EA025687B1 - Output stage of audio-frequency power amplifier - Google Patents

Abstract

The invention is related to electronics and radio engineering, namely, to multi-pole electronic amplifiers, in particular, to Hi-Fi, Hi End audio-frequency amplifiers of class AB, B. A simpler design and higher energy and economical efficiency are attained. The output stage comprises at least N filters with different amplitude-frequency characteristics, and N>1 series circuits of the first and the second voltage followers connected between the first and the second DC power terminals. The points of pairwise connection of the first and second voltage followers are outputs of the stage, and control inputs of the first and second voltage followers in each of the above-said pairs are connected with each other through one of the filters by a bias resistor. The output stage includes also a power transformer with two windings, each having a central tap. The ends of the first winding are connected, through the first rectifier unit, to the first power terminal, and the ends of the second winding are connected, through the second rectifier unit, to the second power terminal. Centre taps of said windings are connected to the common power terminal; the third voltage follower in the form of a source follower, the input of which is connected to the input of the output follower, and the output is connected, through respective filters, to the control input of each of the first voltage followers; the first current generator having an output that is connected, through respective filters, to the control input of each of the second voltage followers.

Description

(57) The invention relates to electronics and radio engineering, in particular to multiband electronic amplifiers, in particular, audio amplifiers Ηί-Ρί, Ηί Εηά of class AB, B. A simplification of the design and increase of energy and economic efficiency are achieved. The output stage contains at least N filters with different amplitude-frequency characteristics, as well as N> 1 serial circuits of the first and second voltage followers connected between the first and second DC power inputs. The pairing points of the first and second voltage followers are the outputs of the cascade, and the control inputs of the first and second voltage followers in each of the above pairs are connected to each other by a bias resistor. Moreover, the output stage also contains a power transformer with two windings, each of which is made with an average output. The ends of the first winding through the first rectifier block are connected to the first power input, and the ends of the second winding through the second rectifier block are connected to the second power input. The middle terminals of said windings are connected to a common power terminal; the third voltage follower, made in the form of a source follower, the input of which is connected to the input of the output stage, and the output through the corresponding filters is connected to the control input of each of the first voltage followers; the first current generator, the output of which through the appropriate filters is connected to the control input of each of the second voltage followers.

025687 B1

Technical field

The claimed invention relates to electronics and radio engineering, namely to multi-band electronic amplifiers, in particular, to sound frequency amplifiers Ηί-Ρί, Ηί Εηά of class AB, B.

State of the art

The prior art multiband amplifier system containing a broadband amplifier, the output of which is equipped with separation filters to which dynamic heads are connected (To help the ham radio: Collection. Issue 104 / B80 Comp. V. A. Nikitin. - M.: DOSAAF, 1989). It’s known that the product will be simple and low cost, but the sound quality will be average (ibid.).

Also known is a high-quality multiband amplifier system containing a preamp-corrector, the output of which is connected to the inputs of three filters (multiband crossover), each of which is connected through a power amplifier to a separate dynamic head (ibid.). The disadvantage of this system is the complexity and high cost of the design, and increased energy consumption.

The latter system is selected as a prototype of the claimed technical solution.

Disclosure of invention

The technical result achieved by the claimed technical solution is to simplify the design and increase energy and economic efficiency.

The essence of the output stage is that it contains at least N filters with different amplitude-frequency characteristics. It differs in that the output stage contains N> 1 serial circuits of the first and second voltage followers connected between the first and second DC power inputs. The pairing points of the first and second voltage followers are the outputs of the cascade, and the control inputs of the first and second voltage followers in each of the aforementioned pairs are connected to each other by a bias resistor. Moreover, the output stage also contains a power transformer with two windings, each of which is made with an average output. The ends of the first winding through the first rectifier block are connected to the first power input, and the ends of the second winding through the second rectifier block are connected to the second power input. The middle terminals of said windings are connected to a common power terminal;

a third voltage follower, made in the form of a source follower, the input of which is connected to the input of the output stage, and the output through the corresponding filters is connected to the control input of each of the first voltage followers;

the first current generator, the output of which through the appropriate filters is connected to the control input of each of the second voltage followers.

The output stage should be supplemented with the following elements:

a second current generator, the output of which is connected to the input of the first current generator and a driving resistor;

a current sensor configured to measure current through the middle terminals of the transformer. The output of the current sensor is preferably connected to the control input of the second current generator.

The current sensor can be installed in the gap of the connection of the middle terminal of the first transformer winding with the common power output, or in the gap of the connection of the middle terminal of the second transformer winding with the common power terminal, or in the gap of the connection of the first rectifier unit with the first power input, or in the gap of the connection of the second rectifier unit with a second power input.

The second current generator can be performed in the form of a bipolar transistor, the base of which is connected to the output of the operational amplifier, the non-inverting input of which is connected to the current sensor through a smoothing KS filter, and the inverting input is connected to the reference voltage source.

The output stage is preferably performed containing three analog outputs, three first voltage followers, three second voltage followers, three filters. Moreover, the three mentioned filters are, respectively, low, medium and high frequency filters.

It is permissible to carry out the output stage containing two analog outputs, two first voltage followers, two second voltage followers, two filters, the two mentioned filters being, respectively, low and medium frequency filters. In this case, the output stage is preferably supplemented by an analog high-frequency output, a high-frequency voltage follower, a high-frequency current generator, and a high-pass filter. The high-frequency voltage repeater and the high-frequency current generator must be connected in series between the first and second DC power inputs, and their connection point is connected to the high-frequency analog output via a capacitor. The control input of the high-frequency voltage follower is preferably connected through the high-pass filter to the output of the third voltage follower. The control input of the high-frequency current generator can be connected to the output of the second current generator.

- 1 025687

Brief Description of the Drawings

In FIG. 1 shows a diagram of the claimed output stage; in FIG. 2 is a cascade diagram of example 1; in FIG. 3 is a diagram of a zero setting; in FIG. 4 is a cascade diagram of example 2; in FIG. 5 is a cascade diagram of example 3.

Options for the implementation of the output stage

The output stage of the audio frequency power amplifier (Fig. 1) contains an analog input (1);

N analog outputs (2), N> 1. To improve the sound quality, it is advisable to perform at least three analog outputs (2) (Ν> 3);

the first (14) and second (15) DC power inputs, respectively, with voltages U ₄ , U ₂ . Preferably Y ₁ = -U ₂ ;

N first (3) and N second (4) voltage followers connected in series between the first (14) and second (15) power inputs. Moreover, each of the first voltage followers (3) is connected to the first power input (14), and each of the second voltage followers (4) is connected to the second power input (15). The connection point of each pair of voltage followers (3, 4) is one analog output (2) of the declared output stage;

N filters (17) with different amplitude-frequency characteristics. Through each of the filters (17), bias resistors (5) are connected to each other control inputs, respectively, of each pair of voltage followers (3, 4);

the third voltage follower (6), made in the form of a source follower, the output of which is connected to the control inputs of each first voltage follower (3) through the corresponding filter (17). A repeater (6) is also connected to the first power input (14). The input of the third voltage follower (6) is connected to the analog input (1) of the declared output stage;

the first current generator (7), the output of which is connected to the control input of each second voltage follower (4) through the corresponding filter (17). Also, the first current generator (7) is connected to the second power input (15). the first current generator (7) can be performed on both field and bipolar transistors;

a second current generator (8), which is a controlled current generator. The output of the second current generator (8) is connected to the input of the first current generator, and through the driving resistor (9) is connected to the second power input (15). The second current generator is configured to smoothly increase the output current when the power is turned on;

power transformer (10) with two windings, each of which is made with an average output. The ends of the first winding through the first rectifier unit (11) are connected to the first power input (14), and the middle terminal of this winding is connected to a common terminal (zero power). The ends of the second winding through the second rectifier unit (12) are connected to the second power input (15), and the middle terminal of this winding is connected to the common terminal (zero power) through the current sensor (13). The current sensor (13) is configured to measure current through the middle terminals of the transformer (10) and therefore can also be placed in the open connection of the middle output of the first winding with the common output (power zero), as well as in the open connection of one of the rectifier blocks (11 or 12) with appropriate power input. The output of the current sensor (13) is connected to the control input of the second current generator (8);

a power transformer (10), rectifier units (11, 12), a current sensor (13) and a second current generator (8) are a quiescent current controller.

Case Studies

Example 1

Y ₁ = +24 V, Y ₂ = -24 V. The output stage (Fig. 2) contains three analog outputs (2), three first voltage followers (3), three second voltage followers (4), three filters (17) = 3). Each of these triples features analog outputs, repeaters, and low, medium, and high-pass filters.

The first low-frequency voltage follower (3) is made in the form of three η-type field-effect transistors in parallel, and the second low-frequency voltage follower (4) is made in the form of three p-type field-effect transistors in parallel. Moreover, the connected sources of these voltage followers (3, 4) are the analog output (2) of low frequencies. The low-pass filter (17) is essentially a pair of such filters included between its poles. The filter circuit is shown in FIG.

2.

The first medium voltage follower (3) is made in the form of two η-type field-effect transistors connected in parallel, and the second medium-frequency voltage follower (4) is made in the form of two p-type field-effect transistors connected in parallel. In this case, the connected sources of these voltage followers (3, 4) are an analog output (2) of medium frequencies. The mid-range filter (17) is essentially a pair of such filters included between its poles. Filter circuit is similar.

- 2,025,687 the high-pass filter circuit shown in FIG. 2.

The first high-frequency voltage follower (3) is made in the form of a p-type field effect transistor, and the second high-frequency voltage follower (4) is made in the form of a p-type field effect transistor. Moreover, the connected sources of these voltage followers (3, 4) are the analog output (2) of high frequencies. The high-pass filter (17) is essentially a pair of such filters included between its poles. The filter circuit is shown in FIG. 2.

An accelerating capacitor (20) is connected in parallel with the bias resistor (5).

The third voltage follower (6) is made in the form of a p-type field effect transistor, the source of which through the filters (17) is connected to the gates of all the transistors of the first voltage followers (3), and the gate through the zero-setting circuit (23) is connected to the input (1) of the claimed output stage.

The zero setting circuit (23) is a capacitor (40) connected between its signal input (41) and output (42) (Fig. 3). The signal input (41) is connected to the input stage (1) of the output stage, and the signal output (42) is connected to the gate of the transistor of the third voltage follower (6).

The zero setting circuit (23) also contains an operational amplifier (44), the output of which through a resistor is connected to the output (42) of the circuit. The non-inverting input of the operational amplifier (44) is connected through a resistance to a common output (power zero). The inverting input of the operational amplifier (44) is connected through a series circuit of two resistors (45, 46) to the control input (43) of the circuit (23), which in turn is connected to the analog output (2) of low frequencies. The inverting input and output of the operational amplifier (44) are connected by a capacitor. The connection point of the resistors (45, 46) is connected to a common terminal (zero power) through a circuit of parallel-connected capacitor and two diodes, one of these diodes being connected to zero by the anode and the other by the cathode.

The first current generator (7) is made in the form of a p-type field effect transistor (Fig. 2), the gate of which is connected to the output of the second current generator (8), the drain through the filters (17) is connected to the gates of all the transistors of the second voltage followers (4), and the source - through resistance - with a second power input (15).

The second current generator (8) (controlled) is made in the form of a bipolar transistor (24), type A1893, the base of which is connected to the output of the operational amplifier (25), the collector with a driving resistor (9), and the emitter through a resistor - with the first power input (14).

The signal from the current sensor (13) is fed to the non-inverting input of the operational amplifier (25) through the smoothing CS filter (26), and the potential of the reference voltage source (27) is supplied to the inverting input.

The reference voltage source (27) is made in the form of a stable current generator to the reference diode (28). Source (27) contains a KT9115 type bipolar transistor, the emitter of which is connected to the first power input (14), and the base, through a resistor, is connected to a common output (power zero). The collector of the aforementioned transistor is connected through a circuit of parallel-connected capacitors (29), a reference diode (28), and a tuning trim (30) to a common terminal (power zero). The output of the reference voltage source (27) is the tuning resistance engine (30).

The capacitor (29) is designed for smooth installation of the reference voltage when you turn on the circuit and change the position of the trimmer resistance engine (30). When you turn on the power at the output of the reference voltage source (27), the reference voltage begins to gradually increase, which is supplied to one of the inputs of the operational amplifier (25). At the same time, a smooth increase in current occurs at the measuring resistance of the current sensor (13).

The current sensor (13) is made in the form of a resistor connected between the midpoint of the second winding of the transformer (10) and the common output (zero power). The output of the current sensor is the connection point of the said resistor of this sensor with the midpoint of the second winding of the transformer (10).

The first rectifier unit (11) is two rectifier diodes, the connected cathodes of which are connected to the first power input (14). The anodes of these diodes are connected to the ends of the first winding of the transformer (10).

The second rectifier unit (12) is two rectifier diodes, the connected anodes of which are connected to the second power input (15). The cathodes of these diodes are connected to the ends of the second winding of the transformer (10).

Rectifier diodes are made in the form of 8K30100 diodes.

Example 2

The output stage is performed analogously to example 1, with the exception of the following. VI = +40 V, ν ₂ = 40 V.

The first low-frequency voltage follower (3) (Fig. 4) is made in the form of a composite transistor of two parallel-connected bipolar transistors of the r-p-p type, connected according to the Shiklai scheme with a field-effect transistor of the p-type. The second low-frequency voltage follower (4) is made in the form of a composite transistor of two parallel-connected bipolar transistors of the p-p-p type, connected according to the Shiklai scheme with a p-type field-effect transistor. Moreover, the connected sources of these voltage followers (3, 4) are the analog output (2) of low frequencies. The low-pass filter (17) is essentially a pair of such filters included between its poles. The filter circuit is shown in

- 3,025,687 of FIG. 4.

The first medium frequency voltage follower (3) is made as a composite transistor according to Shiklai with an η-type field effect transistor at the input, and the second medium frequency voltage follower (4) is made as a composite transistor according to Shiklai's circuit with a p-type field effect transistor at the input . In this case, the connected sources of these voltage followers (3, 4) are an analog output (2) of medium frequencies. The mid-range filter (17) is essentially a pair of such filters included between its poles. The filter circuit is shown in FIG. 4.

The first (3) and second (4) high-frequency voltage repeaters are made similar to the medium-frequency repeaters of the same name (3, 4). Moreover, the connected sources of these voltage followers (3, 4) are the analog output (2) of high frequencies. The high-pass filter (17) is essentially a pair of such filters included between its poles. The filter circuit is shown in FIG. 4.

Example 3

V = +40 V, Y ₂ = -40 V. The output stage (Fig. 5) contains two analog outputs (2), two first voltage followers (3), two second voltage followers (4), two filters (17) ( Ν = 2). In each of the mentioned two analog outputs, repeaters and low and medium frequency filters are distinguished.

The output stage further comprises an analog output (2) of high frequencies, a high frequency voltage follower (18), a high frequency current generator (19), and a high pass filter (21).

The first (3) and second (4) voltage followers and filters (17) of low and medium frequencies are made analogously to example 2.

The high-frequency voltage follower (18) is made similarly to the first high-frequency voltage follower (3) according to Example 2. The drain of this repeater (18) is connected to the first power input (14), and its shutter is connected to the output via a high-pass filter (21) third voltage follower (6). A high pass filter circuit (21) is shown in FIG. 5.

The high-frequency current generator (19) is made in the form of a composite transistor according to the Shiklai circuit with an η-type field effect transistor at the input. The gate of this composite transistor, which is the control input of the high-frequency current generator (19), is connected to the output of the second current generator (8), and the source, through resistance, is connected to the second power input (15). The drain of the high-frequency current generator (19) is connected to the source of the high-frequency voltage follower (19) and, through the capacitor, to the analog high-frequency output (2).

Analogously to example 1, a bias resistor (5), an accelerating capacitor (20), a third voltage follower (6), a zero setting circuit (23), a first current generator (7), a second current generator (8), a current sensor (13), the first rectifier block (11), the second rectifier block (12).

The implementation of the structural elements of the claimed invention is not limited to the above examples.

Description of the output stage

When using the claimed output stage, its input (1) is connected to the analog output of the sound source, mainly to the output of the digital-to-analog converter, and the outputs to sound reproducing devices. The power inputs (14, 15) are connected to the corresponding terminals of the power source. When the power is turned on, a smooth increase in current occurs on the current sensor (13).

If the supply voltage VI> ν ₂ , then the current from the first winding of the power transformer (10) through the first rectifier block (11) is sent to the power bus with voltage VI. Further, the current through the first (3) and second (4) voltage followers flows into the power rail with a voltage of ν ₂ , from where it is sent through the second rectifier unit (12) to the second winding of the power transformer (10). Further, from the midpoint of the second winding of the transformer (10), the current is directed to the current sensor (13). The voltage corresponding to the measured current value is supplied from the current sensor (13) to the control input of the second current generator (8), which regulates the current through a driving resistor (9).

At the same time, in the output stage performed according to Examples 1-3, the voltage from the current sensor resistor (13) is supplied through a KS filter (26) to the non-inverting input of the operational amplifier (25). In the cascade of examples 1-3, the mismatch signal of the reference and measured voltage is supplied to the base of the transistor (24), which regulates the current through the master resistor (9) depending on the mentioned mismatch signal.

If at a certain point in time the controlled current increases, then the second current generator (8) will increase its output current. The voltage at the driving resistor (9) will increase. This will lead to a decrease in the current of the first current generator (7) and the current through the resistor (5), which is responsible for the bias of the first (3) and second (4) voltage followers. The voltage at the control inputs of these repeaters (3, 4) will decrease, which will lead to a decrease in current through the repeaters (3, 4), that is, to a decrease in current and through the current sensor (13).

Due to the presence of filters (17), a dynamic change in the controlled current will affect the change in current through the repeaters (3, 4) differently depending on the frequency response of the filters (17).

In the absence of a signal at the input (1), the analog outputs (2) have a midpoint potential between VI and ν ₂ . Because according to the preferred design VI = -ν ₂ , then in the absence of a signal at the input (1), the analog outputs (2) have a ground potential. When a signal is input (1), it is repeated by voltage at the outputs (2) taking into account the frequency response of the filters (17).

In the claimed output stage, the claimed technical result: simplification of the design and increasing energy and economic efficiency is achieved due to the fact that the output stage contains at least N filters with different amplitude-frequency characteristics, as well as N> 1 serial circuits of the first and second voltage followers, connected between the first and second DC power inputs. The pairing points of the first and second voltage followers are the outputs of the cascade, and the control inputs of the first and second voltage followers in each of the aforementioned pairs are connected to each other by a bias resistor. Moreover, the output stage also contains a power transformer with two windings, each of which is made with an average output. The ends of the first winding through the first rectifier block are connected to the first power input, and the ends of the second winding through the second rectifier block are connected to the second power input. The middle terminals of said windings are connected to a common power terminal;

a third voltage follower, made in the form of a source follower, the input of which is connected to the input of the output stage, and the output through the corresponding filters is connected to the control input of each of the first voltage followers;

the first current generator, the output of which through the appropriate filters is connected to the control input of each of the second voltage followers.

Thus, the technical result is achieved by separating the output pairs of transistors and combining the output pairs with a multi-band filter.

Industrial applicability

The author made prototypes of the claimed device, tests of which confirmed the achievement of the technical result.

The claimed invention is implemented using industrially produced devices and materials, can be assembled at any radio engineering enterprise and will be widely used in radio engineering.

Claims (6)

CLAIM 1. The output stage containing at least N filters (17) with different amplitude-frequency characteristics, characterized in that the output stage contains N> 1 serial circuits of the first (3) and second (4) voltage followers connected between the first (14) and the second (15) DC power inputs, the pairing points of the first (3) and second (4) voltage followers are the outputs (2) of the cascade, and the control inputs of the voltage followers (3, 4) in each of the above pairs through one of the filters (17) interconnected a bias resistor (5), while the output stage also contains a power transformer (10) with two windings, each of which is made with an average terminal, while the ends of the first winding through the first rectifier unit (11) are connected to the first power input (14), and the ends of the second winding through the second rectifier unit (12) are connected to the second power input (15), while the middle terminals of said windings are connected to a common power output; the third voltage follower (6), made in the form of a source follower, the input of which is connected to the input (1) of the output stage, and the output through the corresponding filters (17) is connected to the control input of each of the first voltage followers (3); the first current generator (7), the output of which through the corresponding filters (17) is connected to the control input of each of the second voltage followers (4). 2. The output stage according to claim 1, characterized in that it further comprises a second current generator (8), the output of which is connected to the input of the first current generator and a driving resistor (9); a current sensor (13), configured to measure current through the middle terminals of the transformer (10), and the output of the current sensor (13) is connected to the control input of the second current generator (8). 3. The output stage according to claim 2, characterized in that the current sensor is installed in the gap of the connection of the middle output of the first winding of the transformer (10) with a common power output, or in the gap of the connection of the middle output of the second winding of the transformer (10) with a common power output, or into a break in the connection of the first rectifier unit (11) with the first power input, or in the break of the connection of the second rectifier block (11) with the second power input. 4. The output stage according to claim 2, characterized in that the second current generator (8) is made in the form of a bipolar transistor (24), the base of which is connected to the output of the operational amplifier (25), the non-inverting input of which through a smoothing CS filter (26) connected to a current sensor (13), and the inverting input to a voltage reference source (27). 5. The output stage according to claim 4, characterized in that it contains three analog outputs (2), three first voltage followers (3), three second voltage followers (4), three filters (17), while - 5 025687 the three mentioned filters (17) are respectively low, medium and high frequency filters. 6. The output stage according to claim 4, characterized in that it contains two analog outputs (2), two first voltage followers (3), two second voltage followers (4), two filters (17), the two mentioned filters (17 ) are respectively low and medium frequency filters, and the output stage additionally contains an analog high-frequency output, a high-frequency voltage follower (18), a high-frequency current generator (19), a high-pass filter (21), and a high-frequency voltage follower (18) and a high-frequency current generator (19) in series They are connected between the first (14) and second (15) DC power inputs, and their connection point is connected to the analog output of the high frequencies through a capacitor, while the control input of the high frequency voltage repeater (18) is connected to the output via the high-pass filter (21) the third voltage follower (6), and the control input of the high-frequency current generator (19) is connected to the output of the second current generator (8).