JPH0460580A - Cathode transmitting circuit for video signal - Google Patents

Abstract

PURPOSE:To match the impedance of a transmission line by terminating a signal in a high frequency range of a cathode-ray tube socket substrate through a high-pass filter and a signal in a low frequency range on a chassis side through a low-pass filter. CONSTITUTION:The signal from a cathode output amplifier 1 as a wide-band video signal source is inputted from an input terminal A arranged on a chassis 7 and a low-frequency load resistance R1 is connected to a power terminal through an inductance L1 which forms the low-pass filter. Further, a transmission line 6 which has characteristic impedance is connected to the input terminal A and the cathode of a cathode-ray tube and a capacitor C1 which forms the high-pass filter are connected through an impedance matching coil L2 mounted on the cathode-ray tube CRT socket substrate 8 and terminated by a high-frequency load resistance R2. Further, the parallel circuit of a resistance R3 and an inductance L3 is connected between the capacitor C1 and resistance R2 when necessary so as to compensate the floating capacity of the resistance R2. Consequently, the impedance matching is realized over a wide range.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a transmission circuit that drives the cathode of a cathode ray tube (CRT).

[Summary of the invention]

In RGB monitors, monitors, etc., by terminating the high frequency range of the video output signal on the cathode ray tube socket board, impedance matching of the transmission line is achieved and the cathode of the cathode ray tube can be driven in a frequency band exceeding 300 MHz. It is.

[Prior art and its problems]

For example, in a cathode ray tube display whose operating frequency has video signal frequency characteristics up to a 300 MHz band,
When driving a cathode at a high frequency, stray capacitance of the transmission line and the cathode of the cathode ray tube becomes a problem. Furthermore, since a wideband video drive amplifier passes a large current, a large heat sink is required, and if this plate is placed on the cathode ray tube socket board, it will put a strain on the neck of the cathode ray tube, making it difficult to implement. As a conventional example that solves these problems, as shown in FIG. 2, a cathode output amplifier 1 which is a wideband video signal source
In a cathode drive circuit for driving a cathode of a cathode ray tube, the first transmission line 1!2 has an input end, an output end, and a characteristic impedance, a second transmission line 4 has an input end, an output end, and a characteristic impedance, and the second transmission line 4 has an input end, an output end, and a characteristic impedance. a terminating resistor 5 terminating the output end of the transmission #i4 with a load matching the characteristic impedance of the second transmission line 4; the output end of the first transmission 112, the cathode of the cathode ray tube, and the input of the second transmission line 4; and impedance matching means 3 for coupling the ends. The impedance matching means 3 sends a signal from the output end of the first transmission line 2 to the cathode, connects an impedance equal to the characteristic impedance of the first transmission line to the output end of the first transmission line 2, and A cathode drive circuit in which an impedance equal to the characteristic impedance of the second transmission line is connected to the input end of the second transmission line to prevent reflection from occurring within the cathode drive circuit. is known (Japanese Unexamined Patent Publication No. 63-69396). In the conventional technology, the terminating resistor 5 serves as a load over a wide band (300 MH2), so it becomes a high-power resistor and is large in size. , parasitic reactance such as stray capacitance occurs, deteriorating high frequency characteristics.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention terminates high-frequency signals on the cathode ray tube socket board via a high-pass filter, and low-frequency signals are low-pass filtered on the chassis side. The present invention will be explained below with reference to FIG. 1, based on the principle that the impedance matching of the transmission line is achieved by terminating the transmission line through a transmission line. In FIG. 1, a signal from a cathode output amplifier l, which is a broadband video signal source, is inputted from an input terminal A disposed on a chassis 7. A load resistor R+ for low frequencies is connected to the input terminal A via an inductance L1 forming a low-pass filter, and connected to a power supply terminal. Further, a transmission line 6 having a characteristic impedance is connected to the input end A, and an impedance matching coil L2 placed on a cathode ray tube (CRT) socket board 8 is connected to the output end of the transmission line 6. and a capacitor C1 forming a high-pass filter are connected and terminated with a high frequency load resistor R2. Further, in order to compensate for the stray capacitance of the resistor R3, a parallel circuit of a resistor R8 and an inductance L is connected between the capacitor C1 and the resistor R2 as necessary.

【Example】

Next, an embodiment of the present invention will be described in detail with reference to FIG. 1. The transmission line employs a feeder line with a characteristic impedance of 200Ω. The resistance value of the low-frequency load resistor R+ and the high-frequency load resistor R3 is set to 200Ω, and the resistor R8 is a resistor for high power, and the resistor R8 is a resistor with good high frequency characteristics and for low power. The cutoff frequencies of the low-pass filter and the high-pass filter are set to approximately 10 MHz, and the cutoff points of both filters are crossed over as shown in FIG. Further, the input terminal A is connected to the collector or drain of a cathode output amplifier composed of cascade-connected bipolar transistors or field effect transistors. CR as shown in section 4 as an impedance matching circuit
A bifilar coil L is formed on the surface of the T-socket board by an etching method (using a pattern width of 1100Lt and a pattern interval of 10100LL).Furthermore, the compensation inductance L1 can also be formed at the same time as the bifilar coil L□ by an etching method.High The capacitor 〇 and the compensation resistor R, which form the pass filter, are wire-connected to the solder dip side of the CRT socket board using chip components, as well as the connection between the feeder wire and the impedance matching coil L2, the high-frequency load resistor, and the compensation circuit. The connection is also made on the solder dip side.

[effect]

Since the present invention is configured as described above, when viewed from the input end A, it appears to be terminated with a pure resistance of 200Ω equivalently from DC to high frequency, and impedance matching can be realized over a wide band, and the impedance of the input end A becomes the load impedance of the video output stage amplifier, so the video output stage amplifier can obtain a stable gain over a wide band. Also, since most of the power is consumed by the terminating resistor R1 at a frequency lower than the cut-off frequency of the low-pass filter, the terminating resistor R2 at a frequency higher than the cut-off frequency of the high-pass filter consumes a small amount of power. A small resistor is required, and it can be installed near the cathode on the cathode ray tube socket board 8, and even if the chassis 7 is used as a heat sink for the termination resistor R1, the high frequency characteristics will not be deteriorated. Further, a resistor with high power and good high frequency characteristics is expensive, but in the present invention, the high frequency load resistor requires low power, leading to cost reduction.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of the present invention, Fig. 2 is a circuit diagram of a conventional example, Fig. 3 is a cross-over characteristic diagram of a filter, and Fig. 4 is a plan view of a cathode ray tube (CRT) socket board. It is a diagram. 1. Wideband video signal source 2.4.6. Transmission line
3. Impedance matching means 5. Terminating resistor 7.
・Chassis 8 ・Cathode ray tube (CRT) socket board R1...Load resistance for low frequency R2...Load resistance for high frequency L,...Inductance L forming the low-pass filter...Impedance matching coil C3...
・Capacitor R3 that forms a high-pass filter...Compensation resistance 1...Compensation inductance

Claims (1)

[Claims] A load resistor for low frequencies is connected to the input end of the transmission line where the video signal is applied via a low pass filter, and a load resistor for high frequencies is connected to the output end of the transmission line via an impedance matching circuit and a high pass filter. A cathode ray tube drive circuit, characterized in that a load resistor is connected to the cathode ray tube to apply a video output signal from the impedance matching circuit to the cathode ray tube.