, and the transfer function G2' is expressed by the following equation.

8-11157 old 2...(lO) K2-(R19/R18)/(R12/R13) Also, in the tree circuit, by adjusting the time constants of resistors R+5 and 1112, the power level of the nonlinear emphasis circuit can be adjusted. Set the output level equal to that of the nonlinear de-emphasis circuit.

Now, in order to make the dynamic value of the characteristic of the compression circuit shown in FIG. 9 much higher than the dynamic value of the nonlinear emphasis circuit, one of the following conditions should be satisfied.

n6'< R6... (11) or n5'> R5... (12) or 1s'< Is - (13) Here, Is and Is' shown in equation (13) are in the opposite direction of the diode. This is the saturation current, and as the reverse saturation current becomes smaller, the dynamic resistance r of the diode becomes smaller.

Therefore, under any of the conditions of equations (11) to 13), the dynamic value (Ra/Rb) of the compression circuit is increased.

Note that although the non-linear de-emphasis circuit for luminance FM signals has been explained here as an example, it goes without saying that the present invention can also be applied to non-linear de-emphasis circuits for color-difference FM signals.

As explained above, in this embodiment, by setting the dynamic value of the compression circuit in the nonlinear de-emphasis circuit to be larger than the dynamic value of the compression circuit in the nonlinear de-emphasis circuit, the difference in the amount of loss in the sideband spectrum is It is possible to compensate for the deterioration of the S/N ratio caused by the input of a small level signal.

[Effects of the Invention] As described above, the present invention makes it possible to provide a reproduced signal processing device configured to obtain a high-quality reproduced information signal during reproduction regardless of the level of the information signal. It becomes like this.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a specific configuration of a nonlinear de-emphasis circuit to which the present invention is applied, Fig. 2 is a block diagram showing a schematic configuration of a video signal recording/reproducing device, and Fig. 3 is a diagram showing the frequency spectrum of a recording signal. 4 is a schematic diagram of a luminance signal or color difference signal recording process circuit; FIG. 5 is a schematic diagram of a luminance signal or color difference signal reproducing process circuit; FIG. 6 is a schematic diagram of a nonlinear emphasis circuit; Figure 7 is a schematic configuration diagram of the non-linear de-emphasis circuit, Figure 8 is a diagram showing an example of a specific circuit configuration of the non-linear de-emphasis circuit shown in Figure 6, and Figure 9 is the compression diagram shown in Figure 8. Circuit characteristic diagram, 1θ diagram (8) and 10th
Figure (B) shows FM for each frequency and each person's power level.
FIG. 3 is a diagram showing a frequency spectrum of a modulated signal. 1... Luminance signal input terminal, 2... Luminance signal recording process circuit, 3... Color difference signal input terminal, 4... Color difference line sequentialization circuit, 5... Color difference signal recording process circuit, 6. ...Switch, 7...Frequency converter, 8...Frequency conversion carrier signal input terminal, 9...L
P.F. DESCRIPTION OF SYMBOLS 10... Adder, 11... Recording amplifier, 12... Switch, 13... Magnetic head, 14... Magnetic recording medium, 15... Preamplifier, 16... LPF. 1f...BPF. 18... Color difference signal reproduction process circuit, 19... Color difference line homogenization circuit, 20... Color difference signal output terminal, 21... HPF. 22... Luminance signal reproduction process circuit, 23... Luminance signal output terminal, 24... Clamp circuit, 25... Non-linear emphasis circuit, 26... Linear emphasis circuit, 27... FM modulation circuit, 28... FM demodulation circuit, 29... Linear de-emphasis circuit, 30... Non-linear de-emphasis circuit, 31...) IPF, 32, 32'... Compression circuit, 33... Coefficient circuit, 34... Adder, 35... Differential amplifier, 36... Coefficient circuit. Figure 5 ■ e @ ■ @ @ ■ [Phase]

Claims (1)

[Scope of Claims] 1) An apparatus that performs nonlinear compression processing when reproducing an information signal recorded by performing nonlinear amplification processing on a recording medium, the apparatus comprising: A reproduction signal processing device comprising a nonlinear compression processing circuit having a larger dynamic value than a dynamic value of nonlinear amplification processing. 2) The nonlinear compression processing circuit has a ratio of Ra/Rb, where Ra is the equivalent impedance when a small level signal is input, and Rb is the equivalent impedance when a large level signal is input.
2. The reproduced signal processing circuit according to claim 1, further comprising a compression circuit in which a dynamic value is set by .