JPS581805A - Signal reproducing circuit - Google Patents

Abstract

PURPOSE:To obtain video signal reproducing circuit having high performance with a simple constitution, by adding a surface acoustic wave filter including high and low pass filters having the flat peaking properties set in parallel to each other to an inversion preventing circuit which processes the luminance signal. CONSTITUTION:One of the reproduced video signals given from the preamplifiers 9 and 10 after receiving the peaking through the fixed capacitors 29, 30 and the feedback resistances 31, 32, etc. and then the matching through the heads 1 and 2 respectively is converted into an FM luminance signal through a switch circuit 13, an AGC circuit 33, a high band converting circuit, etc. This signal is processed through an inversion preventing circuit consisting of a surface acoustic wave filter 36 including an HPF and an LPF having the flat peaking properties, a limiter 19, an amplifier 21, an adder circuit 22, etc. to be turned into a luminance signal. This peaking process is not done by the LC resonance, and at the same time a surface acoustic wave filter is used to the inversion preventing circuit to exclude an equalizer, etc. Thus a simple constitution is possible for a video signal reproducing circuit having good peaking properties with high performance.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides signal equalization K used in signal reproducing circuits such as VTRs.
II.

FIG. 1 shows a conventional example of a reproduction circuit for a home-use (for example, VH5 type) VTR, in which the signal read out from the head 1.2 is transmitted through a rotary transformer 3.4° for resonance; Damping resistance7. Preamplifier 9 via swo
, 10K is added. Head 1゜Rotary transformer 3 and resonance conductor 5. Head 2. The rotary transformer 4 and the resonance capacitor 6 are connected to the white signal (V) of the FM luminance signal.
For H5, the peaking frequency is selected to be around 4.4 MHz. The damping resistor 7.8 is used to adjust the Q of peaking. Figure 2 shows the gain 11 of the conventional docking system. An example of the group delay characteristic 12 is shown.

When peaking occurs due to LC resonance, the group delay characteristic does not become flat as shown in FIG. The purpose of peaking is the head 1.2 and preamp 9.10 i, temp (NFeo).
& Used in ugly places). The output of preamplifier 9.10 is
A continuous signal is generated by a switch circuit 15FC that is switched by a 5OHz pulse (in the case of NTSC), and part of it passes through a high-pass filter 14 (hereinafter abbreviated as HpF) to the FM luminance signal gK, and a part passes through a low-pass filter 15 (hereinafter LP).
(abbreviated as F), the chroma signal is generated. After passing through an equalizer 16 that primarily equalizes the amplitude, the FM brightness signal line passes through an equalizer 17 that primarily equalizes the phase. HPllB
High frequency component C passing through filter 19 and LPF 20. The low frequency component d passes through the amplifier circuit 21 and is further mixed in the mixing circuit 22.

Equalizer 17. HP11@, Rita19. LP120
．． The amplifier circuit 21 and the mixing circuit 22 constitute an inversion prevention circuit. In other words, when the head reproduction output decreases due to an increase in the space between the head and the tape, the high frequency component C remains at a constant level due to the sum ξ19, but the low frequency component d decreases in proportion to the head reproduction output level. However, the S combined signal has a high frequency band that is emphasized. The head reproduction output generally decreases at high frequencies, due to the high frequency of FMM.
However, due to the circuit structure described above, the high frequency band is emphasized and one inversion can be prevented.

The mixed signal is sent to the limiter 23. Demodulator 24, LPF 2
5, the luminance signal becomes f by de-emphasis 26.

Chroma signal passed through the signal processing circuit 27! and mixing circuit 28
'c is mixed into the video signal ν.

In the conventional circuit shown in the first WJK.

+l) Because peaking is performed by LC resonance,
The group delay characteristic is not flat (2nd @) (2) The equalizer 16 is used to correct the 1st group delay characteristic.
However, the performance is insufficient.

(3) Requires HPF i 4 to separate luminance signals.

(4) In the inversion prevention circuit, the high frequency component C and the low frequency component d
The phase compensating equalizer 17 between the two and the same is inevitably present, which is a major drawback in terms of performance and cost.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art described above and to provide a high-performance, low-cost reproduction equalization circuit and an inversion prevention circuit.

The present invention provides equalization to conventional LC resonance peaking circuits and inversion prevention circuits.

In place of the HPF and LPF, a single-manufactured two-output surface acoustic wave filter (hereinafter abbreviated as 5AIi'74 router) is used to improve group delay characteristics at peaking 1. Inversion prevention performance is improved. Furthermore, when converting a reproduced FM luminance signal to a SAW filter band (approximately 11 to 17 MHz), the conversion frequency is changed depending on the purpose.

The present invention will be explained in detail below based on specific examples. Fig. 5 shows an embodiment of the signal reproducing circuit of the present invention, and the difference from the conventional example of the first WA is that the resonant capacitor 5.6 is replaced by a fixed capacitor □Fusa 29.50, and a damping capacitor 5.6. Feedback resistor 51. instead of resistor 7.8. '
S2, HPF 14, equalizers 16, 17 . The point is that an automatic gain control circuit 35 (hereinafter abbreviated as AGC), a high frequency conversion circuit 340, an oscillator 55, and a SAW' filter 36 are used in place of the HpFls and LPF 20. As a result, it is possible to apply feedback damping without degrading the NF of the preamplifier, to make the reproduction f411 at the preamplifier input section almost flat from 1 to 6 MHz, and to absorb variations in the inductance of the head. For this reason, the resonant capacitor 5
．． 6. There is no need to adjust the damping resistor 7.8 for variations in the damping resistance. Peaking is performed using SAW as described below.
It performs inferiorly to filter 56.

Further, the equalizer 1y, HPllB, and LPF2° in the conventional peaking circuit and the conventional inversion prevention circuit are all formed in the intermediate voltage of one SAV' filter 56. SAI! 'The operating band of the filter 34 is set to 11 to 17 MHz K based on the shape of the element, propagation characteristics, etc.
) Since the band of the raw FM luminance signal is 1 to 7 MHz (in the case of VH5 system), the oscillator (approximately 10 MIh) 3
5.

The high frequency conversion circuit 54 performs high frequency conversion of approximately 1QMHχ.

In addition, C55 is provided in front of the high frequency conversion circuit 54, and
Do 1. 5AI even if the reproduction output amplitude of head 2 is different
The L' film 360 input signal input sum is kept constant. The installation location of AGC55 is high frequency conversion circuit 54 and S
It is also possible between AW' filters 560.

The function K of the 5Alf' filter 56 will be described in detail below.

FIG. 4 shows the electrode configuration of the KSAIF' filter. A single crystal of lithium niobate with a 1281 Y-axis cut was used as the piezoelectric substrate, and the propagation direction of one surface acoustic wave was set to be the X-axis direction. The input electrodes 37 had a center frequency of 14.62NH4, 4 or 5 pairs of regular shoe electrodes in which the intersecting width and pitch of the interdigital electrodes were constant, and the electrode width was 542μ. The output electrodes 5B and 59 were 10 pairs of weighted phase electrodes in which the intersecting width and pitch of the interdigital electrodes were varied. These electrodes were formed using a 6000A aluminum vapor-deposited film using photophosphorography technology. VH5 system VTRK is available, but SAW filter! 4 has a peaking characteristic of q o MHz high frequency conversion as shown in Fig. 5 40. A group delay characteristic 41 is obtained. What are the features that are different from conventional ones?

(!)　　Group within the band - Both characteristics are flat.

(2) A filter 42 (trap filter or HpF) for removing the FM audio signal frequency-multiplexed between the low-frequency converted chroma signal or the low-frequency converted chroma signal and the FM luminance signal can be configured at the same time.

(3) 17-18MHz K) Kt with rap
, high-frequency noise can be reduced by having LPFql properties.

etc.

In this second tone, since the inversion prevention circuit described later is configured with a 5AIF filter 36, not only the above-mentioned peaking characteristic (the HpF characteristic 43°LPF characteristic 44 shown in the 4th!l1lK) are also present at the same time.It should be noted that the HPF Characteristic 45
The sum of LPF l characteristic 44 is flat characteristic 45
becomes.

FIG. 7 shows the output characteristics of the SAME' filter 360. The characteristics obtained by the product of the transfer functions of the input electrode 57 and the output electrode 58 are the peaking characteristics 40 and the HPF
The peaking characteristic 40 and the characteristic obtained by multiplying the transfer functions of the input electrode 37 and the output electrode 59 are defined as the peaking characteristic 40 and the LPFql characteristic 44.
The low-pass bee commanding characteristic 47 is obtained by adding the above.

The outputs of the output electrode s8 and the output electrode 59 are of the same polarity, and t:
When tCC is met, the input/output characteristic becomes 48, which diverges from the peaking characteristic of 4Ω in FIG. Note that it is also possible to reverse the polarities of the outputs of the output electrodes 58 and 59, and also reverse the polarities of the subsequent limiter 19 and amplifier 41 circuit 21, so that they have the same polarity as a whole.

Further, for one input electrode and two output electrodes, any combination of official zero weight versus temperature is possible.

8th FI! J is the SAW filter 36 in the first embodiment (FIG. 5) K with one filter. Limiter 19. amplifier circuit 21,
The operation of the mixing circuit 22 and the inversion prevention circuit consisting of A and C3i5 will be explained. The output 49 of the switch circuit 15 consists of the output 5o of the head 1 and the output 51 of the head 2, and there are differences in the head output due to variations. Kl! The output may drop for i period t. The period of 1.2 is 1 field 53 (1/40 m) for NTSC't;rv.

AGC55t! The input of the 5AIP' filter 56 after high frequency conversion has no output difference between fields as shown in 54, and has a time constant suitable for correcting the output difference (between 74-kV') and has a time constant suitable for correcting the output difference The amplitude is constant.

However, it is assumed that the time constant is selected so as not to respond to a short-term output drop such as 52. After the signal is input to the 5All' filter 34, the output of the output electrode 38 having bypass peaking characteristics is added to the limiter 19#C, and the output of the printer 19 becomes 55. Here, the limiter 19 also responds to a decrease in the output of t for a short period of time, resulting in a constant amplitude. On the other hand, the output of the output electrode 39 having low-pass peaking characteristics is applied to the amplifier circuit 21, and the output of the amplifier circuit becomes 56. Here, a short-term output drop is caused by its tt@ゎ. The gains of the limiter 19° amplifier circuit 21 and the AGC 55 are selected so that 55 and 56 have the same amplitude except for a short period of time. 55 and 56 are mixed in the mixing circuit 22, but except for the period, the HpF characteristic and the LpFql characteristic cancel each other out, and normal peaking shown by K in FIG. 9 57 (same as FIG. 5 40) is applied. During the period t, since the output of the limiter 19 is larger than the output of the amplifier circuit 21, peaking is applied in which the high frequency range shown in #I9 diagram 584C is raised more. As mentioned above, when the output decreases, the higher the frequency, the greater the decrease, and an inversion occurs in which the levels of the 1M carrier and lower sideband are reversed.
The above configuration can prevent reversal. Peaking circuit 9 SAI anti-rolling circuit! 'A particularly big effect of configuring it with filters.

(1) Even if the peaking characteristic changes depending on the reproduction output level, the group delay characteristic 59 within the band is always flat.

(2) Bypass peaking system Draw pass peaking system slow grinding time adjustment is based on the center position of the regular pumping electrode '57 and the weighted output voltage 4ii 58.5? This can be easily realized by adjusting the position of the maximum intersection width.

etc. Further, the KIF has great advantages such as a reduction in the number of parts and a simplification of the circuit configuration.

FIG. 10 shows another example I11 in which dropout compensation 1118 is provided in the signal regeneration circuit of the present invention, and the difference from FIG. 5 is that dropout detection @circuit 60. switch 61,
1Hj! This is the point where the ft line 62 exists. Dropout detection is preferably performed from the output of the ξ 19 or an intermediate stage of the ξ 19 where the 1M carrier is emphasized, but it is also possible to perform dropout detection from between the mixing circuit 22 and the switch 610. In addition, the I Hjl arc wire 62 has a signal frequency of 1
Since the frequency is 1 to 17 MHz, which is higher than the conventional one, a Gala λ delay line with a wide pass band can be used, and there is almost no deterioration of the dropout compensation signal.

In the above embodiment, the position of the AGC 55 is shown in Fig. 11 (g
), in front of the high frequency conversion circuit 34 as shown in (A).

In this case, the chroma signal is extracted before the AGCFS (118th!la) and before the AGC55 (111ig).
ijS) are both possible. Also #111 figure (c)
A configuration in which the KAGC 55 is placed between the high frequency conversion circuit 34 and the S, 4F filter 36 is also possible. In this case, the chroma signal is extracted before the high frequency conversion circuit 54. From the point of view of ease of circuit creation, the 11th model, which can perform AGC at low frequency,
Figure (α) or Figure 11 (b)) is preferred. Further, although the high frequency conversion frequency was set to 10 MHz in the above II example, it can be used in a wide range of frequencies in practice. The lower limit is determined mainly from the pattern spacing and shape of the 5AIF' filter, and the upper limit is determined from the circuit configuration.

In addition, as shown in Fig. 12, the color subcarrier 1uis (NTSC Teha!,
! It is also possible to use 1α74 MHz by multiplying 45 by 5 from the 5-bit overseas circuit 6411C.

Furthermore, in FIG. 5 or FIG. 97710, by changing the oscillation frequency of the oscillator 35, the peaking point of the kFM luminance signal can be changed.

The pi1s diagram (α) is the reproduced signal spectrum in the conventional VH5 system.
4.4Hχ) and low-frequency converted chroma signal 66 (subcarrier 629KHz), the first sFm(b)+tFM
Seki KF of liy141 No. 65 and low frequency conversion chroma signal 64
Since the M audio signal 67 exists, the FM luminance variable signal 45 is shifted to the high frequency range by if with respect to (α)k in FIG. 15. In general, for signals in which the carrier frequency of the K FM luminance signal is shifted by if, as shown in Fig. 15(g) and (b), it is conventional to change the peak frequency without changing the shape of the keeping characteristic. The LC resonance method is extremely unstable.

In the present invention, oscillation for high frequency conversion 1) 350 waste wave number f 9
You can easily do K11ll by just changing tif. For example, in the case of Fig. 1s (a), if the KSAW'y filter 56 is designed to obtain the optimum peaking at f==1oMgz, in Fig. 13(A), f-=1o-if
MHz may be used. The 5A11' filter 154 is designed to sufficiently remove the low-frequency converted chroma signal 64 in the case of FIG. 15E(a).
6. It is possible to reduce both the FM audio signals 670 to a level that does not cause problems. The above concept and structure can be easily applied to the case where the beakink frequency is changed depending on the tape used (for example, oxide, metal, vapor deposition).

FIG. 14 shows still another embodiment of the signal reproducing circuit of the present invention,
The difference from the embodiment shown in FIG. 3 is that the HPF 14 is present and the frequency characteristics of the 5AIL' filter 48 do not include the chroma signal or FJi audio signal removal filter 42 shown in FIG.

The advantage of this case is that the resolution of the video signal is tape 139@
This can be changed depending on the IIC. Now, let's consider a metal tape or a vapor-deposited tape that has improved single-frequency characteristics and a higher high-frequency output than the conventional oxide tape.

- As an example, the recording sickle for oxide tape is the conventional VH5 system (brightness FM carrier 54-4.4MHz) (first
Figure 5 (11) ),! : L, in the case of metal tape or vapor-deposited tape, for example, increase q5MHz to 59~
4.9 MHz (Fig. 15 (h)). The purpose of this is to improve resolution. In this case, when using the 5AIF' filter 36 including the filter 42 shown in FIG.
The effect of z improvement does not appear. On the other hand, in the embodiment shown in FIG. 14, the chroma signal and FM voice signal are removed by the HP 114 in the baseband (before high frequency replacement).

Figure 15 (tt) (h) The characteristics of K HPF 14 are shown in 69. Furthermore, the characteristics of the 5AIP' filter 68 are shown at 70. At the same time, the FM luminance signal spectrum after baseband and high frequency conversion is shown by curves 71 and 72. Baseband KsP and spectrum 72 are spectrum ha α
5 MHz shifted to the high frequency range. Here, Spectrum 71 is 1offz, Spectrum 72 is ? ,
s MHz When high frequency conversion is performed, 5AIi' filter 6
The relationship with the peaking % of 8@7° is that both are dispersed and optimal peaking is performed. On the other hand, HPF 14 with a fixed cutoff frequency has a high conversion frequency of 15 g.
Since the difference between (a) and FIG. 15(b) is ^, after high-frequency conversion, the frequency in FIG. 15(b) is lower by α5 MHz than that in FIG. 15(α). That is, in FIG. 15(A), the band of the %FM lower sideband wave is extended and the resolution is improved compared to FIG. 15(α).

In the case of the embodiment shown in FIGS. 14 and 15, the same inversion as in the embodiment shown in FIG. A prevention circuit can be constructed.

FIG. 16 shows a further @ embodiment of the present invention, in which a 5AIF' filter 73 has one input electrode 74 and two output electrodes ys,
The point with y6 is the same as the example in Figure 3, but the peaking characteristic of the point with J% is line symmetrical with respect to frequency as shown by curve 77 in Figure 1117 with respect to -948 in Figure 1117. It is. Accordingly, the input/output characteristics due to the input electrode 74 and the output electrode 75 connected to the output electrode 19 have a low-pass peaking characteristic 78, while the input/output characteristics of the output electrode 760 connected to the input electrode 74 and the amplifier circuit 21K have a bypass peaking characteristic. It is 79,
The electrode configuration and input/output characteristics of the SAM7 filter 56 are different from those of the first E. In this practical example, for example, 18 MHz is used as the frequency of one oscillator 350. High frequency conversion circuit 34
Generally, a multiplier is used, so if the center of the reproduced signal from the head is, for example, 4 MHz.

A signal of 18±4 MHz is obtained at the output of the high frequency conversion circuit @54. Fact - The example uses 1@-4MHz-14Mig as the signal. This is the 5th IllllO! In J example, using H) MHz as the oscillation frequency, the output of the high frequency conversion circuit 54 is 10±4 Mlh #) medium f) 1 G +
Compared to the case using 4-14 Mix, the only difference is that the peaking characteristics are line symmetrical with respect to the frequency VcII.

As described above, in the present invention, the peaking rotation 1 reversal cost stop circuit is configured with 5AII' filters, and compared to the conventional circuit, it has a high performance, 9 parts reduction, 0 function expansion, etc. When applied to such applications, the effect of improving performance and reducing costs is extremely large.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional VTR signal reproducing uM, Fig. 2 is a gain/group delay characteristic curve diagram of a conventional peaking circuit, and Fig. 5 is a block diagram showing an example of the signal reproducing circuit of the present invention. 4 is an internal configuration diagram of the 5AII' filter of the present invention, FIG. 5 is a peaking characteristic diagram of the SAW filter, and FIG. 6 is a diagram of the HPF used in the inversion prevention circuit.
LPF v4I characteristic curve diagram, Figure 7 is a characteristic curve diagram showing the difference in peaking characteristics depending on the electrode of the 5AFE' filter, Figure 8 is a diagram explaining the operation of the inversion prevention circuit, and Figure 9 is the peaking during operation of the inversion prevention circuit. Change characteristic diagram, 10th
Figure 11 is a block diagram showing another embodiment of the signal regeneration circuit of the present invention, Figure 11 is a block diagram explaining the position of AGC, Figure 12 is a block diagram of a high frequency conversion circuit, and Figure 13 is a block diagram of the peaking point. FIG. 14 is a characteristic diagram illustrating changes; FIG. 14 is a block diagram showing another embodiment of the signal reproducing circuit of the present invention; FIG.
FIG. 16 is a characteristic diagram explaining changes in degree of resolution, and FIG. 16 is a block diagram 1 showing another embodiment of the signal reproducing circuit of the present invention.
FIG. 7 is a peaking characteristic curve diagram of the SAW' filter. 1.2...Head 19...
・・・・・・・・・・Limiter 33 ・・・－・・・・・・
・・・・・・AGC34・・−・−・・・High frequency conversion circuit 35・・・・・−・・・Oscillator 54
------・-・・・・・・・・5AIF'y Iruta 37
・・・・・・・・・−・・Input electrode 58.59・・
・・・・・・Output electrode closed Figure 4 j Pef G Start 6 Figure 12 Iff 14 15 7G same wave number (
-Hz) Figure 7 ++ 12 13 14 151G l'7rj1
Namishiki (MHz) Fig. 6 Hatona 5Fil1 Fig. (L) (G) Fig. 12 Punishment 15 Fig. IZ34567 Surrounding skin po Reiji (gate) b 0 1 2 3 ヰ 5c”r τ-Sl cloak 115 + 1.ff 2.5 5.5 4.
5 5.5 G, 5 75 τ-Snowed W
i-wave It bar H1) Porridge 16 figure + 9 Closing figure ++ 12 1514 1518 Wave number for 17 (M
Hz)

Claims (1)

[Claims] (t) A high-frequency conversion circuit that converts a signal reproduced by a video head or the like into a high frequency range, and a high-frequency conversion circuit installed after the high-frequency conversion circuit,
A surface acoustic wave filter has a first filter that mainly peaks high frequencies and a second filter that mainly peaks low frequencies built in parallel, and a surface acoustic wave filter that is installed after the first filter in the surface acoustic wave filter. The present invention is characterized by comprising an amplification circuit installed after the second filter in the elasticity filter, and an adder for adding the output of the limiter circuit and the output of the wrinkle amplification circuit. signal regeneration circuit. 2. The signal reproducing circuit according to claim 1, characterized in that the number of high frequency conversion cycles of the high frequency conversion circuit is made variable. (5) The signal reproducing circuit according to claim 1, further comprising an automatic gain control circuit provided either before the high-frequency conversion circuit or between the high-frequency conversion circuit and the surface acoustic wave filter. 4 After the first filter, add a second IWIi path.
2. The signal regeneration circuit according to claim 1, wherein a limiter circuit is installed after each of the filters.