RU36590U1 - Broadband Power Amplifier Output Stage - Google Patents

Description

The proposed utility model relates to the field of electronic technology and can be used to build high-precision transistor amplifiers that do not distort the amplified electrical signal of sound and ultrasonic frequencies. The inventions can be used in the technique of sound reproduction and can simplify, reduce the cost of equipment with broadband power amplification devices.

A known c-stage transistor amplifier (see AS USSR. No. 327568, published in the bulletin "Discoveries. Inventions. Industrial samples. Comrade Signs, 1972, 5).

In the well-known cascade transistor amplifier, the cascades are built of RPR and PRP transistors connected by emitters, resistive loads are included in the collectors of one of the transistors, the base of one of the transistors of each subsequent stage, starting from the second, is connected to the load of the previous stage, the bases of all others transistors are connected together, forming a common cascade control electrode connected to a power source through one common cascade feedback element.

The disadvantage of a multistage amplifier is the appearance of nonlinear distortions of the output signal, since a significant number of auxiliary

elements (RC circuits), each of which introduces nonlinear distortion during transients.

It is known that the quality of a field-effect transistor, and in particular, its switching speed, depends on the possibility of suppressing the Miller effect due to the existence of an SZS parasitic capacitance, which is a negative feedback between the input and output of the transistor (see the book: “Power electronics for amateurs and professionals , B. Yu. Semenov, “Solon-R, M., 2001, p. 69).

The field effect transistor is an amplifier stage, the output signal of which is removed from the load in the drain circuit. In such a cascade, the output signal will be shifted in phase relative to the input by 180 °. Feedback Szs so much reduces the amplitude of the output signal that with respect to it, the input capacitance of the transistor seems to be larger than it actually is: C input Szi + (1 + K y) Szs, where K y SR n is the gain of the cascade; S is the power slope of the transistor. The power slope S of the transistor is a parameter that determines the amplitude of the output current for a given control action. As a rule, in the circuit design of the transistor, it is necessary to take into account the possibility of the appearance of amplitude distortions of the amplified output signal that can destroy the positive properties of the field effect transistor.

The quality of the structure of a field-effect transistor is the higher, the higher the slope and the less complex dynamic load on the audio power amplifier, including the less stray dynamic capacitance that occurs only when the control signal is amplified at the output electrodes of the transistor.

Spurious dynamic capacitance depends on the gear ratio and has a negative effect on stabilization

voltage. If the transistor operates at a voltage gain of 1, then it has little effect on voltage stabilization. But if the transistor starts to work at a voltage gain greater than 1, for example, equal to 100, then the output parasitic dynamic capacitance multiplied by the gain increases 100 times and the amount of control current required to absorb this dynamic capacitance also increases by 100 time.

Known output stage of the power amplifier according to patent R f No. 2094942, M. Kl.7: H03F 3/26, publ. 10/27/97, selected as the closest analogue.

The known output stage of the power amplifier contains output transistors connected according to the scheme with a common collector (drain) having source (emitter) resistors of interstage negative feedback. The known output stage of the power amplifier also contains the first, second current-carrying elements, the first, second linear, first, second non-linear voltage-to-current converters, the first, second voltage dividers of the feedback elements, including the first, second and third, fourth resistors, respectively, and also - the first and second switching elements on capacitors, the first conclusions of which are connected to non-inverting inputs, and the second conclusions with the outputs of the first and second linear voltage to current converters correspond to Enno. The first and second feedback elements are made in the form of voltage dividers on the first and fourth resistors, respectively, the terminals of the first and third resistors are connected to the non-inverting inputs of the first and second nonlinear voltage-to-current converters, and the second conclusions with

inverting inputs of the first and second non-linear voltage to current converters, respectively.

The known output stage of a power amplifier for its implementation has the following disadvantages:

-significant nonlinear distortion of the output signal when voltage changes at the output electrodes of transistors;

- the negative effect of the complex dynamic load on the audio power amplifier, distortion of the amplitude and frequency parameters of the output signal in comparison with the parameters at the input and, as a consequence, the deterioration of sound quality;

- significant value of the quiescent current, equal to 1 ampere, the complexity of the circuit.

The technical result of the proposed utility model is to eliminate these disadvantages of the prototype, namely, in:

-stabilization of the voltage at the transistor by reducing non-linear distortion of the output signal when voltage changes at the output electrodes of the transistors;

-Reducing the effect of the complex dynamic load on the power amplifier of sound frequency by eliminating the effect on the amplitude and frequency parameters of the output signal arising from the “Earley effect, and, as a result, improving sound quality;

-Reducing the quiescent current by 20 times (up to 50 amperes);

- Simplification of the circuit by reducing the number of amplification stages in the audio power amplifier;

-reduction of power dissipation at the transistors of the output stage;

-Reducing temperature loads by 3-4 times on the transistors of the output stage;

- expanding the bandwidth of the output stage.

The technical result is achieved by the following solution.

In the output stage of a broadband power amplifier containing output transistors connected according to a common collector (drain) circuit, having source (emitter) resistors of interstage negative feedback, according to a utility model, the connection point of the source of the first transistor with a negative feedback resistor is connected to the first reference a constant voltage source, for example, a zener diode powered by a first direct current source, the drain of the first transistor is powered from the first repeater voltage taken from the first direct current source and connected by a current source, made on the current-setting resistor, to the drain of the second transistor and the output of the second voltage follower, while the first transistor and voltage follower connected to the first reference constant voltage source are complementary to the second transistor and repeater voltage, the source of the second transistor is connected to a second reference DC voltage source, powered by a second DC source.

Connecting the connection point of the source of the first transistor with a negative feedback resistor to the first reference DC voltage source, for example, a zener diode powered by the first DC source, and connecting the drain point of the first transistor with both the first voltage follower taken from the first DC source and through a current source made on a current-setting resistor, with the drain of the second transistor and the output of the second voltage follower, reduces non-linear and distortions of the output signal

with changes in voltage at the output electrodes of transistors, as well as improving the frequency characteristics of the amplifier as a whole.

The first and second reference DC sources (zener diodes) convert the current into constant voltage and feed the first, second voltage followers.

The first, second voltage followers maintain alternately a constant voltage on the first, second output transistors through the current source of the current-setting resistor, fixing the voltage at the drain points of the first or second transistor relative to their source points. Voltage followers work actively only in one direction, the first follower repeats the voltage during the positive half-wave, when the second follower is closed, and vice versa.

The input sinusoidal voltage from the first DC source is supplied to the drain of the first output transistor from the first voltage follower, and to the source point from the first reference DC voltage source. During amplification of the positive half-wave of the input driving signal, the first output transistor is open, at its drain-source points the optimal stable voltage is maintained within 10-12 volts, the second output transistor is closed, and the second repeater can be closed.

During amplification of the negative half-wave of the signal, the first output transistor is closed, the second output transistor is open, and at its drain-source points, the optimal stable voltage is also maintained within 10-12 volts.

The connection of the first transistor and the voltage follower with the first reference constant voltage source is complementary to the second transistor and the second follower

voltage, and the connection of the source of the second transistor with the second reference constant voltage source, powered by the second constant current source, can reduce the influence of the complex dynamic load, especially the dynamic stray capacitance of the output stage of the audio frequency power amplifier.

This is because at the moment of transition through the upper point of the conversion of the negative half-wave to the positive, when the second transistor closes and the first opens, the second voltage follower closes and automatically stops the source-drain capacitance of the second transistor.

The connection of the drain of the first transistor with the current source, made on the current-setting resistor, with the drain of the second transistor and the outputs of the first, second voltage followers, ensures the absorption of the drain-source capacity through the resistor with the current of the second voltage follower.

The lead-in resistor, the first and second voltage followers keep the voltage at the output electrodes of the first, second transistors constant, excluding dynamic capacitance, while the input signal of the output stage is not loaded with dynamic capacitance.

Maintaining at the output electrodes of the transistor an optimal stable voltage within 10-12 volts, in turn, reduces the effect of the "Earley effect by almost 2 orders of magnitude, the output signal of the amplifier repeats the input with a greater degree of accuracy, non-linear distortions are significantly reduced and, as a result, the sound quality of the amplifier improves power. In addition, this reduces the quiescent current of the cascade controlling

OUTPUT transistors, up to 5-10 milliamps for a load current of 30 amperes.

Eliminating the influence of dynamic capacitance allows you to expand the bandwidth of the entire amplifier and increases the speed of the amplifier, i.e. allows the amplifier to correct its internal distortion.

The sushiness of the claimed technical solution is illustrated by the functional diagram of the output stage of the broadband power amplifier shown in the figure.

On the electrodes of the drain-source transistors of the output stage of the broadband power amplifier, output transistors 1,2 are provided in the output stage of the broadband power amplifier, which are connected according to the common collector (drain) circuit, having source (emitter) resistors 3.4 of the internal cascade negative feedback. The connection point of the source of the first transistor 1 with a negative feedback resistor is connected to the first reference DC voltage source 5, powered by the first DC source 6. The drain of the first transistor 1 is powered from the first voltage follower 7, taken from the first DC source 6, and is connected by a current source made on the current-setting resistor 8, to the drain of the second transistor 2 and the output of the second voltage follower 9.

The first transistor 1 and the voltage follower 7 connected to the first reference DC voltage source 5 are complementary to the second transistor 2 and the voltage follower 9. The source of the second transistor 2 is connected to a second reference DC voltage source 10, powered by a second DC source 11.

The process of stabilizing the voltage on the elektrooda drain-source transistors of the output stage of a wide-band power amplifier is carried out in the following sequence:

- they remove the voltage from the source electrode of the first transistor and set a constant operating voltage relative to it, taken from the first reference constant voltage source, powered by the first constant current source;

- the drain electrode of the first transistor is supplied with a constant operating voltage from the first voltage follower, taken from the first direct current source;

- the drain electrode of the first transistor is connected by a current source to the drain of the second transistor and the output of the second voltage follower complementary to the second transistor and the voltage follower;

- remove the voltage from the source electrode of the second transistor and set a constant operating voltage relative to it, taken from the second reference constant voltage source, powered by the second constant current source.

When the input voltage is applied to the first 6, second 11 gates (bases) of the output transistors 1,2, the positive half-wave of the input driving signal is amplified on the first output transistor 1, the voltage begins to change, its parameters change. So that the voltage at the first output transistor 1 does not change, its drain is connected to the first voltage follower 7, taken from the first DC source 6, and the connection point of the source of the first transistor 1 with a negative feedback resistor is connected to the first reference DC voltage source (zener diode) 5, powered by the first DC source 6.

The voltage follower 7 repeats the voltage of the DC voltage source 5, fixing the voltage on the drain relative to the source of the transistor 1 within 8-12 volts. Since the drain of the first transistor 1 is powered from the first voltage follower 7 and is connected to a current source made on the current-sensing resistor 8, during the positive half-wave of the input driving signal, all parameters of the output transistor, depending on the drain-source voltage, remain unchanged.

During amplification of the negative half-wave of the signal, the first voltage follower 7 operates as a voltage follower, and the first output transistor 1 is closed, the second follower 10 and the second output transistor 2 are open.

The second voltage follower 10 repeats the voltage of the constant voltage source 9, fixing the voltage relative to the source of the transistor 2 in the range of 8-12 volts at the drain, i.e. at its drain-source points, the optimum stable voltage is also maintained.

Since the drain of the second transistor 2 is powered from the second voltage follower 10 and connected to a current source made on the current-sensing resistor 8, during the negative half-wave of the input driving signal, all parameters of the second output transistor 2, depending on the drain-source voltage, also remain unchanged.

When the positive half-wave of the input voltage begins to decrease in absolute value, the first voltage follower 7 is closed and the constant voltage at the first output transistor 1 is maintained by the second voltage follower 10 through the current source of the current-setting resistor 8.

When the negative half-wave of the input voltage begins to decrease in absolute value, the first voltage follower maintains a constant voltage at the second output transistor.

When passing through the upper point of conversion of the negative half-wave of the signal to positive, when the second transistor 2 closes and the first 1 opens, the second voltage follower 10 closes and the source-drain capacitor of the second transistor 2 automatically stops absorbing.

When passing through the upper point of conversion of the positive half-wave of the signal to negative, when the first transistor 1 closes and the second 2 opens, the first voltage follower 7 closes, automatically stops the resorption of the sources of the sources of the second transistor 2.

At the drain-source capacitance of the first transistor 1, the initial voltage remains, the value of which can be equal to the amplitude of the previous positive half-wave.

The output stage circuit can operate in hard mode B, while the output stage of the prototype operating in the A-B mode has significant internal distortion.

Claims (1)

The output stage of a broadband power amplifier, containing output transistors connected according to a common collector (drain) circuit, having source (emitter) resistors of interstage negative feedback, characterized in that the connection point of the source of the first transistor with a negative feedback resistor is connected to the first reference source DC voltage, for example a zener diode powered by a first DC source, the drain of the first transistor is powered from the first voltage follower, squeezed from the first direct current source, and is connected by a current source, made on the current-setting resistor, to the drain of the second transistor and the output of the second voltage follower, while the first transistor and voltage follower connected to the first reference DC voltage source are complementary to the second transistor and voltage follower, the source of the second transistor is connected to a second reference DC voltage source, powered by a second DC source.