JPH01309484A - Recording system discriminator - Google Patents

Abstract

PURPOSE:To discriminate the system without being affected by the contrast of a video signal by extracting a sink tip level of a video signal of a base band subject to FM demodulation, comparing its level with a reference so as to discriminate the recording system. CONSTITUTION:In the normal system, the FM modulation carrier is set to 7.0MHz, the sink tip is set to 6MHz, and the peak white is set to 7.5MHz. In the high band system, the sink tip is set to 7.7MHz, the peak white is set to 9.7MHz to improve the resolution. In a detection circuit 8 and a comparator circuit 9, an output (video signal output) of an FM demodulation circuit 7 is fed to the cathode of a diode 10. Then a voltage of the lowest level (sink tip level) of the video signal is held in a capacitor 12. Then a reference voltage (set by a variable resistor 13) of the voltage comparator circuit 14 is set to the intermediate value between the high band system and the normal system. Then as the discrimination output, an H level is obtained in the case of the high band system and an L level is obtained in the case of the normal system.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a recording method discriminating device for discriminating between a normal method and a high band method.

(Explanation) Conventional technology Japanese Patent Application Laid-Open No. 61-253605 (GI IB5102
7) discloses a video tape recorder (VTR) that uses the fact that the voltage of a video signal after demodulation differs depending on the deviation of the recorded FM signal due to the difference in the system to determine the system by comparing the voltage with a reference voltage. There is.

(C) Problems to be Solved by the Invention However, in the conventional example as described above, there is a risk that the DC level of the video signal after demodulation may vary depending on the brightness of the image. There is a possibility that the discrimination of the high band type 5 may malfunction due to fluctuations in the DC level.

(d) Means for Solving the Problems In the present invention, the sync tip level of the FM demodulated baseband video signal is extracted and compared with a reference to determine the recording method.

Furthermore, considering that the FM demodulation output is an emphasized waveform, the level of a portion of the sync chip that is not affected by emphasis is zumbled and compared with the reference.

(e) By extracting the level of the sync chip section whose corresponding frequency is determined by the operation standard, it is possible to perform the discrimination in formula 5 without being affected by the brightness of the video signal.

(f) Examples Examples of the present invention will now be described with reference to the drawings. FIG. 1 is a block diagram showing the main parts of the first embodiment, FIG. 2 is a waveform diagram related to FIG. 1, FIG. 3 is a block diagram related to the first embodiment, and FIG. A block diagram showing the main parts of the embodiment, FIG. 5 is a waveform diagram related to FIG. 4, FIGS. 6 and 7 are characteristic diagrams showing the frequency distribution of each method, and FIG. 8 is an explanation showing the influence of emphasis. It is a diagram.

First, the frequency distributions of the normal method and the high band method will be explained according to FIGS. 6 and 7. FIG. 6 shows the normal method, and FIG. 7 shows the high band method. What is shown is related to an electronic still camera ball. For an overview of electronic still cameras, please refer to Nikkei Electronics 1.
It is explained in February 984 issue pp, so~85.

In the normal system shown in Figure 6, the FM modulation gear is 7.0MH.
z, sync tip: 6 MHz, beak white: 7, 5 MHz. In the high band method (Fig. 7), the sync chip is set at 7.7 MHz and the peak white is set at 9.7 Hz, achieving the highest resolution. Due to these differences in specifications, the characteristics of the equalizer circuit, the emphasis circuit, the low-pass filter for noise removal provided after the FM demodulator, etc. are changed.

In Fig. 3, (1) is a magnetic head on which an FM modulated video signal is recorded, (2) is a magnetic head, (3) is a reproduction preamplifier, (4) is an equalizer, and (5) is a chroma signal. The trap circuit to be removed, (6) is the limiter circuit, (
7) is an FM demodulation circuit, (8) is a detection circuit that detects the zinc depth level of the demodulated video signal, and (9) is a comparison circuit that compares the output voltage of the detection circuit with a reference voltage to obtain a method discrimination output. be.

FIG. 1 shows a concrete example of the detection circuit (8) and the comparison circuit (9). The output (video signal output) of the FM demodulation circuit (7) is applied to the cathode power of the diode (10). Therefore, the content-1 no (12) is a video signal (Fig. 2 (a))
The voltage at the lowest level (sync tip level) will be held (Figure 2 (b)).

Then, the reference voltage of the voltage comparator circuit (14) (variable resistor (1
3) is set to an intermediate value between the high band type 5 case (A>) and the normal method (B), as shown in Fig. 2 (c). Therefore, as a discrimination output, , an H level is obtained when using the high band method, and an L level when using the normal method.

Note that the FM demodulator (7) has a characteristic that the higher the frequency of the input signal, the greater the value of the output voltage.

Next, a second embodiment will be described. In magnetic recording and reproduction using FM modulation, pre-emphasis is performed to emphasize the high frequency range of the video signal to be recorded.

Therefore, the video signal after FM demodulation has a waveform as shown in FIG. 8, and even in the case of the high band method (A>), there is a possibility that the voltage held by the capacitor <12 will be lower than the reference voltage. Second
This embodiment takes into consideration countermeasures against this problem.

FIG. 4 shows a specific example of the detection circuit (20) in the second embodiment. The demodulated video signal (Fig. 5 (a)) from the demodulator (7) is, on the other hand, zinc-chip clamped by a capacitor (15) and a diode 16), and a voltage (resistance) set slightly higher than the clamp level is applied. 17)
(1g)) to perform synchronous separation (voltage comparator (19) output (FIG. 5 (b))).

Furthermore, the synchronization signal is delayed by a predetermined time (time corresponding to the overshoot in FIG.
3) Output (Figure 5 (c)). and inverter (23)
The monomulti (24) is triggered at the timing of the rise of the output. The metastable period of this monomulti (24) is set within the zinc chip period.

(25) is a sample bold circuit, and a switch (
27). Therefore, the hold capacitor (26) holds a sync tip level voltage that is not affected by overshoot.

Note that the output impedance of the FM demodulator (7) is set to be sufficiently low, and the input impedance of the voltage comparison circuit (9) is set to be sufficiently large.

Therefore, even if there is a large autoshoot due to the preemption assist, it is possible to correctly determine the system, and the signal processing circuit can be correctly controlled accordingly.

Furthermore, it goes without saying that the present invention can be applied to a VTR.

(g) Effects of the Invention As described above, according to the present invention, the recording method can be reliably determined, so the effects are outstanding.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the main parts of the first embodiment, Fig. 2 is a waveform diagram related to Fig. 1, Fig. 3 is a block diagram showing the discrimination device, and Fig. 4 is the main part of the second embodiment. Block diagram showing 5th
This figure is a waveform diagram according to FIG. 4, FIGS. 6 and 7 are characteristic diagrams showing the characteristics of the system, and FIG. 8 is an explanatory diagram showing the influence of emphasis. (8)...Detection circuit, (9>...Voltage comparison circuit.

Claims (1)

[Claims] (1) A discrimination device for discriminating recording modes with different frequencies of recorded FM signals during playback, characterized in that the recording mode is discriminated by extracting the sync tip level of the video signal and comparing it with a reference voltage. Device.