Signal level controllers and amplifiers with such a

Abstract

Signal level control with two input connectors (IN1, IN2, IN1A, IN1B, IN2A, IN2B) for receiving a balanced input signal I E and two outputs (OUT1, OUT2) for outputting a symmetrical output signal I A with an adjusting element which can be switched between at least two positions, wherein in the first position I A = k1 · I E and in the second position I A = k2 · I E, where k2 ≠ k1, wherein two transmission lines are provided, one end of which is each connected to a power source, wherein each transmission line is assigned a coupling element (C1, C2, T1A, T1B), with the aid of which the current flow through the transmission lines can be influenced in such a way that the setting element is supplied with a direct current during operation of the signal level regulator, wherein the first coupling element (C1) is connected to the first input terminal (IN1, IN1A, IN1B) and is controlled by an alternating voltage signal which is applied to the first input terminal (IN1, IN1A, IN1B), and the second coupling element (C2) is connected to the second input terminal (IN2, IN2A, IN2B) and is controlled by an alternating voltage signal which is applied to the second input terminal (IN2, IN2A, IN2B), wherein the first output terminal (OUT1) is connected via a third coupling element (T1A,C7) is connected to the first transmission line and the second output terminal (OUT2) is connected to the second transmission line via a fourth coupling element (T1B, C8).

Description

[0001] The present invention relates to a signal level controller with two input terminals for receiving a symmetrical input signal I E and two outputs for outputting a symmetrical output signal I A with an adjusting element which can be switched back and forth between at least two positions, with the first position being I A = k1 · I E and in the second position I A = k2 · I E , where k2 ≠ k1.

[0002] Symmetrical signal transmission is used particularly in audio and video technology because it ensures interference-free signal transmission even over longer transmission distances. The signal is transmitted via two signal conductors that essentially transmit an identical signal but with opposite polarity. By forming the difference, interference signals that essentially affect both signal conductors in the same way can be filtered out.

[0003] A signal level control of this type is often used in audio amplifiers and usually has not just two, but a multitude, such as 48 positions. Such amplifiers are primarily used to increase voltages, currents, or signal strengths.

[0004] A linear amplifier provides signal amplification with no or very low distortion, so that the output is generally directly proportional to the input. Linear amplifiers are used for audio and video signals, among other things. Audio amplifiers, such as those found in radios, televisions, two-way radios, and especially hi-fi systems, typically operate in frequency ranges below 20 kHz. They amplify the electrical signal, which is then converted into sound by one or more loudspeakers.

[0005] Examples of electrical amplifiers can be found in US 6 239 655 B1, DE 37 31 643 A1 or WO 93 / 14 564 A1.

[0006] Electrical amplifiers have electrical input and output signals. Audio amplifiers are designed to proportionally amplify small, time-dependent electrical signals (voltages or currents). The output function should be as accurate a representation of the input function as possible, but multiplied by a constant factor. However, since it is generally not desired to transmit the audio signal to the speakers at the same signal level at all times, but rather to adjust the volume, signal level controls or volume controls of the type mentioned above are used. This control generally features a voltage divider, which can be used to reduce the magnitude of the output signal gradually or almost continuously.

[0007] An example of such a signal level controller is shown in Fig. 1. Here, the symmetrical input signal is coupled in via the two inputs IN1 and IN2. Any DC voltage component is diverted via resistors R3 and R4. The AC voltage component, on the other hand, is coupled in via the two capacitors C1 and C2. Two symmetrical resistor cascades are provided for volume control. The first resistor cascade has the resistors R6, R9, R11 and R22, which can be switched into the signal transmission path using switches K1 to K4. The second resistor cascade has the resistors R7, R8, R10 and R21, which can also be switched into the signal transmission path using switches K1, K2, K3 and K4. In the position shown, switches K2 to K4 are open, while switch K1 is closed. In this case, the signal is not attenuated, but transmitted directly via capacitors C7 and C8 to the two output terminals OUT1 and OUT2.If the signal needs to be attenuated, for example, switch K1 can be opened and switch K2 closed. The signal is then attenuated via resistors R6 and R7. Depending on the desired degree of attenuation, additional resistors can be added to the signal transmission path. In the case of the circuit shown in . Fig. In the embodiment shown in Figure 1, only four resistors are shown. However, volume controls typically allow for much more graduated volume control, so the use of, for example, 48 resistors or more in a cascade is not uncommon.

[0008] This design places high demands on switches K1 to K4. Not only is switch K1 required to switch both components of the balanced signal at exactly the same time, but it is also necessary that one of switches K2 to K4 closes simultaneously when switch K1 opens. If the switching is not performed exactly synchronously, this can lead to voltage spikes in the transmission signal, which can cause unwanted noise in the loudspeakers connected to the output terminals.

[0009] In addition, this design features a large number of contacts which generally do not behave "ideally". As a rule, contacts only exhibit "ideal" behavior, i.e. the current flow through the contact is proportional to the input voltage, when a certain voltage is reached. The contacts therefore cause distortion of the output signal which arises solely from the presence of at least one contact and which cannot be eliminated even by an ideal amplifier. In other words, each contact within an amplifier can be assigned a harmonic distortion factor. The distortion occurs due to the increased contact resistance immediately following the current- or voltage-free state. This increased contact resistance after zero crossing finds its mechanical analogue in the static friction which is higher than sliding friction when mechanical bodies rub against each other.

[0010] It is therefore an object of the present invention to provide a level control or volume control and an amplifier with such a control which does not exhibit the problems mentioned or at least significantly reduces them.

[0011] According to the invention, this object is achieved by a signal level regulator of the type mentioned at the outset, which has two transmission lines, one end of which is each connected to a power source, wherein each transmission line is assigned a coupling element with the aid of which the current flow through the transmission lines can be influenced in such a way that the setting element is supplied with a direct current during operation of the signal level regulator, wherein the first coupling element is connected to the first input terminal and is controlled by an alternating voltage signal applied to the first input terminal, and the second coupling element is connected to the second input terminal and is controlled by an alternating voltage signal applied to the second input terminal,wherein the first output terminal is connected to the first transmission line via a third coupling element and the second output terminal is connected to the second transmission line via a fourth coupling element.,

[0012] Therefore, a current always flows along the transmission lines, with the input signal influencing the current flowing through the transmission lines. A zero voltage crossing in the input signal therefore does not result in a zero current crossing through the transmission lines. It is now possible to apply a direct current to the volume-controlling switches, which can be used to connect corresponding resistors into the transmission path, so that no zero crossing occurs and the distortion of the contacts is significantly reduced.

[0013] In a particularly preferred embodiment, the adjusting element therefore has at least two pairs of resistors, wherein in the first position of the adjusting element, each transmission line is connected to ground via a resistor of the first pair of resistors, and in the second position of the adjusting element, each transmission line is connected to ground via a resistor of the second pair of resistors. A pair of resistors can have very small resistances, which are formed, for example, by the line resistance of the line that connects the transmission line to ground. If the transmission lines are connected to ground via these resistors, the so-called "mute" state occurs, i.e. the signal on the transmission lines is attenuated to zero or almost zero.

[0014] If the higher resistances of the other pair of resistors are connected between the transmission line and ground instead, the signal is not attenuated as much.

[0015] Since the two transmission lines are connected to a power source, the resistances of the resistor pair through which the transmission lines are connected to ground determine the potential at which the two transmission lines are located.

[0016] If the resistance between the transmission lines and ground is increased using the adjustment element by inserting a larger or wider resistor, this will, on the one hand, change the potential at which the transmission lines are located. On the other hand, it will also amplify or attenuate the AC voltage component of the signal coupled in via the coupling elements for the transmission line. By adjusting the resistors with the adjustment element, the volume or signal level can be changed. In a preferred embodiment, the resistances of a resistor pair are equal.

[0017] In a preferred embodiment, the current sources connected to one end of the transmission lines are each formed by a transistor, preferably a PNP transistor, whose emitter terminal is connected via a resistor to a first voltage source providing a first potential, and whose base terminal is connected, optionally via a resistor, to a second voltage source providing a second potential different from the first potential. In this case, the first and second coupling elements are best configured as capacitors, with one side of the capacitor connected to the first and second input terminals, respectively, and the other side of the capacitor connected to the base terminal of the transistor of the respective current source.

[0018] The signal to be transmitted at the base terminals thus determines the amount of current the current source passes from the emitter terminal to the collector terminal. The current source is thus a controllable current source, controlled by the signal applied to the corresponding input terminal.

[0019] This ensures that all contacts are always supplied with a specific direct current, which may be superimposed by an alternating voltage signal.

[0020] It is understood that the current source is dimensioned such that an input signal is unable to reduce the current flowing through the transmission lines to zero. Since the signal level regulator is designed for specific expected input signal levels, it must be ensured that the potential differences between the first and second potentials, minus the transistor's base-emitter voltage, are greater than the maximum expected input signal level.

[0021] In a further preferred embodiment, the third and fourth coupling elements each comprise a transistor, preferably a pnp transistor, wherein the first and second transmission lines are connected to the base terminal of one of the transistors, the emitter terminals are connected to a current source, if necessary via a resistor, and the collector terminals are connected to the first and second output terminals, respectively, via a capacitor. In this embodiment, the third and fourth coupling elements not only serve to output the signal, but are simultaneously a differential amplifier, with the aid of which the signal is amplified. This embodiment is thus an amplifying signal level controller.

[0022] In a further preferred embodiment, the adjustment element has at least one pair of switches with which the pair of resistors can be moved essentially simultaneously from the first to the second position and back. These switches can be relays, for example.

[0023] However, it is not possible to switch the relays exactly at the same time, which can lead to an undesirable “crackling” on the signal to be transmitted.

[0024] Therefore, in a further, particularly preferred embodiment, the switch pair is formed by two MOSFETs, preferably a dual MOSFET. MOSFETs (metal oxide semiconductor field-effect transistors) are designed for conducting and blocking large electrical currents and voltages. MOSFETs have a significantly faster switching time. Particularly when using a dual transistor or dual MOSFET, in which two transistors are arranged on one substrate, simultaneous switching of the switch pair can be ensured by switching the gate terminals.

[0025] Preferably, therefore, the transmission lines are each connected to a drain terminal of a MOSFET, the source terminals of the MOSFETs are connected to ground, and the gate terminals can be selectively supplied with a control voltage by means of the adjusting device.

[0026] It goes without saying that the control voltages can also be controlled using a remote control.

[0027] Furthermore, the described signal level controller can also be used for unbalanced signals. In this case, a corresponding circuit must be provided to convert the unbalanced signal into a nearly balanced one.

[0028] Further advantages, features, and possible applications of the present invention will become clear from the following descriptions of some preferred embodiments and the accompanying figures. They show: Fig. 1 a state-of-the-art signal level controller, Fig. 2 a first embodiment of the invention, Fig. 3 a second embodiment of the invention and Fig. 4 a third embodiment of the invention.

[0029] Fig. Figure 1 shows a circuit diagram of a prior art signal level controller already discussed.

[0030] In Fig. Figure 2 shows a circuit diagram of a first embodiment of the invention. This embodiment has two input terminals IN1 and IN2 for receiving a balanced input signal and two outputs OUT1 and OUT2 for outputting a balanced output signal. Any DC voltage component contained in the input signal is dissipated via resistors R3 and R4. The AC voltage component at the inputs IN1 and IN2 is coupled via capacitors C1 and C2. The signal coupled via capacitor C1 is applied to the base terminal of the coupling element embodied as transistor T2B.

[0031] Transistor T2B is a PNP transistor. The emitter terminal is connected to a positive voltage (voltage source) via resistor R13B. Similarly, the signal coupled via capacitor C2 is applied to the base terminal of the second coupling element, which is a PNP transistor T2A. Here, too, the emitter terminal is connected to the positive voltage via resistor R13A. The signals coupled via capacitors C1 and C2 therefore determine the current output at the collector terminal of transistors T2A and T2B. The collector terminal is connected in the Fig. 2, the relay switch K1 is connected directly to ground, i.e. only via the small line resistances. This results in the so-called "mute" state, i.e. the signal level controller has regulated the signal level to 0. If the relay switch K1 is opened and, for example, the relay switch K2 is closed instead, the collector outputs of the two transistors T2A and T2B are no longer directly connected to ground, but via the resistors R6 and R7. Consequently, a potential builds up on the transmission lines, and the signal level is # 0. If a different relay switch K3 or K4 is closed instead of the relay switch K2, or if no relay switch is closed at all, the collector connections of the transistors T2A and T2B are connected to ground via several resistors connected in series, e.g. R6, R9, R11 and R22, whereby a greater potential builds up on the transmission lines due to the greater leakage resistance.

[0032] The transmission lines connected to the collector terminals of transistors T2A and T2B are, in turn, each connected to the base terminals of two transistors T1A and T1B. Here, a current source CR4 is connected to the emitter terminals of transistors T1A and T1B via resistors R17 and R17B. The signal output on the transmission lines at the collector output of transistors T2A and T2B thus controls the amount of current output by transistors T1A and T1B at their collector outputs. This output is then passed through capacitors C7 and C8 to the two output terminals OUT1 and OUT2.

[0033] In the described embodiment, all contacts are basically “flooded” with a direct current, so that the distortion factor typical for unloaded contacts can be avoided.

[0034] This design has the disadvantage, which is undesirable in some applications, that the relay switches K1 to K4 cannot be switched exactly simultaneously, so that switching peaks can occur.

[0035] Therefore, the relay switches in the Fig. 3, the second embodiment has been replaced by dual MOSFETs T17A-T17B, T18A-T18B, T19A-T19B, and T20A and T20B. The MOSFETs can be switched by applying a control voltage to the gate terminals. The operation of the embodiment of Fig. 3 otherwise corresponds to the functionality of the embodiment of Fig. 2. Here, too, transistors T1A and T1B are used as the third and fourth coupling elements. This arrangement also serves as a differential amplifier, so that with the circuit shown, the signal level can not only be reduced but is first amplified due to the differential amplifier arrangement of transistors T1A and T1B, resistors R17A and R17B, and current source CR4. The gain factor can be reduced by correspondingly reducing the shunt resistors using the MOSFET switches.

[0036] Fig. Figure 4 shows a third embodiment of the invention. In this embodiment, a corresponding amplifier has two input pairs IN1A, IN1B, and IN2A and IN2B, via which two different audio sources, e.g., a CD player and an FM tuner, can be connected.

[0037] Using relay switches K1 and K2, either the first or second input pair can now be coupled to the transmission line without having to de-energize the transmission lines. The relay switch contacts are also not de-energized.

[0038] The present invention enables volume control with a few, and above all, cost-effective, components, while simultaneously achieving precise reproduction fidelity, especially at low signal strengths. The distortion factor of the contacts is significantly reduced.

Claims

[1] Signal level control with two input terminals (IN1, IN2, IN1A, IN1B, IN2A, IN2B) for receiving a balanced input signal I E and two outputs (OUT1, OUT2) for outputting a symmetrical output signal I A with an adjusting element which can be switched between at least two positions, wherein in the first position I A = k1 · I E and in the second position I A = k2 · I E, where k2 ≠ k1, wherein two transmission lines are provided, one end of which is each connected to a power source, wherein each transmission line is assigned a coupling element (C1, C2, T1A, T1B), with the aid of which the current flow through the transmission lines can be influenced in such a way that the setting element is supplied with a direct current during operation of the signal level regulator, wherein the first coupling element (C1) is connected to the first input terminal (IN1, IN1A, IN1B) and is controlled by an alternating voltage signal which is applied to the first input terminal (IN1, IN1A, IN1B), and the second coupling element (C2) is connected to the second input terminal (IN2, IN2A, IN2B) and is controlled by an alternating voltage signal which is applied to the second input terminal (IN2, IN2A, IN2B), wherein the first output terminal (OUT1) is connected via a third coupling element (T1A,C7) is connected to the first transmission line and the second output terminal (OUT2) is connected to the second transmission line via a fourth coupling element (T1B, C8). [2] Signal level controller according to claim 1, characterized by that the adjusting element has at least two pairs of resistors (R6, R7, R8, R9, R10, R11, R21, R22), wherein in the first position of the adjusting element each transmission line is connected to ground via a resistor of the first pair of resistors and in the second position of the adjusting element each transmission line is connected to ground via a resistor of the second pair of resistors. [3] Signal level controller according to claim 1 or 2, characterized bythat the current sources which are connected to one end of the transmission lines are each formed by a transistor (T2A, T2B), preferably a pnp transistor, the emitter terminal of which is connected via a resistor (R13B, R13A) to a first voltage source which provides a first potential, and the base terminal of which is optionally connected via a resistor to a second voltage source which provides a second potential which is different from the first potential, wherein the first and the second coupling element (C1, C2) are each designed as a capacitor (C1, C2), one side of which is connected to the first and the second input terminal (IN1, IN2, IN1A, IN1B, IN2A, IN2B) respectively and the other side of which is connected to the base terminal of the transistor (T2A, T2B) of the respective current source (CR4). [4] Signal level controller according to one of claims 1 to 3, characterized bythat the third and fourth coupling element (T1A, T1B) each have a transistor, preferably a pnp transistor, wherein the first and the second transmission line are connected to the base terminal of one of the transistors (T1A, T1B) in each case, the emitter terminals are optionally connected via a resistor (R17B, R17) to the current source (CR4) and the collector terminals are connected via a capacitor (C7, C8) to the first and second output terminals, respectively. [5] Signal level controller according to one of claims 1 to 4, characterized by that the adjusting element has at least one pair of switches (K1, K2, K3, K4) with which the pair of resistors (R6, R7, R8, R9, R10, R11, R21, R22) can be moved essentially simultaneously from the first to the second position and back. [6] Signal level controller according to claim 5, characterized bythat the switch pair (K1, K2, K3, K4) is formed by two MOSFETs (T17A, T17B, T18A, T18B, T19A, T19B, T20A, T20B), preferably by a dual MOSFET. [7] Signal level controller according to claim 6, characterized by that the transmission lines are each connected to a drain terminal of a MOSFET (T17A, T17B, T18A, T18B, T19A, T19B, T20A, T20B), the source terminals of the MOSFETs (T17A, T17B, T18A, T18B, T19A, T19B, T20A, T20B) are connected to ground and the gate terminals can be optionally supplied with a control voltage using the setting device. [8] Amplifier with a signal level controller according to one of claims 1 to 7.

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