JPH0370439B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording and reproducing apparatus for SECAM television color signals (hereinafter referred to as SECAM color signals).

First, an example of a magnetic recording and reproducing apparatus for SECAM color signals used in the conventional VHS magnetic recording and reproducing system will be described with reference to FIG. In Figure 1, numerals 1 to 6 and 7 to 11 are block diagrams showing the flow of signals in the recording system and reproduction system, respectively, and 1 is a block diagram that is separated from the SECAM system television signal during recording and amplified as necessary. This is the input terminal for the SECAM color signal. The SECAM color signal input to this terminal is frequency modulated, so in order to improve the signal-to-noise ratio (hereinafter referred to as S/N ratio) of frequency components that are frequency-distant from the subcarrier, the following formula
In the frequency characteristic shown in (1), the signal level that is far away in frequency from the subcarrier is emphasized.

A=10log ₁₀ 1+256x ² /1+1.6x ² (Signal amplitude) dB...(1) However, x=/o-o/,: Signal frequency, o=4.286MHz...(2) Also, in the figure , 2 is a filter (hereinafter referred to as a recording bell filter) having a frequency characteristic opposite to the frequency characteristic shown in equation (1) above, that is, 1/A, and the SECAM color signal 3 output from this recording bell filter 2 has a frequency The signal level remains constant regardless of the 4
is a frequency 1/4 frequency dividing device, and the frequency of the SECAM color signal is divided by 1/4 (hereinafter, this 1/4 divided SECAM color signal will be referred to as 1/4 SECAM color signal).
5, its frequency characteristic A′ is A′=10log ₁₀ 1+256x′ ² /1+1.6x′ ² (signal amplitude)
dB ……(3) However, x′=/o−′o/: Signal frequency, ′o=o/4≒1.07MHz ……(4) With the filter (hereinafter referred to as recording equivalent filter) By passing the signal through this filter, the S/N ratio of the 1/4 SECAM color signal is improved. Reference numeral 6 denotes an output terminal for a 1/4 SECAM color signal, and this signal is combined with a SECAM luminance signal recorded by another system and recorded on a recording medium.

Next, the time of playback will be explained. 7 is an input terminal for the reproduced 1/4 SECAM color signal which is reproduced from the recording medium, separated from the SECAM luminance signal, and amplified as necessary; A filter with the inverse characteristic 1/A′ (hereinafter referred to as
It is called a reproduction equivalence filter). 9 is frequency 4
10 is a multiplier whose frequency characteristics are as described in (1) above.
This is a filter (hereinafter referred to as a regenerative bell filter) that has the characteristics shown by the formula. Therefore, by guiding the reproduced signal from the recording medium to each of the circuit systems 7 to 10 and allowing it to pass therethrough, a SECAM color signal at the time of reproduction can be obtained at the output terminal 11.

Next, the above-mentioned four types of conventionally used filters will be explained in detail with reference to FIGS. 2 and 3.

FIG. 2 shows the recording bell filter 2 in FIG.
is an example of the reproduction equivalent filter 8, and 21 is
This is the input terminal for the SECAM color signal. 22-25
is the emitter series resonance impedance of the transistor 26 for obtaining a frequency characteristic of 1/A or 1/A', and 27 is the output collector impedance (R ₃ ) of the transistor 26. resistance 2
By selecting the values of 3 (R ₂ ), capacitance 24C, inductance 25L, and attenuation resistance 22 (R ₁ ),
Output the frequency characteristics of 1/A or 1/A' at the terminal 28.
can be obtained. Note that 29 is a circuit power supply.

FIG. 3 shows the regenerated bell filter 10 in FIG.
is an example of the recording equivalence filter 5, and 31 is
It is an input terminal for SECAM color signals, 32 is a damping resistor (R' ₁ ), and 33 to 35 are parallel resonance impedance components. According to this, a resistor 33 (R' ₂ ), a capacitance 34C', and an inductance 35 constitute the emitter parallel resonant impedance of the transistor 36.
By selecting the values of L' and the attenuation resistor 32 (R' ₁ ), the frequency characteristics of A or A' can be obtained at the output terminal 7. In addition, 37 is the output collector impedance (R' ₃ ) of the transistor 36, 38 is the output terminal,
39 is a circuit power supply.

In order to accurately reproduce SECAM color signals, for example, the bell filters described above must have exactly opposite frequency characteristics during recording and reproduction. However, in the conventional method, these filters have a large Q value, so in order to accurately create characteristics near the resonant frequency, the inductance value must be adjusted, and the inductance value must be adjusted during recording and playback. Due to reasons such as the fact that the characteristics of a series resonant circuit and a parallel resonant circuit are used at different times, the circuit constants cannot be made the same during recording and playback.
The disadvantage is that there are a large number of adjustment points.

The present invention aims to avoid these drawbacks of the conventional method, achieve accurate reverse characteristics during recording and playback, and further reduce costs by reducing the number of elements configuring the circuit. be. The basic principle of the apparatus of the present invention is to share a bell filter and an equivalent filter during recording and reproduction, respectively.

The operational functions thereof will be described below with reference to embodiments. Although the bell filter and the equivalent filter handle different frequencies, they are basically the same, so the bell filter will be described in detail. FIG. 4 shows an embodiment of the invention. 41 is at the time of recording
This is the input terminal for the SECAM color signal, and is biased to a certain DC potential. 42 is a short-circuit switch to ground that is open during recording and short-circuited during playback. 43 is an output terminal of a bell filter during recording. 44 is an input terminal of a bell filter during reproduction, and is biased to a certain DC potential. 45 and 46 are short-circuit switches to ground that are open during reproduction and short-circuited during recording. 47 is an output terminal of a bell filter during reproduction.

First, during recording, switches 45 and 46 are shorted,
Since the switch 42 is open, the transistor 48 is in the off state, and the transistor 49 is in the off state.
emitter impedance (hereinafter referred to as R _6E )
is a parallel impedance of a series resonant impedance (hereinafter referred to as Z) consisting of a resistor 50, a capacitor 51, and an inductance 52 and a resistor 53 (hereinafter referred to as _R8 ). Therefore, R _6E = ZR ₈ /Z+R ₈ (5), and the characteristics of the output terminal 43 are determined by the ratio of this R _6E and the collector impedance 54 of the transistor 49 (hereinafter referred to as R _6C ). , if the input signal is Vi and the output signal is Vo, then Vo/Vi = −R _6C / R _6E = −R _6C (Z + R ₈ ) / ZR ₈ ...(6), and set Z and R ₈ to the required values. By selecting this, the frequency characteristic of 1/A can be obtained.

On the other hand, during reproduction, the switch 42 is short-circuited and the switches 45 and 46 are open, so the transistor 49 is in a disconnected state, and the SECAM color signal inputted from the input terminal 44 during reproduction has an impedance R ₈ and Z, and output to the output terminal 47, so if the input signal is V'i and the output signal is V'o, the frequency characteristic of the output is V'o/V'i=Z/R ₈ +Z... (7), and as _is clear from the comparison with equation (6) above, the frequency characteristic A is
has been realized, and also has exactly opposite characteristics (A and 1/
A). In addition, in FIG. 4, 55 is a damping impedance, and 56 is a power supply terminal.

As described in detail above, the apparatus of the present invention is more effective in terms of cost and performance than conventionally used filters, and greatly contributes to the recording and reproduction of SECAM signals.

[Brief explanation of drawings]

Figure 1 is a schematic configuration diagram of a conventionally used SECAM color signal magnetic recording and reproducing device, Figure 2 is a circuit diagram of a conventionally used recording bell and reproduction equivalent filter, and Figure 3 is a conventionally used one. Circuit Diagram of Reproducing Bell and Recording Equivalent Filter, FIG. 4 is a circuit diagram of a bell filter according to an embodiment of the present invention. 1, 41...SECAM color signal input terminal, 2...
Recording bell filter, 3... SECAM color signal recording bell filter output, 5... Recording equivalent filter, 6...
...1/4SECAM color signal output terminal, 7...Playback 1/4
SECAM color signal input terminal, 8...Reproduction equivalent filter, 9...Frequency 4 multiplier, 10...Reproduction bell filter, 11...Reproduction signal output terminal, 42, 4
5, 46...Switch, 43...Output terminal, 44
...Bell filter input terminal during playback, 48, 49
...Transistor.

Claims (1)

[Claims] 1 A differential circuit consisting of a first and a second transistor whose collector current paths are each connected to a first power supply terminal and whose emitters are commonly connected through a resistor;
A resonant circuit is provided between the emitter of the first transistor and the second power supply terminal, and a resonant circuit is provided at both input terminals of the differential circuit, and when one is short-circuited, the other is opened, and when one is opened, the other is opened. first and second switch means that short-circuit the other and alternately turn on and off the supply of the input signal to both the input terminals, in accordance with the turning on of the supply of the input signal to the input terminal of the first transistor; A SECAM signal recording and reproducing device comprising: third switch means for short-circuiting the emitter of the second transistor and the second power supply terminal; and output terminals at the collector and emitter of the first transistor, respectively.