JPS6250903B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for controlling some of the circuit components that perform common operational functions in the signal processing circuits of the recording device and the playback device in a video signal recording and playback device such as a magnetic recording and playback device during recording and playback. The purpose of this is to simplify the circuit configuration and improve the performance of the device by sharing the same information.

More specifically, the nonlinear circuit element that functions as a nonlinear emphasis circuit during recording functions as a nonlinear de-emphasis circuit during reproduction, thereby attempting to share circuit elements.

Household magnetic recording and reproducing device (hereinafter referred to as VTR)
Recently, high-density recording methods have been actively developed from the viewpoint of economical efficiency of magnetic tapes.

However, one of the problems when using the high-density recording method is the deterioration of the S/N ratio of the video signal as the reproduction signal level decreases. As a solution to this problem, a method has been used in which a video signal is subjected to signal processing by a nonlinear emphasis circuit during recording, and then subjected to frequency modulation, and then recorded on a magnetic tape.

This will be explained below using the drawing of FIG. Figure 1 is a block diagram of the signal processing circuit section of a conventional VTR, which has a non-linear emphasis circuit and a non-linear de-emphasis circuit independently configured. Figure 1 a shows the circuit configuration during recording, and Figure 1 b shows the circuit during playback. This shows the configuration. The configuration at the time of recording will be explained according to FIG. 1a.

The video signal input to the terminal 1 is controlled by the AGC circuit 2 so that the output signal level is at a constant level, and after passing through the low-pass filter 4, is input to the nonlinear emphasis circuit 5. The output is input to a frequency modulator 9 via a clamp circuit 6, an emphasis circuit 7, and a clip circuit 8.
The output FM signal is amplified by a recording amplifier 10 and recorded on a magnetic tape (not shown) via a video head 11. Note that 3 is an AGC detection circuit.

Next, the configuration during reproduction will be explained with reference to FIG. 1b.

The signal recorded on the magnetic tape is sent to video head 1.
1, regenerative amplifier 12, limiter circuit 1
3. The FM demodulator 14 reproduces the FM signal into a video signal. Furthermore, it is reproduced into a regular video signal by the respective signal processing circuits of the de-emphasis circuit 15, the low-pass filter 16, and the non-linear de-emphasis circuit 17, and is outputted from the output terminal 19 via the output circuit 18.

Next, the nonlinear emphasis circuit will be explained with reference to the circuit configuration diagram in FIG. 2 and the characteristic diagram in FIG. 3.

In FIG. 2, the transfer function of the circuit configuration block 32 expressed by the ratio of the input signal E ₁ input to the terminal 31 and the output signal E ₂ output to the terminal 33 is expressed as G.
(s). At this time, assuming that diodes D ₁ and D ₂ are short-circuited, transfer function G (s) = G ₁
(s) is However, S=jω.

Also, assuming that both diodes D ₁ and D ₂ are open, the transfer function G (s) = G ₂ (s) is becomes.

Here, whether the diodes D ₁ and D ₂ are in a short-circuited state or an open state, respectively, can be in substantially equivalent states in the following conditions. i.e. resistance R ₁ ,
The magnitude of the input signal E 1 supplied to the diodes D ₁ and _{D 2 via} the capacitors C ₁ and C ₂ is
If the level is large enough to make D ₁ and D ₂ conductive, it can be considered that the diodes D ₁ and D ₂ are almost short-circuited, and if the level of the input signal E ₁ is small, the diodes D ₁ and D ₂ become conductive. Otherwise, diodes D ₁ and D ₂ are considered open.

Also, in Fig. 2, the circuit time constant R ₁・C ₁ =
Resistor R ₁ , R ₂ , capacitor so that R ₂・C ₂
When the values of C ₁ and C ₂ are set, the transfer function G ₁ (s) when the diodes D ₁ and D ₂ are short-circuited is G ₁ (s) = R ₂ /R ₁ + R ₂ , and the input signal E ₁ is The frequency will not depend on the input frequency.

Figure 3 shows the nonlinear emphasis circuit shown in Figure 2, where R ₁ C ₁ = R ₂ C ₂ , and the signal level of input signal E ₁ is 0 dB (2V _p - _p ), -10 dB, and -20 dB. This figure shows an example of the frequency characteristics of . In other words, due to the nonlinear operation of the diodes D ₁ and D ₂ , the output signal power E ₂ is hardly emphasized when the level of the input signal E ₁ is high (at 0 dB input), and when the level of the input signal E ₁ is low (− (at 20dB input) is emphasized.

Next, a circuit configuration in which a signal nonlinearly emphasized during recording using the circuit configuration shown in FIG. 2 is nonlinearly de-emphasized during reproduction will be described with reference to FIG. 4. The transfer function G'(s) expressed as the ratio of the input signal E ₃ input to the terminal 34 and the output signal E ₄ output to the terminal 36 is the transfer function G'(s) of the differential amplifier 35.
The gain of is A ₀ and the transfer function of the feedback loop 37 is G ₀
(s), then becomes. Here, if the output signal E ₂ during recording is input as the input signal E ₃ during playback, then E ₃ = KE ₂ (K is a constant) Also, since E ₂ /E ₁ = G (s), E ₃ = K・G(s)・E becomes ₁ . Therefore, E ₄ /E ₁ =E ₄ /E ₃・E ₃ /E ₁ =G′(s)・
K・G(s) Therefore, in order to reproduce the characteristics of the output signal _E4 during playback with the same characteristics as the input signal _E1 during recording, it is sufficient that G'(s) = 1/G(s). .

Therefore, in the circuit configuration shown in FIG. 4, the gain A ₀ of the differential amplifier 35 is sufficiently large, and the transfer function G ₀ (s) of the feedback loop 37 is the same as that of the circuit configuration block 32 shown in FIG. If used, since G'(s)≈1/G(s) is satisfied, the output signal _E4 at the time of reproduction can be reproduced as a signal with almost the same characteristics as the input signal _E1 at the time of recording.

Therefore, the circuit configuration block 32 shown in FIG. 2 can function as the nonlinear emphasis circuit 5 during recording shown in FIG. 1a, and in the circuit configuration shown in FIG. Using the configuration block 32, the circuit configuration of FIG.
Nonlinear de-emphasis circuit 17 during playback in Figure b
can function as

However, in the conventional example shown in FIGS. 1a and 1b, two circuit configuration blocks 32 shown in FIG. 2 are used as the nonlinear emphasis circuit 5 and the nonlinear de-emphasis circuit 17, respectively.
It is wasteful in terms of parts man-hours and direct material costs, and has drawbacks such as differences in characteristics during recording and playback due to variations in nonlinear elements such as resistors, capacitors, and diodes that make up the circuit configuration block 32. .

In order to eliminate the above drawbacks, the present invention provides a circuit configuration block 32 including nonlinear elements as shown in FIG.
By using the same circuit for both recording and reproduction, it is possible to simplify the circuit configuration, reduce direct material costs, and improve performance.

FIG. 5 shows an embodiment of the present invention.
In FIG. 5, parts that perform the same functions as those in the conventional examples shown in FIGS. 2 and 4 are designated by the same reference numerals. Further, 38 is a switch for switching the signal between R during recording and P during reproduction. During recording, the input signal E ₁ input to the terminal 31 is supplied via the R terminal of the switch 38 to the circuit configuration block 32 including nonlinear elements shown in FIG. 2, and the nonlinear emphasized output signal E ₂ is output to the terminal 33. is output. On the other hand, during playback, the input signal E ₃ input to the 34 terminals
is supplied to one input of the differential amplifier 35, and the output signal of the differential amplifier 35 is sent to the differential amplifier 3 via the P terminal of the switch 38 and the circuit configuration block 32.
If the input signal E 3 applied to the terminal 34 is equal to the non-linearly emphasized output signal E ₂ of the terminal 33 during recording, the output signal E ₂ is applied to the other input of the terminal 36. The output signal E ₄ is reproduced as a signal substantially equal to the input signal E ₁ at the time of original recording, as explained in the conventional example of FIG.

Therefore, if the circuit configuration as shown in FIG. 5 is implemented, the number of circuit configuration blocks including nonlinear elements required for each of recording and reproduction can be reduced to one, and as a result, the circuit configuration can be simplified. This means that performance can be improved.

FIG. 6 is a concrete example of a structure in which the structure of the present invention is implemented in the block diagram of the signal processing circuit section of the conventional VTR shown in FIG. In FIG. 6, 20 is a switch for switching R during recording and P during playback, 21 is a low-pass filter that shares the low-pass filter 4 during recording and the low-pass filter 16 during playback in FIG. 1, and 22 is a switch for switching between R during recording and P during playback. As explained in the embodiment of FIG. 5, the differential amplifier 35,
It is composed of a switch 38 and a circuit configuration block 32, and operates as a nonlinear emphasis circuit during recording, and as a nonlinear de-emphasis circuit during reproduction.

Therefore, by configuring as in the embodiment shown in FIG. 6, the circuit configuration block 32 having the function of a nonlinear emphasis circuit can be used in common for recording and reproduction, thereby simplifying the circuit configuration.
Furthermore, as non-linear circuits are shared, the reproducibility of reproduced video signals is extremely excellent, leading to improvements in characteristics and performance. Furthermore, by configuring as in the embodiment shown in FIG. 6, compared to the conventional configuration shown in FIG. It is also possible to share them.

Also, in the above explanation, we talked about the VTR video signal processing circuit that converts the video signal into a frequency modulation signal, records it on magnetic tape, and plays back this signal to reproduce the original video signal. It is clear that the present invention can also be applied to magnetic sheets, disk memories, etc., where video signals are recorded or stored on a recording medium with nonlinear emphasis in order to improve the S/N ratio, and this signal is reproduced to reproduce the original video signal. It is.

[Brief explanation of the drawing]

Figure 1 is a block diagram of the signal processing circuit section of a conventional VTR, Figure 2 is a diagram showing a specific circuit example of a nonlinear emphasis circuit, Figure 3 is a characteristic diagram of the nonlinear emphasis circuit shown in Figure 2, and Figure 4. 5 is a block diagram showing an embodiment of the present invention, and FIG. 6 is a diagram illustrating an example of the configuration of a nonlinear de-emphasis circuit. FIG. 6 is a block diagram showing an embodiment of the invention. FIG. 2 is a block diagram showing a specific example of a configuration in which the invention is implemented. 31, 34...Input terminal, 32...Circuit configuration block, 33, 36...Output terminal, 35...Differential amplifier, 38...Switch circuit.

Claims (1)

[Claims] 1 It has a nonlinear emphasis circuit, a differential amplifier circuit, and a switch circuit, and when recording, the input video signal is supplied to the nonlinear emphasis circuit through the switch circuit and the obtained signal is recorded, and when playing back, , the regenerated signal is input to one input terminal of the differential amplifier circuit, the output signal of the differential amplifier circuit is supplied to the nonlinear emphasis circuit via the switch circuit, and the output signal of the nonlinear emphasis circuit is A video signal recording/reproducing device characterized in that the video signal is input to the other input terminal of the differential amplifier circuit, and a nonlinear de-emphasized video signal is obtained from the output terminal of the differential amplifier circuit.