JP3070258B2 - Video amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video amplifier for a high definition cathode ray tube display device.

[0002]

2. Description of the Related Art In recent years, with the spread of various new media, Clear Vision Television (EDTV) / High Definition Television (HDTV): High Definition
Television) and other video displays,
There is an increasing demand for display devices that support graphic display such as CAD / CAM, and a cathode ray tube (hereinafter, CRT: Cathode) that satisfies a wide band and large amplitude characteristic.
Video amplifiers for driving (referred to as Ray Tube) have become important. Hereinafter, a conventional video amplifier will be described.

FIG. 2 shows a conventional video amplifier. In FIG. 2, reference numeral 1 denotes an input signal subjected to video signal processing by a signal source. 2 is a transistor and 3 is an emitter resistor. 4 is a resistor, 5 is a transistor, 6 is a resistor and is a common emitter amplifier. 7 is a PNP transistor, 8 is N
A PN transistor, a resistor 9 and a capacitor 10 constitute a cascade amplifier. 11 is a capacitor. 1
Reference numeral 2 denotes a peaking coil, and 13 denotes a series peaking circuit for compensating for a high-frequency gain reduction by a damping resistor. 14 and 15 are diodes. 16 is a peaking coil,
Reference numeral 17 denotes a parallel peaking circuit that compensates for a decrease in gain in the middle band by a damping resistor. 18 is a load resistance. 19 is a PNP transistor, 20 is an NPN transistor, 21
And 22 are resistors and complementary emitter follower circuits. Reference numerals 23 and 24 are resistors and feedback circuits.
27 is a CRT, K is a cathode, and G1 is a first grid. 28 is a high power supply voltage supply terminal, and 29 is a low power supply voltage supply terminal. The operation of the video amplifier configured as described above will be described below.

First, a signal source 1 is a signal source that has been subjected to video signal processing. The video signal of the signal source 1 is impedance-converted by the collector-grounded amplifier of the transistor 2 and input to the base of the transistor 5 through the resistor 4. A negative feedback signal is applied to the base of the transistor 5 from the output side through the feedback circuit of the resistor 23 and the resistor 24 to the signal input from the transistor 2 to amplify the voltage and to output the P of the cascade amplifier.
Current amplification by the collector-grounded amplifier of the NP transistor 7,
The voltage is amplified by the base-grounded amplifier of the NPN transistor 8, and the output is applied to the transistors 19 and 20.
Complementary emitter follower with low impedance
It is converted into a dance and the cathode of the CRT 27 is driven.

Since the characteristics of the negative feedback amplifier, such as frequency characteristics and linearity, are improved in proportion to the amount of negative feedback, an open loop
It is necessary to increase the gain and the amount of negative feedback. For this purpose, the gain of the common-emitter amplifier of the transistor 5 and the gain of the cascade amplifier may be increased. However, since the load resistance 18 and the frequency characteristic are in inverse proportion, the gain of the cascade amplifier performing large amplitude amplification is increased. -There is a limit to the up in relation to the band characteristics. Therefore, it is easier to obtain the desired performance by increasing the gain of the transistor 5 to increase the open loop gain of the negative feedback amplifier.

The current flowing through the load resistor 18 is controlled by the voltage difference between the emitter voltage of the base-grounded transistor 8 and the emitter voltage of the collector-grounded transistor 7, that is, the voltage across the resistor 9. Is a constant voltage determined by the base-bias voltage of the transistor 8, the load current is controlled by the emitter voltage of the transistor 7. The current amplification of the base grounded amplifier of the transistor 8 is substantially 0 dB, and the voltage amplification of the grounded collector amplifier of the transistor 7 is also substantially 0 dB, and the operating characteristics of the transistor 5 are important factors that can determine the basic characteristics of the amplifier. become.

[0007]

However, in the above conventional configuration, the gain of the common-emitter amplifier of the transistor 5 is high, and the transistor 8 is operated at the input level in the non-linear region from the cut-off region of the transistor characteristic to the active region. Since the voltage is output from the collector of the transistor 5, there is a problem that the transmission characteristics deteriorate on the low-level side of the signal.

The present invention solves the above-mentioned conventional problems, and provides a video amplifier in which a transistor is operated in an active region having good linearity sufficiently separated from a cut-off region of transistor characteristics to improve transmission characteristics. The purpose is to do.

[0009]

SUMMARY OF THE INVENTION To achieve this object, a video amplifier according to the present invention is provided with a grounded emitter amplifier of a transistor 5 for a base bias voltage of a grounded base amplifier of a cascade amplifier. The cascade amplifier is cut off until the bias current of the common emitter amplifier reaches a certain level or more.

[0010]

With this configuration, a sufficient bias current can be supplied to the common-emitter amplifier when there is no signal, and the cascade amplifier can be operated in the linear region of the transistor characteristics, so that the transmission characteristics of the amplifier can be improved.

[0011]

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 30 denotes a base bias supply terminal, and reference numeral 31 denotes a power supply voltage supply terminal. Since the drawings other than those described above have the same configuration as the conventional example, the same reference numerals as those in FIG. 2 are given and the description of the common reference numerals is omitted. The operation of the video amplifier configured as described above will be described with reference to FIG.

The video signal processed from the signal source 1 is impedance-converted by the common-collector amplifier of the transistor 2, and the negative feedback signal is fed back from the output through the feedback circuit of the resistors 23 and 24 via the resistor 4. The voltage is amplified by the emitter amplifier of the transistor 5 and inputted to the base of the PNP transistor of the cascade amplifier composed of the PNP transistor 7 and the NPN transistor 8, the current is amplified by the transistor 7, and the voltage is increased by the transistor 8. The CRT is amplified through a complementary emitter follower composed of transistors 19 and 20.
27 is driven.

The peaking coil 12 and the damping resistor 13 connected to the collector side of the transistor 8 compensate for a high frequency in a series peaking circuit, and the peaking coil 16 and the damping resistor 17 are connected in parallel. -Compensation of the mid-frequency by the king circuit. A capacitor 10 connected in parallel with the resistor 9 is an emitter peaking. The peaking coil 25 and the damping resistor 2
Reference numeral 6 denotes a series peaking circuit for compensating for the deterioration of the frequency band due to the load capacity of the CRT cathode.

In order to improve the basic characteristics such as the frequency characteristics in the negative feedback video amplifier operating as described above, it is necessary to increase the open loop gain. Therefore, it is necessary to increase the gain of the common emitter amplifier and the cascade amplifier of the transistor 5,
The gain of the cascade amplifier has a frequency characteristic of load resistance 18.
Is limited by the current capacity of the transistor 8 and the limitation on the collector loss, the gain of the emitter amplifier of the transistor 5 is increased.

This prevents the cascade amplifier from being driven in the non-linear region at the rise of the transistor characteristic, so that the voltage of the base bias supply terminal 30 of the transistor 8 is changed with respect to the power supply terminal of the common emitter amplifier. The voltage of terminal 31 is set high, and terminals 30 and 31
By applying a bias current when there is no signal so that a voltage drop corresponding to the difference voltage of the transistor 5 can be obtained at the collector of the transistor 5, the operation in the non-linear region at the rise of the transistor characteristic is eliminated, and the cascade is performed only in the linear region. Since the amplifier can be driven, a video amplifier having excellent transmission characteristics can be obtained.

[0017]

As described above, according to the present invention, the reverse bias is applied so that the information in the non-linear region at the rise of the operation of the common emitter amplifier is not transmitted to the next stage amplifier. Since the information is transmitted by biasing the stage amplifier in the forward direction, a video amplifier having excellent transmission characteristics can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a video amplifier according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional video amplifier.

[Explanation of symbols]

 1 Signal source 2, 5, 7, 8, 9, 19, 20 Transistor 3, 4, 6, 21, 22, 23, 24 Resistance 10, 11 Capacitor 12, 16, 25 Peaking coil 13, 17, 26 Damping resistor 14, 15 Diode 18 Load resistor 27 CRT 28 High power supply voltage supply terminal 29 Low power supply voltage supply terminal 30 Base bias voltage supply terminal 31 Power supply voltage supply terminal

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 5/14

Claims (1)

(57) [Claims] 1. A common collector of a PNP transistor and N
In a video amplifier comprising a cascade amplifier in which PN transistors are connected in cascade with a base ground, and a video amplifier formed by driving a collector-grounded transistor of the cascade amplifier, the base ground of the cascade amplifier is used. When the supply voltage of the common emitter amplifier is set higher than the base bias voltage of the transistor, and the bias point of the common emitter amplifier when there is no signal is in the non-linear region of the rising characteristic of the transistor characteristic, ,
A reverse bias is applied to the common-collector amplifier of the cascade amplifier due to the voltage difference between the base bias voltage and the supply power supply voltage, and when the bias point is set in the linear region of the transistor characteristics, the common-collector amplifier becomes forward. A video amplifier characterized in that the cascade amplifier is operated by biasing in the direction and the transmission characteristics are improved by driving the cascade amplifier only in the linear region of the transistor characteristics.