Broadband power amplifiers on field-effect transistors. Scheme, description

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Broadband power amplifiers on field-effect transistors. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / RF power amplifiers

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Power amplifier with neutralization of the pass capacitance of the transistor

A single-ended amplifier of this type can only operate in class A. Its energy performance is similar to that of low-frequency single-ended transformer amplifiers. The typical efficiency value usually does not exceed 35...40% (at the same time, non-linear distortions, caused primarily by the second harmonic, are quite noticeable). The amplifier based on the VMP1 transistor at Uc=24 V provides Pout=4 W at Ku=15 dB and the amplified frequency band from 2 to 150 MHz.

Fig.1 (click to enlarge)

T1 is wound with a twist of two wires with a diameter of 0.3 mm and contains 4 turns. Core type F625-BQ2. You can use a domestic RF ring with low magnetic permeability.

Power Amplifier with Parallel Negative Feedback Circuit

This version of the amplifier without an input transformer and without neutralizing the capacitance SZS has half the bandwidth.

Broadband power amplifiers based on field-effect transistors
Ris.2

Various variants of such amplifiers (depending on the design of transformers and used transistors) provide gain Ku=12...30 dB in the frequency band up to 300 MHz with a noise figure of 3...5 dB.

Push-Pull Broadband Power Amplifier

A significant improvement in the energy parameters of broadband PA is possible only when using push-pull cascades operating in class AB mode. This version of the circuit is shown in Fig.3. At K=15 dB in the band 2...100 MHz, it provides Рout=8 W. The input and output impedance of the amplifier is 50 ohms.

Broadband power amplifiers based on field-effect transistors
Ris.3

Capacitors Cn are used for neutralization. The developers of this amplifier recommend reducing the parasitic inductance of the resistor R2 by connecting four or five larger resistors in parallel. On the contrary, in order to reduce the parasitic capacitance of the resistors R1 and R4, it is advisable to make them in the form of several series-connected resistors with a lower rating.

The transformers are made similarly to the circuit in Fig. 1 (twisting of 3 wires - 4 turns). The type of field-effect transistors is not given in the article (I think you can use transistors of the KP901 type).

Literatureа

1. EDN Magazine, June 20, 1974, p.71-75.
2. Circuitry of devices based on powerful field-effect transistors. Directory. Ed. V.P. Dyakonova.

Publication: N. Bolshakov, rf.atnn.ru

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