JPH01114182A - Balancing transmission circuit for video signal - Google Patents

Abstract

PURPOSE:To obtain a video signal balancing transmission circuit offering small size, low cost and space saving by applying an unbalanced signal to a base of a transistor(TR) of a circuit employing NPN and PNP TRs and resistors. CONSTITUTION:A collector of an NPN TR 4 connects to a positive power supply and an output terminal and a collector of a PNP TR 5 connects to a negative power supply and an output terminal. Emitters of the TRs 4, 5 are connected together via a resistor 8. A base of the TR 5 is connected to ground via a capacitor 7. A video signal is given to the base of the TR 4. The collector current of the TRs 4, 5 is controlled by a voltage applied to the base of the TR 4 to attain balanced transmission of the video signal. The voltage applied to the collector of the TR 4 and the feedback resistor 8 is used in common by a DC voltage fed to the output terminal. The amplitude voltage ratio of the input and output signals is decided by the ratio of load impedances of the resistor 8 and the monitor TV.

Description

[Detailed Description of the Invention] [Technical Field] The present invention transmits video signals from the camera side to a parallel two-wire cable.
The present invention relates to a system for a video signal transmission circuit of a two-wire video monitoring device that sends DC power supplied to the camera from the monitor television side.

[Background technology]

As a method for transmitting a baseband video signal using a parallel two-wire cable, there is a method shown in FIG. 1 that uses a video transformer 1. In this circuit, an unbalanced video signal is converted into a balanced signal by a transformer, and then transmitted. If an unbalanced signal is injected into a parallel two-wire cable, unnecessary radiation will cause interference to other equipment, such as an AM radio.

If a camera power supply is superimposed on this system, a power supply separation circuit 2 and a DC cutoff capacitor 3 will be added. This circuit is shown in FIG. Here, the power supply separation circuit must maintain a high impedance with respect to the power supply or ground in the baseband video signal frequency band. The drawbacks of this circuit system are: (i) Since the video transformer 1 transmits baseband video signals, it has a transmission band from a low frequency of several tens of H2 to a high frequency of several MH2, so the shape It has the disadvantages of being large and expensive.

(ii) The DC cutoff capacitor must pass the low frequency of several tens of H8 of the baseband video signal, and a large capacity capacitor must be used, resulting in a large size.

There are two points.

[Purpose of the invention]

An object of the present invention is to provide a video signal balanced transmission circuit that is inexpensive, small in size (and space saving).

[Disclosure of the invention]

The present invention provides a video signal transmission circuit that transmits a video signal to a parallel two-wire cable on which a power supply voltage is superimposed, in which the collectors of an NPN transistor and a PNP transistor are connected to a pair of output terminals to which the parallel two-wire cable is connected. Connect, 2
Connect the emitters of two transistors through a resistor,
The configuration is such that an input signal voltage is applied to the base of one transistor.

An embodiment of a video signal balanced transmission circuit according to the present invention is shown in FIG. 4 is an NPN type transistor, 5 is a PNP type transistor, 6 is a bias resistor, 7 is a capacitor, and 8 is a feedback resistor. The collector of PNP transistor 5 is connected to the output terminal on the positive side of the power source, and the collector of PNP transistor 5 is connected to the output terminal on the negative side of the power source. The emitters of the NPN transistor 4 and the PNP transistor 5 are connected via a resistor 8. The base of the P, NP type transistor 5 is grounded via a capacitor 7. Video signal is NP
Input to the base of N-type transistor 4. Here NP
Due to the voltage applied to the base of the N-type transistor 4,
Collector currents flowing through the NPN transistor 4 and the PNP transistor 5 are controlled, allowing balanced transmission of video signals. Here, the voltage applied to the collectors of the NPN transistor 4 and the feedback resistor 8 is the DC voltage applied to the output terminal. The amplitude voltage ratio between the input signal and the output signal is determined by the ratio of the feedback resistor 8 and the load impedance on the monitor TV side. For reference, the circuit on the monitor TV side is shown in Figure 4. 9.10 is the power supply superimposition circuit, 11 is the load impedance, 12 is the DCL and necessary capacitors, and 13 is,
It is a differential amplifier. Here, the ground in FIG. 3 and the ground in FIG. 4 have different potentials. A differential amplifier 13 converts the balanced signal into an unbalanced signal.

In addition, NPN type transistor 4 and PNP type) transistor 5
It is also possible to use a P-channel FET and an N-channel FET instead.

〔Effect of the invention〕

According to the present invention, by configuring a balanced signal sending circuit in which the collectors of an NPN transistor and a PNP transistor are connected to both ends of a parallel two-wire cable on which power supply voltages are superimposed, and the emitters of both transistors are connected via a resistor. By applying an unbalanced signal to the base of one transistor, a balanced signal can be sent to a parallel two-wire cable, and there is no need to use a capacitor between the cable and the balanced signal sending circuit, and the above circuit is constructed with a transformer. Since it is not a plastic material, the size can be reduced and costs can be reduced.

[Brief explanation of the drawing]

Figures 1 and 2 show conventional examples. Figure 1 is a conventional video signal balanced transmission circuit using a video transformer, Figure 2 is a video signal balanced transmission circuit with a power separation circuit added, and Figure 3 and FIG. 4 shows an embodiment, FIG. 3 shows a video signal balanced transmission circuit according to the present invention, and FIG. 4 shows a video signal receiving circuit on the monitor television side. Patent Applicant Matsushita Electric Works Co., Ltd. Patent Attorney Toshimaru Takemitsu and 2 others Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] In a video signal transmission circuit that transmits a video signal to a parallel two-wire cable with a superimposed power supply voltage, an NPN transistor and a P
A video signal balanced transmission circuit characterized in that the collectors of NP type transistors are connected, the emitters of two transistors are connected via a resistor, and an input signal voltage is applied to the base of one transistor.