DK161486B - PROCEDURE AND CIRCUIT FOR SOFT-CLIPPING LIMITATION OF POWERFUL VIDEO SIGNALS FOR AMPLIFYING THE SIGNALS - Google Patents

Description

DK 161486 B

The present invention relates to a method of rounding the amplitude limitation of an audio signal before amplifying the signal by a signal-carrying apparatus which is amplitude overload and having a control signal controllable amplitude limiting means which affects the amplitude of the input signal supplied to the amplitude overload apparatus. The invention further relates to a circuit suitable for carrying out the method.

The invention thus relates to a rounded amplitude limitation of a signal conveyed to an apparatus which is amplitude overloadable such as an electronic amplifier or other apparatus passed by an electronic audio signal and wherein such a rounded amplitude limiting means is inserted. in the signal path leading to the amplitude overload device.

It is well known in the art to connect antiparallel-coupled limiter diodes or a field-effect transistor in parallel with the signal path through, or also in association with a signal amplifier. The diodes are selected such that effective limitation of the passing signal is effectively imparted when its amplitude exceeds a selected value, or the field effect transistor control electrode is applied to a bias which causes the field power transistor to short circuit signal amplitudes exceeding a certain value. . Since field-effect transistors are capable of conducting current in both directions between their source and drain electrodes, in such a case a transistor alone will be able to effectively limit both the positive and negative amplitude proportions of the signal.

The disadvantage of this well-known kind of limitation is that limitation occurs "sharply", so that the amplitude peaks are cut away. Thus, sharp-edged 35 signal forms inevitably contribute to a significantly increased signal distortion and are thus not desirable

DK 161486 B

2 or suitable by e.g. high-quality equipment. However, limitation is necessary to reduce congestion and avoid damage to e.g. connected speakers, etc.

5 The practical solution has e.g. passed using suitable compression circuits to compress the original dynamic range of an input signal. A compression circuit could consist of an amplifier with a suitable controlled volume control for the signal amplitude, so that the gain provided by the amplifier is reduced at large signal amplitudes.

In the case of a high quality amplifier with associated speakers, the use of a compression circuit serves no purpose, since even a modest and * 15 more or less evenly distributed compression of the dynamic range of the signal introduces a distortion that is noticeable to the human ear when the signal has been converted into audible signals via speakers or headphones, thus stating that the compression intends to eliminate the possibility of distortion by overloading speakers, headphones or output or preamplifiers, and thus compression used to overcome this problem will only counteract the won.

25 An approximation for solving this problem is proposed in accordance with the contents of SE presenting publication no.

371 350. Accordingly, as already described, one or two different biased field power transistors are used as limiting elements. The control electrodes of the transistors are controlled by the output signal provided by the amplifiers and / or the input signal, a suitable integration circuit being inserted, e.g. consists of one or more parallel capacitors arranged in the control electrode circuit. It is clear that an amplitude limitation will occur as described and signal level fluctuations in the signal near or above

DK 161486 B

3 the restriction level is unable to pass through.

A somewhat better, but far more complicated solution is described in German publication publication no.

5 3,004,713. Here, several control voltages are applied to the limited field power transistor, and the individual outputs are connected to the output terminals of the amplifier. Hereby, a sinusoidal signal is deformed to produce rounded peaks, and square signals passing through retain their square shape, but the square shapes have been appropriately compressed.

This solution is better. The purpose of this solution is to compress the dynamic range of the output signals in such a way as to obtain the least possible signal distortion in the compression process. In addition, the signal level at which compression occurs is fixed and not adaptable to gain fluctuations due to altered values of the amplifier's parameters, such as variations in the magnitude of the amplifier's supply voltage or due to aging or due to manufacturing tolerances associated with the components used in the amplifier which determine the actual signal amplitude level at which compression or constraint should or should first occur, and which level may thus vary in practice.

The present invention aims to provide a rounded amplitude limitation where the actual signal amplitude level at which compression 30 or constraint occurs is self-adjusting to be as large in value as is practically permissible independent of changes in signal processing conditions or independent of amplitude. overload-only device.

35 Furthermore, it must be achieved as another purpose that the signaling circuit is always usable

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4 in full.

A sharp cut when it enters an audio amplifier connected to a multi-way speaker with crossover filter will produce a large number of undesirable high frequency distortion components which are inevitably supplied from the crossover high frequency speakers which are small in size. Therefore, there is a potential danger that these necessarily small speakers are overloaded as a result of the mowing. Such an overload can either completely destroy the high-frequency or loudspeaker, or the performance of this speaker may be impaired.

It will be seen that an overload of the speaker will occur if the amplifier is supplied with too strong input signal or, at work, behaves 15 as overloaded. In the present context, the term "amplitude-overload apparatus" is to be interpreted as the amplifier or other signal-carrying apparatus having a signal input and a signal output and that this may have its output connected to another subsequent element.

In a signal amplitude-limiting system of the type mentioned in the introduction, according to the method according to the invention, the input signal of the comparator circuit is connected to the amplitude limiting means, and the output signal is connected to the second input of the comparator circuit, the comparator circuit comprising a differential circuit and for fully or partially compensating gain level differences between the input and output signals, and comparing the instantaneous value of the two input signals for proportionality and for essentially or substantially deviating from the shape of the output signal, generates a control signal applied to the amplitude limit applied to the amplitude limit. 35 limiting the input signal amplitude to such an extent that amplitude overload in the

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5 essentials are avoided.

Thus, when the output of the comparison circuit from a state of non-overload of the overload device due to an entered overload 5 begins to indicate that overload has occurred, this output signal of the comparison circuit is used as a control signal to reduce or reduce the overload inducing working signal. led to the overloadable device. This, in turn, 10 leads to a somewhat diminished indication of overload from the comparison circuit and an increase in the amplitude of the working signal supplied to the overloadable apparatus. In this way, an "average" reduction of the amplitude is achieved, which will be able to prevent 15 overload damage from occurring. However, one can always reach the "overload threshold".

As mentioned, the invention also relates to a circuit capable of being used in the practice of the method of the invention, namely for rounded amplitude limitation of a signal processing or signal conducting apparatus which is amplitude overload and having a signal input and a signal output. and having a control signal controllable amplitude limiting means adapted to actuate the amplitude of the input signal supplied to the amplitude overload apparatus and in accordance with the invention for the first input of a comparator circuit, the input signal is connected to the amplitude limiting device. means, and wherein the output signal is connected to the second input of the comparator circuit and wherein the comparator circuit comprises a differential coupling and means for fully or partially compensating gain level differences between the input and output signals, and wherein the comparator circuit is arranged for comparison of the two 5 provided the instantaneous value of proportionality and at substantially or substantially from the output signal.

DK 161486 B

Deviations from the shape of the signal from an output of the comparison circuit produce a control signal applied to the amplitude limiting means to limit the input signal amplitude to such an extent that 5 amplitude overload is substantially avoided.

The fact of the invention lies in the fact that the comparison circuit, theoretically independent of reference voltages, acts to cause the amplitude limiting means to amplitude limitation when the detection of signal shape discrepancies between the input signal of the amplitude overload device and the output signal of the apparatus occurs. Thus, these signal shape differences may well occur even at small signal amplitudes. Therefore, according to the invention in the circuit, no actual reference voltage is used to control the amplitude limiter. In the detailed embodiment of the circuit according to the invention, reference voltage is used, however. for other purposes, such as detailed on page 9 of line 16.

According to the invention, it is thus detectable

ringing differences in amplitude moment values, i.e. detecting moment differences in the difference of the signal forms from input to output on the overloadable apparatus, and then from here impose an amplitude limitation which may be instantaneous but may also be of

general art.

in

By using circuit designs according to claim 3, according to the invention, advantageous cooperation is obtained with the aforementioned and practically required counter-regulation from 30 temperature effects, fluctuations in supply voltage, etc., in addition to the current amplitude limitation, field transistors which, however, exhibit a not overwhelmingly linear characteristic. The designs of the circuit according to the invention 35 take optimal account of this in order to obtain the best result according to the invention.

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In claim 4, a further design of the circuit according to the invention is provided to achieve a simple as well as more efficient design with the means according to claim 3.

5 Further advantages obtained by the invention are set forth in the last five sections of the following description of embodiments of the invention. In particular, these advantages are achieved by the means of claims 5 and 6.

It will be seen that, by means of all these measures, an exploitation is obtained to a greater extent at each time of the available dynamic range of amplitude of the overloading apparatus, preventing dangerous overloading according to the invention. It is now possible to move closer to the outer boundaries of the dynamic workspace, 15 without the risk of destruction due to damage. border crossings. On the other hand, no complete avoidance of incoming signal distortion has been sought at signal values near the outer limits. However, with the inventive means less distortion is obtained.

Embodiments of the invention are described in more detail below with reference to the drawing, in which: FIG. In block diagram form, the main features of the invention show, FIG. 2A, 2B and 2C show signal shapes in the case of supplying a sinusoidal signal at 3 different amplitudes of the signal and shown acting at three different locations according to the block diagram shown in FIG. 1, and FIG. 3 shows in more detail an electronic circuit operating according to the block diagram shown in FIG. First

In FIG. 1, there is shown an overloadable audio amplifier 5 with an input 3 and an output 7. Via the connection element 12A, the output of an amplitude-reducing means 6A is applied to the amplifier 5, whose input is supplied to an input signal at a connection element 1. . The output of the overloadable device 5

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8 7, an output element 11 is connected via a connection element 9, which can be a loudspeaker or, by high quality audio reproduction, a speaker set as described above and containing a divider for splitting the audio signal frequency to the individual loudspeakers in the loudspeaker set.

From the input 3 and the connecting element 12A, respectively, the input signal at 3 or from the corresponding signal is derived to the one input 2OA of 10 a comparison circuit 4A. From the connection element 9, the signal is output from the output 7 or derived from the second input 22A on the comparator circuit 4A. Of course, with the system shown, the function would still be achieved within the method even when the input 22A of the comparator circuit 4A is instead connected to the output element 11, especially if this had to be overloaded at a signal amplitude that is relatively lower than from the amplifier output relative to the output. to the input signal to induce the overload when the amplitude of the input signal becomes high (too high).

For ideally operating systems, the two signals at 3 and at 9 at lower amplitudes will be uniform. By a completely linear amplifier, the comparison circuit will receive 25 uniform but slightly phase-shifted signals at the inputs. Such a situation, which is probably a boundary case in practice, is indicated by signal shapes at the low amplitudes according to FIG. 2A, 2B and 2C, assuming a uniform, common sinusoidal shape.

30 With increasing amplitude as shown in FIG. 2A, FIG. 2B

and FIG. 2C, just a cut of the amplitude peak shown in FIG. 2C, which causes activation of the comparator circuit 4A so that some amplitude limitation occurs at 3 if the amplitude of the arriving signal is increased in amplitude to the high value shown in FIG. 2A, FIG. 2B and FIG. 2C.

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9 In the drawing FIG. 3 is shown part of an amplifier input stage 2, a comparison circuit 4 and an amplitude limiting means 6. Thus, the amplifier input stage 2 may be included as part of an audio amplifier to which 5 is connected a speaker set such as 11 according to FIG. 1 to an overall amplifier 5, 2 of which according to FIG. 3 forms part. The connecting element 12 corresponds to the connecting element 12A shown in FIG. 1. The conduit 38 shown in FIG. 3 carries a signal identical to the output at 7 in FIG. 1 or a signal derived from this output signal 7, so that appropriate identity is present. Via a transistor 10, the derived signal from 38 in FIG.

3 to the diode 22 of FIG. 3, which corresponds to the input 22A of FIG. 1. Similarly, the input signal of the connector 12 in FIG. 3 via a transistor 8 fed to a diode 20 corresponding to the input 20A of FIG.

1. A suitable bias is applied at + to the detector 4 in FIG. 3, such that the magnitude of this voltage helps determine at what voltage level and hence at which signal amplitude value should occur indicating the overload of the overload amplifier. Thus, this reference voltage is compatible with a suitable connecting element for e.g. the supply voltage of the overload amplifier so that its up and down fluctuations co-operate with a corresponding up and down shift of the overload indication limit.

Thus, in the illustrated embodiment, the two transistors 8, 10 shown constitute two differential coupled transistors whose collectors are connected via resistors 14,16 to a subsequent indicated but not shown amplifier stage 40 via connecting elements 34,36. The transistor 10 is thus included in this amplifier 40's circuitry. The output 42 of the amplifier 40 corresponds to a connector element 9 as shown in FIG. 1, which e.g.

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10 connects the amplifier output to a speaker or speaker system or other signaling means which acts as a subsequent means for the amplifier output. The emitters of transistors 8, 10 are connected to 5 a suitable voltage source designated "-" via elements 46, 44, e.g. could be a balancing potentiometer 46 between the transistors and a circuit 44, which could be a temperature compensated circuit for maintaining a constant total current through the two transistors 8,10 so that the temperature working conditions of the amplifier 407 are suitably adjusted, and thus that overload indication via circuit 4 takes place as high in amplitude at any time as possible for the purpose of amplifier 40. In its simplest form, element 44 could also theoretically be a simple resistance chain or filter chain for adaptation in otherwise known manner of differential step 8, 10. It is noted that with the illustrated embodiment, a particularly component simple way is provided, whereby the comparator circuit 4 with two diodes 20 and 24 is provided with the two necessary inputs to the circuit and these can be directly coupled to the transistors 8, 10 which may be present. as a differential amplifier of otherwise known kind as the fr emgår.

The output of the comparator 4 provides a control signal as already described for one in FIG. 3 shows amplitude limiting means 6. This means comprises a single field effect transistor 28 known per object, whose one electrode (drain or source) is connected to the input signal connection 12, while the other electrode (source or drain) is connected to a neutral voltage level to which the conductive field effect transistor 28 can connect the connecting element 12 when amplitude limitation is to be established. It is to be understood that the signal source connected to supply of signal from outside to 12 must have a suitably high internal impedance, so that the field power transistor 28 is partly capable of functioning as

DK 161486B

11, the amplitude limiting parallel element is switched on, partly not itself overloaded and partly by its function, the signal source overloaded to 12 is not overloaded.

The control signal to the field power transistor 28 is applied via a voltage sharing resistor chain 32, 30 cooperating with a resistor 26 connected to a suitable low voltage voltage source "-". The resistor 26 is connected in parallel with a capacitor 24. The time constant of the condenser-resistor circuit is adapted such that the time constant is suitably large so that the amplitude limiter is rapidly activated but slowly returns to non-amplitude limiting state. For use in the audio area e.g. Suitably, 10 Hz to 20 kHz can be activated within the order of 1 millisecond, while the time lapse for return to non-amplitude debugging can be of the order of 500 milliseconds.

The magnitude of the control signal acting on the field power transistor 28 influences to a more or less powerful amplitude limitation of, depending on the control, the signal size.

With the aid of the present "soft-clipping" amplitude limiting device, it has been achieved that the full dynamic working range of an amplifier can be utilized at any one time, the device causing dangerous overload to always be prevented at the outer limits of this dynamic working area, the device following changes in the size of the dynamic range described above.

In this respect, it can be naturally observed that field effect transistors generally exhibit, among other things, some curvature voltage amplification characteristic, and this will of course influence it by means of e.g. the circuit of FIG. 3 obtained amplitude limitation. Thus, using an appropriate signal amplitude at 12 and selecting a field power transistor 28

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field power transistor with a suitable curvature transfer characteristic, a nonlinear control is obtained, with which the signal peaks are further subjected to a rounded amplitude limitation. It may be appropriate, e.g. by loudspeaker reproduction, to avoid a seemingly general decrease in sound level by a strongly onset rounded amplitude limitation. The 2B and FIG. The signal curves shown in Fig. 2C express this particular situation.

10 It is noted that the amplifier 40 according to the embodiment shown in FIG. 3 compared to the embodiment shown in FIG. 1 is included as part of the overloadable element 5, but also as part of the output element 11.

15 20 25 30 35 / i

Claims (6)

A method of rounding amplitude limitation of an audio signal prior to amplifying the signal by a signal-carrying apparatus which is amplitude overload and having a control signal controllable amplitude limiting means which affects the amplitude of the input signal supplied to the amplitude overload apparatus. the input signal is connected to the first input of a comparison circuit according to the amplitude limiting means, and the output signal is connected to the second input of the comparison circuit, the comparison circuit comprising a differential coupling and means for fully or partially compensating amplification level differences between input differences and and comparing the comparative instantaneous value of the two input signals for proportionality and for major or substantially deviations of the output signal form 20, produces a control signal applied to the amplitude limiter. end means for limiting the input signal amplitude to such an extent that amplitude overload is substantially avoided. 2. A circuit for performing the method of claim 1 for rounding the amplitude limitation of an audio signal before amplifying the signal by a signal-carrying apparatus (5) which is amplitude-overloaded and having a signal input (3) and a signal output (7) and having 30, an amplitude limiting means (6A) controlled by a control signal adapted to actuate the amplitude of the input signal (from 1 to 3) supplied to the amplitude overload device (5), characterized in that a The first input (2AA) of the circuit 35 (4A) is connected to the input signal (at 3) according to the amplitude limiting means DK 161486 B, and the output signal (at 7) is connected to the second input (22A) of the comparator circuit (4A). the comparison circuit (4A) comprises a differential differential coupling and means for fully or partially compensating 5 gain level differences between the input and output signals, and the comparison circuit (4 A) is arranged for comparing the instantaneous value of the two input signals for proportionality and for substantially or substantially deviating from the form of the output signal from an output (18A) of the comparator circuit (4A) generating a control signal applied to the amplitude limiting means (6A) for limiting the input signal amplitude (at 3) to such an extent that amplitude overload is substantially avoided. 15 Circuit according to claim 2, characterized in that the comparison circuit (4A) is constituted by the differential stage of an amplifier (6) connected to a detector (4), wherein the detector (4) comprises a transistor 20 (18). the base of which is connected to both of the two serial diodes (20 and 22) and whose emitter is connected to a voltage potential (+) which is derived from and fluctuates jointly with the amplitude overload device (5, 5 and 11, respectively), and whose collector 25 outputs the specified control signal associated with the control input of the controllable amplitude limiting means (6 corresponding to 6A). Circuit according to claim 3, characterized in that the inputs of the detector (4) comprise serial diodes (20 and 22) arranged so that they are turned and biased so that they take on a conductive state when the input to the amplitude-overload device (5) (at 3) arriving signal has an amplitude that at least 35 induces amplitude overload of the amplitude overloadable apparatus (5). DK 161486 B Circuit according to claim 4, characterized in that the controllable amplitude limiting means (6 corresponding to 6A) comprises a rechargeable capacitor (24), one of which is connected to a reference voltage (-) and the other of which is connected to the control input. on the controllable amplitude limiting means (6 corresponding to 6A). 6. A circuit according to claim 1, 2, 3, 4 or 5, characterized in that the controllable amplitude limiting means (6A and 6, respectively) is arranged to initiate amplitude limitation with a small time delay after the occurrence of the control signal (via 18A) and terminate. 15, the amplitude limitation with greater time delay after the cease of the control signal (via 18A) which produces amplitude limitation.