JPH0430860Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to an electronic viewfinder that stabilizes the operation of a synchronous separation/video amplification circuit and a deflection circuit connected to a picture tube for the viewfinder.

[Prior art] A video camera with an electronic viewfinder is
By projecting the object to be imaged on the viewfinder picture tube, the photographer can concentrate on shooting while directly checking the imaged content, and is becoming indispensable for this type of video camera. The conventional electronic viewfinder 1 shown in FIG. 2 is a sync separation/video amplification circuit that separates the sync signal necessary for screen scanning of the viewfinder picture tube 2 from the video signal, amplifies the video signal, and shapes the waveform of the sync signal. 3, a deflection circuit 4 that deflects and scans the electron beam irradiated onto the finder picture tube 2 based on the horizontal oscillation pulses supplied from the synchronous separation/video amplification circuit 3, and a display circuit 5 that displays video conditions inside the tube.
and a DC power supply +B, which is a battery power supply, connected to the synchronous separation/video amplification circuit 3, the deflection circuit 4, or the display circuit 5. The synchronous separation/video amplification circuit 3 is composed of a semiconductor integrated circuit such as AN2510S (IC number name), and includes a vertical oscillation circuit (not shown) that generates vertical oscillation pulses in addition to the circuit shown in the figure. The two pins, pin 2 and pin 12, are power supply terminals 3 ₂ and 3 ₁₂ for oscillation and video amplification, respectively. The video signal supplied from the video input terminal 3 ₁₆ to the sync separation/video amplification circuit 3 is first separated into a horizontal sync signal by the sync separation circuit 3a, passes through the amplifier circuit 3b, and then is sent to the outside of the sync separation/video amplification circuit 3. It passes through a contrast adjustment circuit 7 and is applied to the grid of the viewfinder picture tube 2. The horizontal synchronization signal separated by the synchronization separation circuit 3a is used to generate horizontal oscillation pulses in the horizontal oscillation circuit 3c, and the horizontal oscillation pulses obtained here are supplied to the deflection circuit 4. The deflection circuit 4 includes a switching transistor Qs to which a horizontal oscillation pulse is applied to the base, and a diper diode.
Dd, resonance capacitor C, or deflection coil L are connected in parallel, and the flyback transformer 4a
The power supply voltage is supplied through the primary winding.
The secondary winding of the flyback transformer 4a is connected to the anode of the finder picture tube 2 via a rectifier diode D, and the high voltage induced in the flyback transformer 4a during the retrace period of horizontal scanning causes the beam to be A current is formed.

By the way, in the case of this example, in order to reduce power consumption and extend the operating period with one charge, it is avoided to connect the synchronous separation/video amplification circuit 3 and the deflection circuit 4 to separate DC power supply circuits. All the loads are commonly driven by a 5 volt DC power supply +B. In order to stabilize the operation of the deflection circuit 4 and avoid interference with the synchronous separation/video amplification circuit 3 side, a relatively large capacitance of about 100 μF is installed between the deflection circuit 4 and the DC power supply +B at both ends of the coil L1. A decoupling wave circuit 8 in which capacitors C1 and C2 are connected in a π-shape, a capacitor C3 for absorbing a rush current when the power is turned on, and the like are arranged.

[Problems to be solved by the invention] In the conventional electronic viewfinder 1 described above, a decoupling wave circuit 8 is interposed between the DC power supply +B and the deflection circuit 4. In this case, the capacitance of the capacitors C1 and C2, which are sensitive to low temperatures, tends to decrease, and as the capacitance decreases, the decoupling function of the wave circuit 8 deteriorates, and fluctuations in the power supply voltage due to the drive of the deflection circuit 4 cause synchronous separation and video amplification. If the voltage fluctuation in the vertical oscillation period that adversely affects the circuit 3 side or appears at the oscillation power supply terminal ₃₂ in the synchronous separation/video amplification circuit 3 is transmitted to the amplifier circuit 3b via the video amplification power supply terminal ₃₁₂ , The stable operation of the entire synchronization separation/video amplification circuit 3 is hindered.
There were problems such as the image projected on the picture tube 2 for the viewfinder becoming unstable.

[Means for solving the problem] This invention solves the above problem, and separates the synchronization signal necessary for screen scanning of the picture tube for the viewfinder from the video signal, amplifies the video signal, and horizontally a synchronous separation/video amplification circuit that forms an oscillation pulse perpendicular to the synchronous separation/video amplification circuit; a deflection circuit that deflects and scans the electron beam of the finder picture tube based on the oscillation pulse supplied from the synchronous separation/video amplification circuit; A DC power supply commonly connected to the circuit and the synchronous separation/video amplification circuit, this DC power supply and its load, the deflection circuit and the synchronous separation/video amplification circuit.
The present invention is characterized in that decoupling wave circuits are separately connected to the lines connecting the video amplification circuits.

[Function] This invention consists of a synchronization separation/video amplification circuit that separates the synchronization signal necessary for screen scanning of the view tube for the viewfinder from the video signal, amplifies the video signal, and forms horizontal and vertical oscillation palaces; A deflection circuit that deflects and scans the electron beam irradiated to the viewfinder picture tube based on the oscillation palace supplied from the synchronous separation/video amplification circuit is connected to a common DC power supply, and this DC power supply and its load Mutual interference between loads is eliminated as much as possible by interposing separate decoupling wave circuits on the lines connecting the deflection circuit and the synchronous separation/video amplification circuit.

[Example] Hereinafter, an example of this invention will be described with reference to FIG. FIG. 1 is a schematic circuit diagram showing an embodiment of the electronic viewfinder of this invention.

In FIG. 1, the electronic viewfinder 11 includes a decoupling wave circuit 12 in which a resistor R12 and a capacitor C12 are connected in parallel to a line connecting the DC power supply +B and the power supply terminals 3 ₂ and 3 ₁₂ of the synchronization/separation video amplifier circuit 3, and a resistor. A decoupling wave circuit 13 in which a capacitor C13 is connected in parallel to R13 is connected to each other. These decoupling wave circuits 12 and 13 absorb fluctuations in the power supply voltage, eliminate mutual interference between the oscillation operation of the synchronization separation/video amplification circuit 3 and the video amplification operation, and absorb the wave of the decoupling wave circuit 8. Power supply voltage fluctuations in the horizontal oscillation period due to functional deterioration may cause synchronous separation and
It plays the role of eliminating interference from reaching the video amplification circuit 3.
Decoupling wave circuit 13 shown in the embodiment
has a wave band below the vertical oscillation frequency,
It has a fairly large time constant, and is a combination of a 33Ω resistor R13 and a 220μF capacitor C13. The decoupling wave circuit 12 only needs to have a wave band that is one order of magnitude higher than that of the wave circuit 13, and also has a wave band that is one order of magnitude higher than that of the wave circuit 13.
100μF capacitor C12 to resistor R12 of about 3Ω
are combined. In any case, mutual interference among the vertical oscillation, image amplification, and horizontal deflection operations can be completely eliminated.

Therefore, even if the capacitors C1, C2, C12, and C13 in the decoupling wave circuits 8, 12, and 13 all decrease their capacitance when shooting in a low-temperature environment, the synchronization separation and It is possible to eliminate as much as possible the inconvenience that fluctuations in the power supply voltage affect each other between the video amplification circuit 3 and the deflection circuit 4. That is, by interposing the decoupling wave circuits 12 and 13 between the synchronous separation/video amplification circuit 3 and the DC power supply +B, the decoupling wave circuits 12 and 13 are interposed between the synchronous separation/video amplification circuit 3 and the DC power supply +B, so that the synchronous separation/video amplification circuit 3 is By stabilizing the voltage supply and at the same time eliminating voltage fluctuations in the vertical oscillation period from the power supply terminal 3 ₂ side to the power supply terminal 3 ₁₂ side, the synchronous separation/video amplification circuit remains stable even under severe temperature conditions. 3 can be operated stably, thereby eliminating the inconvenience that the screen of the viewfinder picture tube 2 is disturbed along with synchronization and image disturbances, and stable screen formation is always possible.

[Effects of the invention] As explained above, this invention separates the synchronization signal necessary for screen scanning of the viewfinder picture tube from the video signal, amplifies the video signal, and generates horizontal and vertical oscillation pulses. A separation/video amplification circuit and a deflection circuit that deflects and scans the electron beam irradiated onto the finder picture tube based on the oscillation pulses supplied from the synchronous separation/video amplification circuit are connected to a common DC power source. With,
By intervening separate decoupling wave circuits in the lines connecting this DC power supply and its loads, which are the deflection circuit and the synchronous separation/video amplification circuit, the configuration stabilizes the voltage supply to the load, making it possible to stabilize the voltage supply to the load even in low-temperature environments. Even if a situation occurs in which the wave function of the decoupling wave circuit deteriorates, the decoupling wave circuit interposed between the sync separation/video amplification circuit and the DC power supply will Eliminating the effects of voltage fluctuations,
In order to stabilize the voltage supply to the sync separation/video amplification circuit, the sync separation/video amplification circuit can be operated stably even under severe temperature conditions, and the picture tube for the finder can be operated stably even under severe temperature conditions. This provides excellent effects such as eliminating the inconvenience of screen distortion and making it possible to always form a stable screen.

[Brief explanation of drawings]

FIG. 1 is a schematic circuit diagram showing an embodiment of the electronic viewfinder of this invention, and FIG. 2 is a schematic circuit diagram showing an example of a conventional electronic viewfinder. 3... Synchronous separation/video amplification circuit, 4... Deflection circuit, 11... Electronic viewfinder, 8, 12,
13... Decoupling wave circuit, +B... DC power supply.

Claims (1)

[Scope of utility model registration request] A sync separation/video amplification circuit that separates the sync signal necessary for screen scanning of the view tube for the viewfinder from the video signal, amplifies the video signal, and forms horizontal and vertical oscillation pulses; A deflection circuit that deflects and scans the electron beam of the finder picture tube based on the supplied oscillation pulse, a DC power supply commonly connected to this deflection circuit and the synchronous separation/video amplification circuit, and this DC power supply and its load. An electronic viewfinder comprising a decoupling wave circuit separately connected to a line connecting the deflection circuit and the synchronous separation/video amplification circuit.