EP0746122A1 - Monolithically integratable mixing device for an audio control desk - Google Patents

Abstract

The mixer has a pre-amplifier (M) with an adjustable pre-amplification for each tone channel and a summation amplifier (S) at the output of the pre- amplifier, for separate adjustment of the summation amplification. A control device (P) coupled to the pre-amplifier and the summation amplifier allows the overall amplification (vk) for each tone channel to be divided between the pre-amplifier and the summation amplifier in a ratio which is dependent on the overall amplification, for optimising the noise ratio.

Description

The invention relates to a monolithically integrable mixer device for a mixer, which as a subcircuit for the control of various sound signal sources in an audio signal processing circuit, e.g. in a PC sound card (= sound processing board for a personal computer) or in a car radio receiver is provided, in which it is intended to gradually switch from one sound signal source to another. An application example for this is a soft cross fade from a music playback to a current traffic announcement, whereby both signals come from different sources. During the traffic announcement, the channel is attenuated with the music signal and the traffic announcement is faded in instead. As is well known, an abrupt switchover of signal sources produces unpleasant crackling noises and, if necessary, strong volume jumps. A further, increasingly important use for such mixer devices is the as unnoticed cross-fading from a disturbed or weakening reception channel to a better one. This operating mode is also known as diversity reception. Such cross-fades require a purely electronic mixer device with an intelligent control, which e.g. by means of a processor which is connected to the actual mixer device via control lines or a bus system.

The circuitry for mixer equipment can be very large, especially if it is professional studio equipment. For consumer areas, for example in the described application for car radio receivers or in a PC or in other applications, the requirements are lower, but the circuitry for an intelligent mixer device is still so great that a compact, monolithically integrable solution has been found for the specified consumer application must be, the circuit complexity, which is ultimately expressed in the required semiconductor crystal area, should remain as low as possible for cost reasons.

A mixer device with active components contains on the input side a preamplifier with adjustable gain and on the output side a summing device to combine the differently amplified signals into a single signal at an output, cf. Fig. 1. For the preamplifiers, circuits with operational amplifiers prove to be expedient because the respective amplification can be easily adjusted by changing a resistance ratio formed by an input and a feedback resistor. In the case of an analog circuit, this takes place via a slider or a potentiometer and, in the case of a digital version, via a resistor network, which can be controlled by tapping or by electronically switching, switching on or off partial resistors - which can also include a parallel or series connection - A change in the resistance ratio digitally allows in a simple manner. The differently amplified signals of the individual channels are then combined using the summing device. If you want to use an operational amplifier arrangement for the summing device, then the known summing amplifier circuit offers itself, which has an input resistor for each channel and a common feedback resistor for all channels. The ratio of feedback resistance and input resistance also determines the respective channel gain component here. The advantages of this combination include the defined channel gain and the low-impedance signal output.

In the arrangement with preamplifier and summing amplifier described above, however, it is disadvantageous that in the case of damping, the useful signal in the preamplifier is reduced by the desired value, but the inherent or external noise that is always present is passed on unchanged or even increased by the amplification of the summing amplifier , so that the signal / noise ratio at the output deteriorates unnecessarily.

It is therefore an object of the invention to provide a circuit arrangement for a monolithically integrable mixer device in which the signal / noise ratio which is dependent on the intrinsic or external noise remains as high as possible in the entire amplification and attenuation range.

• ein in der Verstärkung (= Vorverstärkung) einstellbarer Vorverstärker für jeden Tonkanal;
• ein Summierverstärker, der an die Ausgänge der Vorverstärker gekoppelt ist und dessen Verstärkung (= Summierverstärkung) je Tonkanal unterschiedlich einstellbar ist; und
• eine Steuereinrichtung, die mit dem Vorverstärker und dem Summierverstärker gekoppelt ist und der Steuerung der den jeweiligen Tonkanal betreffenden Gesamtverstärkung (= Kanalverstärkung) dient, die zwischen dem Vor- und dem Summierverstärker nach einem vorgegebenen, von der einzustellenden Kanalverstärkung abhängigen Verhältnis aufgeteilt ist, das sich im Dämpfungsbereich bei zunehmender Signaldämpfung dahingehend ändert, daß die Summierverstärkung im Verhältnis stärker reduziert ist als die Vorverstärkung.

This object is achieved according to claim 1 for a monolithically integrable mixer device for a mixer by the following features:

• a preamplifier with adjustable gain (= pre-amplification) for each audio channel;
• a summing amplifier which is coupled to the outputs of the preamplifiers and whose amplification (= summing amplification) can be set differently for each audio channel; and
• a control device which is coupled to the preamplifier and the summing amplifier and serves to control the overall amplification (= channel amplification) relating to the respective sound channel, which is divided between the preamplifier and the summing amplifier according to a predetermined ratio which is dependent on the channel amplification to be set and which changes in the attenuation range with increasing signal attenuation in such a way that the summation gain is reduced more than the preamplification.

It is therefore a matter of realizing an intelligent gain setting that takes place in the background and that cannot be carried out without electronic aids.

Fig. 1

zeigt schematisch eine bekannte Mischereinrichtung mit aktiven Bauelementen,

Fig. 2

zeigt ein Beispiel für ein Widerstandsnetzwerk mit einer Serienschaltung von Teilwiderständen und mit einer Vielzahl von Widerstandsabgriffen,

Fig. 3

zeigt ein ausführlicheres Schaltbild der Mischereinrichtung nach Fig. 1,

Fig. 4

zeigt ein Schaltbild einer Mischereinrichtung nach der Erfindung,

Fig. 5

zeigt in Tabellenform an einem Beispiel, wie die jeweilige Kanalverstärkung oder -dämpfung zwischen dem Vor- und Summierverstärker aufgeteilt ist.

The invention and advantageous embodiments are now explained in more detail with reference to the figures of the drawing:

Fig. 1

schematically shows a known mixer device with active components,

Fig. 2

1 shows an example of a resistance network with a series connection of partial resistors and with a large number of resistance taps,

Fig. 3

1 shows a more detailed circuit diagram of the mixer device according to FIG. 1,

Fig. 4

shows a circuit diagram of a mixer device according to the invention,

Fig. 5

shows in table form an example of how the respective channel gain or attenuation is divided between the preamplifier and summing amplifier.

1 shows a mixer device with active circuit parts for three channels, which are connected to a first, second and third signal input e1, e2, e3. The active circuit parts consist of first operational amplifiers v1, which, with corresponding circuits, form first operational amplifier arrangements OP1 and form a first, second and third preamplifier M1, M2, M3 for the signals supplied. The outputs of the preamplifiers are interconnected by means of a second operational amplifier arrangement OP2 in order to combine the signals of all three channels into a single signal which can be tapped at the output o. The second operational amplifier arrangement OP2 forms a summing amplifier S which contains an operational amplifier, the second operational amplifier v2, as an active element. Transconductance amplifiers and other active circuits with corresponding wiring can also be used as active elements in both operational amplifier arrangements OP1, OP2. 1, the operational amplifier v2 is connected as a summing amplifier and has an input resistance Rsv for each channel and a feedback resistance Rsr for all channels.

The amplification of the three preamplifiers M1, M2, M3 is set in each case via an input resistor Rmv and a feedback resistor Rmr. The input resistance Rmv lies between the respective channel input e1, e2, e3 and the inverting input of the first operational amplifier v1. The output signal of the operational amplifier v1 is also fed back to this input via the feedback resistor Rmr.

Other gain adjustment circuits are also known. However, the first and second operational amplifier arrangements OP1, OP2 shown in FIG. 1 prove to be advantageous in that the respective gains are determined directly by the ratio of feedback resistance Rmr or Rsr and input resistance Rmv or Rsv. The gain is set in the first Operational amplifier arrangement OP1, in that the input resistance and the feedback resistance are formed by a potentiometer or slider rs (see FIG. 3), the tap a1 of which is located at the inverting input of the first operational amplifier v1 and the other two connection nodes k1, k2 of which are input e1 and are connected to the operational amplifier output. By changing the potentiometer or slider setting, the signal in the respective sound channel can be amplified or damped over a very wide range.

With a potentiometer or slider rs, the analog setting is usually done manually or using a servomotor. Electronic adjustment is easier if only discrete gain values need to be set, but the step size can be narrow. For example, a step size of 1.5 dB is sufficient for the intended consumption range. For this purpose, the input resistor Rmv and the feedback resistor Rmr of the preamplifier M as a resistor network rp (see FIG. 2) are formed from a large number of partial resistors r, which can be switched on, off or on via electronic switches, a series connection or parallel connection also being provided of partial resistances r is possible.

A particularly simple arrangement for such a resistance network rp is represented by a resistance chain made up of mostly different partial resistors r, part or all of the connection nodes k of the partial resistors being provided with taps ai. By means of a switching device s shown schematically in FIG. 3, which corresponds to a sliding contact in a slide controller rs, one of the taps ai can be connected to the inverting input of the first operational amplifier v1. A single switch contact divides the tapped resistor network rp into two parts via the respective tap a1 and forms a first and a second resistor R1, R2 coupled to it.

The invention only requires a second sliding or switching contact s2 for this resistor chain, with which the total resistance value of the resistor chain is divided into three resistors R1, R2, R3 in a particularly simple manner. The realization of the matchable resistor network rp as a resistor chain is also very suitable for monolithic integration. This resistance chain thus allows the resistance ratio in the case of the two resistors R1, R2 or the three resistors R1, R2, R3 to be changed in a very simple manner in a wide ratio. In the case of a fine gradation, this is paid for by a large number of partial resistances r, which thus form a relatively long chain. The number of partial resistors r can, on the other hand, be reduced if the structure of the resistor network rp can be changed by the switching device, but this requires a complex switching device. A combination of both methods is of course also possible. Because all three resistors R1, R2, R3 are coupled to one another in the resistor chain, the change in a resistor has a direct effect on the value of the adjacent resistor, that is to say connected to the same tap ai, and changes it. By parallel displacement of both taps a1, a2, the change in resistance can also be carried out in such a way that only the two external resistances R1, R2 change and the mean resistance R2 remains constant. In the exemplary embodiment of the invention according to FIG. 4, the mutual coupling of the three resistors R1, R2, R3 is cleverly used in order to effect a sliding gain distribution.

FIG. 3 shows the circuit arrangement of FIG. 1 described in more detail, in particular in the area of the first operational amplifier arrangement OP1. The gain control in the preamplifier M1 contains, as an adjusting resistor, a slider rs whose tap a1 is connected to the inverting input of the first operational amplifier v1 via a sliding contact s. The input of the slider rs, the first circuit node k1, is connected to the signal input e1 via a fixed resistor Rmv '. The tap a1 divides the resistance of the slider rs into two parts and forms the first and second resistor R1 and R2. The output of the slider, which is formed by a second circuit node k2, is connected to the output of the first operational amplifier v1 and to the one terminal of a fixed resistor Rsv ', which serves as the input resistor Rsv of the summing amplifier S for this channel. In the first operational amplifier arrangement OP1, the sum resistance of the fixed resistor Rmv 'and the first resistor R1 forms the input resistor Rmv and the second resistor R2 the Feedback resistor Rmr (see Fig. 1). The connection point between the fixed resistors Rsv and Rsr forms a third circuit node k3, which is connected via a summing line s1 to the inverting input of the second operational amplifier v2. A second or a third preamplifier M2 or M3 is connected to this summing line s1 via further input resistors. The actuation of the slide controller rs, s can be controlled manually or electronically by means of an auxiliary device from a control device P. In the case of a digital version of the slider rs or potentiometer, the electronic control becomes simpler in that, as already stated, only electronic switching devices have to be operated. The slider rs or the potentiometer is replaced by a resistor network rp with taps ai.

The differences of the invention can be clearly seen in FIG. 4 compared to FIG. 3, the same circuit parts being provided with the same reference numerals and therefore no longer having to be explained in more detail. In the preamplifier M, the slider rs is replaced by a resistor network rp. A first and second electronic switch s1 and s2 establish a connection to the first or tap a1 or a2, as a result of which the resistor network is divided into three sub-areas which form the first, second and third resistor R1, R2, R3. The permissible ranges for the first and second taps a1 and a2 do not overlap. 4, the associated areas are shown schematically by the length of the respective sliding contact lines.

In the first operational amplifier arrangement OP1, as in FIG. 3, the fixed resistor Rmv 'together with the first resistor R1 forms the input resistor Rmv (see FIG. 1) and the second resistor R2 forms the feedback resistor Rmr. In the second operational amplifier arrangement OP2, the third resistor R3 together with the fixed resistor Rsv 'forms the input resistor Rsv (ex. FIG. 1). Since the feedback resistor Rsr of the second operational amplifier arrangement OP2 is constant, its amplification or damping is controlled by the change in the third resistor R3. Since the second tap a2 is connected to the output of the first operational amplifier v1 via the second switch s2, the gain vm of the preamplifier can M can be controlled jointly or independently of one another both via the position of the first switch s1 and via the position of the second switch s2. The gain vm of the preamplifier M is formed by the ratio of the second resistor R2 to the sum of the fixed resistor Rmv 'and the first resistor R1. It is pointed out that the resistors Rmv ', Rsv' and Rsr can of course also be included in the resistor network rp.

des Vor- und Summierverstärkers M bzw. S.The electronic switches s1, s2 and any other switches are controlled by means of the control device P, which uses a stored table T to assign the respective position of the switches s1, s2 to the desired channel gain vk. The total channel gain vk results from the channel-related gain product $\text{vk = vm × vs}$

of the preamplifier and summing amplifier M or S.

In Fig. 5 an example of such a distribution of the channel gain is shown in a table form, which indicate an appropriate division for the individual gain and attenuation areas in order to solve the desired task.

The entire modulation range from +12 dB to -34.5 dB is divided into two areas 1 and 2 (see FIG. 5), the first area 1 from +12 dB to about -6 dB and the second area 2 from about -6 dB to -34.5 dB ranges.

ist) des Summierverstärkers S weist dabei seinem Minimalwert auf, nämlich nur noch den Wert des Festwiderstandes Rsv'. Bei der Maximalverstärkung +12 dB entspricht der erste Abgriff a1 dem ersten Schaltungsknoten k1. Der Rückkopplungswiderstand Rmr des Vorverstärkers M, der durch den zweiten Widerstand R2 gebildet wird, nimmt somit seinen Maximalwert an, nämlich den Wert des gesamten Widerstandsnetzwerkes rp, wobei $\text{R1 = R3 = 0}$

ist. Mit abnehmender Verstärkung wandert der Abgriff a1 in Richtung des zweiten Schaltungsknotens k2, bis schießlich bei der Kanalverstärkung -6 dB ein maximaler Wert für den ersten Widerstand R1 (und damit den gesamten Eingangswiderstand Rmv, mit $\text{Rmv = Rmv' + R1}$

) erreicht wird, dem ein Abgriff a1max entspricht.In the first area 1, which thus comprises the entire channel gain range from 0 dB to +12 dB and also the weak attenuation range to -6 dB, the summation gain vs remains constant at 0 dB. The channel gain vk is thus set only by changing the resistance ratio in the preamplifier M, for which the position of the first tap a1 is varied. If the two fixed resistors Rsv 'and Rsr of the second operational amplifier arrangement OP2 are given the same size, in the assumed example of FIG. 4 each 3 kOhm, then the second tap a2 for this amplification range is identical to the second circuit node k2. The input resistance Rsv (where $\text{Rsv = Rsv '+ R3}$

is) of the summing amplifier S has its minimum value, namely only that Fixed resistance value Rsv '. At the maximum gain +12 dB, the first tap a1 corresponds to the first circuit node k1. The feedback resistor Rmr of the preamplifier M, which is formed by the second resistor R2, thus assumes its maximum value, namely the value of the entire resistor network rp, where $\text{R1 = R3 = 0}$

is. With decreasing amplification, the tap a1 moves in the direction of the second circuit node k2, until finally, with the channel amplification -6 dB, a maximum value for the first resistor R1 (and thus the entire input resistor Rmv) $\text{Rmv = Rmv '+ R1}$

) is reached, which corresponds to a tap a1max.

) einen Maximalwert erreicht, dem ein Abgriff a2min (die Zählrichtung beginnt bei k1) entspricht. Der Eingangswiderstand Rsv wächst dadurch von 6 kOhm auf ca 67 kOhm an. Dem entspricht eine Änderung der Summierverstärkung vs von -0 dB auf -27 dB.According to the knowledge of the invention, in the attenuation area, in particular with strong attenuation, which corresponds to the lower part of the second area 2 in FIG. 5, the channel gain vk should be divided such that the attenuation takes place in the summing amplifier S and not in the preamplifier M. This is achieved in that the first resistor R1 is no longer changed after the maximum value has been reached. The preamplification vm therefore only changes between -6 dB and -7.5 dB due to the only relatively slight reduction in the second resistance R2 in the second region 2, while the total channel gain vk changes between -6 dB and -34.5 dB changes. For this purpose, the second tap a2 is changed in the direction (starting from the second circuit node k2) of the first circuit node k1 until the third resistor R3 (and thus the entire input resistor Rsv, with $\text{Rsv = Rsv '+ R3}$

) reaches a maximum value which corresponds to a tap a2min (the counting direction starts at k1). This increases the input resistance Rsv from 6 kOhm to approx. 67 kOhm. This corresponds to a change in the summation gain vs from -0 dB to -27 dB.

If, in certain amplification and damping areas, for example in FIG. 5 in the first and in the second area 1 or 2, it is possible to proceed in a uniform manner, for example by only having to change a single tap ai, the table to be stored is simplified T in the control device P. Its scope also depends on the smallest step size of the gain change, for which 1.5 dB is sufficient in the assumed example. The function of the control device P can optionally also take over a processor which is integrated on the semiconductor chip.

Of course, the control of the gain distribution and ultimately the control of the taps can also be defined using a more or less descriptive formula that is then calculated in the processor. The channel gain vk forms the variable for the formulaic representation of the gain distribution, in which the function can even be defined differently in sections. The formulaic representation is particularly simple if a linear dependency is given as an approximation for individual areas or sections, because then the intermediate values can easily be calculated using a linear interpolation.

Claims (9)

Monolithically integrable mixer device for a mixer with a preamplifier (M) adjustable for the amplification, the preamplification (vm) for each audio channel, with a summing amplifier (S) which is coupled to the outputs of the preamplifiers (M) and its amplification, the Summing gain (vs), can be set differently for each sound channel, and with a control device (P), which is coupled to the preamplifiers (M) and the summing amplifier (S) and the control of a total gain relating to the respective sound channel, the channel gain (vk), serves, which is divided between the preamplifier (M) and the summing amplifier (S) according to a predetermined ratio, which is dependent on the channel gain (vk) to be set, and which changes in the attenuation range with increasing channel attenuation in such a way that the summing gain (vs) is relatively stronger is reduced as the preamplification (vm). Mixer device according to claim 1, characterized in that the respective preamplification (vm) and the associated summing amplification (vs) can be set digitally by the preamplifier (M) and the summing amplifier (S) forming a first and second operational amplifier arrangement (OP1, OP2) , whose channel gain (vk) is digitally adjustable via a tapped resistor network (rp) and an electronic switching device (s1, s2). Mixer device according to claim 2, characterized in that in the preamplifier (M) the tapped resistor network (rp) by means of the electronic switching device (s1, s2), which is coupled to the control device (P), to form the first operational amplifier arrangement (OP1) a first operational amplifier (v1) is connected that a first part of the tapped resistor network (rp), the forms a first resistor (R1), an input resistor (Rmv) and a second part of the tapped resistor network (rp), which forms a second resistor (R2), is assigned to a feedback resistor (Rmr). Mixer device according to claim 3, characterized in that the second operational amplifier arrangement (OP2) has a second operational amplifier (v2) and a first and a second fixed resistor (Rsv 'or Rsr), which are connected to the input (Rsv) or the feedback resistor (Rsr) are assigned to the second operational amplifier arrangement (OP2). Mixer device according to claim 4, characterized in that a third part of the tapped resistor network (rp), a third resistor (R3) is assigned to the associated input resistor (Rsv) of the second operational amplifier arrangement (OP2). Mixer device according to claim 5, characterized in that the tapped resistor network (rp) contains a series circuit made up of partial resistors (r) and some connection nodes (k) of the partial resistors are designed as taps (ai) which are formed by means of a first and a second electronic switch (s1 , s2) form the first, second and third resistor (R1, R2, R3) via a first and second tap (a1, a2). Mixer device according to Claim 6, characterized in that the input resistance (Rsv, R3) of the second operational amplifier arrangement (OP2) is set to a minimum value (Rsv ') in a first region (1) of the channel gain (vk), which corresponds to a high signal gain the respective value of the channel gain (vk) is defined via the position of the first tap (a1), whereas in a second area (2) of the channel gain (vk), which corresponds to a high signal attenuation, the first resistor (R1) is set to a maximum value and the respective value of the channel gain (vk) is defined via the position of the second tap (a2). Mixer device according to claim 7, characterized in that in an intermediate region of the channel gain (vk), which corresponds to a low signal gain and / or a low signal attenuation, the input resistance (Rsv; R3, Rsv ') of the second operational amplifier arrangement (OP2) to a minimum value ( Rsv ') and the respective value of the channel gain (vk) is defined via the position of the first tap (a1). Mixer device according to one of claims 2 to 8, characterized in that in the control device (P) the distribution of the channel gain (vk) between the pre-gain (vm) and the summing gain (vs) by means of a stored table (T) and / or by means of a the formula is based on a calculation.

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