WO1995010881A1

WO1995010881A1 - Chopper amplifier

Info

Publication number: WO1995010881A1
Application number: PCT/CH1994/000199
Authority: WO
Inventors: Nenad Tomljenovic
Original assignee: Thomcast Ag
Priority date: 1993-10-11
Filing date: 1994-10-06
Publication date: 1995-04-20
Also published as: EP0673562A1

Abstract

A chopper amplifier may supply both positive and negative output voltages. For that purpose, the chopper amplifier (1) has a number of switching stages (2.1-2.N). These switching stages (2.1-2.N) are interconnected by their outputs and connected in series to the load (5). They comprise each at least one direct voltage source (3) and switching means (8.1 - 8.4). The switching means are driven by a driving unit (4) in such a way that they switch through a positive or negative direct voltage (+/- Uo), or no voltage, to the outputs. In the latter case, the outputs are simultaneously bridged.

Description

DESCRIPTION

Switch amplifier

Technical field

The invention relates to the field of switching amplifiers.

It is based on a switching amplifier according to the preamble of claim 1. Such a switching amplifier is e.g. known from the European patent EP-B1-0 066 904 or the German Offenlegungsschrift DE-Al-30 44 956.

State of the art

The known amplifier consists of a number of switching stages, each of which has a DC voltage source, formed by a secondary winding of a transformer and a rectifier circuit, and a switch connected downstream. The outputs of the switching stages are connected in series, and the output voltages of the switching stages can optionally be added using a diode network. Such a digitally operating amplifier is used where high voltage and power are required, for example as a modulator in radio transmitters, where the amplified signal in the transmitter tube modulates the carrier oscillation, so that an amplitude-modulated oscillation arises. whose amplitude changes in accordance with a low-frequency input signal. Only as many switching stages are switched on as are required for the most accurate approximation of the input signal curve at a higher level.

The output voltage of the amplifier used as a modulator is of constant polarity because the amplified input signal is superimposed with a high DC voltage, which is required as an anode DC voltage for the transmitter tube. Accordingly, the switches in the individual switching stages are exclusively connected to one pole of the DC voltage source. Since the voltage generated at the load can only assume values between zero and a maximum voltage of a (e.g. positive) polarity, only signals can be amplified which only take positive values. For many applications, however, high-performance amplifiers are required, which emit both positive and negative load voltages. Examples of this are tube-less radio transmitters, high-performance function generators, network couplings, transmitters for wired communication, etc.

Presentation of the invention

It is therefore an object of the present invention to provide a switching amplifier in which the output signal can have both positive and negative values, but which is nevertheless constructed as simply as possible and works reliably.

This object is achieved in a switching amplifier of the type mentioned at the outset by the features from the characterizing part of claim 1.

The essence of the invention therefore consists in the fact that, by suitable selection of the switching means in the switching stages and corresponding activation of these switching means at the output of the individual Neither switching stages either a positive or a negative voltage is delivered. By summing the output voltages of the switching stages, the input signal curve can then be approximated in the positive as well as in the negative value range in a step-like manner.

In principle, it is conceivable for the amplifier according to the invention - unlike the known amplifier - to have all switching stages switched on continuously, intermediate values between the maximum positive and negative load voltage being achieved in that some of the stages are positive and some of the stages outputs negative output voltages that subtract completely or partially from one another when the output voltages are summed.

According to a first preferred embodiment, however, the switching stages are designed such that, in addition to supplying a positive or negative voltage, they can also be without voltage, the outputs being bridged. In this way, intermediate values can be achieved in that individual stages are removed from the series circuit.

In principle, it is also conceivable to provide two identical DC voltage sources with opposite polarity for each switching stage in the amplifier according to the invention, which can optionally be connected to the output of the switching stage by the switching means.

However, the circuit structure becomes particularly simple if, according to a further preferred embodiment of the amplifier according to the invention, a) each switching stage comprises a bridge circuit as the switching means, the outputs of which form the outputs of the switching stage, and b) the control unit controls the bridge circuit in such a way that it activates either the positive or negative DC voltage or no voltage occurs at the outputs of the bridge circuits. Here, each switching stage manages with only one DC voltage source, which can be switched to the stage outputs by means of the bridge circuit with alternating polarity, or can be switched off entirely in the case of bridged outputs.

The bridge circuit preferably comprises two half bridges, which in turn each comprise two switches connected in series. The common node of the switches forms a middle connection, which is assigned to the output of the bridge circuit. The center connections of the half bridges are connected in series with one another and with the load. If a positive or negative voltage is to be applied to the output of the bridge circuit, diagonally opposite switches of the half bridges are closed. If no voltage is to be emitted, a pair of switches located directly opposite one another is closed.

According to a further embodiment, the DC voltages of the DC voltage sources of all switching stages are the same. According to a first development, an improved approximation accuracy of the input signal is achieved in that the DC voltages of the DC voltage sources of a plurality of the switching stages are the same and that the DC voltage sources of some of the switching stages emit a voltage which is a fraction of the DC voltage of the other DC voltage sources.

A second development is characterized in that the control unit controls a part of the switching stages in such a way that they emit an output voltage that is modulated by pulse duration. The two further developments, namely the (preferably binary-weighted) voltage division and the additional pulse duration modulation, can substantially improve the approximation of the input signal curve with a constant or even reduced number of stages. The step-shaped output signal superimposed with a pulse duration modulated signal can also be achieved by performing the pulse duration modulation with all the available stages. In this case, the control unit controls the stages so that the desired signal results overall. Short pulses are achieved by switching on one stage and switching off another one a little later. If there is no remainder in the rough approximation, the pulse duration modulation has either a duty cycle of 0% or 100%. A further advantage of this exemplary embodiment just explained is that the effective switching frequency of the stages is somewhat lower than the frequency of the pulse duration modulation.

It is particularly favorable if the control - as already described for a conventional amplifier in EP-B1-0 124 765 - is carried out in such a way that if a switching stage has to be switched off, the one that has been switched on longest is switched off. Likewise, when switching on, the switching stage that was switched off longest is switched on. This results in a significantly improved distribution of the performance and thermal load on the individual stages, which is directly reflected in a significantly improved service life of the switching stages. For the same reason, the cooling of the stages can also be made smaller. Of course, it can also be provided in this connection to monitor the individual stages and to remove from the control those stages which are defective.

Further exemplary embodiments result from the subclaims.

The overall advantage of the construction according to the invention is that the switching stages can give both the positive and the negative voltage value of the DC voltage sources to their outputs. As a result, the voltage at the load can assume both positive and negative values. As a result the switching amplifier according to the invention has a substantially expanded area of application and can in particular also be used for the applications mentioned at the beginning. In addition, the switching amplifier according to the invention is characterized by a simple, modular structure, which does not even require a transformer for summing the output voltages of the switching stages.

Brief description of the drawings

The invention is explained in more detail below on the basis of exemplary embodiments in conjunction with the drawings.

Show it:

1 shows the circuit diagram of a first exemplary embodiment of the switching amplifier according to the invention, in which all stages are the same;

2 shows the circuit diagram of a second exemplary embodiment of the switching amplifier according to the invention, in which, in order to improve the approximation, some of the switching stages have output voltages graded in fractions;

3 shows the circuit diagram of a further exemplary embodiment of the switching amplifier according to the invention, in which a part of the switching stages is operated with pulse duration modulation to improve the approximation;

Fig. 4 The principle of approximation of an amplified

Input signal curve with a switching amplifier according to FIG. 1;

5a, b The principle of improved approximation with binary weighted or pulse duration modulated fine tuning. fen by means of a switching amplifier according to FIG. 2 or FIG. 3;

Fig. 6 The principle of uniform load distribution on all levels; such as

7 shows a variant of the PDM fine approximation according to FIG. 5b.

The reference symbols used in the drawings and their meaning are summarized in the list of names. In principle, the same parts are provided with the same reference symbols in the figures. For reasons of clarity, not all switching stages are provided with all reference symbols.

Ways of Carrying Out the Invention

FIG. 1 shows a circuit diagram of a first preferred exemplary embodiment of the switching amplifier according to the invention. The switching amplifier 1, to which a load 5 is connected, comprises N, N> 2, switching stages 2.1 - 2.N. Each switching stage contains a DC voltage source 3, which outputs a DC voltage U ₀ , and a bridge circuit 6. The bridge circuits 6 are composed of two half bridges 7.1 and 7.2, which are connected in parallel to the DC voltage source 3. The half bridges 7.1 and 7.2 in turn each consist of a series connection of two switches, a first and third switch 8.1 and 8.3, and a second and fourth switch 8.2 and 8.4. The switches 8.1 to 8.4 are preferably power semiconductors which can be switched off, for example turn-off thyristors or IGBTs, and each form a center connection 9.1 or 9.2 with the common node. Parallel to the switches 8.1-8.4, freewheeling diodes 10 are arranged in a manner that is conventional per se. The switching amplifier 1 also includes a control unit 4, to which one to be amplified Input signal S-j_ _n can be connected and which controls the switches 8.1 - 8.4 of the bridge circuit 6.

The half bridges 7.1 and 7.2 of the switching stages 2.1 - 2.N are connected to one another in such a way that, apart from the first switching stage 2.1 and the Nth switching stage 2.N, the middle connection 9.2 of the second half bridge 7.2 with the middle connection 9.1 of the first half bridge 7.1 of the preceding switching stage is connected. The first middle connection 9.1 of the N-th switching stage 2.N, however, is connected to the load 5. With this type of interconnection, the output voltages U _{out of} all bridge circuits are added across the load 5.

The control unit 4 now controls the switches 8.1-8.4 of the switching stages in accordance with the input signal S_ _n such that a signal S _out occurs at the load 5 which corresponds to the amplified input signal Si _n . In other words, the input signal level is divided into a number of voltage levels corresponding to the number of stages. The number of voltage levels covered by the input signal is now determined and the switching stages are controlled such that an output signal S _ou t is applied to the load, which approximates the input signal curve at an amplified level. This means that with a number of switching stages corresponding to the number of covered voltage levels, depending on the sign of the input signal, either the positive or negative direct voltage + U ₀ or -U _{0 is switched} to the output. The remaining switching stages are controlled in such a way that there is no voltage at their outputs, but that their outputs are bridged, ie that a load current can still flow through them in both directions.

For the switching stages that are not required, switches 8.1 and 8.2 or 8.3 and 8.4 are closed. The switching stages controlled in this way do not contribute to the output signal, but a load current can still be used in both directions. prevents them from eating. By closing switches 8.1 and 8.4, the positive DC voltage + U _{0 is given} to the output; when switches 8.2 and 8.3 are closed, the negative DC voltage -U ₀ occurs at the output of the bridge circuit.

This gives an output signal curve at the load 5, which corresponds to a step-like approximation of the input signal curve at a higher level (see FIG. 4). As can also be seen from FIG. 4, the approximation is relatively coarse, if, as in the switching amplifier explained above, all DC voltage sources have the same value. In a further development of the amplifier according to FIG. 1, FIG. 2 therefore shows a preferred exemplary embodiment in which, in addition to the switching stages 2.1 to 2.N, a number of switching stages 11.1 to 11.M are provided which have a DC voltage whose value is only is a fraction of the DC voltage U ₀ remaining switching stages. This so-called fine stages (11.1, ..., 11.) Can in particular binary gradated voltage values U _0/2 to have U ₀ / (2) ^M. The corresponding FIG. 5a shows that the approximation of the input signal curve is significantly improved by switching on these additional fine stages.

FIG. 5b shows the approximation in a further embodiment according to FIG. 3, in which instead of fine stages with binary stepped DC voltages, a number of additional switching stages 12.1 to 12.K are controlled in a pulse-duration modulated manner. This also results in a considerably improved approximation of the input signal curve.

If the assignment of the switching stages to the voltage levels is fixed, of course the loads assigned to the lowest voltage levels are stressed far more than those assigned to the upper levels. FIG. 6 now shows a possibility of how the load on the individual stages can be compensated for as far as possible. The stage that was switched off the longest or the switched off the one that was switched on the longest. The assignment of the switching stages to the voltage stages is thus no longer fixed, and the load on the individual stages is balanced. The switching sequence of the stages can be determined according to a predetermined scheme (see US Pat. No. 5,099,203). However, it can also be determined on the basis of its operating state (for example temperature) or in some other way (see EP-Bl-124 765). In addition, positive and negative output voltages can also be switched on simultaneously for a specific output signal value.

FIG. 7 finally shows a further variant of the approximation of the signal curve. Here the step-shaped output signal ^s out, superimposed with a pulse duration modulated signal, is achieved in that the pulse duration modulation is carried out with all available stages. The possibly very short pulse peaks of the pulse duration modulated signal are not achieved by briefly switching on and off only one stage, but rather by switching on a specific stage and switching off another stage a short time later. Together with the load distribution principle explained above, this results in an extremely uniform loading of the individual stages. If there is no remainder in the rough approximation, the pulse duration modulation has either a duty cycle of 0% or 100%. The great advantage of this embodiment, which has just been explained, is that the effective switching frequency of the stages is somewhat smaller than the frequency of the pulse duration modulation.

Overall, the switching amplifier according to the invention thus has a structure with which both positive and negative signals can be amplified. The switching amplifier according to the invention can thus be used for numerous applications. In addition, it has a simple and robust construction, which in particular does not require a large space-consuming summation transformer. Label list

1 switching amplifier

2.1-2.N switching stages

3 DC voltage source

4 control unit

5 load

6 bridge circuit

7.1 / 7.2 half-bridge circuit

8.1-8.4 switch

9.1 / 9.2 center connection

10 freewheeling diode

11.1-11. M fine level

12.1-12. K pulse duration modulated stage

U ₀ , Ul DC voltage

^U OUt output voltage ^s in input signal ^s out output signal

Claims

P A T E N T A N S P R Ü C H E

Switching amplifier (1), comprising a) a plurality of N, N> 2, switching stages (2.1-2.N), each of which has outputs to which a DC voltage is applied as the output voltage (U _ou t), and which with their Outputs are connected in series such that the output voltages (U _ou t) of the individual switching stages (2.1-2.N) are summed up, b) at least one DC voltage source (3) within each of the switching stages (2.1-2.N) , which outputs a DC voltage (U ₀ ) between a positive and a negative pole, c) switching means controllable within each of the switching stages (2.1-2.N), which optionally connect the at least one DC voltage source (3) to the outputs of the switching stage , and d) a control unit (4) which is connected to the switching means in the switching stages (2.1-2.N) and which controls them in accordance with an input signal (Sj_ _n ) which can be connected to the control unit (4) that on a load (5) which is connected to the switching stages (2. 1-2.N) can be connected, an output signal (S _out ) occurs which corresponds to the amplified input signal (Si _n ) and is composed of a sum of the output voltages (U _ou t) of the controlled switching stages (2.1-2.N) , characterized in that e) the switching means are designed such that, by means of control by means of the control unit (4), the positive or negative direct voltage (+ U ₀ or -U ₀ ) of the direct is optionally selected at the outputs of each switching stage ¬ voltage source (3) is available as output voltage (U _out ).

2. Switching amplifier according to claim 1, characterized in that the switching means are designed such that, by means of control by means of the control unit (4), either the positive or negative DC voltage (+ U ₀ or - U ₀ ) is present as the output voltage (U _out ), or no voltage is present and the outputs are bridged.

3. Switching amplifier according to claim 2, characterized in that a) each switching stage (2.1-2.N) comprises as switching means a bridge circuit (6), the outputs of which form the outputs of the switching stage, and b) the control unit (4) Controls the bridge circuit (6) in such a way that either the positive or negative DC voltage (+ U ₀ or -U _σ ) or no voltage at all occurs at the outputs of the bridge circuits (6).

4. Amplifier according to claim 3, characterized in that a) the bridge circuits (6) consist of a first and two half bridge (7.1, 7.2) which are arranged parallel to the DC voltage source (3), b) the first half bridge (7.1 ) consist of a first and third switch (8.1, 8.3) and the second half-bridge (7.2) consist of a second and fourth switch (8.2, 8.4), each of which is connected in series, and their common node each has a central connection (9.1, 9.2), with each center connection forming an output of the bridge circuit (6), c) the center connection (9.2) of the second half bridge (7.2) of the first voltage stage (2.1) and the center connection (9.1) of the first Half-bridge (7.1) of the N-th voltage stage (2.N) are connected to the load, d) the middle connections (9.1) of the first half-bridges of the other switching stages with the middle connections (9.2) of the second half-bridge (7.2) of the next one Switching stage are connected or that the middle connections (9.2) of the second half bridges (7.2) of the other switching stages are connected to the middle connections (9.1) of the first half bridge (7.1) of the preceding switching stage.

5. Amplifier according to claim 4, characterized in that a) the control unit (4) closes the first and fourth switches (8.1 and 8.4) if a positive voltage (+ U ₀ ) is given to the output of a bridge circuit (6) shall be; b) the control unit (4) closes the second and third switches (8.2 and 8.3) if a negative voltage (- U ₀ ) is to be given to the output of a bridge circuit (6); and c) the control unit (4) either closes the first and second switches (8.1 and 8.2) or the third and fourth switches (8.3 and 8.4) if no voltage is given to the output of a bridge circuit (6) should.

6. Amplifier according to one of claims 1 to 5, characterized ge indicates that the DC voltages (U ₀ ) of the DC voltage sources (3) of all switching stages (2.1-2.N) are the same.

7. Amplifier according to one of claims 1 to 5, characterized ge indicates that the DC voltages (U ₀ ) of the DC voltage sources (3) of a plurality of switching stages (2.1-2.N) are the same, and that the DC voltage sources (3) of a part (11.1-11.N) of the switching stages emit a voltage (Ul) which is a fraction of the DC voltage (U ₀ ) of the other DC voltage sources (3).

8. Amplifier according to one of claims 1 to 5, characterized in that the control unit (4) has a part (12.1-12.K) controls the switching stages so that they emit a pulse duration modulated output voltage (U _ou t).

9. Amplifier according to one of claims 1-8, characterized gekenn¬ characterized in that the control unit (4), the switching stages (2.1-2.N or 11.1-11.M or 12.1-12.K) in accordance with the input signal (Sj_ _n ) controls that the stages to be switched on or off are assigned on the basis of their operating state.

10. Amplifier according to claim 9, characterized in that a) if a switching stage has to be switched off, that switching stage is switched off which has been switched on for the longest, and b) if a switching stage has to be switched on, that switching stage is switched on which longest was turned off.

11. Amplifier according to one of claims 1-10, characterized gekenn¬ characterized in that the control unit (4) controls all stages (2.1-2.N) so that an output signal (S _ou t) results, which is a superimposition of a corresponds to step-like rough approximation and a pulse duration modulated fine approximation.

12. Amplifier according to claim 4, characterized in that the switches (8.1-8.4) comprise turn-off thyristors or IGBTs and freewheeling diodes in parallel with the switches

(10) are provided.