JPS6219016Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a video signal processing device that amplifies a video signal, and aims to provide a device that can amplify the high frequency components of the video signal without dropping it.

In television receivers, video amplification circuits have relatively flat output frequency characteristics. The output of this video amplification circuit is applied to a video signal drive circuit via an emitter follower circuit, amplified, and applied to a cathode ray tube. The video signal drive circuit increases the gain to obtain a signal with a large amplitude. However, increasing the gain deteriorates the frequency characteristics at high frequencies. Therefore, it is advisable to increase the gain at high frequencies before the video drive circuit. In the present invention, peaking at high frequencies is performed using the emitter follower circuit described above, and embodiments of the present invention will be described below with reference to the drawings.

Generally, an emitter follower circuit of a transistor is constructed as shown in FIG. The equivalent circuit is as shown in FIG. 2, taking into account the capacitance component of the load and the impedance of the base circuit. Here, hie and hfe are the H parameters of transistor 2, Rs is the resistance of signal source 1, R is the resistance of the base circuit, L is the inductance component of the base circuit, and C
is a capacitance component in parallel with the emitter resistance R _E . In addition, hfe generates an imaginary part in the high range and becomes a complex number, and if it is denoted by β, it can generally be expressed as β=β _R −jβ _I. 3 is an output terminal, and +B is a DC power supply. Here, if the impedance seen from signal source 1 to the base side of transistor 2 is Zi,
Zi is expressed by the following formula.

Zi=R+hie+jwL+(1+β)Z _L Z _L =R _E /(1-jwc _RE ) If we rearrange this and set Zi=Z _R +jZ _I , then Z _R =R+hie+(1+β _R −β _I wc _RE )Z _E Z _I = j{w _L - [(1+β _R ) wc + β _I ] Z _E } Here, Z _E = R _E /(1-w ² c ² R _E ² ).

From these equations, this emitter follower circuit has Z
It resonates at a frequency wo where _I = o, and the resonance characteristics can be corrected by changing the magnitudes of R and hie.

If we express the above in terms of frequency characteristics, we get the third
It will look like the figure in (c). The smaller the resistance value R, the larger the peak. Also, the larger the values of L and C, the lower the resonant frequency. Since L and C are generally small, the resonant frequency in the circuit shown in Figure 1 is sufficiently high and has flat characteristics for the video signal.

Therefore, in the present invention, as shown in FIG. 4, a coil 4 and a resistor 5 are connected between the base of the transistor 2 and the output terminal of the video amplification circuit 3. Further, a capacitor 7 is connected in parallel to the emitter resistor 6 of the transistor 2. Both the coil 4 and the capacitor 7 may be connected, but only one may be connected if necessary. The resistor 5 may also be connected as necessary. This coil 4
By the action of the capacitor 7 and the resonant frequency Wo, it is possible to make the resonance frequency near the high range of the video signal, and it is possible to peak the high range part of the video signal. The amount of peaking can be adjusted by the resistance value 5.

Since the output frequency characteristic of the video amplifier circuit 3 is fairly flat, the frequency characteristic of the video signal at the emitter of the transistor 2 has a high frequency band. Since the video signal drive circuit 8 that amplifies the emitter signal of the transistor 2 has a large gain, its frequency characteristics are poor and the gain of the high frequency portion of the video signal decreases. Therefore, the frequency characteristics of the final video signal will be good.

The smaller the value of the resistor 5, the greater the amount of peaking, but if it is too small, oscillation may occur. Even if the resistor 5 is omitted, an appropriate resistance may be provided by the output resistance of the circuit 3, so in this case, the resistor 5 is unnecessary.

As described above, according to the present invention, it is possible to improve frequency characteristics using an emitter follower circuit.

[Brief explanation of drawings]

Figure 1 is an emitter follower circuit diagram, Figure 2 is an equivalent circuit of the same circuit, Figure 3 is a frequency characteristic diagram of the same circuit,
FIG. 4 is a circuit diagram of a video signal processing device according to an embodiment of the present invention. 2...Transistor, 3...Video amplification circuit, 4
...Coil, 5, 6...Resistor, 7...Capacitor, 8...Video signal drive circuit.

Claims (1)

[Scope of utility model registration request] The output of a video signal amplification circuit with relatively flat output frequency characteristics is applied to the base of a transistor connected as an emitter follower, and a coil is connected between the base of this transistor and the output terminal of the video signal circuit, or the emitter of the transistor is connected to the output terminal of the video signal circuit. A capacitor is connected in parallel to the resistor, or both are connected to perform frequency peaking, and a resistor is connected as necessary between the output terminal of the video signal amplification circuit and the base of the transistor, A video signal processing device in which the emitter of the transistor is connected to an input terminal of a high gain video signal drive circuit whose frequency characteristics drop considerably near the peaking frequency set in the circuit portion of the transistor.