Power microwave transistors Philips Semiconductors. Domestic microwave transistors

Powerful low-voltage microwave transistors for mobile communications

The Radio magazine constantly informs its readers about new developments at the Voronezh Research Institute of Electronic Technology in the field of creating high-power microwave transistors for various applications. In this article, we introduce specialists and radio amateurs to the latest developments of 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 ranges. Tightening requirements for the functional and operational parameters of modern communications equipment places correspondingly higher demands on the energy parameters of high-power microwave transistors, their reliability, as well as on the design of devices.

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

Considering 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 its output power level 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 set of design and technological problems, issues related simultaneously to the problem of reducing the collector-emitter saturation voltage and increasing the critical collector current density must be optimally solved.

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

The transistors discussed in this article are designed taking into account their main use in power amplifiers in class C mode when connected in a common emitter circuit. At the same time, their operation is permissible in the mode of classes A, B, and AB under a voltage different from the rated value, provided that the operating point is within the safe operation area and measures are taken to prevent entry into the self-generation mode.

The transistors are operational even if the value of Up is less than the nominal value. But in this case, the values ​​of the electrical parameters may differ from the passport values. It is allowed to operate transistors with a current load corresponding to the value of IК max, if the maximum permissible average power dissipation of the collector in continuous dynamic mode РК.ср max does not exceed the limit value.

Due to the fact that the crystals of the transistor structures of the devices under consideration are manufactured using basic technology and have common design and technological features, all transistors have the same level of breakdown voltage. In accordance with the technical specifications for devices, their scope of application is limited by the value of the maximum permissible direct voltage between the emitter and the base UEBmax< 3 В и максимально допустимого постоянного напряжения между коллектором и эмиттером UКЭ max < 36 В. При этом указанные значения пробивного напряжения справедливы для всего интервала рабочей температуры окружающей среды.

The main conceptual idea, which made it possible to take another step in the field of creating powerful low-voltage transistors in miniature design, was the development of new original design and technological solutions when creating a series of unpackaged 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 metallized tape leads on a flexible carrier - 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 the contact to the multi-cell transistor structure and the external terminals of the device are simultaneously formed. All elements of the internal strip 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 terminals are coated with a layer of gold. The type and dimensions of the transistor are shown in Fig. 1, a. For comparison, we note that the smallest foreign transistors in a metal-ceramic 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 terminals must be done at a temperature of 125...180 ° C for no more than 5 s.

Thanks to the implementation of reserves in electrical and thermophysical parameters, it was possible to significantly expand the range of consumer functions of packageless microwave transistors. In particular, for transistors of the KT8197 series with a nominal voltage value Upit = 7.5 V and the KT9189, KT9192 series (12.5 V), the boundary of the safe operation area in dynamic mode is expanded 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 accordingly increase the radio range. Transistors are capable of operating without reducing power dissipation in continuous dynamic mode throughout 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, the transistors turned out to be approximately five times cheaper than foreign ones of the same class in a metal-ceramic housing. 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. Obviously, their most effective use is in wearable portable radio stations.

The output stages of mobile transmitters are usually powered directly from the vehicle battery. Transistors for the output stages are designed for a rated supply voltage Upit = 12.5 V. The parametric series of transistors for each connected range are constructed taking into account the permitted maximum output power level for portable transmitters Pout = 20 W. The development of powerful 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 crystal topology of power transistors has a very developed emitter structure, characterized by low impedance. To ensure the required frequency band, simplify matching and increase the power gain, an LC internal matching circuit at the input is built into the transistors. Structurally, the LC circuit is made in the form of a microassembly based on a MIS capacitor and a system of wire leads that act as inductive elements.

In development of the power range of previously developed transistors of the 2T9175 series, transistors 2T9188A (Pout = 10 W) and KT9190A (20 W) were created for use in the VHF range. For the UHF range, transistors KT9193A (Pout = 10 W) and KT9193B (20 W) have been developed. The transistors are made in a standard KT-83 package (see Fig. 1, b).

The use of this metal-ceramic housing at one time made it possible to create highly reliable dual-purpose transistors for electronic devices with increased requirements for external factors and with the ability to operate in harsh climatic conditions. In order to ensure guaranteed reliability at a housing 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 permissible average power dissipation in continuous dynamic mode must be linear reduce in accordance with the formula RK.sr max=(200-Tcorp)/RT.p-c (where Tcorp is the housing temperature, °C; RT.p-c is the thermal resistance of the junction-case transition, °C/W).

Currently, 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 domestic transistor elements.

In addition, since 1995, a federal network of cellular mobile subscriber communication systems has been deployed in Russia 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 the 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 miniaturizing equipment and, accordingly, its elemental base affected not only wearable portable radio transmitters. In a number of cases, for portable radio communication equipment, as well as 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 wafer-free housing design has been developed based on KT-83 (Fig. 1, c), 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 a 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 transistors under consideration are presented in table. 1. The efficiency of the collector circuit of all transistors is 55%. The values ​​of the maximum permissible direct collector current correspond to the entire operating temperature range.

Table 1

In Fig. 2a shows the complete circuit of transistors 2T9188A, KT9190A, and in Fig. 2,b - transistors of the KT8197, KT9189, KT9192, 2T9175 series (l - distance from the soldering boundary to the adhesive seam of the sealing cap or sealing coating of the crystal holder. This distance is regulated in the recommendations for the use of microwave transistors in technical specifications on them and is necessarily 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 amplification 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 what has already been developed in order to improve its electrical parameters, reduce weight, dimensions and cost.

table 2

Literature

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

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