JPS63244444A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To simplify the structure of a reproducing signal processing system and to reduce the cost by changing over the passive element composing an active blow pass filter according to the level of DC voltage impressed on a control input terminal. CONSTITUTION:The active blow pass filter 12 connected to a demodulator 2 is composed of plural passive elements, e.g., a 1st resistance body 13 and 1st and 2nd variable capacity diodes 14, 15. In this case, the variable capacity diodes 14, 15 in one active blow pass filter 12 are selected with the level of DC voltage impressed on a control input terminal 11 to correspond with the band-limit mode of FM modulation frequency. The need for using a low pass filter on each mode of the respective band limitation is thus eliminated, the circuit structure is simplified and becomes inexpensive.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention switches and sets a plurality of FM modulation frequencies for video signal modulation into a plurality of modes during recording, and during playback, the above-mentioned FM modulation frequencies are set according to the setting mode of the frequency. The present invention relates to a magnetic recording/reproducing device that selects a modulation frequency band.

[Conventional technology]

A conventional reproduced signal processing system for this type of device is shown in FIG. In the figure, (1) is an input terminal for a reproduced FM signal, (2) is an FM demodulator connected to the input terminal (1), (3) is an active low-pass filter connected to the FM demodulator (2), (4) is a first amplifier connected to the active low-pass filter (3).

(5) is a de-emphasis circuit consisting of a resistor (5a) and a capacitor (5b) and connected to the output stage of the FM demodulator (2), and (6) is a de-emphasis circuit (5).
a second amplifier (7) connected to the second amplifier (6
), and (8) is a third amplifier connected to the low-pass filter (7). (9)
is the output from the first amplifier (4) and the third amplifier (8)
A changeover switch (11) is a control input terminal that controls the switching operation of the changeover switch (9).

Next, the operation will be explained. The signal recorded on the recording medium is taken out by the video head, passed through a rotary transformer, and amplified by a preamplifier (none of which is shown).The signal is then amplified by a preamplifier (none of which is shown), and further processed by amplitude, phase equalization, dropout compensation, and amplitude limiting. After processing, the signal is reproduced by an FM demodulator (2). This reproduced video signal is processed in a de-emphasis circuit (5) with a characteristic opposite to the pre-emphasis characteristic at the time of recording.

Now, the FM modulation frequency settings are, for example, 8 and 4 MHz for the synchronization signal part and the white peak signal part, respectively.
−4,4MHz first mode and 5.4MHz~6,
Assume that the second mode of 4 MHz is selected.

An active low-pass filter (3) is used as a band-limiting low-pass filter corresponding to the first mode,
A low-pass filter (
7) is used. That is, when the first mode is set, the video signal that has undergone de-emphasis processing passes through the active low-pass filter (3) and the first amplifier (4) and reaches the changeover switch (9).

When the DC voltage level of the control input terminal αη is “L”, the output terminal α
A video signal is output to O. When setting the second mode, the second amplifier (6), low-pass filter (7),
It reaches the selector switch (9) through the third amplifier (8), and is output to the output terminal α0 at the DC voltage level “H” at the control input terminal αυ.

[Problem that the invention seeks to solve]

In the conventional magnetic recording/reproducing apparatus, the reproduction signal processing system is configured as described above, and includes a band-limiting low-pass filter (3) corresponding to the first and second modes.

(7) respectively, and the output signal thereof must be switched using a changeover switch (9) according to each mode, which has disadvantages such as a complicated circuit configuration and increased cost.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and aims to provide a magnetic recording and reproducing device that can simplify the configuration of a reproduced signal processing system and reduce costs. .

[Means for solving problems]

The magnetic recording/reproducing device according to the present invention comprises an active low-pass filter with a plurality of passive elements, and when a DC voltage that changes depending on the setting mode of the FM modulation frequency is applied to the control input terminal, the passive element selection circuit activates the active low-pass filter. Passive elements are selected according to the above mode.

[Effect]

In this invention, when a DC voltage corresponding to the setting mode of the FM modulation frequency is applied to the passive element selection circuit, the passive element corresponding to the mode is selected by the passive element selection circuit. Therefore, it is no longer necessary to provide a filter for band limiting the reproduced video signal for each setting mode of the FM modulation frequency, which simplifies the configuration and reduces costs.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of a reproduced signal processing system of a magnetic recording and reproducing apparatus according to the present invention, and the same parts as those in the conventional system are given the same reference numerals and the explanation thereof will be omitted.

In the figure, @ is an active low-pass filter connected to the demodulator (2), and is connected to multiple passive elements, such as the first resistor (to) and the first and second variable capacitance diodes α →, Qυ. When the band limit of the FM modulation frequency of the video signal is set to the first mode, the first and second variable capacitance diodes 0→QO are selected, and the band limit of the FM modulation frequency is set to the first mode. When mode 2 is set, the first variable capacitance diode α→ is selected.

αQ is a first transistor that biases the first variable capacitance diode αυ, and αη is a constant current source connected in series with the first transistor Qf9 (g).

α is a second resistor and a diode, respectively.

(a) is a second transistor that biases the first variable capacitance diode a→, and ■υ is the second transistor (a) that is turned on according to the level of the DC voltage input to the control input terminal αυ.・The third transistor (A) and I23 that are turned off are the eighth transistors (goods).
a collector resistor and a base resistor, and the first
．． The variable capacitance diode α→ together with the second and third transistors 0Q, (A), eυ, etc.

A circuit (c) is configured to select 0υ according to the level of the DC voltage.

Next, the operation of the above configuration will be explained.

The input video signal reaches the output terminal 00 through the first resistor.

Here, the band limit of the FM modulation frequency of the video signal is the second
Assume that the level of the DC voltage applied to the control input terminal α◇ in the setting mode is “L”.

The first variable capacitance diode Qf9 has an appropriate base bias voltage applied to the first transistor QQ, and operates as a capacitor corresponding to the bias voltage. Its capacitance value is selected to limit the band of the second setting mode of the FM modulation frequency together with the first resistor alpha field. At this time, the mode switching limit input terminal 0]) has a DC voltage of “L”.
” level, the second transistor wire is cut off. Therefore, the second variable capacitance diode α
Bias voltage is not evenly supplied and it does not operate as a capacitor.

Next, the band limitation of the FM modulation frequency is selected as the first mode, and the DC voltage level of the control input terminal αυ becomes “■
”, the second transistor (a) is turned on because the base voltage is applied by the second resistor (to) and the diode a, and the second variable capacitance diode αυ
Supply an appropriate bias voltage to the Therefore, the capacitance corresponding to the bias voltage is the first variable capacitance diode α
The capacitance of a is added in parallel. The composite capacitance is selected to limit the first mode band.

Here, the variable capacitance diode 0→, 0 in one active low-pass filter @ is selected by the level of the DC voltage applied to the control input terminal αη to correspond to the band-limiting mode of the FM modulation frequency. The circuit configuration is simpler than that using a low-pass filter for each band-limiting mode, resulting in lower cost.

In the above embodiment, the variable capacitance diode as a passive element constituting the low-pass filter (2) is selected according to the DC voltage level applied to the control input terminal. ) may be selected.

[Effects of the Invention] As described above, according to the present invention, the band of the FM modulation frequency is switched by selecting the passive elements constituting the active low-pass filter according to the level of the DC voltage applied to the control input terminal. This configuration has the effect of simplifying the configuration and making it cheaper.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a reproduction signal processing system of a magnetic recording/reproducing apparatus according to the present invention, and FIG. 2 is a block diagram showing the configuration of a reproduction signal processing system of a conventional magnetic recording/reproducing apparatus. θυ...Control input terminal, @...Active low-pass filter, α3.0.4), a$...Passive element, (
)...Passive element selection circuit. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] (1) Magnetic recording and playback in which multiple FM modulation frequencies for video signal modulation are switched and set to multiple modes during recording, and during playback, the band of the reproduced video signal is selected according to the setting mode of the FM modulation frequency. The device includes: a plurality of passive elements constituting an active low-pass filter for band limiting of a reproduced video signal; a control input terminal to which a DC voltage that changes according to the setting mode of the FM modulation frequency is applied as a control voltage; A magnetic recording/reproducing device comprising: a passive element selection circuit that selects the passive element according to a DC voltage applied to an input terminal.