RU2116693C1 - Device for stabilization of transistor mode - Google Patents

Abstract

FIELD: radio engineering, in particular, transistor power amplifiers. SUBSTANCE: device has transistor 1, temperature detection transistor 2, which collector is connected to base of transistor 1 and emitter is connected to common line, resistor 3, which is inserted between power supply line and collector of transistor 2, transistor 4 which is connected as diode, its emitter is connected to power supply line and collector and base are connected to each other. In addition device has resistor 5 which is inserted between collectors of transistor 1 and 4, transistor 6 which base is connected to collector of transistor 1, resistor 7 which is inserted between power supply line and emitter of transistor 6, resistor 8 and variable resistor 9 which are connected in series and inserted between common line and emitter of transistor 1. In addition device has resistor 10 which is inserted between base of transistor 2 and connection point of resistor 8 and 9, at least one adjusting circuit 11, which has input potentiometer 12, which one terminal serves as input of adjusting circuit 11 and another terminal is connected to common line. In addition device has correction circuit 13, which may be designed as integrating RC circuit with resistor 14, which is inserted between input and output of correction circuit 13, and capacitor 15, which is connected in parallel to input of correction circuit 13. Input of correction circuit is connected to middle terminal of input potentiometer 12. In addition device has resistor 16, which is inserted between output of correction circuit 13 and output of adjusting circuit 11. Inputs of adjusting circuit 11 are connected to collector of transistor 6, its outputs are connected to each other. In addition device has splitting capacitor 17 which is inserted between base of transistor 2 and connection point of terminals of adjusting circuit 11. Output of stabilization unit is emitter of transistor 1. EFFECT: decreased non-linear inertial distortions, which appear in course of amplification of amplitude-modulated oscillations and are caused by inertial thermal processes in transistors. 4 dwg

Description

 The proposed device relates to radio engineering and can be used in transistor power amplifiers, in particular transistor power amplifiers of television radio transmitters.

 As is known, to increase the energy efficiency of radio transmitters, transistors in powerful amplification stages operate in collector current cutoff modes. Moreover, to ensure high linearity of amplification of signals with varying amplitude, it is necessary to establish the optimal operation mode of the transistor, essentially the optimal bias voltage (Zavrazhnov Yu.V., Fedotov M.G. Temperature stabilization of the linear operation mode of the transistor amplifier. / Radio engineering, 1974, t. 29, N 5, p. 96-100).

 A change in the crystal temperature of the amplifying transistor caused by a change in power dissipation or ambient temperature leads to a change in the transistor cutoff voltage (approximately 2 mV / deg). To obtain small nonlinear distortions, a change in the cut-off voltage of the amplifying transistor must be accompanied by a corresponding (same exact) change in the bias voltage, roughly speaking, the cut-off angle of the collector current of the transistor must remain constant regardless of the crystal temperature of the amplifying transistor.

 A device is known for stabilizing a transistor mode, comprising a resistor and a forward biased semiconductor diode connected in series between a power supply source and a common bus, the housing of which has thermal contact with the housing of an amplifying transistor (I.P. Stepanenko. Fundamentals of the theory of transistors and transistor circuits. M .: Energy, 1973, 608 p., S. 410). In this case, the output voltage, i.e. bias voltage to the base of the amplifying transistor, supplied from the diode.

 However, this device does not allow a wide range to change the bias voltage, and therefore, to establish the optimal mode of operation of the amplifying transistor.

 In addition, it is known a device for stabilizing the transistor mode (Zavrazhnov Yu.V. et al. Powerful high-frequency transistors. / Under the editorship of EZ Mazel. M: Radio and communications, 1985, 176 p., S.168), which prototype of the invention. This device contains a first transistor, a second transistor - a temperature sensor, the collector of which is connected to the base of the first transistor, the first and second resistors connected between the power bus and the collectors of the first and second transistors, a third resistor and a fourth variable resistor connected between the emitter of the second transistor and respectively, the power bus and the common bus, the fifth resistor connected between the base of the second transistor and the common bus, the first and second capacitors connected respectively to the bases Am of the first and second transistors, the output of the device is the emitter of the first transistor.

 However, this device provides a constant mode of operation of the transistor (a constant cutoff angle of the collector current) only in the steady state thermal mode, when the temperature of the crystal of the amplifying transistor is equal to the temperature of the crystal of the transistor - the temperature sensor of the stabilization device or differs from it by a constant value.

 When amplified by amplitude-modulated oscillations, a change in the amplitude of the amplified signal leads to a change in the dissipated power on the crystal of the amplifying transistor and, accordingly, to a change in the temperature of the crystal, and therefore, the cutoff voltage of the transistor. Thus, when amplifying amplitude-modulated oscillations in transistors operating in collector current cutoff modes, cutoff voltage and modulation occur, and due to thermal inertia of the processes in the transistor, the transistor cutoff voltage modulates with some delay. However, for modulation frequencies from a few Hertz and higher, a change in the temperature of the transistor's crystal with a modulation frequency does not lead to a corresponding change in the temperature of the transistor case due to thermal inertia. It is determined by the average power dissipation.

 In this stabilization device of the regime of the transistor of powerful amplifiers, the output voltage (bias voltage) is set in accordance with the temperature of the housing of the amplifier transistor, since the transistor - temperature sensor of the stabilization device can have thermal contact in the best case only with the housing of the amplifier transistor. Therefore, this stabilization device does not provide a constant cutoff angle of the collector current of the amplifying transistor when the amplitude of the amplified signal changes, which leads to specific nonlinear inertial distortions of the amplified amplitude or pulse modulated signal (L.B. Kalinin, S. G. Tikhomirov. Distortions of the type Hesteresis in power amplifiers. // Telecommunication, 1976, N 8, pp. 43-46.). These distortions are especially pronounced when amplifying television signals in cascades built on modern powerful transistors.

 The analysis of the prior art indicates that the objective of the invention is to provide a device for stabilizing the transistor mode, which allows to reduce non-linear inertial distortions that occur in powerful transistor amplifiers when amplified by amplitude-modulated oscillations and due to inertial thermal processes in transistors.

 This is achieved by the fact that in the stabilization device of the transistor mode containing the first transistor, the second transistor is a temperature sensor, two capacitors, four constant resistors and one variable resistor, and the collector of the second transistor - temperature sensor is connected to the base of the first transistor, the first resistor is connected between the bus the power and collector of the second transistor, a third transistor in diode switching, a fourth transistor, a fifth permanent resistor and at least one corrective link, including e includes an input potentiometer, a corrective circuit, and an output resistor, while the emitter of the second transistor - temperature sensor is connected to a common bus, the emitter of the third transistor is connected to the power bus, and the collector and base are connected to each other, the second resistor is connected between the collectors of the first and third transistors , the base of the fourth transistor is connected to the collector of the first transistor, the third resistor is connected between the power bus and the emitter of the fourth transistor, the fourth resistor and a variable resistor are connected afterwards between the common bus and the emitter of the first transistor, the fifth resistor is connected between the base of the second transistor and the connection point of the fourth resistor and the variable resistor, the inputs of the corrective links are connected to the collector of the fourth transistor, the outputs are interconnected, the capacitor is connected between the base of the second transistor and the connection point of the outputs of the corrective links, the input of the correction link is one extreme output of the input potentiometer, the other is connected to a common bus, the middle output of the input potential The meter is connected to the input of the correction circuit, the output resistor is connected between the output of the correction circuit and the output of the correction link, the output of the stabilization device is the emitter of the first transistor.

 Figure 1 shows a circuit diagram of the proposed device; in FIG. 2 shows a fragment of a circuit of a powerful RF amplifier stage with a transistor operating in class AB mode, to stabilize the mode of which the proposed device for stabilizing the transistor mode with two corrective links is used; in FIG. 3 shows voltage plots demonstrating the operation of a known device for stabilizing a transistor mode — a prototype of the invention; figure 4 is a plot of voltages demonstrating the operation of the proposed device stabilization mode of the transistor with two corrective links.

 The proposed device for stabilizing the transistor mode (Fig. 1) contains a transistor 1, transistor 2 - a temperature sensor, the collector of which is connected to the base of transistor 1, and the emitter - with a common bus, a resistor 3 connected between the power bus and the collector of transistor 2, transistor 4 in diode switching, the emitter of which is connected to the power bus, and the collector and base are interconnected, a resistor 5 connected between the collectors of transistors 1 and 4, transistor 6, the base of which is connected to the collector of transistor 1, resistor 7 connected between the bus power supply and emitter of transistor 6, resistor 8 and variable resistor 9 connected in series between the common bus and emitter of transistor 1, resistor 10 connected between the base of transistor 2 and the connection point of resistors 8 and 9, at least one correction link 11 containing an input potentiometer 12, one extreme terminal of which is the input of the correction link 11, the other is connected to a common bus, the correction circuit 13, made, for example, in the form of an integrating RC circuit with a resistor 14 connected between the input and output of the correction circuit 13, and a capacitor 15 connected in parallel to the output of the correction circuit 13, the input of which is connected to the middle output of the input potentiometer 12, and a resistor 16 connected between the output of the correction circuit 13 and the output of the correction link 11, and the inputs of the correction links 11 are connected to the collector of the transistor 6 , the outputs are interconnected, an isolation capacitor 17 connected between the base of the transistor 2 and the connection point of the outputs of the correcting links 11, the output of the stabilization device is the emitter of the transistor 1.

 The device operates as follows.

The output voltage of the device (according to the scheme of figure 1) can be written
U _cm = U _k2 - U _{from 1} , (1)
Where
U _k2 - voltage at the collector of transistor 2;
U _from1 - cutoff voltage of transistor 1.

U _k2 = E - R • B • S • (U _b2 - U _from2 ), (2)
Where
E- device power supply voltage;
U _b2 - voltage based on transistor 2;
U _from2 - voltage cutoff transistor 2;
B is the static gain of the transistor 2;
S is the slope of the input characteristic of transistor 2.

U _b2 = k • U _cm + k ₁ • U ₁ + k ₂ • U ₂ + ... k _N • U _N , (3)
Where
k = 1 / (R ₁₀ • g);
k ₁ = 1 / (R ₁ • g), k ₂ = 1 / (R ₂ • g), ....;
k _N = 1 / (R _N • g);
g = S + 1 / R ₁₀ + 1 / R ₁ + 1 / R ₂ + ... + 1 / R _N ;
R ₁₀ is the resistance of the resistor 10;
R ₁ , R ₂ ,. .., R _N is the resistance of the resistor 16, respectively, of the first, second ... N-th corrective link;
U ₁ , U ₂ , ..., U _N - output voltage, respectively, of the first, second. .. N-th corrective link.

Given (2) and (3), the expression for the output voltage (1) can be written as
U _cm = (E - U _{from 1} - R • B • S • (k ₁ • U ₁ + k ₂ • U ₂ + ... + k _N • U _N - U from ₂ )) / (1 + R • B • S • k).

Since in the real circuit R • B • S • k >> 1, and (E - U from ₂ ) / (R ₄ • B • S) << 1, this output voltage of the stabilization device can be approximately written as
U _cm = (U from ₂ - k ₁ • U ₁ - k ₂ • U ₂ - ... - k _N • U _N / k.

From this expression it follows that the output voltage of the proposed device stabilization mode of the transistor - U _cm depends on several terms. The first term U _from2 is the cutoff voltage of the transistor - temperature sensor 2, which has thermal contact with the transistor housing of the power amplifier. A change in the temperature of the transistor case leads to a change in voltage U _from2 at a speed of approximately 2 mV / deg. Thus, with an appropriate choice of circuit elements, the device provides stabilization of the transistor mode of the amplifier when the temperature of the case. This part of the circuit works similarly to the known device for stabilizing the terminal stage mode - the prototype of the invention (Zavrazhnov Yu.V. et al., Powerful high-frequency transistors. / Ed. By E.Z. Mazel. M .: Radio and communication, 1985, 176 p. , p.168).

 The remaining terms are determined by the output voltages of the corresponding corrective links and allow one to stabilize the operation of the amplifier transistor when amplifying amplitude-modulated oscillations causing modulation of the cutoff voltage of the amplifying transistor with a frequency above several Hertz, i.e., they can reduce non-linear inertial distortions caused by thermal inertial processes in the amplifying transistor.

 Let us consider in more detail the operation of the proposed device in this part by the example of amplification by a powerful radio-frequency amplifying cascade with a transistor operating in class AB mode, to stabilize the operation mode of which the proposed stabilization device is used (a fragment of the circuit is shown in Fig. 2), TV test signal "Pulse modulation 50 Hz "(GOST 20532 83).

 For comparison, we first consider the case when a known device is used as a prototype of the invention to stabilize the transistor mode of the amplifier stage. In FIG. 3 shows stress plots explaining the operation of the known stabilization device.

 In FIG. The plots of the modulating TV test signal "Pulse Modulation 50 Hz" are shown. Black level corresponds to a higher level of high-frequency signal, white level - to a lower level.

 In FIG. 3b shows a plot of the voltage cutoff amplifier transistor VT. With a higher signal level (black level), the heating of the crystal of the amplifying transistor leads to a gradual decrease in the cutoff voltage, with a lower signal level (white level), on the contrary.

In the known device, the output voltage is the bias voltage supplied to the base of the amplifying transistor, U _cm is determined by the temperature of the transistor housing, which, due to the thermal inertia of the transistor, remains unchanged for the duration of the modulating signal. Accordingly, U _cm does not change over the period of the modulating signal (Fig.3c). A comparison of the cutoff voltage of the amplifying transistor (Fig.3b) and the output voltage of a known device for stabilizing the transistor mode (Fig.3c) shows that at a black level the cutoff angle of the collector current of the amplifying transistor increases from a certain minimum value to a maximum, and the gain of the amplifier increases accordingly. When switching from black to white, on the contrary, a gradual decrease in the cutoff angle of the collector current of the amplifying transistor occurs with a corresponding decrease in the gain of the amplifier. This leads to distortion of the flat part of the half-frame pulses, as shown in FIG. 3G, in an amplifier stage with a known device for stabilizing the transistor mode.

 When using the proposed device to stabilize the operation of the transistor (figure 2), the distortion of the flat part of the half-frame pulses can be fully compensated.

 In FIG. 4a and FIG. 4b shows diagrams of the voltage of the modulating signal and the cutoff voltage of the amplifying transistor, similar to the diagrams of FIG. 3a and FIG. 3b.

 The voltage waveform at the collector of transistor VT3 will be as shown in FIG. 4c, since at a higher signal level (black level) the collector current VT1 also increases, approximately equal to the DC component of the base current of the amplifier transistor VT, respectively, the voltage drop across the resistor R5 increases and the voltage across the collector VT3 increases to the maximum level.

 In FIG. 4g shows the shape of the voltage at the output of the first corrective RC circuit with a smaller time constant, FIG. 4e is a second corrective RC circuit with a large time constant; FIG. 4e is the sum of these stresses.

The output voltage of the proposed device for stabilizing the regime of transistors U _cm is the bias voltage supplied to the base of the transistor of the amplifier stage VT, will have the form shown in Fig.4g. By choosing the time constants and the signal level of the correcting circuits, one can obtain the shape of this voltage corresponding to the shape of the cut-off voltage of the amplifying transistor (Fig. 4b). In this case, the cutoff angle of the collector current of the transistor, and therefore, the operation mode of the amplifying transistor (respectively, the gain of the cascade) will be unchanged both at the black level and at the white level, which eliminates the appearance of distortion of the flat part of the field frequency pulses (Fig.4z), due to thermal inertial processes in high-power amplifying transistors.

 In a similar way, the operation mode of transistors in power amplifiers is stabilized with the proposed stabilization device when amplifying arbitrary AM (IM) signals, which can significantly reduce (depending on the number of correcting links used) non-linear distortions due to thermal inertial processes in powerful transistors.

Claims (1)

 A device for stabilizing a transistor mode comprising a first transistor, a second transistor - a temperature sensor, two capacitors, four constant resistors and one variable resistor, the collector of the second transistor - temperature sensor is connected to the base of the first transistor, the first resistor is connected between the power bus and the collector of the second transistor, characterized in that a third transistor in diode switching, a fourth transistor, a fifth permanent resistor and at least one corrective correction element are additionally introduced into it a link that includes an input potentiometer, a correction circuit and an output resistor, while the emitter of the second transistor - temperature sensor is connected to a common bus, the emitter of the third transistor is connected to a power bus, and the collector and base are connected to each other, the second resistor is connected between the collectors of the first and the third transistor, the base of the fourth transistor is connected to the collector of the first transistor, the third resistor is connected between the power bus and the emitter of the fourth transistor, the fourth resistor and a variable resistor are connected in series between the common bus and the emitter of the first transistor, the fifth resistor is connected between the base of the second transistor and the connection point of the fourth resistor and a variable resistor, the inputs of the correction links are connected to the collector of the fourth transistor, the outputs are interconnected, the capacitor is connected between the base of the second transistor and the connection point of the outputs corrective links, while the input of the corrective link is one extreme output of the input potentiometer, the other is connected to a common bus, the middle the output of the input potentiometer is connected to the input of the correction circuit, the output resistor is connected between the output of the correction circuit and the output of the correction link, the output of the stabilization device is the emitter of the first transistor.

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