Powerful low-voltage microwave transistors for mobile communications. Reference data

Encyclopedia of radio electronics and electrical engineering / Reference materials

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The magazine "Radio" constantly informs its readers about new developments of the Voronezh Research Institute of Electronic Technology in the field of creating high-power microwave transistors for various applications [1-3]. In this article, we introduce specialists and radio amateurs to the latest developments in the group of microwave transistors KT8197, KT9189, KT9192, 2T9188A, KT9109A, KT9193 for mobile communications with an output power of 0,5 to 20 W in the MV and UHF bands. The tightening of requirements for the functional and operational parameters of modern communication equipment imposes, accordingly, higher requirements for the energy parameters of high-power microwave transistors, their reliability, and also for the design of devices.

First of all, it must be borne in mind that portable and portable radio stations are powered directly from primary sources. For this purpose, chemical current sources are used (small batteries of cells or batteries) with a voltage, as a rule, from 5 to 15 V. The reduced supply voltage imposes restrictions on the power and amplifying properties of the generator transistor. At the same time, high-power low-voltage microwave transistors should have high energy parameters (such as the power gain KP and the efficiency of the collector circuit ηK) in the entire operating frequency range.

Taking into account the fact that the output power of the generator transistor is proportional to the square of the fundamental harmonic voltage on the collector, the effect of reducing the level of its output power with a decrease in the supply collector voltage can be constructively compensated by a corresponding increase in the amplitude of the useful signal current. Therefore, when designing low-voltage transistors in combination with solving a complex of design and technological problems, issues related simultaneously to the problem of reducing the saturation voltage of the collector-emitter and increasing the critical current density of the collector should be optimally solved.

The operation of low-voltage transistors in a mode with higher current densities compared to conventional generator transistors (designed for use at Upit = 28 V and higher) exacerbates the problem of ensuring long-term reliability due to the need to suppress a more intense manifestation of degradation mechanisms in current-carrying elements and contact metallization layers transistor structure. For this purpose, a highly reliable multilayer gold-based metallization system is used in the developed microwave low-voltage transistors.

The transistors discussed in this article are designed for their primary use in class C power amplifiers when switched on in a common emitter circuit. At the same time, their operation in the mode of classes A, B, and AB under a voltage different from the nominal value is permissible, provided that the operating point is within the safe operation area and measures are taken to prevent entering the autogeneration mode.

Transistors are operable even when Upit is less than the nominal value. But in this case, the values ​​of the electrical parameters may differ from the passport ones. It is allowed to operate transistors with a current load corresponding to the value of IK max, if the maximum allowable average dissipated power of the collector in continuous dynamic mode RK.av max does not exceed the limit value.

Due to the fact that the crystals of the transistor structures of the considered devices are manufactured according to the basic technology and have common structural and technological features, all transistors have the same level of breakdown voltage. In accordance with the technical specifications for devices, their scope is limited by the value of the maximum allowable DC voltage between the emitter and base UEBmax < 3 V and the maximum allowable DC voltage between the collector and emitter UKE max < 36 V. At the same time, the indicated breakdown voltage values ​​\uXNUMXb\uXNUMXbare valid for the entire operating temperature range environment.

The main conceptual idea, which made it possible to take another step in the field of creating powerful low-voltage transistors in a miniature version, was the development of new original design and technological solutions when creating a series of packageless transistors KT8197, KT9189, KT9192. The essence of the idea is to create a transistor design based on a ceramic crystal holder made of beryllium oxide and tape metallized leads on a flexible carrier - a polyimide film.

A tape carrier with a special photolithographic pattern in the form of a lead frame serves as a single conductive element, on which a contact is simultaneously formed to the multi-cell transistor structure and external leads of the device. All elements of the internal tape reinforcement are sealed with a compound. The dimensions of the base of the metallized ceramic holder are 2,5x2,5 mm. The mounting surface of the crystal holder and the leads are covered with a layer of gold. The type and dimensions of the transistor are shown in fig. 1a. For comparison, we note that the smallest foreign transistors in a ceramic-metal package (for example, CASE 249-05 from Motorola) have a round ceramic base with a diameter of 7 mm.

The design of transistors of the KT8197, KT9189, KT9192 series provides for their installation on a printed circuit board using the surface mount method. In accordance with the recommendations for the use of these transistors, soldering of external leads must be carried out at a temperature of 125 ... 180 ° C for no more than 5 s.

Thanks to the realization of reserves in terms of electrical and thermal parameters, it was possible to significantly expand the area of ​​consumer functions of unpackaged microwave transistors. In particular, for transistors of the KT8197 series with a nominal voltage value Upit = 7,5 V and the series KT9189, KT9192 (12,5 V), the boundary of the safe operation area in dynamic mode is extended to Upit max = 15 V. An increase in the supply voltage relative to the nominal value allows raise the output power level of the portable transmitter and increase the radio range accordingly. Transistors are able to operate without reducing the dissipated power in a continuous dynamic mode over the entire operating temperature range.

In general, when developing these transistors, in a fundamental way, the issues of not only miniaturization, but also cost reduction were resolved. As a result, transistors turned out to be about five times cheaper than similar foreign transistors in a ceramic-metal package. The developed miniature microwave transistors can find the widest application both in traditional use in the form of discrete components and as part of hybrid microcircuit RF power amplifiers. It is obvious that their use is most effective in wearable portable radio stations.

The output stages of mobile transmitters are usually powered directly from the car battery. The transistors for the output stages are designed for the rated supply voltage Upit=12,5 V. The parametric series of transistors for each communication range are built taking into account the provision of the allowed maximum output power level for portable transmitters Pout=20 W [4]. The development of high-power low-voltage microwave transistors (with Pout > 10 W) is associated with more complex design problems. Additionally, there are problems of adding dynamic power and removing heat from large crystals of microwave structures.

The topology of a crystal of power transistors has a highly developed emitter structure, characterized by a low impedance. To provide the required frequency band, simplify matching and increase the power gain, an LC circuit for internal matching at the input is built into the transistors. Structurally, the LC circuit is made in the form of a microassembly based on an MIS capacitor and a system of wire leads that act as inductive elements.

In the development of the power range of previously developed transistors of the 2T9175 series for use in the VHF band [2], transistors 2T9188A (Pout = 10 W) and KT9190A (20 W) were created. For the UHF range, transistors KT9193A (Pout \u10d 9193 W) and KT20B (83 W) were developed. The transistors are made in a standard KT-1 package (see Fig. XNUMXb).

The use of this ceramic-metal package at one time made it possible to create highly reliable dual-purpose transistors for electronic equipment with increased requirements for external factors and with the ability to operate in harsh climatic conditions. In order to ensure guaranteed reliability at a case temperature of +60°C in relation to transistors with an output power Pout = 10 W, and with Pout = 20 W - from +40 to +125°C, the maximum allowable average power dissipation in continuous dynamic mode must be linear reduce in accordance with the formula РК.ср max=(200-Тkorp)/RT.p-to (where Тkorp - case temperature, °С; RT.p-to - thermal resistance of transition-case junction, °С/W).

At present, a federal radio communication network is being created in Russia according to the NMT-450i standard (at a frequency of 450 MHz). The developed series of devices KT9189, 2T9175, 2T9188A, KT9190A can almost completely cover the need in the considered sector of the market for equipment based on the domestic transistor element base.

In addition, since 1995, Russia has been deploying a federal network of a cellular system of mobile subscriber communication within the GSM standard (900 MHz) and a cellular system for regional communications according to the American AMPS standard (800 MHz). To create these cellular radio communication systems in UHF, small-sized transistors of the KT9192 series with an output power of 0,5 and 2 W, as well as the KT9193 series with an output power of 10 and 20 W, can be used.

The solution to the problem of miniaturization of equipment and, accordingly, its element base affected not only wearable portable radio transmitters. In a number of cases, for portable radio communication equipment, as well as for special-purpose equipment, there is a need to reduce the weight and dimensions of high-power microwave low-voltage transistors.

For these purposes, a modified flangeless housing design based on KT-83 (Fig. 1, c) was developed, in which transistors 2T9175A-4-2T9175V-4, 2T9188A-4, KT9190A-4, KT9193A-4, KT9193B-4 are produced. Their electrical characteristics are similar to the corresponding transistors in the standard design. These transistors are mounted by low-temperature soldering of the crystal holder directly to the heat sink. The body temperature during the soldering process should not exceed +150°C, and the total heating and soldering time should not exceed 2 minutes.

The main technical characteristics of the considered transistors are presented in Table. 1. The efficiency of the collector circuit of all transistors is 55%. The values ​​of the maximum allowable DC collector current correspond to the entire operating temperature range.

Table 1

On fig. 2,a shows the complete circuit of transistors 2T9188A, KT9190A, and in fig. 2,b - transistors of the KT8197, KT9189, KT9192, 2T9175 series (l is the distance from the soldering boundary to the adhesive seam of the sealing cover or the sealing coating of the crystal holder. This distance is regulated in the recommendations for the use of microwave transistors in specifications for them and must be taken into account when calculating reactive elements transistors). The parameters of the reactive elements shown in the diagrams are summarized in Table. 2. These parameters are necessary for calculating the matching circuits of the amplifying path of the devices being developed.

The development of a new transistor element base opens up a broad prospect for both the creation of modern professional commercial and amateur radio communication equipment, and the improvement of the already developed one in order to improve its electrical parameters, reduce weight, dimensions and cost.

Table 2

Literature

1. Assessors V., Kozhevnikov V., Kosoy A. Scientific search for Russian engineers. The development trend of high-power microwave transistors. - Radio, 1994, No. 6, p. 2, 3.
2. Assessors V., Kozhevnikov V., Kosoy A. New microwave transistors. - Radio, 1996, No. 5, p. 57, 58.
3. Asessorov V., Asessorov A., Kozhevnikov V., Matveev S. Linear microwave transistors for power amplifiers. - Radio, 1998, No. 3, p. 49-51.
4. Angle-modulated radio stations in the land mobile service. GOST 12252-86 (ST SEV 4280-83).

Authors: V.Kozhevnikov, V.Assessors, A.Assessors, V.Dikarev, Voronezh

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