Amplifiers – With semiconductor amplifying device – Including plural amplifier channels
Patent
1990-04-03
1991-09-10
Mottola, Steven
Amplifiers
With semiconductor amplifying device
Including plural amplifier channels
330286, H03F 368
Patent
active
050477323
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to wide band amplifiers using transistors, and more particularly to a high-quality wide-band amplifier using transistors, which is used for transmissions, voice, video, high-vision applications, etc., in CATV.
BACKGROUND TECHNIQUES
Any conventional amplifiers used for transmission cables and so on in CATV are high-power branch amplifiers using LCs therein and plural amplifiers for special purposes are used in combination for each band.
Such a conventional amplifier is, however, required to be of a negative feedback type to eliminate distortions, which may cause oscillation and so on in a GHz-band thereby rendering the amplifiers unstable as well as rendering the circuit configuration complicated.
The present invention has been achieved in perception of the facts that if the output current of a transistor is reduced, for example, to about 10 mA, a possible distortion in the output of the transistor shall be reduced greatly, while the upper limit of operational frequency f.sub.T shall be raised to about 3 GHz, and that the distortion in the output current of the transistor can be canceled by inserting into its input circuit a transistor being the same characteristic as the former transistor. It is an object of the present invention to provide a high-quality wide-band amplifier which eliminates the above drawbacks due to use transistors.
DISCLOSURE OF THE INVENTION
A wide-band amplifier according to the present invention is arranged such that an input signal is applied in common across the bases and corresponding emitters of a plurality of transistors, and that the output currents are obtained from the corresponding collectors of the transistors. Thus, if five transistors Tr are used, for examples, the combined output current of 50 mA may be obtained and the output power becomes high, for example, 5.sup.2 (=25) times that of a single transistor. This will suffice for an amplifier for a 100-channel CATV to thereby be appropriate for a wide band of DC-3 GHz or so. The respective output currents of the transistors contain a very small distortion and respective distortions in the transistor output currents will not additively act on a circuit.
The wide-band amplifier according to the present invention includes transistors connected in parallel, a constant current circuit serving as an input power source for the transistors, and at least one diode having the same characteristic as the transistors and connected in parallel with an input circuit of the transistors. Thus, in the inventive wide-band amplifier, a voltage drop across a series circuit of a transistor Tr.sub.D and a resistor R.sub.E0 due to a constant current flowing through the series circuit varies depending on a non-linear portion of the base-emitter characteristic of the transistor Tr.sub.D compared to an amplifier without a transistor such as Rt.sub.D.
Therefore, without such transistor Tr.sub.D, namely, if a constant input voltage is applied across the base and emitter of the first transistor Tr.sub.1, its output current involves a distortion depending on its base-emitter characteristic. If a transistor Tr.sub.D is inserted in the input circuit as in the present invention, the input voltage changes depending on the inserted transistor Tr.sub.D, as mentioned above, and hence distortions due to the transistor characteristics of the respective transitor circuits are canceled by distortions due to the transistor characteristic of the transistor Tr.sub.D. Thus, the respective output currents I.sub.1, I.sub.2, . . . , I.sub.n of the transistors Tr.sub.1, Tr.sub.2, . . . , Tr.sub.n involve no distortions, so that a wide-band high-power amplifier without a feedback structure can be obtained very easily.
The beneficial effects of the present invention are that a voltage and a current can be amplified in a DC-GHz band without distortions, that a greatly stabilized amplifier without feedback and distortions and with an excellent temperature characteristic can be obtained, that the output power can be increas
REFERENCES:
patent: 2957143 (1960-10-01), Enloe
patent: 3531730 (1970-09-01), Steckler
patent: 3947637 (1976-03-01), Seki et al.
patent: 4103245 (1978-07-01), Yokoyama
Naito Michiko
Tanaami Minoru
Kabushiki Kaisha ENU ESU
Mottola Steven
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