Video Amplifier


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video amplifier

[′vid·ē·ō ′am·plə‚fī·ər]
(electronics)
A low-pass amplifier having a band width on the order of 2-10 megahertz, used in television and radar transmission and reception; it is a modification of an RC-coupled amplifier, such that the high-frequency half-power limit is determined essentially by the load resistance, the internal transistor capacitances, and the shunt capacitance in the circuit.

Video Amplifier

 

a wide-band tube or semiconductor amplifier used in television, radar, oscillographs, and other equipment to amplify video signals before passing them on to a cathode-ray tube. To preserve the shape of the video signals, a video amplifier must amplify them uniformly (with no more than 1-3 decibels’ variation) over a wide frequency pass band (from 10-30 Hz up to 4-6 MHz) without appreciable phase distortion. Circuits of one- and two-stage video amplifiers, with a low-value resistor and various combinations of inductance coils, capacitors, and resistors in the load circuit of the gain stage, are the most commonly used. These combinations are selected in such a way as to increase the gain in the low and high-frequency regions, thus producing uniform gain and reducing phase distortions over a very wide frequency band. The circuit and amplitude-frequency response of a one-stage tube video amplifier are shown in Figure 1.

Figure 1. Typical circuit of a one-stage tube video amplifier (the dotted line indicates the Cstr connections) and its gain characteristic when various loads are applied to the tube’s plate circuit: (a) the resistor Rp, (b) the resistor Rp and the decoupling network RfCf, (c) the resistor Rp and the correcting inductances Lp and Lc; A is the relative amplification, which is equal to the ratio of the amplification at any frequency to the maximum gain; f is the frequency.

The gain increase (correction) at high frequencies is attained as a result of resonance phenomena in the oscillatory circuits formed by the inductances Lp and Lc with the stray (spurious) circuit capacitances Cstr, and at low frequencies by the choice of the parameters for the plate circuit decoupling network RfCf.

REFERENCES

Kreitser, V. L. Videousiliteli. Moscow, 1952.
Lur’e, O. Usiliteli videochastoty, 2nd ed. Moscow, 1961.

A. IA. KLOPOV

Video amplifier

A low-pass amplifier having a bandwidth in the range from 2 to 100 MHz. Typical applications are in television receivers, cathode-ray-tube computer terminals, and pulse amplifiers. The function of a video amplifier is to amplify a signal containing high-frequency components without introducing distortion.

Modern video amplifiers use specially designed integrated circuits. With one chip and an external resistor to control the voltage gain, it is possible to make a video amplifier with a bandwidth between 50 and 100 MHz having voltage gains ranging from 20 to 500. See Amplifier, Integrated circuits

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