JPH081732B2 - Signal separation circuit - Google Patents

Description

TECHNICAL FIELD The present invention relates to a signal separation circuit for separating or removing one or more signals from other signals in a system in which a plurality of signals are multiplexed at frequencies close to each other. It is about.

[Prior Art] There is an 8 mm video as a device for transmitting a signal which requires a certain transmission band and a signal which is close in frequency to the signal and whose frequency is changed with time by frequency multiplexing.
The conventional signal separation circuit will be described by taking the 8 mm video as an example.

FIG. 7 is a block diagram of a reproduction system for video / audio and pilot signals in 8 mm video, and FIG. 8 is a diagram showing an arrangement of frequency spectra.

In FIG. 7, (22) is a magnetic tape, (23) is a reproducing head, (24) is a rotary transformer, (25) is a reproducing head amplifier, (26) is a high-pass filter, and (27) is a band-pass filter. , (28) a low pass filter, (29) a band pass filter, (30) a luminance signal processing circuit, (31) a chrominance signal processing circuit, (32) a pilot signal processing circuit,
(33) is an audio signal processing circuit.

FIG. 8 shows the spectrum distribution of each signal at the output section of the reproducing head amplifier (25) shown in FIG.
In FIG. 8, (16) is a luminance signal, (17) is an audio signal,
(18) is a color signal, (19) is four frequencies Is a pilot signal.

Next, the operation will be described. The signal recorded on the magnetic tape (22) is detected by the reproducing head (23) and input to the reproducing head amplifier (25) via the rotary transformer (24). The spectrum of each signal contained in the reproduced signal (1) amplified by the reproducing head amplifier (25) is as shown in Fig. 8. This signal is individually processed by each signal processing circuit from (30) to (33). From (26) to (2
Signals are separated by the signal separation filters up to 9).

Here, the color signal (18) included in the reproduction signal (1) is a signal whose carrier frequency has been converted to 743 KHz, and −
The 3dB band is ± 500KHz. Generally, in modulation transmission, there is information in the sideband, so a bandwidth that can transmit the sideband with a good SN ratio is required, and if the bandwidth becomes narrow, the amount of information drops,
The resolution of the video signal will deteriorate. The low-pass conversion color signal of 8 mm video is shown in Fig. 8, and its lower sideband is the pilot signal (19). And frequency overlap. This pilot signal is used for tracking servo, and four frequencies are switched for each field (60 Hz), and there is always only one frequency in terms of time. However, the bandpass filter (27) that extracts the color signal is closest to the color signal band. In order to remove the pilot signal of, the steep attenuation characteristic (solid line in the figure) is given as shown in FIG. 9 (a). With such a steep filter, the cutoff frequency
The group delay (Gd) becomes very large near f _b1 and f _b2 . Therefore, in a screen in which the phase of the color signal changes abruptly, the delay becomes large and ringing occurs.

In order to prevent this, the attenuation amount of the pilot signal can be made sufficiently large by making the attenuation characteristic somewhat gentle (Gd) and narrowing the band (FIG. 9 (b)).

However, by narrowing the band in this way,
The color resolution is deteriorated, a phenomenon such as color bleeding occurs, and the quality of a reproduced image is deteriorated. Further, when the cutoff frequencies are kept at f _b1 and f _b2 and the attenuation characteristic is made gentle, the residual portion of the pilot signal component becomes noise and appears as a beat in the color signal.

Also, Japanese Patent Laid-Open No. 61-208670 proposes a device combining a subtraction circuit and a limiter in order to remove noise contained in a luminance signal, but it is designed to separate only a specific frequency. There was no.

[Problems to be Solved by the Invention] Since the conventional signal separation circuit is configured as described above, if a signal that is close in frequency to a signal that requires a certain bandwidth is sufficiently removed, the bandwidth is narrowed. The group delay increases near the cutoff frequency of the filter and the filter, and the signal requiring the band deteriorates. In addition, if it is attempted to suppress the variation of the group delay and widen the band, there is a problem in that adjacent signals cannot be completely removed and the signals also deteriorate.

The present invention has been made to solve the above-mentioned problems, and it is possible to secure a band of a signal that requires a band, suppress fluctuations in group delay, and sufficiently attenuate signals that are close in frequency. The purpose is to obtain a signal separation circuit that can be used for.

[Means for Solving Problems] Since the frequency component of the second signal adjacent to the first signal requiring a certain transmission band is mixed, the latter signal is extracted and subtracted. It should be done. A signal separation circuit according to the present invention follows a signal whose frequency is temporally changed, changes the resonance frequency of a filter means for extracting the signal, and extracts a signal of a specific frequency temporally changed. Then, this is subtracted from the signal that requires a certain band. Therefore, a filter and a subtraction circuit for extracting the specific frequency are provided.

[Operation] The filter means for extracting a signal whose frequency is changed in time according to the present invention causes the level difference due to the changed frequency to be generated in advance by another filter means, and the level difference is detected by the limiter circuit. The amount of feedback is changed to change the effective frequency of the circuit for different frequencies.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 (a) is a block diagram of the signal separation circuit of the present invention. (1) is the output of the reproducing head amplifier which is the input of the signal separation circuit, and (2) is the first filter means (in the figure, Band pass filter BPF1), (3) is the output signal of the first filter means (2), (4) is the first subtraction circuit, (5) is the output signal of the first subtraction circuit (4),
(6) is a third filter means (a low-pass filter LPF2 in the figure), (7) is an output signal of the third filter means (6), (8) is a second subtraction circuit, (9) ) Is the output signal of the second subtraction circuit (8), (10) is the limiter circuit, (11) is the output signal of the limiter circuit (10), (12) is the third subtraction circuit, and (13) is the second (14) is an output signal of the second filter means (13), and (15) is an output of the signal separation circuit.

Next, the operation of the present invention will be described with reference to the drawings. The reproduction output signal (1) from the reproduction head amplifier is input to the left end of FIG. The frequency spectrum of this reproduction output signal is shown in FIG. Here, (16) is a frequency-modulated luminance signal, and in the case of 8 mm video, the carrier frequency is 4.2 MHz to 5.4 MHz, and sideband components exist on both sides thereof. (17) is a frequency-modulated audio signal with a carrier frequency fa = 1.5 MHz.

(18) is a low-pass converted color signal whose carrier frequency is fcc = 743KHz and the bandwidth is approximately ± 3dB.
It is 500 KHz.

The frequency is switched for each field in the order of. Therefore, the lower sideband of the low-frequency converted color signal and the pilot signal overlap in frequency. Here, the first filter means (2) is shown in FIG.
Assuming that it has a bandpass characteristic as shown in (20), the level of the pilot signal increases as the frequency increases.
Although the level of the pilot signal in the reproduction output signal input to the first filter means (2) does not differ greatly among the four frequencies, the level (Eim) of each frequency is generated by the first filter means (2). In Fig. 3 (a) Shall be

The characteristic of the second filter means (13) is such that it includes the low frequency conversion color signal and the pilot signal as shown in (21) of FIG. 2 (a).

Next, the characteristics of the circuit composed of the first subtraction circuit (4) to the limiter (10) shown in FIG. Here, in the limiter circuit (10), when the input level is considered to be constant, the output level is uniquely determined. Therefore, it may be expressed by the gain K (K is a constant). To be precise, this limiter circuit distorts the waveform (increases odd-order distortion) and cannot be treated linearly, but even if you think that a sine wave with a level equivalent to the output level of that limiter is output, There is no problem.

Therefore, since the limiter circuit can be handled linearly, the system as a whole is linear and the transfer function can be obtained. FIG. 5 shows a block diagram in which portions (4) to (10) in FIG. 1 are rewritten in a linear representation. G ₃ (s) in the figure is the transfer function of the third filter means (6), and the concrete circuit of the third filter means (6) is shown in FIG. When the gain in the subtraction circuit is 1, the transfer function showing the relationship between the input Vi (s) and the output Vo (s) in FIG. 5 is given by the following expression (1).

H (s) = Vo (s ) / Vi (s) = K [1-G 3 (s)] / [1-KG 3 (s)] ...... (1) G 3 (s) is Substituting equation (2) into equation (1), H (s) = K (s / T) ² / [1-K + (s / T) ² ] ... (3) ∴ | H (jω) | = K (Ω / T) ² / | -1 + K + (ω / T) ² | (4) From equation (4), the resonance frequency ω ₀ is the denominator = 0. Is. Therefore, ω ₀ is equal to the resonance frequency T of the third filter means. You can see that it doubles. K is the limiter gain,
Since it changes depending on the input level, ω
₀ can be controlled by the input level. As described above, in the first filter means, among the four frequencies of the pilot signal, the lower the frequency, the more the level is attenuated.
The limiter characteristic as shown in, that is, the pilot signal P ₁
(frequency _Assuming a polygonal line characteristic having E _t4 , E _t3 , E _t2 , and E _t1 , the limiter gain K changes to K ₁ , K ₂ , K ₃ , K ₄ depending on each frequency, and K ₁
A magnitude relationship of ＞ K ₂ ＞ K ₃ ＞ K ₄ occurs. For example, the resonance frequency of the third filter means Selecting a pilot signal P ₄ is because the input level high, the limiter gain K ₄ in FIG. 3 (a) and K ₄ ≒ 0, was calculated from the formula (4) Therefore, the resonance frequency ω _{04 at} that time is ω ₀₄ ≈T. next
Input level of P ₃ Therefore, the limiter gain is K ₃ , which can be larger than K _4, so the resonance frequency ω _{03 at} that time is And move to a lower frequency than in the case of P ₄ . Similarly,
At P ₂ and P ₁ , the input level decreases and K increases, so that the resonance frequency gradually decreases. Calculating the pilot signal of 8 mm video as a concrete example, ω ₀ at P ₄ is K ₄ ≈ 0 This is P ₁ , Therefore, K _{1 at} this time is Becomes

Similarly, K ₂ and K ₃ are successively larger than K ₄ , so in this case, in the end, it is sufficient to realize a limiter (polygonal line characteristic) having an inclination from 0 to 0.6.

From the above, the frequency characteristics from the first subtraction circuit (4) to the limiter (10) in FIG.
The resonance frequency is changed by P ₁ , P ₂ , P ₃ , and P ₄ as shown in FIG. 6 (a). Their maximum amplitude can be approximately equal. In the third filter means as shown in FIG. 4, if the Q (selectivity) is increased (specifically, the value of the inductor L with respect to the capacitor C is increased), each frequency (ω ₀₁ , ω _02). , Ω ₀₃ , ω ₀₄ ), the full width at half maximum becomes smaller and only the pilot signal that matches the resonance frequency is extracted. This is (11) in Fig. 1 (a).
Therefore, in the third subtraction circuit (12), only the pilot signal appearing at that time is subtracted from the output (14) of the second filter means (13). The pilot signal can be sufficiently removed without narrowing the band of the converted color signal or increasing the group delay. In the above embodiment, the second filter means is a low pass filter, but it may be a band pass filter.

Another embodiment of the present invention will be described with reference to the drawings. FIG. 1 (b) is a block diagram thereof, (1) is the output of the reproducing head amplifier and becomes the input of the signal separation circuit, and (2) is the first filter means (low-pass filter in the figure).
LPF1), (3) is the first filter means (2)
Output signal, (4) is the first subtraction circuit, (5) is the output signal of the first subtraction circuit (4), and (6) is the third filter means (low-pass filter LPF3 in the figure). ),
(7) is the output signal of the third filter means (6), (8)
Is the second subtraction circuit, (9) is the output signal of the third subtraction circuit (8), (10) is the limiter circuit, (11) is the output signal of the limiter circuit (10), and (12) is the third output signal. The subtracting circuit (13) is a second filter means (a low-pass filter in the figure).
LPF2), (14) is the second filter means (13)
Is an output signal of the signal, and (15) is an output of the signal separation circuit.

The difference from FIG. 1 (a) is that the first filter means (2) in FIG. 1 (a) is a low pass filter.
Therefore, the positive and negative of each input supplied to the second subtraction circuit are opposite.

Next, the operation of this embodiment will be described with reference to the drawings. The common parts with FIG. 1 (a) are omitted.

The first filter means (2) is, as shown in (20) of FIG. 2 (b), Since it has a lower cut-off frequency, the level of each frequency is set by the first filter means (2) in FIG. 3 (b).
of Shall be

The characteristics of the second filter means (13) are the same as those of FIG. 2 (a), as indicated by (21) in FIG. 2 (b).

Next, the characteristics of the circuit composed of (4) to (10) in FIG. 1 (b) are slightly different from those in the case of FIG. 1 (a). As the characteristic of the first filter means (2) changes, the sign of the input of the second subtraction circuit (8) becomes opposite, so that the gain of the limiter circuit (10) changes.

In this case, assuming that the gain in the subtraction circuit is 1, the transfer function showing the relationship between the input Vi (s) and the output Vo (s) in FIG. 5 becomes the following expression (1).

H = (s) = Vo ( s) / Vi (s) = K [G 3 (s) -1] / [1 + KG 3 (s)] ......
(1 ′) G ₃ (s) is the same as in the previous embodiment.

Substituting this into equation (1), H = (s) = -K (s / T) ² / [1 + K + (s / T) ² ] ... (3 ') ∴ | H (jω) | = K (ω / T) ² / | 1 + K- (ω / T) ² | ... (4 ') From the formula (4'), the resonance frequency ω ₀ is the denominator = 0. Is. Therefore, ω ₀ is equal to the resonance frequency T of the third filter means. It turns out that it becomes. ω ₀ can be controlled by the input level. As described above, in the first filter means (2), the higher the frequency, the more the level is attenuated. Therefore, the limiter characteristic as shown in FIG. Assuming a polygonal line characteristic having t ₃ , E _t2 , and E _t1 , the limiter gain K changes to K ₄ , K ₃ , K ₂ , and K ₁ depending on each frequency, and K ₄ > K ₃ > K ₂
A magnitude relationship of> K ₁ will occur. For example, the resonance frequency of the third filter means Since the input level of the pilot signal P ₁ is large, if the limiter gain K ₁ in FIG. 3 (b) is K ₁ ≈0, the resonance frequency ω ₀₁ will be ω ₀₁ ≈T. Next, since the input level of P ₂ is ep ₂ , the limiter gain is K ₂ and can take a value larger than K _1, so the resonance frequency ω _{02 at} that time is And move to a higher frequency than in the case of P ₁ . As well
P _3, P becomes _4, the input level is small, because the order K increases, the resonant frequency gradually increases. Calculating the pilot signal of 8mm video as a concrete example, P ₁
Since ω ₀ at K ₁ ≈ 0 This is P ₄ , Therefore, K _{4 at} this time is Becomes Similarly, since K ₃ and K ₂ are successively smaller than K ₄ , in this case, in the end, a limiter (polygonal line characteristic) having an inclination of 0 to 1.6 should be realized.

Although the first and second filter means are low-pass filters in the above embodiment, they may be band-pass filters. In the first filter means, the higher cut-off frequency of the band-pass filter is temporally changed. The same effect can be achieved by lowering the lowest frequency of the frequency varying signal.

In the above-described embodiment, the signal to be removed is single in time, but it may be plural. In that case, a plurality of signals can be simultaneously removed by connecting the required number of circuits in parallel.

[Advantages of the Invention] As described above, according to the present invention, the resonance frequency of the filter circuit is configured to change so as to follow the signal whose frequency is temporally switched. A signal requiring a band is effectively extracted in a wide band, with a small group delay variation and a signal whose frequency changes temporally is sufficiently attenuated.

[Brief description of drawings]

1 (a) and (b) are circuit block diagrams of an embodiment of the present invention in which the characteristics of the first filter means are different, and FIG. 2 (a).
(B) is the frequency spectrum in the 8 mm video corresponding to each of FIG. 1, and FIGS. 3 (a) and (b) are the first.
Input and output characteristic diagram of the limiter circuit corresponding to each of the figures,
FIG. 4 is a concrete circuit of the third filter means of one embodiment of the present invention, FIG. 5 is a circuit block diagram of one embodiment of the present invention when linearized, and FIGS. 6 (a) and 6 (b). Is a variation diagram of respective frequency characteristics corresponding to FIGS. 1 (a) and (b), FIG. 7 is a VTR reproduction circuit block diagram including a conventional signal separation circuit, FIG. 8 is a frequency spectrum of the reproduction signal,
FIG. 9 is a frequency characteristic diagram of amplitude and group delay of a conventional signal separation circuit, where (a) has a steep attenuation characteristic and (b) has a gentle attenuation characteristic. In the figure, (2) is a first filter means, (4) is a first subtraction circuit, (6) is a third filter means, (8) is a second subtraction circuit, and (10) is a limiter circuit. (12) is the third
(13) is the second filter means.

Claims (4)

[Claims] 1. A first signal requiring a certain transmission band,
A device for transmitting a second signal, which has a plurality of frequencies close to one of the low band side and the high band side of the first signal and whose frequency is switched in time, by frequency multiplexing, A first filter means for extracting only the signal and giving a level difference between respective frequency components of the second signal; and a second filter for extracting both the first signal and the second signal
Filter means, a first subtraction circuit to which the output signal of the first filter means is supplied to its non-inverting input, and an output signal of the first subtraction circuit to the A third filter having a narrow band frequency rejection characteristic in which the resonance frequency is adjusted to the highest frequency or the lowest frequency, and the output signal of the third filter means is supplied to its inverting input or non-inverting input, A second subtraction circuit, the output signal of the first filter means is supplied to the non-inverting input or the inverting input, and the difference between the output of the third filter means and the output of the first filter means is calculated; The output signal of the second subtraction circuit is supplied, and the output signal of the limiter circuit is changed from the output signal of the second filter means and the limiter circuit whose gain changes according to its input level. A third subtracting circuit is provided, the output signal of the limiter circuit is supplied to the inverting input of the first subtracting circuit, and the difference between the output signal of the first filter means and the output signal of the limiter circuit is obtained. A signal separation circuit characterized by the above. 2. The signal separating device according to claim 1, wherein the first filter means attenuates the level of each frequency component of the second signal toward a lower frequency or a higher frequency. circuit. 3. The signal separation circuit according to claim 1, wherein the third filter means is a second-order low-pass filter including an inductor and a capacitor. 4. The input / output characteristic of the limiter circuit approximately forms a polygonal line characteristic, and the input level at the break point is E _t1 , E _t2 ,
………, E _tn (where n is a positive integer, E _t1 , E _t2 , ………,
E _tn > 0), the gain of the limiter circuit at the input levels E _t1 , E _t2 , ..., E _tn of each break point is K ₁ , K ₂ , ..., K _n , the first filter means. The level of each frequency component of the second signal given the level difference by E _i1 , E _i2 ,
………, E _im (where m is a positive integer and n = m, E _i1 , E _i2 ,
........, E _im > 0), and 0 <E _i1 <E _t1 <E _i2 <E _t2 <......... <E _im <E _tn , the magnitude relation of the gain of the limiter circuit is , K ₁ ＞ K ₂ ＞ ……
...> K _n , The signal separation circuit according to any one of claims 1 to 3.