JP3013482B2 - FM equalization circuit and recording / reproducing apparatus using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal processing circuit of a recording and reproducing apparatus , and more particularly to an FM equalizing circuit for correcting a frequency characteristic of a reproduced FM signal and a recording and reproducing apparatus using the same. I do.

[0002]

2. Description of the Related Art A home video tape recorder (hereinafter referred to as V)
TR), an FM-modulated luminance signal and a low-frequency-converted chroma signal are frequency-multiplexed and recorded on a magnetic tape. At the time of reproduction, the signal reproduced from the magnetic head is converted into FM luminance. After being separated into a signal and a low-band chroma signal, each is processed and output.

[0003] In the reproduced FM luminance signal, a low band is emphasized by an emphasis effect of a lower band wave generated in a recording / reproducing process.
An FM equalization circuit for correcting this is required. FM
The equalizing circuit includes a passive type including a capacitor, a coil, and a resistor, and a cosine filter using a delay element. In the cosine filter, the phase changes linearly within the band, that is, the group delay time is flat,
It has no phase distortion and is superior to the passive type in performance. A typical FM equalizer using a cosine filter is disclosed in, for example, Japanese Patent Application Laid-Open No. 62-248108. According to this, a reproduced image with good waveform reproducibility can be obtained by detecting the state of the signal at the time of reproduction and changing the frequency characteristic of FM equalization.

[0004]

However, the configuration of the cosine filter shown in the conventional example has a disadvantage that the degree of freedom to change the characteristics with respect to the FM equalization characteristics is small. Assuming that the delay time of the delay element is τ, the cosine filter has a peak frequency of ττ, and a frequency at which the output becomes zero is 0, 1 / τ.
Thus, the characteristic is vertically symmetric with respect to the peak frequency.
On the other hand, as for the FM equalization characteristics used in the VTR, since the peak amount and the frequency characteristics are different depending on the VTRs such as the VHS standard and the 8 mm video standard, there is a certain degree of freedom with respect to the frequency characteristics. If not, it is a practical problem. Japanese Unexamined Patent Application Publication No. 62-248108 has a certain degree of freedom with respect to a change in peak amount, but does not have a degree of freedom with respect to frequency characteristics.

An object of the present invention is to solve such a problem,
Reproduced FM suitable for various VTRs using cosine filter
An object of the present invention is to provide an equalizing circuit.

[0006]

In order to achieve the above object, the present invention realizes a narrow band frequency characteristic by feeding back a part of a signal of a cosine filter to an input side. A filter that changes the low-frequency response by adding a certain amount of the output of a filter that shows the opposite characteristic (the peak point and the zero point have the opposite frequency), thereby improving the degree of freedom for the frequency characteristic. It is.

[0007]

In the case of a cosine filter constituted by one delay element, the output of the filter having the opposite characteristic to that of the cosine filter is negatively fed back to the input side, thereby acting to narrow the pass band. By adding the output of the filter to the output of the cosine filter, it acts to change the low-frequency response. Further, the band of the delay element is limited so that the group delay time increases on the high frequency side of the peak frequency, thereby acting to limit the band of the cosine filter on the high frequency side.

Further, a high-pass filter is inserted into the feedback loop to change the feedback coefficients of the low frequency and the high frequency so that the peak is reduced.
It acts to narrow the band characteristics above the clock frequency.

In the case of a cosine filter composed of two delay elements, a signal at the center of the two delay elements is applied to the input side with a negative signal.
By returning , it works to narrow the pass band,
By adding the output of the filter having the opposite characteristic to that of the cosine filter to the output of the cosine filter, it acts to change the peak amount of the FM equalization circuit.

[0010]

An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a block diagram showing an embodiment of an FM equalization circuit according to the present invention, wherein 1 is an input terminal, 2 and 5 are subtraction circuits, 3 is a delay element, 4 and 8 are addition circuits, and 6 and 7 are A coefficient circuit 9 is an output terminal. Assuming that the delay time of the delay element is τ, the transfer function of the delay element is expressed by exp (−jωτ), and the output vo of the subtraction circuit 5 is expressed by the following equation. vi indicates an input signal.

[0011]

(Equation 1)

The characteristics when the feedback coefficient K1 is changed are as follows:
As shown in FIG. When the feedback coefficient K1 is 0, 0.2, 0.5, 0.
When the peak frequency f0 is changed to 7 and the peak frequency f0 is 1 / 2.tau., The response of the frequency 1 / 4.tau. Is -3 dB and -5.1 d.
B, -10 dB, and -15.1 dB. As described above, the narrow band characteristic is realized by increasing the feedback coefficient K1.

The output of the adder circuit 4, that is, the output of the filter having the opposite characteristic to that of the cosine filter, is represented by a coefficient K2.
After the above adjustment, the addition circuit 8 adds the signal to the output of the cosine filter, that is, the subtraction circuit 5, so that the frequency characteristic can be varied as shown in FIG. FIG. 6 shows K2 when K1 = 0.5.
Are changed to 0, 0.2, 0.4, 0.6, 0.8 and 1. As described above, by changing K1 and K2, it is possible to give a considerable degree of freedom to the characteristics of the FM equalization circuit.

Next, the fact that the characteristics on the high frequency side of the FM equalization circuit can be varied by the band characteristics of the delay element will be described with reference to FIGS. FIG. 4 shows the spectrum of the FM luminance signal and the FM equalization characteristics. 19 is the FM equalization characteristic, 20 is the fundamental wave component of the FM luminance signal, 21
Is a secondary distortion component of the FM luminance signal. In reproducing a VTR, the signal is converted into a video signal via an FM demodulation circuit after FM equalization. At this time, when there are many secondary distortion components, FM
A so-called carrier leak disturbance occurs in which the carrier signal leaks into the demodulated video signal. In particular, it appears on the edge portion of the screen where the color suddenly changes from white to black, which leads to image quality deterioration. Therefore, as shown in FIG. 4, it is necessary to lower the high frequency characteristics so as to suppress the vicinity of the center frequency f1 of the secondary distortion component. One way to achieve this is to use a delay element 3
May be set to the characteristics as shown in FIG. That is, if the amplitude characteristic is set so as to be flat near the center frequency f1 of the secondary distortion, and the group delay characteristic is set so as to be flat near the peak frequency f0 and the delay time is increased at frequencies higher than that. Good. For example, taking a VHS standard VTR as an example, the FM carrier signal is from 3.4 MHz to 4.4 MHz. In order to set the center frequency of FM equalization in the vicinity of the upper 5 MHz of the FM carrier signal and reduce the frequency in the vicinity of 8 MHz, the delay time to the vicinity of 5 MHz is about 100 ns, and the delay time in the vicinity of 8 MHz is about 12 ns.
By setting the time to 5 ns, desired FM equalization characteristics can be obtained.

As described above, according to the present embodiment, the band characteristics and the peak amount can be freely set by K1 and K2, and the characteristics above and below the peak frequency can be changed by the characteristics of the delay element. An unbalanced design can be performed, and the FM second-order distortion component that causes carrier leakage can be suppressed.

FIG. 2 is an embodiment showing delay time adjustment in an actual circuit design. Here, the subtraction circuit 2,
5, the description will be made assuming that the delay time of the adder circuits 4 and 8 is 0. If the delay time of each part does not match, the desired characteristics cannot be obtained, so it is necessary to find the delay conditions for each route. Dotted lines 13, 14, 15, 16, 17, 18,
The delay time of each route indicated by 19 is t1, t2, respectively.
Assuming that t3, t4, t5, t6, and t7, t2-t1 =
Conditions such as τ, t3 = τ, t4-t5 = τ, and t6 = t7 are required. The delay time generated in the coefficient circuit 6 is Δτ
Assuming that the delay time is 1, the delay time of the delay element 3 is set to (τ−Δτ1), and the delay circuits 10 and 11 are inserted to adjust the delay of each unit.
3 is defined as Δτ2 = Δτ3 = Δτ1. If the delay time generated in the coefficient circuit 7 is Δτ4, a delay circuit 12 having a delay time Δτ5 equal to Δτ4 can be inserted between the subtraction circuit 5 and the addition circuit 8 to perform delay compensation.

Next, another embodiment will be described with reference to FIG.
This embodiment is one means for making the characteristics of the FM equalization circuit unbalanced at frequencies above and below the peak frequency. The same parts as those in the embodiment shown in FIG. A coefficient circuit 25 and a high-pass filter (HPF) 24 are inserted in the feedback route from the addition circuit 4 to the subtraction circuit 2 to change the low-frequency and high-frequency feedback coefficients. FIG. 8 shows a specific example of the HPF 24. Resistance R1, R
2. It is composed of a rugged HPF comprising a capacitor C, and its frequency characteristics are shown in FIG. Frequency f
It shows the characteristic of bending at a and fb, and fa and fb can be expressed by the following equations, respectively.

[0018]

(Equation 2)

[0019]

(Equation 3)

For example, R1 = 600, R2 = 400, C
= 80 pF, fa = 3.3 MHz, fb =
8.3 MHz, and the coefficient K3 of the coefficient circuit 25 = 0.5
Then, assuming that the total feedback coefficient of the HPF 24 and the coefficient circuit 25 is K, as shown in FIG. 10, K = 0.2 in a band lower than the frequency fa and K = 0.5 in a band higher than the frequency fb. FIG. 9 shows the FM equalization characteristics at this time. K = 0.2 on the low frequency side of the peak frequency f0, K = 0.
5, which increases the degree of freedom in setting the frequency characteristics.

Next, a second embodiment will be described with reference to FIG. FIG. 11 is a block diagram of an FM equalization circuit using a cosine filter using two delay elements. 30
Is an input terminal, 31, 37 are subtraction circuits, 32, 33, 34
Is a coefficient circuit, 35 and 36 are delay elements, 38 and 39 are coefficient circuits, and 40 is an output terminal. Assuming that the delay time of the delay elements 35 and 36 is τ, the transfer function of the delay element is exp (−
jωτ). Assuming that the input signal of the delay element is A, the signal delayed by τ is B, and the signal delayed by 2τ is C, the addition circuit 37 calculates 0.25A + 0.5B + 0.25C to form a cosine filter. The coefficient (1-K) of the coefficient circuit 39 is used to correct the peak value at the output terminal 40 to be equal to the level of the input terminal 30 because the peak value changes due to the feedback coefficient K. In the present embodiment, the band characteristic of the cosine filter is narrowed by negatively feeding back the signal B delayed by τ to the input side via the coefficient circuit 38. The negative feedback circuit includes a subtraction circuit 31
It consists of. The output of the cosine filter at the output terminal 40 can be expressed by the following equation.

[0022]

(Equation 4)

FIG. 14 shows the frequency characteristics of the present embodiment.
As described with reference to FIG. 3, as the feedback coefficient K increases, a narrow band characteristic is obtained. Peak frequency f0
(= １ ／ τ), the response of １ ／ τ is −6 dB, −8.1 dB, and −12.9 dB as the feedback coefficient K changes to 0, 0.2, 0.5, and 0.7. , -1
It changes to 8.2 dB. It can be seen that the response at ４τ is further reduced by 3 dB as compared with the cosine filter using one delay element shown in FIG. That is,
A cosine filter using two delay elements can obtain a narrower band characteristic.

FIG. 12 shows another embodiment. As compared with the embodiment of FIG. 11, the degree of the peak at the peak frequency has a degree of freedom. 41 and 47 are coefficient circuits; 39 and 46 are coefficient circuits for level adjustment;
2, 43 and 44 are coefficient circuits, and 45 and 48 are addition circuits. For the cosine filter obtained by the subtraction circuit 37,
The output signal of the filter having the opposite characteristic to that of the cosine filter obtained by the addition circuit 45 is multiplied by the coefficient K2 set by the coefficient circuit 47 and added by the addition circuit 48.
FIG. 15 shows frequency characteristics with respect to the coefficient K2 at this time. This is a characteristic when the feedback coefficient K1 is 0.5. Coefficient K
As the peak amount changes with the change of 2, the frequency characteristics of the FM equalization circuit have more degrees of freedom.

FIG. 13 shows an embodiment for realizing the delay time adjustment of each part in an actual circuit design. The delay time of the route indicated by the dotted line is represented by t8, t9, and t1, respectively.
Assuming that 0, t11, t12, t13, and t14, t8 =
τ, t10−t9 = τ, t12−t11 = τ, t13 =
The relationship t14 is required. To simplify the explanation,
It is assumed that there is no delay time generated in the coefficient circuits 52, 53, 54, 60, 61, 62, the addition circuits 63, 69, and the subtraction circuit 59. Coefficient circuit 64, delay circuits 56, 5
8, 66, the delay time of the coefficient circuit 68 is Δτ6, Δτ7,
Assuming that Δτ8, Δτ9, and Δτ10, the delay elements 55, 5
7 as (τ−Δτ6), Δτ6 = Δτ7
= Δτ8, Δτ9 = Δτ10, so that the delay adjustment of each unit is enabled.

FIG. 16 shows an embodiment in which the HPF 78 is connected in series to the coefficient circuit 79 in the feedback route in the embodiment shown in FIG. 12, and the same parts as those in FIG. . The HPF 78 is a ratchet as shown in FIG.
It can be realized by a dope type HPF. As in the embodiment shown in FIG. 7, the band above the peak frequency can be narrowed.
As described above, FIG. 11, FIG. 12, FIG.
The embodiment shown in FIG. 6 is an FM equalization circuit using a cosine filter using two delay elements, and can achieve a narrower band than a circuit using one delay element.

[0027]

According to the present invention, it is possible to narrow the band characteristics of the FM equalizer by negatively feeding back the output signal or the intermediate signal to the input side in the FM equalizer comprising a cosine filter. There is a possible effect.

Further, adding the output signal of the filter shown opposite properties Pi of the FM equalizer in the cosine filter to the output signal outputted cosine filter - it is possible to vary the click amount, this used for example VHS standard, serial, such as a VTR of 8-mm video standards such as the various standards
A recording and reproducing device can be realized .

By gradually increasing the delay time of the delay element used in the cosine filter above the peak frequency, the effect of reducing the secondary distortion component of the FM luminance signal at the time of reproduction and preventing the carrier leakage interference. There is.

Inserting the HPF into the negative feedback loop also has the effect of changing the characteristics in frequency bands above and below the peak frequency.

[Brief description of the drawings]

FIG. 1 is a block diagram of an FM equalization circuit showing one embodiment of the present invention.

FIG. 2 is a block diagram of an FM equalization circuit showing another embodiment of the present invention.

FIG. 3 is a graph showing frequency characteristics according to the present invention.

FIG. 4 is a spectrum diagram showing a frequency characteristic and an FM signal spectrum according to the present invention.

FIG. 5 is a graph showing frequency characteristics of a delay element used in the present invention.

FIG. 6 is a graph showing frequency characteristics according to the present invention.

FIG. 7 is a block diagram of an FM equalization circuit showing one embodiment of the present invention.

FIG. 8 is a specific circuit diagram of an HPF used in the present invention.

FIG. 9 is a graph showing the frequency characteristics according to the present invention.

FIG. 10 is a graph showing frequency characteristics of the HPF used in the present invention.

FIG. 11 is a block diagram of an FM equalization circuit showing another embodiment of the present invention.

FIG. 12 is a block diagram of an FM equalization circuit showing another embodiment of the present invention.

FIG. 13 is a block diagram of an FM equalization circuit showing another embodiment of the present invention.

FIG. 14 is a graph showing the frequency characteristics according to the present invention.

FIG. 15 is a graph showing frequency characteristics according to the present invention.

FIG. 16 is a block diagram of an FM equalization circuit showing another embodiment of the present invention.

[Explanation of symbols]

3, 35, 36, 55, 57 ... delay element, 6, 7, 38, 41, 47, 64, 68, 79 ... coefficient circuit, 24, 78 ... high-pass filter.

Claims (14)

(57) [Claims] 1. An FM equalization circuit for inputting an FM signal to a delay means and calculating an input signal and a signal delayed by the delay means to obtain an output signal, wherein the delay time of the delay means is τ. , first to obtain the amplitude characteristic having a peak at frequency 1 / 2.tau
Calculating means for obtaining an amplitude characteristic having a zero point at a frequency 1 / 2τ;
Calculating means, means for attenuating the output signal of the second calculating means and providing a negative feedback to the input signal, and means for attenuating the output signal of the second calculating means to obtain the first signal.
Means for adding to the output signal of the arithmetic means; and an FM equalization circuit. 2. An FM signal is input to delay means, and the input signal is
And the signal delayed by the delay means to calculate the output signal
In the obtained FM equalization circuit, a second subtraction means for inputting an input signal to the FM equalization circuit
If a delay unit of the delay time τ for inputting the output signal of the subtraction means second, a signal delayed by said delay means from the output signal of the second subtraction means 1: first subtracting 1 ratio 1 subtraction means , first addition means for adding an input signal to the FM equalization circuit and a signal delayed by the delay means at a ratio of 1: 1, and an output signal of the first addition means a first coefficient means for attenuate and a second coefficient means for attenuate the output signal before Symbol first addition means, the output signal of said second coefficient means, the first subtraction means possess a second adding means for adding an output signal, wherein the second subtracting means from the input signal to the FM equalizer circuit
An FM equalizer circuit for subtracting an output signal of the first coefficient means . 3. An FM signal is input to delay means, and the input signal is
And the signal delayed by the delay means to calculate the output signal
In the obtained FM equalization circuit, a second subtraction means for inputting an input signal to the FM equalization circuit
If the two delay means cascade of delay time τ for inputting the output signal of the subtraction means second, from the signal of the middle point of the two delay means, upstream and downstream of said two delay means the signals 1: first subtraction means and a first coefficient means for pre SL is two signals reduced the Decay midpoint of the delay means, prior Symbol first subtraction means for subtracting a proportion of 0.5 possess a second coefficient means for reducing the output signal attenuation and said second subtracting means from the input signal to the FM equalizer circuit
An FM equalizer circuit for subtracting an output signal of the first coefficient means . 4. An FM signal is input to delay means, and the input signal is
And the signal delayed by the delay means to calculate the output signal
In the obtained FM equalization circuit, a second subtraction means for inputting an input signal to the FM equalization circuit
If the two delay means cascade of delay time τ for inputting the output signal of the subtraction means second, from the signal of the middle point of the two delay means, upstream and downstream of said two delay means the signals 1: first subtraction means and, before Symbol a first coefficient means for attenuate the midpoint signal of two delay means, prior SL two delay means for subtracting a proportion of 0.5 the midpoint signal, 1 upstream and downstream signals of the two delay means: a first adding means for adding at a ratio of 0.5, to attenuate the output signal of the first adding means a second coefficient means, the output signal of said second coefficient means, have a, a second adding means for adding an output signal of said first subtracting means, the second subtraction means, FM From the input signal to the equalizer
An FM equalizer circuit for subtracting an output signal of the first coefficient means . 5. The delay means has a low cut-off frequency fc in the amplitude characteristic which is equal to or lower than a frequency of 1 / τ, and has a flat group delay time of 1 / 2τ and a range of 1 / 2τ to the low cut-off frequency fc. 5. The FM equalizer according to claim 2, wherein the frequency is gradually increased. 6. The FM equalizer according to claim 2, wherein said first coefficient means has a high-pass filter characteristic. 7. A recording and reproducing apparatus for recording or reproducing an FM modulated luminance signal on a recording medium, and enter the F M signal to the delay means calculates a signal delayed by said input signal and said delay means An FM equalization circuit that obtains an output signal by using the first equalization circuit that obtains an amplitude characteristic having a peak at a frequency 1 / 2τ , where τ is a delay time of the delay unit .
Calculating means for obtaining an amplitude characteristic having a zero point at a frequency 1 / 2τ;
Calculation means, means for attenuating the output of the second calculation means to provide a negative feedback to the input signal, and means for attenuating the output of the second calculation means to perform the first calculation.
And a means for adding to an output of the means. 8. A recording / reproducing apparatus for recording / reproducing an FM-modulated luminance signal on / from a recording medium, wherein the FM signal is inputted to a delay means, and the input signal and the delay means are inputted.
FM equalization to obtain the output signal by calculating the signal delayed by
Comprising a circuit, the FM equalizer circuit, a second subtracting means for input signals to the FM equalizer circuit inputs
If a delay unit of the delay time τ for inputting the output signal of the subtraction means second, a signal delayed by said delay means from the output signal of the second subtraction means 1: first subtracting 1 ratio 1 subtraction means , first addition means for adding an input signal to the FM equalization circuit and a signal delayed by the delay means at a ratio of 1: 1, and an output signal of the first addition means a first coefficient means for attenuate and a second coefficient means for attenuate the output signal before Symbol first addition means, the output signal of said second coefficient means, the first subtraction means possess a second adding means for adding an output signal, wherein the second subtraction means, whether the input signal to the FM equalizer circuit
Recording / reproducing apparatus configured to subtract the output signal of the first coefficient means from the output signal . 9. A recording / reproducing apparatus for recording or reproducing an FM-modulated luminance signal on / from a recording medium, wherein the FM signal is inputted to a delay means, and the input signal and the delay means are inputted.
FM equalization to obtain the output signal by calculating the signal delayed by
Comprising a circuit, the FM equalizer circuit, a second subtracting means for input signals to the FM equalizer circuit inputs
If the two delay means cascade of delay time τ for inputting the output signal of the subtraction means second, from the signal of the middle point of the two delay means, upstream and downstream of said two delay means the signals 1: first subtraction means and a first coefficient means for pre SL is two signals reduced the Decay midpoint of the delay means, prior Symbol first subtraction means for subtracting a proportion of 0.5 possess a second coefficient means for reducing the output signal attenuation and said second subtracting means, either the input signal to the FM equalizer circuit
Recording / reproducing apparatus configured to subtract the output signal of the first coefficient means from the output signal . 10. A recording / reproducing apparatus for recording or reproducing an FM-modulated luminance signal on / from a recording medium, wherein the FM signal is inputted to a delay means, and the input signal and the delay means are inputted.
FM equalization to obtain the output signal by calculating the signal delayed by
Comprising a circuit, the FM equalizer circuit, a second subtracting means for input signals to the FM equalizer circuit inputs
If the two delay means cascade of delay time τ for inputting the output signal of the subtraction means second, from the signal of the middle point of the two delay means, upstream and downstream of said two delay means the signals 1: first subtraction means and, before Symbol a first coefficient means for attenuate the midpoint signal of two delay means, prior SL two delay means for subtracting a proportion of 0.5 the midpoint signal, 1 upstream and downstream signals of the two delay means: a first adding means for adding at a ratio of 0.5, to attenuate the output signal of the first adding means a second coefficient means, the output signal of said second coefficient means, have a, a second adding means for adding an output signal of said first subtracting means, said second subtracting means, said Input signal to FM equalizer
Recording / reproducing apparatus configured to subtract the output signal of the first coefficient means from the output signal . 11. The delay means has a low cut-off frequency fc in the amplitude characteristic thereof equal to or lower than a frequency of 1 / τ, and has a group delay time which is flat to 1 / 2τ and extends from 1 / 2τ to the low cut-off frequency fc. 11. The recording / reproducing apparatus according to claim 8, wherein the recording / reproducing apparatus gradually increases. 12. The recording / reproducing apparatus according to claim 8, wherein said first coefficient means has a high-pass filter characteristic. 13. An FM equalization circuit for inputting an FM signal to two cascaded delay means and calculating an input signal and a signal delayed by the two delay means to obtain an output signal. A delay time of the delay means being τ, a first calculation means for obtaining an amplitude characteristic having a peak at a frequency ττ, a second calculation means for obtaining an amplitude characteristic having a zero point at a frequency ττ, A means for attenuating the output of the preceding delay means of the two delay means to negatively feed back the input signal; and attenuating the output of the second arithmetic means and adding the result to the output of the first arithmetic means. Means, and an FM equalization circuit comprising: 14. A recording / reproducing apparatus for recording or reproducing an FM-modulated luminance signal on or from a recording medium. An FM equalization circuit that obtains an output signal by calculating a delayed signal, wherein the FM equalization circuit sets a delay time of the delay unit to τ, and obtains an amplitude characteristic having a peak at a frequency ττ. Calculating means for obtaining an amplitude characteristic having a zero point at a frequency 1 / 2τ; and means for attenuating the output of the preceding delay means of the two delay means and negatively feeding back the input signal. And a means for attenuating the output of the second arithmetic means and adding the result to the output of the first arithmetic means.