The power amplifier audio frequency

 

(57) Abstract:

The amplifier includes an input stage # 1 at the operational amplifier 2 with the purpose of negative feedback is common for AC and DC currents, in the form of a voltage divider. Power operational amplifier 2 via parametric stabilizers transistors 3 and 4. Cascade 22 increasing the tension made for the symmetric scheme two transistors 23 and 24 connected in the circuit with a common base, and has a circuit that sets the potential on the bases of these transistors 23 and 24, includes two groups of series-connected diodes 26,27 and 28,29, United resistor 30. The block 31 of the current amplification performed on the symmetric scheme and contains the cascade transistors 32 - 37 included with the collector. Output stage block 31 contains two series-connected resistors 38 and 39 connected respectively to its transistors 36 and 37. In addition, the block 31 contains thermo stabilizer 43 transistors 44 and 45 different patterns, and the amplifier includes a negative feedback circuit that is common to both DC and AC. Effect: reduce harmonic distortion and improve reliability. 1 Il.

The invention relates deposits with discharge current, in which the load is not directly connected with the pre-gain stages voltage (P. Skritek. Reference manual for the audio circuitry, M.: Mir, 1991, S. 215-218). As a preliminary stage of amplification in such amplifiers operational amplifier is used, which is associated with the subsequent amplification stages voltage via the current sensors (resistors). Subsequent amplification stages voltage are performed on the transistors included with a common emitter. This inclusion of transistors allows to obtain a large voltage gain and agree to a low-resistance current sensors with subsequent amplification stages current.

However, when using such cascades at high frequency sound range on the performance of the amplifier is affected by the capacitance base-collector, which, in turn, reduces the total depth feedback and increase distortion. In addition, in the case of penetration in amplifying the signal path with a steep rise front of or excitation of the amplifier there is a risk of failure of the operational amplifier, because the base current of the transistors acting as voltage amplifiers, consumed by the circuit such solutions require a single operating point for the symmetric branches, therefore, the only possible mode, characterized by a high level of harmonic distortion.

Known power amplifier audio frequency (I.e. Humala. The quality and the circuitry of USC, Radio, N 9, 1985, S. 31-35), based on the principle of discharge current. It contains the input stage, performed at the operational amplifier, the power through the voltage regulators performed on the transistors of different patterns. Bases of the transistors connected to the voltage dividers, the emitters to respective shoulders of the power operational amplifier, and their collectors connected to the current sensors, power consumption operational amplifier, in the form of a low-resistance resistors. The amplification of the known voltage of the amplifier is made by the symmetric scheme two transistors of the corresponding structure, the base of which is connected to the resistors of the current sensors, and their emitters connected to the respective power rails. The collectors of these transistors are connected to the diodes, which is the load block of the current amplification cascade which is made under the symmetric scheme on a powerful transistors included in the circuit with a common header and mode Century.

Load operational amplifier ableiter covered by negative feedback. Midpoints of the amplification voltage and the output stage is connected to a low-resistance resistor, allowing to keep the chain overall feedback in static mode small signal as the transistors of the output stage operate without the quiescent current. Compensation of the nonlinearity of the input characteristics of the output stage is carried out through the bridge, the shoulders of which is composed of inductance, capacity, and two resistors.

When it arrives at the non-inverting input of the operational amplifier of the signal of positive polarity current consumption positive leverage the power amplifier increases the amplitude of the input signal, which leads to an increase of the voltage drop across the resistor in one output in the collector circuit of the voltage regulator, and another conclusion is that the positive bus of the power amplifier.

The increase in the voltage drop across the resistor leads to the opening of the transistor acting as a voltage amplifier and current. Then the next transistor acting as a current amplifier, which, through the collector junction and bus positive power supply sends current to the load.

To make ostoich the m resistance of the resistor, connected by its output to the connection point between the emitters of the transistors of the output stage, and a second output connected to the inverting input of the operational amplifier, and a resistor, one lead of which is connected to the shared bus, and the second output to the inverting input of the operational amplifier.

Correction of the phase-frequency characteristics by using a capacitor, is included as an output in the midpoint predominance cascade, and the second to the inverting input of the operational amplifier. The emitters of transistors predominance cascade-connected diodes connected in forward bias. The current flowing through these transistors causes a voltage drop across the diodes to such a value that the output transistors, bases connected to the respective diodes and the emitter - to mid-point, were securely locked. Thus the output transistors are in the mode Century.

The inclusion of transistors with common emitter and amplification path leads to the degradation of dynamic performance of the amplifier due to the fact that with increase in the frequency of signal a significant role due to the effect of Miller's play capacitance collector transitions. In addition, when a large coefficient pilotmain the excitation frequencies, close to the boundary unity gain frequency of the transistor.

Therefore, the switching transistor common-emitter as a voltage amplifier undesirable.

The use of transistors of the output stage mode In it is undesirable for the following reasons:

a) in the absence of no-load current crystal having a large area is not heated, so when a signal with a steep front and a large amplitude through the transistor is the local heating of the crystal, leading to strain it, and, as a consequence, either to the breakdown of the transistor, or to cause emission of harmonics;

b) due to non-linearity of the output stage operating in mode B, it is necessary to apply special measures for compensation of nonlinear distortion, which requires more complex circuitry and fine tuning bridge, compensating them;

C) a transistor acting as voltage amplifier and included common-emitter, consumes the base current through the respective voltage regulator and through the output stage of the operational amplifier.

Since the amplifier operates on the inductive load, at some frequencies, audio range load resistance may decrease the cascade operational amplifier loaded at a load much lower than the nominal the possible failure of its output transistors, which reduces the reliability of the amplifier.

The objective of the invention is the creation of a power amplifier audio frequency with such a circuit implementation of its cascades, which would reduce harmonics, improve reliability and to reduce the requirements to the used hardware components.

The problem is solved in that the power amplifier audio frequency containing the input stage, performed at the operational amplifier output low impedance load, the power pins which are connected to the corresponding voltage stabilizers performed on the transistors, the collectors of which are connected with sensors current consumption of the operational amplifier, in the form of resistors, the amplifier voltage, made under the symmetric scheme two transistors connected to the resistors current sensing input stage, the unit current amplification performed on the symmetric scheme and containing the cascade transistors, included in the common-collector and United by their bases to the collectors of the transistors of the amplifier voltage, and a negative feedback circuit, the total for direct and alternating currents, according to the AC and DC currents made in the form of a voltage divider, the transistor amplifier voltage connected in the circuit with a common base, and in addition, this cascade further comprises a circuit that sets the potential on the bases of its transistors and including two groups of series-connected diodes, United resistor, and the base of the transistor shoulder of positive polarity amplifier is connected to the cathode of the first diode group, in which the anode of the last diode connected to the bus of positive polarity, and the base of the transistor shoulder of negative polarity amplifier is connected to the anode of the first diode group, in which the cathode of the last diode is connected to the bus of negative polarity, and the block of the current amplification further comprises at least two cascaded transistors included in symmetric circuit with the collector, while the output stage unit contains two series-connected resistors, the output of one of which is connected to the emitter of the transistor shoulder of positive polarity, and the output of another resistor connected to the emitter of the transistor shoulder of negative polarity, and, in addition, the block of the current amplification additionally has thermo stabilizer containing two transistors of different patterns, Baslertor connected to the bases of the respective transistors grooms cascade.

Performing input stage for an operational amplifier covered by the negative feedback reduces distortion, balancing operational amplifier and DC better stability to the excitation. Turning on the transistors of the amplification voltage scheme with a common base allows to exclude the effect of Miller and to increase the cutoff frequency of the transistor, amplifying the voltage, and to reduce harmonic distortion. In addition, the inclusion of transistors provides good matching low impedance signal source and a large input resistance of a transistor connected with a common manifold. In the proposed amplifier transistor connected with a common base, consumes no current flowing through the operational amplifier, which is beneficial to reducing harmonic distortion and improving the reliability of the operational amplifier.

The execution of the block of the current amplification according to the invention provides the work of its transistors in active mode AB (quiescent current). This greatly reduces harmonic distortion and provides heating of the crystals of the transistors in the static mode. Increase colagrossi, having a complex impedance (real acoustic system). In addition, with the increase of the cascade amplifier is not critical to the variation in characteristics of transistors included in the unit current amplification.

Introduction to power thermo stabilizer for grooms and output cascades provides adjustment of the quiescent current.

The power amplifier audio frequency according to the invention contains the input cascade 1 made at the operational amplifier 2, a power which is exercised through parametric stabilizers performed on the transistors 3 and 4, the emitters of which are connected respectively with the positive and negative power pins of the amplifier 2. The base of transistor 3 is connected to the cathode of the Zener diode 5 and one terminal of the resistor 6, the other output of which is connected to the bus 7 positive polarity power source. The anode of the Zener diode 5 is connected to the bus 8 zero potential. The base of transistor 5 is connected to the anode of the Zener diode 9 and one terminal of the resistor 10, the other output of which is connected to the bus 11 negative polarity of the power source and the cathode of the Zener diode 9 is connected to the bus 8 zero potential.

Non-inverting input of op is from the conclusions of the coupling capacitor 13, connected to the other output to the input of the power amplifier. In addition, the non-inverting input of the operational amplifier 2 is connected to one terminal of the resistor 14, the other output of which is connected to the bus 8 zero potential, and to one terminal of the resistor 15 of the negative feedback circuit, shunted by a capacitor 16.

Operational amplifier 2 includes a negative feedback circuit, made in the form of a voltage divider formed by resistors 17 and 18, some conclusions which are connected to the inverting input of the operational amplifier 2. Another of the resistor 17 is connected to the bus 8 zero potential, and the other of the resistor 18 is connected to the output of the operational amplifier 2 and one terminal of the output low impedance load 19 is connected to the bus 8 zero potential.

The collectors of transistors 3 and 4 are connected with sensors current consumption of the operational amplifier 2, in the form of resistors 20 and 21 are connected respectively to the tire 7 and 11 positive and negative polarity.

Cascade 22 increasing the tension made for the symmetric scheme transistors 23 and 24 with a common base, the emitters of which are connected to the resistors 20 and 21 of the current sensors with the kad 22 gain voltage contains circuit, sets the potential at the bases of transistors 23 and 24. This circuit includes two groups of series-connected diodes 26, 27 and 28, 29, United resistor 30. The base of the transistor 23 of the shoulder of positive polarity amplifier is connected to the cathode of the diode 27, and the anode of diode 26 this group is connected to the bus 7 positive polarity. The base of transistor 24 is connected to the anode of the diode 28, and the cathode of diode 29 this group is connected to the bus 11 negative polarity.

The block 31 of the current amplification of the proposed power amplifier contains the cascade transistors 32-37, enabled by the symmetric scheme with a common manifold. The collectors of transistors 32, 34 and 36 connected to the bus 7 positive polarity, and the collectors of the transistors 33, 35 and 37 to the bus 11 negative polarity. Bases of the transistors 32 and 33 are connected to the collectors of transistors 23 and 24, respectively. Bases of the transistors 34, 35 and 36, 37 of the other two stages connected respectively to the emitters of transistors 32, 34 and 33, 35 of the previous stages. Output stage unit 31 of the current amplification contains two series-connected resistors 38 and 39, while the output of the resistor 38 is connected to the emitter of the transistor 36 of the shoulder of positive polarity, and the output resistor 39 with the emitter transit the respective terminals of the resistor 15 and capacitor 16 of the negative feedback circuit, and also to one terminal of the coil 40 inductance, the other output of which is connected to the load 41 power amplifier connected to the bus 8 zero potential. In the block 31 is entered, in addition, a capacitor 42 connected by its output to the base of transistor 32, the collector of transistor 23 and to the corresponding output resistor 25.

The block 31 of the current amplification has thermo stabilizer 43 containing the transistors 44 and 45 different patterns, the base of which is connected to the emitters of transistors 34 and 35 grooms cascade. The emitters of transistors 44 and 45 are connected, and their collectors connected to the bases of transistors 34 and 35 grooms cascade. Thermo stabilizer 43 also includes a resistor 46, the findings of which are connected with the emitters of transistors 34 and 35.

The input stage # 1 power amplifier is made at the operational amplifier 2, a power which is exercised through parametric stabilizers performed on the transistors 3 and 4. Operating voltage of the transistors 3 and 4 in the static mode is set by the Zener diodes 5 and 9 and the resistors 6 and 10. Operational amplifier 2 covered deep negative feedback DC current through the divider formed by resistors 17 and 18. This required the district amplifier 2 has a current consumption, which causes the voltage drop across the resistors 20 and 21. The emitters of transistors 23 and 24 21 cascade amplification of the voltage connected to the corresponding resistors 20 and 21, and the base to the circuit consisting of diodes 26 to 29 and resistor 30, the resistance of which is chosen in such a way as to ensure the rated current through the diodes 26 to 29, which, in turn, causes a voltage drop on them by an amount sufficient to secure opening of the transistors 23 and 24. The current flowing through the resistor 20, transistor 23, the resistor 25, the transistor 24, the resistor 21 causes the voltage drop across the resistor 25 is required to open the transistors 32 and 33 of the block 31 of the current amplification due to which there is a current through the transistors 32, 44, 45 and 33, causing the voltage drop across the collector junctions of transistors 44 and 45. This voltage drop opens the transistors 34 and 35 grooms cascade, the current through which creates a voltage drop across the resistor 46. This voltage drop opens the transistors 36 and 37 so that they work in AV mode.

Resistors 38 and 39 are elements of the circuit negative feedback DC and act as additional "oven" elements.

Main ro the existing way. Transistors 36 and 37 of the output stage are located next to the transistors 34 and 35 grooms cascade and have them temperature relationship. When the supply voltage to the power amplifier using transistors 36 and 37 current flows, which leads to the heating of their crystals and increase the current through them. This causes an increase of the voltage drop across resistors 38 and 39, which leads to the reduction of the voltage drop at the junctions of the base-emitter voltage of the transistors 36 and 37 and prescribing them. In addition, increasing the temperature of the transistors 36 and 37 due to temperature due heats crystals of transistors 34 and 35, causing an increase in voltage drop across the resistor 46, which opens the transistors 44 and 45. As a result, the resistance of the transistors 44 and 45 is reduced, which reduces the voltage drop across the collector junctions of transistors 44 and 45, causing the transistors 34 and 35 prescrived. Thus the circuit is stabilized and is in working mode.

The power amplifier is covered by a negative feedback DC current through the resistor 15, so you can balance the power amplifier DC.

Since the power amplifier is symmetrize the al positive polarity is supplied via an isolating capacitor 13 and the resistor 12, designed to increase the input impedance of the amplifier, non-inverting input of the operational amplifier 2. Since the operational amplifier 2 is loaded by a low impedance load 19, the current leverage the power of positive polarity causes a proportional voltage drop across the resistor 20. As a result, the potential at the junction of transistor 23 is reduced and it is locked, so that the transistors 32, 34 and 36 are closed. At the same time, by reducing the current through the resistor 21 is opened, the transistor 24, which leads to an increase of negative potential on its collector and base of transistor 33, and thus opening it and transistors 35 and 37 subsequent cascades.

Thereby inverting the phase of the signal. The output signal from the power amplifier through a resistor 15 is fed to non-inverting input of the operational amplifier 2, the result is an inverting amplifier.

Input cascade 1 made at the operational amplifier 2, covered deep overall negative feedback, the total for direct and alternating currents. This leads to increased stability, linearity and reduce distortion.

Casket good matching low impedance loads - resistors 20 and 21 and the high input resistance of the transistors 32 and 33, connected in circuit with a common manifold.

The switching transistors 23 and 24 with a common base has a number of advantages.

1. A large voltage gain

TO1= gR1,

where K1- gain voltage;

R1- load resistance;

g - slope characteristics of the transistor.

Load resistance for a stage 22 with a common base in the dynamic mode is the input resistance of the subsequent cascade of 31, is made for the General collector, having a very large input resistance (hundreds of ohms).

2. Very stable current gain

,

where K2- gain current;

- gain current of the transistor.

With increasing collector current of one transistor 32 or 33, included with the collector, the input resistance decreases.

< / BR>
where R2- input resistance of the transistor 32 or 33;

- transfer ratio of the transistor 32 or 33 current;

R3- load resistance cascade;

r is the resistance of the collector junction of transistor 32, 33.

3. The transistors 23 and 24 that are included with a common base, is not affected by the capacitance base - collector, therefore, such a cascade has a better frequency response compared to the cascades with a common emitter and a great performance, which is important for cascade 22 increasing the tension.

In dynamic mode, the resistors 20 and 21 perform the role of local negative feedback to transistors 23 and 24 due to the fact that with the opening of the transistor 23 positive potential at its collector rises and increases the base current of the transistor 32 as a result of its opening. This leads to an increase in the voltage drop across the resistor 20, which is the effect of local negative feedback for 22 cascade amplification voltage, therefore, the depth of this feedback depends on the gear ratio of the transistors 32, 34, 36, 33, 35, 37, perform the function of current amplifiers, and allows you to counteract the negative effects from the use of transistors with different transmission ratios current in different shoulders.

The block 31, the gain of current swest, which consider the example of operation of the transistors 32 and 33. The rest of the cascades operate in the same manner.

Bases of the transistors 32 and 33 is connected to the resistor 25 and the respective collectors of transistors 23 and 24, and their emitters connected to the respective collectors of transistors 44 and 45. Resistance on the collector junctions of transistors 44 and 45 is a load for transistors 32 and 33 in the static mode.

In dynamic mode, the switching transistors 23 and 24 depending on the polarity of the input signal leads respectively to the switching transistors 32 and 33. Since the basic capacity of powerful transistors constitute a significant value, then the switching transistors in the standard inclusion of the accumulation of charges on the underlying containers, this, in turn, causes an increase in harmonic distortion. The proposed amplifier is efficient resorption of the underlying charges of transistors, such as transistor 36, the supply voltage of the opposite polarity through resistor 46 to the base of transistor 36 when closed.

The present invention can be used to amplify the electrical signals of audio frequency in the Oba is ASI input cascade, performed at the operational amplifier output low impedance load, the power pins which are connected to the corresponding voltage stabilizers performed on the transistors, the collectors of which are connected with sensors current consumption of the operational amplifier, in the form of resistors, the amplifier voltage, the inputs of which are connected to the terminals of the resistors current sensing input stage and which is made with transistors of different patterns and the resistor, the findings of which are the outputs of amplifier power, the unit current amplification, the output of which is the output of the power amplifier audio frequency and through a chain of negative feedback, the total for direct and alternating currents, connected to the input of the power amplifier audio frequency, and the unit current amplification performed on the symmetric scheme and contains the cascade transistors having different structure and connected in the circuit with the collector, the base of which are the corresponding inputs of the unit current amplification and connected to the outputs of the amplification voltage, wherein the operational amplifier input stage has a negative feedback circuit that is common to both AC and DC currents, the emitters are the inputs of the amplification voltage, and, in addition, the amplification of the voltage introduced to the circuit that sets the base potential and performed on serially connected between the power rails of the first group of serially connected diodes, a resistor and a second group of serially connected diodes, and the terminals of the resistor are the conclusions of the circuit that sets the base potential, and is connected to the bases of the respective transistors of the amplification voltage and the AC current amplification further comprises at least two cascaded transistors different structures included in the common-collector, with one of the stages is the output stage of the unit current amplification and additionally contains two series-connected resistors, the findings are connected to the emitters of the transistors of the cascade, and, in addition, the unit current amplification introduced thermo stabilizer containing two transistors of different patterns and the resistor, the findings of which are connected to the emitters of transistors grooms cascade block current amplification and the bases of the transistors of thermo stabilizer, the emitters of which are connected, and their collectors to the bases of the respective transistors grooms cascade.

 

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