JPH03273571A - Emphasis circuit and de-emphasis circuit - Google Patents

Abstract

PURPOSE:To obtain satisfactory emphasis after FM modulation by adding the delay signal of an FM modulation signal and the FM modulation signal, multiplying a coefficient, and further adding the multiplied result to the FM modulation signal. CONSTITUTION:The FM modulation signal is delayed by a delay circuit 43 and this delay signal is added to the FM modulation signal by a first adder 41. The coefficient is multiplied to this added signal by a coefficient multiplier 44 and the multiplied output of this coefficient multiplier 44 is added to the FM modulation signal by a second adder 42. Then, the emphasized FM modulation signal is obtained from the added output of this second adder 42. Thus, the emphasis of the FM modulation signal can be satisfactorily executed with simple configuration.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an emphasis circuit and a de-emphasis circuit necessary for performing FM modulation recording in a VTR or the like.

[Summary of the invention]

The present invention is an emphasis circuit necessary for performing FM modulation recording in a VTR or the like, and in the emphasis circuit that emphasizes the sideband of an FM modulated signal, the FM modulation signal is delayed by a delay circuit, and the delayed signal is and the FM modulation signal by a first adder, multiplying this addition output by a coefficient by a coefficient multiplier, and adding the multiplication output of the coefficient multiplier and the FM modulation signal by a second adder, An emphasized FM modulation signal is obtained from the addition output of the second adder, so that good emphasis after FM modulation can be achieved.

Further, the present invention provides an FM track played on a VTR or the like.
(In the de-emphasis circuit that de-emphasizes the i-th signal and de-emphasizes the sideband of the FM modulated signal before FM demodulation, the FM modulated signal is supplied to the first adder,
The addition output of the adder is delayed by a delay circuit, this delayed signal and the addition output of the first adder are added by a second adder, and the addition output of this second adder is added by a coefficient multiplier. multiplying by a coefficient, supplying the multiplication output of the coefficient multiplier to a first adder and adding it to the FM modulation signal, and obtaining a de-emphasized FM modulation signal from the addition output of the first adder; This enables good de-emphasis before FM demodulation.

[Conventional technology]

Conventionally, when recording a video signal using FM modulation in a general VTR (video tape recorder), the baseband signal before FM modulation is emphasized, and then this emphasized signal is subjected to FM modulation. During playback, the baseband signal after FMtil was de-emphasized.

On the other hand, in recent years, some devices have been constructed in such a way that the signal after FM modulation is emphasized during recording, and the signal before FM modulation is de-emphasized during reproduction. By emphasizing and de-emphasizing the FM modulation signal in this way, the modulation index can be equivalently increased, which is effective in reducing the generation of unnecessary components called moiré and improving overmodulation.

When emphasizing this FM modulation signal, as shown in FIG. 3, centering on the carrier wave fc of the FM modulation signal,
Perform processing to lift the side band.

Emphasis circuits for emphasizing and de-emphasizing such FM modulated signals have conventionally been constructed using transversal filters. That is, as shown in FIG. 4, the emphasis circuit supplies the FM modulation signal obtained at the input terminal (1) to a series circuit of first and second delay circuits (2) and (3). In this case, the delay amount of both delay circuits (2) and (3) is τ
(r is the unit delay amount).

Then, the FM modulated signal obtained at the input terminal (1) is
The output of the first delay circuit (2) is supplied to the second coefficient multiplier (5), and the output of the second delay circuit (3) is supplied to the third coefficient multiplier (4). Supplied to a multiplier (6).

The outputs of the coefficient multipliers (4), (5) and (6) are then supplied to an adder (7), and the addition output of the adder (7) is supplied to an output terminal (8). In this case, the coefficient to be multiplied by the first coefficient multiplier (4) and the coefficient to be multiplied by the third coefficient multiplier (6
), an emphasized FM modulated signal as shown in Figure 3 is obtained at the output terminal (8) without changing the phase, and this output signal is recorded on a video tape or the like. .

Further, as shown in FIG. 5, the de-emphasis circuit converts the reproduced FM modulation signal obtained at the input terminal (11) into
．． Second. Third and fourth delay circuits (12).

It is supplied to the series circuits (13), (14) and (15). Each of these delay circuits (12), (13), (14)
And (15) also assumes that the amount of delay is τ. Then, the FM modulation signal obtained at the input terminal (11) is transmitted to the first coefficient multiplier (
16), and the output of the first delay circuit (12) is supplied to the second delay circuit (12).
coefficient multiplier (17) and the second delay circuit (13
) is supplied to the third coefficient multiplier (18), the output of the third delay circuit (14) is supplied to the fourth coefficient multiplier (19), and the output of the fourth delay circuit (15) is supplied to the third coefficient multiplier (18). The output is fed to a fifth coefficient multiplier (20). And each coefficient multiplier (16
), (-17), (Ig).

The outputs of (19) and (20) are supplied to an adder (21), and the addition output of the adder (21) is supplied to an output terminal (22). In this case, the coefficient multiplied by the first coefficient multiplier (16) and the coefficient multiplied by the fifth coefficient multiplier (20) are made equal, and the coefficient multiplied by the second coefficient multiplier (17) is made equal to the coefficient multiplied by the fifth coefficient multiplier (20). , and the coefficient multiplied by the fourth coefficient multiplier (19), the de-emphasized FM modulation signal is output to the output terminal (2) without changing the phase.
2) and the FM modulated signal obtained at the output terminal (22) is demodulated by an FM demodulation circuit (not shown) in the subsequent stage.

[Problem to be solved by the invention]

However, in the emphasis and de-emphasis circuits that use such transversal filters, the product of the transfer functions of both circuits is not exactly 1, and the coefficients to be multiplied by each coefficient multiplier are adjusted to improve the transfer. We had to approximate so that the product of the functions approaches 1. Therefore, either the emphasis circuit or the de-emphasis circuit,
This requires a transversal type filter with a large number of taps, resulting in an increase in circuit scale and the inconvenience that there are many adjustment points during manufacturing.

Note that the transfer function H(
f) and the amplitude G are as follows. In this case, a
o is the coefficient of the second coefficient multiplier (5), al is the coefficient of the first
and the coefficients of the third coefficient multipliers (4) and (6).

H(z) = e-”(al e-sr+ ao+ a
l-1-e")...(1) Q= a, + 2 a
+ 1cosωr - (2) An object of the present invention is to enable emphasis and de-emphasis of an FM modulation signal to be satisfactorily performed with a simple configuration.

[Means to solve the problem]

As shown in FIG. 1, for example, the emphasis circuit of the present invention is an emphasis circuit that emphasizes the sideband of a signal FM modulated by an FM modulation circuit (32), in which the FM modulation signal is delayed by a delay circuit (43),
This delayed signal and the FM modulation signal are added to the first adder (41).
This added signal is multiplied by a coefficient by a coefficient multiplier (44), and the multiplication output of this coefficient multiplier (44) and the FM modulation signal are added by a second adder (42). An emphasized FM modulation signal is obtained from the added output of the second adder (42).

Further, the de-emphasis circuit of the present invention, as shown in FIG. is supplied to the adder (61>), the addition output of the first adder (61>) is delayed by the delay circuit (62>, and this delayed signal and the addition output of the first adder (61>) are The addition output of this second adder (63) is multiplied by a coefficient by a coefficient multiplier (64), and the multiplication output of this coefficient multiplier (64) is added to the first adder (63). Adder (61
> is added to the FM modulation signal, and then added to the first adder (6
A de-emphasized FM modulation signal is obtained from the addition output of 1).

[Effect]

According to the emphasis circuit and de-emphasis circuit of the present invention, the transfer functions of both circuits can be set to 1 with a simple circuit configuration.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 1 and 2.

In this example, an emphasis circuit and a de-emphasis circuit are used for a VTR which records a video signal by FM modulation. First, the emphasis circuit will be explained using FIG. 1.

In FIG. 1, (31) indicates an input terminal for a video signal recorded by FM modulation, and the signal obtained at this input terminal (31>) is supplied to an FM modulation circuit (32).

The FM modulation circuit (32) then supplies the FM modulated signal to the emphasis circuit (40).The emphasis circuit (40) converts the FM modulation signal supplied from the FM modulation circuit (32) into the first and second It is supplied to one input terminal of the second adders (41) and (42) and the delay circuit (43). In this case, the delay amount of the delay circuit (43) is set to τ. ) is supplied to the other input terminal of the first adder (41).

Then, the addition output of this first adder (41) is supplied to a coefficient multiplier (44), and multiplied by a coefficient K. Then, the multiplication output of this coefficient multiplier (44) is supplied to the other input terminal of the second adder (42>).The addition output of the second adder (42) is then supplied to the emphasis circuit (40). ) as the output of the output terminal (3
3> and from this output terminal (33>) to a subsequent recording system circuit (not shown), where it is recorded on a videotape in a predetermined format.

Next, a de-emphasis circuit for processing a reproduced signal from a video tape on which a video signal has been recorded in this manner will be described with reference to FIG.

In FIG. 2, (51) indicates an input terminal to which an FM-modulated and recorded video signal is reproduced and supplied, and the FM-modulated signal obtained at this input terminal (51) is sent to a de-emphasis circuit (60). supply This de-emphasis circuit (60) is connected to the FM signal supplied from the input terminal (51).
The modulation signal is supplied to a first adder (61), and the addition output of this first adder (61> is supplied to one input terminal of the delay circuit (62>) and the second adder (63). In this case, the delay amount of the delay circuit (43) is assumed to be τ.Then, the signal delayed by the delay circuit (62>) is sent to the second adder (62).
3) to the other input terminal.

Then, the addition output of this second adder (63) is supplied to a coefficient multiplier (64), and multiplied by a coefficient K. The multiplication output of this coefficient multiplier (64) is then supplied to the other input terminal of the first adder (61).

Then, the addition output of the first adder (61) is supplied to the FM demodulation circuit (52>) as a signal de-emphasized by this de-emphasis circuit (60), and the
The reproduction signal FM demodulated by the M demodulation circuit (52) is supplied to the demodulation signal output terminal (53).

The transfer function HR (Z) of the emphasis circuit (40) and the transfer function HP (Z) of the de-emphasis circuit (60) configured in this way are as follows. In this case, K is the coefficient of the coefficient multipliers (44) and (64).

Hll(Z) = 1 + K (1+ e-”)
...(3)HP(,,=
...(4)1 + K (1+ e-s
r) Therefore, HR(z)・Hpcz)=1...(
5), the emphasis circuit (40) and the de-emphasis circuit (60) are inverse circuits with a transfer function of 1, and the recorded signal emphasized by the emphasis circuit (40) is transferred to the de-emphasis circuit (60) during playback. ) shows that it returns to its original state.

In addition, the stability of the system by this emphasis circuit (40) and de-emphasis circuit (60) is explained in (4) above.
The following equation is shown by Z-transforming the equation.

Hp(z)= 1+K (1+27') This circuit is always stable.

Further, the amplitude G of the signal emphasized by the emphasis circuit (40) is expressed by the following equation.

G= 1+ (2 to +2 to 2) (1+CO3ωτ)...
...(7) This amplitude G is different from the amplitude G of the emphasis circuit shown in FIG. 4 as a conventional example (see equation (2)), but the emphasis characteristic is that the sideband of the carrier frequency fc is emphasized. The characteristics are almost the same as those shown in Figure 3. In this case, τ is selected as follows.

τ=1/2fc (8) Note that the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various other configurations may be adopted.

〔Effect of the invention〕

According to the present invention, in an emphasis circuit and a de-emphasis circuit for emphasizing and de-emphasizing an FM-modulated signal, the transfer functions of both circuits are completely equal to 1 with a simple circuit configuration that does not use a transversal filter. Emphasis and de-emphasis are performed. In addition, there are fewer adjustment points in the circuit than in a transversal type filter, and adjustment can be made easily.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a recording system according to an embodiment of the present invention, and FIG.
Figure 3 is a configuration diagram showing a reproduction system of one embodiment, Figure 3 is a characteristic diagram showing emphasis characteristics, Figure 4 is a configuration diagram showing an example of a conventional emphasis circuit, and Figure 5 is an example of a conventional de-emphasis circuit. FIG. (32) is an FM modulation circuit, (40) is an emphasis circuit, (52) is an FM demodulation circuit, and (60) is a de-emphasis circuit. Agent Hidemori Matsukuma to the 1st ward

Claims (1)

[Claims] 1. In an emphasis circuit that emphasizes the sideband of an FM modulated signal, the FM modulated signal is delayed by a delay circuit, and the delayed signal and the FM modulated signal are combined by a first adder. The added output is multiplied by a coefficient by a coefficient multiplier, the multiplication output of the coefficient multiplier and the above FM modulation signal are added by a second adder, and the emphasis is calculated from the added output of the second adder. An emphasis circuit characterized in that it obtains an FM modulated signal. 2. In a de-emphasis circuit that de-emphasizes the sideband of the FM modulation signal before FM demodulation, the FM modulation signal is supplied to a first adder, and the addition output of the first adder is delayed by a delay circuit. The delayed signal and the addition output of the first adder are added by a second adder, and the addition output of the second adder is multiplied by a coefficient by a coefficient multiplier. A de-emphasis system characterized in that the multiplication output is supplied to the first adder and added to the FM modulation signal to obtain a de-emphasized FM modulation signal from the addition output of the first adder. circuit.