JPS60154791A - Signal recording and reproducing circuit - Google Patents

Abstract

PURPOSE:To improve clip distortion of an FM luminance signal and to have contour emphasis effect by constituting a pre-emphasis circuit and a de-emphasis circuit of two delay lines, an adder, subtractor, and a level regulator. CONSTITUTION:A pre-emphasis circuit is composed of delay lines 21 and 22, subtractors 23 and 24, adders 25 and 26, and level regulators 27 and 28. When this structure is compared with conventional one; a white peak goes to peaks 151 and 152, black peak goes to peaks 161 and 162, and two peaks go to about 1/2 in size, thereby a clip amount is made small. In case of a de-emphasis circuit, a difference from the pre-emphasis circuit is that level regulators 31 and 32 are incorporated. In overall characteristics of both circuits, the phase changes in proportion to the frequency, thereby causing no waveform distortion.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a signal recording and reproducing circuit for a magnetic recording and reproducing device, and particularly to a signal recording and reproducing circuit suitable for use in a video tape recorder (hereinafter referred to as VTR). It is something.

[Background of the invention]

As shown in FIG. 1, in a urinary VTR (for example, VH5 system), an FM-modulated luminance signal 1 and a low-frequency converted color signal 2 are frequency-multiplexed and recorded on a tape.

An example of a luminance signal circuit is shown in FIG. Luminance signal α during recording
The pre-emphasis circuit 3 emphasizes the high frequency range to B, then the clip circuit 4 converts it to C, and the FM modulator 5. It passes through a recording amplifier 6 and is recorded on a tape 8 by a head 7.

At the time of reproduction, the brightness signal on the tape 8 is reproduced by the head 7, demodulated by the preamplifier q and the FM demodulator 10 to obtain signal d, and then the high frequency signal is suppressed by the digital amplifier circuit 11 to obtain the video signal C. Note that FIG. 3 shows an example of an emphasis circuit, and FIG. 4 shows an example of a de-emphasis circuit. ν is input, ν is output.

A sufficiently large operational amplifier with a gain of 12, R1, R,.

C is a resistance and a capacitance that determine the time constant.

The characteristic B0 of the pre-emphasis circuit and the characteristic B of the Tien Fan 2 circuit are, however, τ, = CxR.

τ, = Cx (R, +R2) ω: Expressed as angular frequency. Gain of B, , H, IH11,1B
An example of the frequency characteristics of No. 21 is shown in No. 13 of FIG. 5, respectively. 6th
It is shown in 14 of the figure.

Performing such pre-emphasis and de-emphasis processing reduces triangular noise during demodulation (the noise becomes more intense as the harmonics increase) in a system that performs FM modulation and demodulation.
As a countermeasure, it will be implemented. However, various problems arise when recording video signals in a limited band as in a VTR. FIG. 7 shows waveforms of various parts in FIG. 2. In the case of the VliS method, in the input video signal α, white......4.1MHz sync...Mountain...5.4 ME z Frequency is set. When the signal α is pre-emphasized, it becomes a signal with the high frequency emphasized as shown in b, and the white peak 15. A black peak 16 and the like occur. This means that the recording frequency band is widened, which causes S/N deterioration and spurious interference, so it is clipped at a certain level of 17.18. As a result, the signal becomes C, and the signal d after demodulation in the reproduction system also almost matches 5C. When this is de-emphasized, it becomes e, and since the high-frequency signal is removed by the clip circuit 4, the distortion is 19 at the rising and falling parts of the waveform.
,20. To counter this, it is necessary to newly emphasize the high frequency range only in the reproduction system, but in this case, the noise existing in the high frequency range is also emphasized at the same time, so the noise at edges such as rising and falling edges increases. Significantly degrades image quality.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a new emphasis circuit in which a video signal is not clipped or clipped in a small amount, and a corresponding de-emphasis circuit. Summary] In order to achieve the above object, the present invention is characterized in that a pre-emphasis circuit and a de-emphasis circuit are configured with two delay lines, an adder/subtractor, and a level adjuster, and the overall characteristic has an edge enhancement effect. That is.

[Embodiments of the invention]

The present invention will be explained in detail below based on specific examples. The eighth white line shows a pre-emphasis circuit according to the present invention, which is composed of delays fi21 and fi22, subtracters 23 and 24, adders 25 and 26, and level adjusters 27 and 28. ! +
7 = ωt, the signals of each part are expressed as follows.

υ1=-ω(-τ) v2=-ω(t-2r) Sim:kl"l-ν2 v,=ni, shi-V.

L15 ” uB+ v4 ” 2 to 1υ1−(shi, +
T) @ )U6 ” k!v11 v6 == J+u6==vH+2u5” CI+2k
Hkl)IJ@.

k*(vt+υ) Here, τ: the gain of the level adjuster 27 at the delay time of the delay line 21. 5tn per month (
r)(t-r) ・-(31. Comparing equation (3) with the input signal V, gain=1+2&, (k,
- house ωτ) = (1+2, k, )-2, (2)
ωτ... Town... Song (4) Delay time = τ (constant) is obtained. Shima "" 11kv = 1/2 sτ = 12
Equation (4) is illustrated with 5 ω = 2πf in the 9th
It is a diagram. That is, a pre-emphasis characteristic with a peak at 4 MHz (1/2τ) is obtained. Further, in this case, since the delay time is constant over the entire frequency band, no waveform distortion occurs.

Further, when the input signal υi is a rectangular wave, the waveforms of each part in FIG. 8 are 101-5. At this time, the pre-emphasis output is at the rising edge of the pulse 29. High frequency components are dispersed before and after the falling edge 30.

In the luminance signal system shown in FIG. 2, when the present invention shown in FIG. 8 is applied as the pre-emphasis circuit 3, the waveforms of each part become as shown by α, S, and c in FIG. 11. , compared with the conventional example shown in FIG.
1,162, and the thickness of the two peaks is approximately 1.
/2. Therefore, it will not be clipped by the chrysoge circuit 4. Alternatively, the amount of clipping can be reduced, and waveform distortion can be prevented.

FIG. 12 shows a de-emphasis circuit according to the present invention, which differs from the pre-emphasis circuit in FIG. 8 in the level adjuster 31 j2.

To obtain the de-emphasis characteristic with the bias characteristic B (inverse characteristic of the target) shown in Fig.
It is necessary to obtain the characteristics that However, since there is a delay term of delay time τ in B(to), oscillation occurs when feedback is applied. Therefore, the de-emphasis circuit needs to be of a feedforward type like the pre-emphasis circuit.

The de-emphasis characteristic of the present invention corresponds to equation (4): 1
+2A:, k, ) +2ktal+sωτ...
・Tap・・・Tap・As shown in (5), the sign of the term ωτ is changed. This can be realized by setting the gain of level adjuster 31 to - and the gain of level adjuster 32 to -. kI” 1r kt =1
/2s τ=125 rL,? (6) in the case of
The characteristics of the equation are shown in FIG. Note that the case of f=0 (ω=0) is defined as QdB. Further, FIG. 14 shows a comprehensive characteristic that combines the pre-emphasis characteristic of the ninth factor with the de-emphasis characteristic of FIG. 13. As can be seen from FIG. 14, the overall characteristics are not flat, but have a peak at 2 MHz.

In both the pre-emphasis and de-emphasis circuits of the present invention, the delay time is constant τ, and the phase changes in proportion to the frequency. Therefore, in the overall characteristic shown in FIG. 14, the delay time is constant at 2τ, and the phase also changes in proportion to the frequency, so no waveform distortion occurs. In other words, the overall characteristics shown in FIG. 14 are a contour emphasizing circuit without waveform distortion.

When the present invention is applied to a video signal, as shown in FIG. 11, the output after de-emphasis becomes a waveform with edge emphasis as shown in C, and both the S/N improvement due to emphasis and the transient characteristic improvement due to edge enhancement are achieved. It can be achieved at the same time.

Furthermore, in the pre-emphasis circuit of FIG. 8 and the de-emphasis circuit of FIG. 12, if an inverting amplifier is added to the level adjusters 27 and 2B, level adjusters 3t and 32 can be obtained, and it is clear that they can be easily shared. .

In addition, the new engine assist circuit of the present invention, and Figures 3 and 4.
It is also possible to use a combination of the conventional emphasis circuits shown in the figure. Furthermore, if a limiter circuit is provided in the level adjusters 28 and 32, so-called dynamic emphasis in which the amount of emphasis changes with respect to the input level is also possible. Further, the selection of the adder and subtractor shown in FIGS. 8 and 12 and the selection of positive or negative gain of the level adjuster are not limited to one type, and various configurations are possible.

As described above, in the present invention, by configuring a pre-emphasis circuit and a de-emphasis circuit using two delay switches, an adder, a subtracter, and a level adjuster, it is possible to improve the clipping distortion of the FM luminance signal and to enhance the contour. The circuit can also be realized at the same time, which has an extremely large effect on improving image quality.

[Brief explanation of drawings]

Figure 1 is a spectrum diagram of the FMlQ degree signal and low frequency conversion chroma signal, Figure 2 is a block diagram of the luminance signal regeneration circuit, Figure 3 is a block diagram of the emphasis circuit, and 4th C is a circuit diagram of the de-emphasis circuit. 5 and 6 are characteristic diagrams of the pre-emphasis circuit and de-emphasis circuit, FIG. 7 is a waveform diagram of a video signal during conventional emphasis, FIG. 8 is a block diagram of the pre-emphasis circuit of the present invention, and FIG. Figure 10 is a characteristic diagram of the pre-amplifier circuit of the present invention, Figure 10 is a waveform diagram for a rectangular wave, Figure 11 is a waveform diagram for a video signal, and Figure 12 is a block diagram of the de-emphasis circuit of the present invention. , FIG. 13 is a characteristic diagram of the de-emphasis circuit of the present invention, and FIG. 14 is a comprehensive characteristic diagram. 3: Pre-emphasis circuit 4: Clip circuit 11: Dien 7 assist circuit 21.22: Delay line 23.24: Subtractor 25.26: Adder 27.28, 31, 32 Nirepel adjuster patent attorney Akira Takahashi Husband and child 1 country t2 day 1 day - 3 years old 14 years old 50 years 76 days / 1 = Ii needle 18 years old 9 years old @ Hong Huan (FtHz) - 10 years old fit same α 1-12 years old 13Kunishima Unnumbered (MHz) 1-14 Figure E 1StCto1hz> Procedural Amendment (Method) % Formula % Title of Invention Person who corrects signal recording and reproducing circuit 1irl and addition (Ma Patent applicant B Name (510) [Monthly Ceremony Kaimon] Co., Ltd. Production agent Subject of person amendments Contents of amendments to the full text of the application and specification

Claims (1)

[Claims] In a recording and reproducing apparatus that records a luminance signal by FM modulation, a pre-emphasis circuit consisting of two delay lines, an adder/subtractor, and a level adjuster, and the polarity of the gain of the level adjuster in the pre-emphasis circuit are reversed, or this A signal reproducing circuit having a de-emphasis circuit configured to obtain characteristics equivalent to that of the de-emphasis circuit.