JPH0470174A - Video signal gain controller - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a video signal gain control device that is effective for use in magnetic recording and reproducing devices (for example, electronic still cameras).

2. Description of the Related Art Conventionally, in an electronic still camera, a video signal reproduced from a magnetic sheet (or magnetic disk) is recorded as a video signal in units of one field in each track on concentric circles of the magnetic sheet.

There are two playback modes for electronic still cameras: frame playback mode and field playback mode. In frame playback mode, two tracks are played alternately, and in field playback mode,
l Tracks are played continuously.

During field playback, if the video signal of the same track is played back continuously, skew distortion (discontinuity of synchronization signals) will occur, resulting in an unsightly image on the monitor TV, so video signal delay elements are generally used for playback. The skew distortion of the video signal is corrected.

In this video signal skew distortion correction, video signal delay elements are switched in units of field frequencies, so flicker occurs if there is an amplitude error.

Therefore, in order to correct this amplitude error, a video signal gain control device that detects and automatically adjusts the amplitude of the video signal is used.

This will be explained below using the drawings.

Fig. 5 is a block diagram showing a magnetic sheet used in a conventional electronic still camera, and Fig. 6 is a block diagram showing a conventional video signal processing circuit. 7-8 are waveform diagrams for explaining FIG. 6.

In FIG. 5, on a concentric track 2 of a magnetic seam 1, 50 tracks of video signals in l-field units are recorded.

Here, the recording amount start point indicates the start and end of writing on the concentric tracks, and is usually located at the vertical synchronization signal -7H.

In FIG. 6, the magnetic head 2 reproduces recording signals (not shown) from concentric tracks on the magnetic sheet l.

The video signal reproducing circuit 3 is constituted by a general FM signal demodulating circuit, and demodulates the recording signal reproduced from the magnetic head 2 into a video signal 0 (see FIG. 7(o)).

Video signal 0 is input to one input terminal of video signal delay circuit 4 .

The video signal delay circuit 4 is composed of, for example, 455 stages of charge transfer devices (CCD), and transfers the video signal 0 (l) using a 4 fsc clock signal (14.3 MHz) input to the other input terminal. 1/2 H video signal p (see FIG. 7(p)) is output (see FIG. 7(p)).

The 1/2 video signal p is input to one input terminal of the gain control circuit 5.

The gain control circuit 5 changes the amplitude of the video signal according to a control signal input to a control terminal, which will be described later.
The video signal 0 and the 1/2H video signal p are adjusted to have the same amplitude and output a video signal q (see FIG. 7(q)).

Next, the video signal 0 and the video signal q are input to respective input terminals of the changeover switch 6.

The control terminal of the changeover switch 6 is connected to, for example, a control signal "(Fig. 7 (r
)), a time-base corrected video signal S (see M in FIG. 7(s)) can be obtained.

However, since the video signal 0 and the video signal q are switched for each field, any amplitude error causes flicker (flickering on the screen).

The detection limit for amplitude error is required to be approximately 45 dB or more.

Therefore, it is necessary to configure the automatic gain control circuit 7 using the gain control circuit 5 described above to minimize the amplitude error.

The operation of the automatic gain control circuit 7 will be explained below.

Video signal 0 is input to detection circuit 8 . The detection circuit 8 is an amplitude detection circuit composed of a filter including, for example, a diode Di, a capacitor C, and a resistor H.
A detected signal t (see FIG. 8 (1)) is output according to the amplitude of the detected signal t. On the other hand, the video signal q is input to the detection circuit 9. Similar to the detection circuit 8, the detection circuit 9 includes a diode Di.
This is an amplitude detection circuit consisting of a filter including a capacitor C and a resistor R, and detects a detection signal U according to the amplitude of the video signal q.
(See Figure 8(u) p! Output.

The detection signals t and U are input to respective input terminals of the differential amplifier IO. The differential amplifier 10 detects the amplitude error between the video signal 0 and the video signal q by amplifying the difference between the detection signals t and U.

Next, the error signal V detected by the differential amplifier 10 (Fig. 8 (
v) It! is input to the filter 11. The filter 11 is a low-pass filter composed of a capacitor 〇 and a resistor R, and provides a control signal (see Fig. 8 (w>)) in which high frequency components included in the error signal V are removed.Control The signal - is input to the control !ll terminal of the gain control circuit 5 to reduce the amplitude error between the video signal 0 and the video signal q.

Problems to be Solved by the Invention By the way, the time constant of the filter 11 described above compensates for the feedback control loop of the automatic gain control circuit 7 and the amplitude and phase characteristics in the control signal vs. the residual amplitude component of the video signal ( ripple). If there is a ripple in the control signal, an unnecessary amplitude fluctuation occurs in the video signal q in the gain control circuit 5.

Therefore, in order to remove the ripple component, the time constant is set to be sufficiently long, for example, the lowest frequency of the video signal is 30H.
It needs to be about 1150 to 1/100 of z.

However, if the time constant is too long, the automatic gain control circuit will not operate when the power is turned on or during a transient period, resulting in excessive flicker.

In view of the problems of conventional video signal gain control devices, the present invention has been developed to make it possible to finish closing the filter during charging in a short time even if the time constant of the filter that determines the response of automatic gain control is long. An object of the present invention is to provide a video signal gain control device that can reduce malfunction time of automatic gain control when power is turned on and can provide a good image.

Means for Solving the Problems The present invention provides a gain control means for controlling and outputting the gain of a video signal, a detection means for detecting the amplitude of input or output to the gain control means, and a detection signal of the detection means. amplitude error detection means for detecting an amplitude error in the video signal from the amplitude error detection means; and low-pass filtering means for removing high frequency components of the error signal of the amplitude error detection means and outputting a control signal to the gain control means. , a reference voltage source, and adjusts the amplitude of the video signal to a constant amplitude by setting the reference potential of the low-pass filter means to the same potential as the reference voltage source. .

Operation The present invention operates so that the error signal is generated around the reference potential by setting the reference potential of the low-pass filtering means for removing high-frequency components of the gain control error signal to the same potential as the reference voltage source. do.

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

FIG. 1 is a block diagram showing a video signal processing circuit used in an electronic still camera using an embodiment of the video gain control device of the present invention, and particularly shows a reproduction signal processing circuit.

2 and 3 are waveform diagrams for explaining FIG. 1. 4. In FIG. 1, the magnetic head 2 reproduces recording signals (not shown) from concentric L tracks of the magnetic sheet l.

The video signal reproducing circuit 3 is constituted by a general FM signal demodulating circuit, and demodulates the recording signal reproduced from the magnetic head 2 into a video signal a (see FIG. 2(a) @).

The video signal a is input to one input terminal of the video signal delay circuit 4.

The video signal delay circuit 4 is composed of, for example, 455 stages of charge transfer devices (CCD), and transfers the video signal a using a 4fsc clock signal (14, 3MH2) inputted to the other input terminal. A 1/2H video signal b (see FIG. 2(b)) delayed by a 1/2 horizontal synchronization signal is output.

The 1/2 video signal is input to one input terminal of a gain control circuit 5, which is an example of gain 11NI1 means.

The gain control circuit 5 can change the amplitude of the input video signal according to a control signal input to a control terminal, which will be described later. C (see FIG. 2(c)).

Next, the video signal a and the video signal C are input to respective input terminals of the changeover switch 6.

The changeover switch 6 inputs a control signal d(
(See Figure 2(d)).
A time-axis corrected video signal e (see FIG. 2(e)) is obtained.

By the way, since the video signal a and the video signal C are normally switched to the l field @ (recording jump start point), if there is an amplitude error, flicker (flickering on the screen) will occur as in the conventional example.

In the present invention, the occurrence of flicker is prevented by constructing an automatic gain control circuit 7 using a gain control circuit 5 and minimizing amplitude errors.

The automatic gain control circuit 7 will be explained below.

The video signal a is input to a detection circuit 8 as an example of second detection means. The detection circuit 8 includes, for example, a diode Di.
・This is an amplitude detection circuit composed of a filter including a capacitor C and a resistor R, and outputs a detection signal f (see Fig. 3(c)) according to the amplitude of the video signal a.

On the other hand, the output video signal C of the gain control circuit 5 is input to a detection circuit 9 as an example of first detection means.

The detection circuit 9 is an amplitude detection circuit composed of a filter including a diode Di, a capacitor C, and a resistor R, similar to the detection circuit 8, and detects a detection signal g according to the amplitude of the video signal C.
(See FIG. 3(g)).

The differential amplifier 10 inputs these detection signals "and 8" to respective input terminals and amplifies the difference between the detection signals f and g, thereby detecting the amplitude error between the video signal a and the video signal C.

The filter 11 is a low-pass filter composed of a capacitor 〇 and a resistor R, and inputs the error signal h detected by the differential amplifier 10 (see Fig. 8 (h)), and calculates the high level included in the error signal. Control signal i from which frequency components have been removed
(See Figure 3(i) p!j). here,
The negative terminal of the capacitor C is connected to the reference voltage -812 and has the same potential.

The potential of the reference voltage source I2 is set to a voltage slightly lower than the range of change of the control signal i.

This W control signal i is input to the control terminal of the gain control circuit 5, and functions to control the gain control circuit 5 to adjust the amplitude error between the video signal a and the video signal C to the same amplitude.

Therefore, by providing a reference voltage in the filter 11, as shown in FIG. 4, the response of the negative feedback loop becomes faster as in the present embodiment (solid line) compared to the conventional fN (broken line).

In addition to the embodiments described above, similar effects can be obtained when automatically adjusting the amplitude of a single video signal.

Further, the video signal for finding the error may be not the output of the gain control circuit, but the video signal input thereto.

Effects of the Invention As described above, according to the present invention, even if the time constant of the filter that determines response closing is long, the filter charging interval can be completed in a short time, and Can reduce closing during malfunction.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a video signal gain control device according to an embodiment of the present invention, Figs. 2 and 3 are waveform diagrams of each signal in the embodiment, and Fig. 4 is an automatic gain control circuit in the embodiment. 5 is a plan view showing the magnetic sheet, FIG. 6 is a block diagram showing a conventional video signal gain side W device, and FIGS. 7 and 8 are waveform diagrams for explaining the device. be. l... Magnetic sheet, 2... Magnetic head, 3... Video signal reproducing circuit, 4... Video signal delay circuit, 5...
Gain control circuit (gain control means), 6... changeover switch, 7... automatic gain control circuit, 8... detection circuit,
9...Detection circuit, 10...Differential amplifier circuit, IN...
・Filter 12...Reference voltage source. Name of agent Patent attorney Matsu 1) Tadashi

Claims (2)

[Claims] (1) A gain control means for controlling and outputting the gain of a video signal, a detection means for detecting the amplitude of input or output to the gain control means, and detecting an amplitude error of the video signal from a detection signal of the detection means. comprising an amplitude error detection means for detecting, a low-pass filtering means for removing high frequency components of an error signal of the amplitude error detection means and outputting a control signal to the gain control means, and a reference voltage source, A video signal gain control device, characterized in that the amplitude of the video signal is adjusted to a constant amplitude by setting the reference potential of the low-pass filter means to be the same potential as the reference voltage source. (2) gain control means for controlling and outputting the gain of the first video signal; first detection means for detecting the amplitude of the input or output to the gain control means; a second detection means for detecting; a differential amplification means for inputting the outputs of the first and second detection means and calculating the difference therebetween to detect an amplitude error between the first and second video signals; low-pass filtering means for removing high frequency components of the error signal of the differential amplification means and outputting a control signal to the gain control means;
a reference voltage source, and adjusts the amplitude of the first video signal to a constant amplitude with respect to the amplitude of the second video signal by setting the reference potential of the low-pass filtering means to the same potential as the reference voltage source. A video signal gain control device characterized by: