JPS58159068A - Video reproducing device provided with speed modulating circuit - Google Patents

Abstract

PURPOSE:To reduce considerably the power loss of an output-stage transistor (TR), by deciding the presence or the absence of a synchronizing signal to detect the presence or the absence of a video signal and controlling the operation of a speed modulating circuit by the detection output in a video reproducing device. CONSTITUTION:Only a vertical synchronizing signal is taken out from the synchronizing signal from an input terminal 19 by an integration circuit of a signal deciding circuit 7; and when the video signal exists, a capacitor 30 is charged and discharged, and its potential becomes low; but when the video signal does not exist, the capacitor 30 is held in a high potential because a TR25 is not turned on, and TRs33 and 39 of a controlling circuit 8 are turned off and on respectively, and the output voltage becomes the earth potential, and the base potential of a TR45 of an amplifying circuit 3 of the speed modulating circuit becomes the earth, and the amplifying operation is stopped, and a driving amplifying circuit 4 and an output amplifying circuit 5 in the next stage are stopped. When the synchronizing signal exists, the video signal of an input terminal 1 is supplied to the amplifying circuit 3 through a differentiating circuit 2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a video reproducing device t equipped with a speed modulation circuit.

In order to obtain a sufficient screen contour compensation effect with the speed modulation circuit, it is necessary to flow a high voltage and a large current into the modulation coil, and the speed modulation circuit output transistor to drive the modulation coil. The power loss is significant. In particular, when there is no input video signal (no signal input), the input signal to the speed modulation circuit is only a noise signal containing high frequency components, and the output stage amplifies the waveform obtained by differentiating the noise signal. The power loss of the output stage transistor becomes extremely large. Also, the screen when there is no signal is
The result is an undesirable glare.

Conventionally, as a means to prevent excessive power loss and screen glare in the speed modulation output transistor when no signal is input, the current in the output stage is detected and converted into voltage, and this voltage is used as a feedback voltage. A method of applying a quadruple return to the drive stage of the speed modulation (9) path has been used. In this conventional method, negative feedback is applied to the speed modulation circuit, and a
Since the loop gain of the l1 circuit decreases, there is a problem that if the feedback voltage is too large, a sufficient contour compensation effect cannot be obtained when a normal video signal is input.

Furthermore, it goes without saying that if the feedback voltage is too small, excessive power loss in the output stage transistor cannot be prevented when no signal is input. For this reason, Japanese Patent Publication No. 56-13064 discloses a method in which a limiter circuit is added to the feedback loop and negative feedback is applied only when the boiling region pressure exceeds a certain set value.

However, in this method, a feedback loop is configured within the speed modulation circuit to prevent excessive power loss and screen glare in the output transistor when no signal is input. Because it performs speed modulation operation, unnecessary force is consumed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a video reproducing apparatus equipped with a speed change i91 circuit that can sufficiently perform speed modulation operation and reduce VCwL power loss.

In the present invention, a circuit for determining the presence or absence of a synchronizing signal is used as a means for determining the presence or absence of the video signal 1#1^, and a speed modulation circuit is controlled to be in an operating state or a non-operating state according to the output signal of the polarization determining circuit. A control circuit is provided so that the speed modulation circuit is inactive when there is no video signal.

The present invention will be explained below with reference to the drawings.

The figure is a circuit diagram showing one embodiment of the present invention.

In the figure, 1 is an input terminal into which a video signal is input, 2 is a differentiation circuit, 6 is an amplifier circuit, 4 is a drive amplifier circuit, 5 is an output amplifier circuit, 6 is a speed modulation coil, 7 is a signal discrimination circuit,
8 is a control circuit.

First, the operation of the signal discrimination circuit 7 will be explained. Input terminal 19
The synchronizing signal from N1 is input to an integrating circuit 22 composed of a resistor 20 and a capacitor 21. By appropriately selecting the time constant of the n1 integrating circuit 22, the horizontal synchronizing signal is removed by the integrating circuit 22, and then passed through a resistor 26 to a transistor. Only the vertical synchronization signal is separated and input to the 250 base. The phase of the vertical synchronization signal is inverted by transistor 25, and the phase of the vertical synchronization signal is inverted by transistor 25.
5 is off, the resistor 26, 28, 4 is connected to the power supply terminal 27.
During the period when the transistor 25 is on, the charge in the capacitor 30 is discharged via the diode 29 and the resistor 47. condensation
If the time constant in the range of 4 to 30 is selected to be sufficiently smaller than the charging time constant, all of the charge in the capacitor 30 will be discharged through the resistor 47 and the diode 29 during the ON period of the transistor 25, so that the capacitor 50 The potential of is relatively low. The above is the operation of the signal discrimination circuit 7 when there is a video input signal.

Next, the operation in the case of no signal input will be explained.

When no signal is input, high-frequency component noise is removed by the integrating circuit 22, but the transistor 25 is not turned on because no periodic vertical synchronization signal is obtained.

Therefore, the potential of the capacitor 30 is charged at the same potential as the power supply terminal 27. As described above, when a video input signal is present, the potential of the capacitor 50 is a relatively low potential, and when no signal is input, the potential of the capacitor 50 is the same potential as the power supply terminal 27 (high potential). This 1 voltage is input to the next stage control line 8 as the signal discrimination circuit output signal.

Control circuit 8 operates as follows. First, the case where there is a video input signal will be explained. In this case, the signal discrimination circuit 7
The output voltage of the transistor 5S is relatively low, the base potential of the transistor 5S is higher than the output voltage of the discrimination circuit 7, and the diode 3261 is in an off state. As a result, transistor 3
Since the transistor 39 is turned on and the transistor 39 is turned off, the collector voltage of the transistor 39 becomes the same potential as the power supply terminal 55.

Next, when there is no signal input, capacitor 3
A potential of 0 becomes a high potential. Connect the terminals 27.3 so that the '1 voltage at this time is higher than the emitter voltage of the transistor 35.
5, the diode 52 is turned on and the transistor 33 is turned off. As a result,
The transistor 39 is turned on, and the collector level of the transistor 39 is grounded. With the above operation,
The output voltage of the control circuit 8 is at the first level of the power supply terminal 55 when there is a video input signal, and at the ground level when no signal is input.

The amplifier circuit 3 of the speed modulation circuit is connected to the resistor 4444.4 by 47.
4? , ) Consists of 4 run rasters and 48 pieces.

According to the explanation so far, when there is a video input signal, the output range voltage of the transistor 39 becomes the first level of the power supply terminal 55, so the diode 40 is turned off, and the amplifier circuit 3 receives the input signal from the base end of the transistor 48. Increase in video signal differential waveform 4! i! Perform 4b production.

Additionally, when no signal is input, the diode 40 turns on and the base potential of the transistor 45 becomes the ground potential.
The amplification circuit 3 stops its amplification operation. As a result, the drive amplifier circuit 4 and output amplifier circuit 5 at the next stage also stop operating, and the operation of the speed modulation circuit when no signal is input is automatically stopped.

In this embodiment, the output of the control circuit 8 is connected to the amplifier circuit 3, but the connection point is not limited to the amplifier circuit 3, but also the differentiating circuit 2.
, drive amplifier circuit 4, and output amplifier circuit 5, it goes without saying that the same operation is possible.

As described above, according to the present invention, the speed modulation circuit stops operating when no signal is input, so the power loss of the output stage transistor is only the loss due to the DC bias, which makes it possible to effectively reduce power loss. Become.

Furthermore, since the speed modulation circuit stops operating when no signal is input, screen glare problems do not occur.

Furthermore, since the present invention does not have a feedback loop inside the speed modulation circuit based on the detection of the output current of the modulation circuit, there is no problem that a sufficient contour compensation effect cannot be obtained due to a decrease in the loop gain of the speed modulation circuit when a video signal is input.

[Brief explanation of the drawing]

The figure is a circuit diagram showing an embodiment of a video reproducing device equipped with a speed modulation circuit according to the present invention. t19... Input terminal, 2... Differentiating circuit, 5... Amplifying circuit, 4... Drive amplifying circuit, 5... Output amplifying circuit, 6... Speed modulation coil, 7... signal discrimination circuit,
8...Control circuit.

Claims (1)

[Claims] In a video playback device equipped with a speed modulation circuit that performs screen contour compensation by modulating the electron beam scanning speed using a speed modulation coil, the operation/non-operation of the discriminator circuit that detects the presence or absence of a synchronization signal and the speed modulation circuit is determined. 1. A video reproducing device equipped with a speed modulation circuit, characterized in that the speed modulation circuit is provided with a control circuit, and stops speed modulation operation when a synchronization signal is not detected.