JPH08329403A - Picture quality improvement circuit - Google Patents

Abstract

PURPOSE: To obtain an optimum picture quality improving effect according to frequency characteristics of various tapes by varying capacity equivalent to an integration circuit according to the recording/reproducing envelope level of the tape. CONSTITUTION: When a video tape recorder is in an optimum recording current automatically setting mode, an output signal of an envelope detection circuit 11 at a recording time is inputted to a system control circuit 13, and the envelope level is A/D converted; and a level value is measured. Then, the circuit 13 leads out step values (1-8) from the envelope value, and takes out control values answering to them by referring to a table in a memory 14. These control values become the output DATA1-3 of the circuit 13. At this time, when a reference value at a design time is made a fifth step, the control values are set until four steps for the tape of the small envelope level, and are set until three steps for the tape of the large envelope level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image quality improving circuit for supplying an optimum recording current to a magnetic head in a magnetic recording / reproducing apparatus such as a video tape recorder.

[0002]

2. Description of the Related Art The image quality of video tape recorders has been remarkably improved due to the recent remarkable performance improvement of magnetic tapes. Along with this, the difference in performance from the existing magnetic tape has widened, and the difference in the optimum recording current depending on the magnetic tape used has become non-negligible in designing a video tape recorder.

In order to eliminate this difference, a method has been devised for automatically setting the current supplied to the magnetic head to an optimum value.

For example, what is called a tape-running type setting system in which only recording is performed while varying the recording current, and then rewinding and reproducing is performed to measure the envelope level of each recording current, or a cylinder using only one head is used. There is a method called a tape static type setting method in which recording and reproduction are repeated every cycle, and the recording current is changed every few times to measure the envelope level of each recording current.

Although these differ in the procedure for measuring the envelope level, they are implemented by the system having the configuration shown in FIG.

In FIG. 1, (1) is a video preamplifier, which makes the recording current supplied to the magnetic head variable according to the voltage applied to the terminal a.

(2) is a recording equalizer circuit, and (3) is a video signal processing circuit.

A system control circuit (4) outputs an envelope measurement from the video preamplifier (1), control at the time of measurement, and a setting control signal of the optimum recording current after the measurement to the voltage control circuit (5).

The voltage control circuit (5) receives an instruction from the system control circuit (4) and controls the voltage applied to the terminal a.

The video tape recorder measures and sets the envelope level at the first recording after the tape is inserted, when the optimum recording current automatic setting system is operating.

A control signal is transmitted from the system control circuit (5) to the video processing circuit (3), and an FM carrier (NTSC is supplied from the FM modulation output terminal of the video signal processing circuit (3)).
3.4 MHz, PAL outputs only 3.8 MHz) and inputs it to the video preamplifier (1) via the recording equalizer circuit (2).

The video preamplifier (1) receives the voltage controlled by the voltage control circuit (4) at the voltage control terminal a by the control signal from the system control circuit (5), and supplies the recording current supplied to the head according to the applied voltage. Change and record on tape.

Next, the recorded portion of the tape is reproduced, and the reproduced RF signal is converted into an envelope detection signal by the video preamplifier (1) and output to the system control circuit (5).

The system control circuit (5) accumulates envelope detection data for each recording current and relatively compares them to determine the optimum recording current.

According to the result, the system control circuit (5)
Outputs a control signal which is an optimum recording current to the voltage control circuit (4), is converted into a voltage and is applied to the voltage control terminal a of the video preamplifier (1).

According to the applied voltage, the video preamplifier (1) supplies an optimum recording current to the head.

After that, the optimum recording current is held until the tape is ejected.

However, according to this method, the optimum recording current for each tape, that is, the recording current level at which the maximum output can be obtained can be automatically set, but the image quality improving effect on the frequency characteristic cannot be obtained.

For example, the effect of improving the reversal phenomenon that occurs when a bad tape having a small reproduction envelope signal is used, and a video frequency characteristic of 2 MHz or more of a high-grade tape such as an SVHS (registered trademark) tape having a large reproduction envelope signal is used. Neither the improvement effect of the phenomenon that the frequency is difficult to come out or the expectation can be expected.

[0020]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is technically possible to automatically set a recording current that provides an optimum image quality improving effect in accordance with the frequency characteristics of various video tapes. It is an issue.

[0021]

In order to solve the above problems, the present invention provides an envelope detection circuit for detecting the envelope level of an RF signal reproduced by a magnetic head,
An equalizer circuit having a variable equalization characteristic according to an input control signal, a system control unit for outputting a control signal to the equalizer circuit, and a memory storing control values corresponding to a plurality of envelope levels, the envelope detection circuit An output level is determined, a control value corresponding to the determined level is read from the memory, and the read control value is output to the equalizer circuit.

[0022]

According to the magnetic recording / reproducing apparatus of the present invention, the data of the envelope level corresponding to the tape of each grade is stored in the memory in advance, and the recording / reproducing envelope level of the tape used is compared with the above-mentioned data to determine the tape grade. Discriminating, and by varying the capacity corresponding to the integrating circuit of the video recording equalizer circuit according to the grade, it is possible to suppress the reversal phenomenon by raising the high range of the recording equalizer characteristic for tapes with a small playback envelope level. ,
Further, with a tape having a high envelope level, the high frequency band of the video frequency characteristic can be obtained by lowering the high frequency band of the recording equalizer characteristic.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the image quality improving circuit of the present invention will be described below with reference to FIGS.

FIG. 2 is a block diagram of the image quality improving circuit of the present invention.

In the figure, (8) is a video preamplifier,
The voltage supplied by the resistors R1 and R2 to the terminal a is fixed and the recording current is controlled to be constant.

Reference numeral (9) is a recording equalizer circuit, which changes the equalizing characteristic according to the input control signals DATA1 to DATA3 and inputs it to the video preamplifier (8).

A video signal processing circuit (10) outputs the video signal to the recording equalizer (9).

(11) is an envelope detection circuit,
The envelope of the RF signal reproduced by the magnetic head (12) is detected.

A system control circuit (13) receives the envelope signal detected by the envelope detection circuit (11) and outputs control signals (DATA1 to 3) to the recording equalizer circuit according to the signal level. .

Reference numeral (14) is a memory, which is accessed by the system control circuit (13).

Thus, when the optimum recording current automatic setting mode is set in the video tape recorder, first, the envelope detection circuit (1
Input the output signal of 1) to the system control circuit (13),
The envelope level is A / D converted and the level value is measured.

Further, the system control circuit (13) transmits a control signal to the video processing circuit (10) so that the FM carrier (NTSC is 3.4 MHz for NTSC) from the FM modulation output terminal of the video signal processing circuit (10). , PAL is 3.8M
Only Hz) is output.

This FM carrier is input to the video preamplifier (8) via the recording equalizer circuit (9).
This equalizer circuit (9) has the integrating circuit shown in FIG.

In the figure, C1, C2 and C3 are capacitors, and the equalizing characteristics are made variable by ON / OFF controlling the switching transistors Q1, Q2 and Q3 by control signals DATA1 to DATA3.

The capacitance ratio of the capacitors is C1: C2:
When C3 = 1: 2: 4, the capacitance value is proportional to the DATA value.

The system control circuit (13) also controls the control signal (DAT) according to the measured envelope level.
A1 to 3) are output.

DATA1 to DATA3 are determined as follows.

The system control circuit (13) determines the step value (1 to 8) by discriminating the envelope level value by a predetermined eight-step threshold value.

The control value corresponding to this step value is retrieved by referring to the table stored in the memory (14).

As shown in the table of FIG. 4, this table corresponds to steps 1 to 8 and DATA 1 to 3 in 8 steps, and is stored in the memory (14) in advance.

The extracted control values are output as DATA1 to DATA3 from the system control circuit (13).

Here, assuming that the reference value at the time of design is the fifth step, it is 4 for a tape having a small envelope level.
Up to 3 steps can be set for tapes with large steps and envelopes.

Thereafter, this output is held until the tape is ejected.

[0044]

As described above, according to the image quality improving circuit of the present invention, in a tape having a small reproduction envelope level,
The reversal phenomenon can be suppressed by increasing the high frequency range of the recording equalizer characteristic, and the high frequency range of the video frequency characteristic can be output by lowering the high frequency range of the recording equalizer characteristic with a tape having a high envelope level. It is possible to improve the effect of improving the reversal phenomenon that occurs when a bad tape having a small reproduction frequency and the phenomenon that the frequency of 2 MHz or more, which is a video frequency characteristic of a high-grade tape such as an SVHS tape having a large reproduction envelope signal, is difficult to appear. .

[Brief description of drawings]

FIG. 1 is a system configuration diagram of a conventional equalizer characteristic automatic setting device.

FIG. 2 is a system configuration diagram of an equalizer characteristic automatic setting device of the present invention.

FIG. 3 is a configuration diagram of an integrating circuit of a recording equalizer circuit.

FIG. 4 is a diagram showing a memory table.

[Explanation of symbols]

 1 Video Preamplifier 2 Magnetic Head 3 Envelope Detection Circuit 4 Recording Equalizer Circuit 5 Video Signal Processing Circuit 6 Voltage Control Circuit 7 System Control Circuit 8 Video Preamplifier 9 Recording Equalizer Circuit 10 Video Processing Signal 11 Recording Equalizer Circuit 12 Magnetic Head 13 System Control Circuit 14 memory

Claims (1)

[Claims] 1. An envelope detection circuit for detecting an envelope level of an RF signal reproduced by a magnetic head, an equalizer circuit having variable equalization characteristics according to an input control signal, and a system control section for outputting a control signal to the equalizer circuit. And a memory storing control values corresponding to a plurality of envelope levels, the output level of the envelope detection circuit is discriminated, the control value corresponding to the discriminated level is read from the memory, and read. An image quality improving circuit for a magnetic recording / reproducing apparatus, which outputs a control value to the equalizer circuit.