FR2465369A1 - Mixer circuit for volume and tone control circuit - has two parallel connected differential amplifiers responsive to three control signals and providing increased signal=to=noise ratio - Google Patents

Abstract

The remote controllable electronic mixer consists of two differential amplifiers connected as electronics potentiometers and run in parallel with each having a signal input and output and two control signal inputs. The signal outputs and one control input is common to both amplifiers so that three control signals and two signal inputs are required. The control signals are derived from two command signals for volume and balance control and are logarithmically and linearly related to the command levels. This relationship is also achieved using two differential amplifiers. Connected as a tone control, one signal input is passed through a high pass filter and the other through a low pass filter prior to mixing.

Description

 The present invention relates to a remote-controlled electronic circuit for mixing two signals and its application to a low-frequency amplifier with volume and tone control for sound signals. The present invention relates more particularly to such circuits produced in the form of integrated circuits.

In the prior art, the volume and tone adjustment circuits produced in integrated circuits derived from the principle diagram illustrated in FIG. 1, that is to say that they included in series two amplifiers 1 and 2 of the potentiometer type. electronics capable of receiving control signals 3 and 4 to act in a determined manner on an input signal 5 transmitted via an amplifier 6 to a loudspeaker 7. The first amplifier 1 was for example intended for adjusting the bandwidth and, depending on the action on 11 control input 3, the bandwidth of a filter or of a set of filters which it contained was modified. As for the second amplifier 2, an action on the input terminal 4 modified its gain and varied the amplitude of the output signal, while the amplitude of the output signal of the first amplifier was constant, the gain of this amplifier being for example chosen equal to 1.

One of the major drawbacks of this type of remote-controlled circuit for adjusting the volume and the tone of an audible signal lies in the fact that amplifiers of the electronic potentiometer type exhibit relatively high noise. The fact of having two electronic potentiometers in series therefore greatly contributes to the degradation of the signal / noise ratio. Thus, if we call G1 the gain of amplifier 1 and G2 the gain of amplifier 2, the signal S at the output of amplifier 2 is equal to G1G2E or E denotes the signal of On the other hand, If e is the noise injected at the input by each electronic potentiometer, the noise B at the output will be

We therefore obtain a signal / noise ratio

If as we saw previously G1 = 1, we get

 An object of the present invention is to provide a new type of circuit for adjusting the volume and tone of the sound signal making it possible to improve the signal / noise ratio.

 To achieve this object, the present invention provides for applying the input signal to two operational amplifiers of the electronic potentiometer type arranged in parallel, each of these amplifiers being preceded by a particular filter, and the outputs of these amplifiers being summed. In response to a first command signal, the gain of these two amplifiers varies simultaneously and in the same direction; in response to a second command signal, the gain of these two amplifiers varies simultaneously and in opposite directions. Thus, in response to the first command signal, only the volume of the signal varies; and in response to the second command signal, only the balancing of the two channels varies without affecting the volume. In this second case, the proportion of the amount of signal having passed through each of the filters varies. It is therefore a tone adjustment.

 Another object of the present invention is to provide electronic circuits for mixing two signals making it possible to simply produce the volume and tone control circuit mentioned above.

To achieve this second object, the present invention provides a remote-controlled electronic circuit for mixing two signals comprising two differential amplifiers connected as electronic potentiometers and arranged in parallel, each comprising a signal input and output and two control inputs, each input of signal being connected to one of the signals to be mixed, the two signal outputs being interconnected to provide an output signal, the first control inputs being interconnected and receiving a first control signal, the second control input of the first electronic potentiometer receiving a second control signal, and the second control input of the second electronic potentiometer receiving a third control signal; this electronic circuit further comprising means for supplying these three control signals in response to two command signals, the first of which acts only on the signal volume and the second only on the proportion of the two input signals in the output signal (or balancing). According to a characteristic of the present invention, the volume of the output signal can vary logarithmically as a function of the first command signal whereas the proportion of mixing can vary linearly or logarithmically as a function of the second command signal.

 The means for supplying the three control signals from the two command signals may comprise two other amplifiers connected as electronic potentiometers, the first amplifier being connected in the following manner: signal input receiving a constant current, first control input at a reference voltage, second control input receiving the first volume command signal, the first signal output providing a first control signal, the second signal output connected to the signal input of the second differential amplifier; and the second amplifier being connected as follows: signal input to the second output of the first differential amplifier, first control input receiving the second balance command signal, second control input receiving a reference voltage, first output signal providing the second control signal, second signal output providing the third control signal.

These objects, characteristics and advantages as well as others of the present invention will be explained in more detail in the following description of particular embodiments made in relation to the attached figures among which
Figure 1 illustrates a block diagram of the prior art volume and tone control circuit
Figure 2 shows a block diagram according to the present invention of volume and tone control circuit
Figure 3 shows schematically and in simplified form a differential amplifier mounted as an electronic potentiometer and this figure will be used to define the terminology adopted in this description
FIG. 4 schematically represents an electronic mixer according to the present invention
Figure 5 shows in more detail although still schematically a mixer according to the present invention; and
Figures 6 and 7 show two embodiments of circuits for supplying control signals to the mixer according to the present invention from two signals of order of volume and proportion of mixture.

Figure 2 shows a block diagram of a low frequency amplifier with volume and tone control according to the present invention. As in the case of FIG. 1, an input signal 5 is sent to a low frequency power amplifier 6 and a loudspeaker 7, via a volume and tone control circuit,
This circuit includes two amplifiers used as electronic potentiometers and designated by the references 11 and 12.

The variation in volume is controlled by a signal arriving at a terminal 13 and the variation in tone is controlled by a signal arriving at terminal 14. The terminals 13 and 14 constitute the input terminals of a circuit 15 transforming the order signals 13 and 14 as control signals for the electronic potentiometers 11 and 12. Thus, when a signal is applied to the volume order terminal 13, the gains of the two amplifiers 11 and 12 vary simultaneously and in the same proportion. When an order signal is applied to terminal 14 to vary the tone, the two electronic potentiometers 11 and 12 are controlled to present variations in gain in the opposite direction and of equal quantity.

The input signal 5 is transmitted to the input of the potentiometer 11 via a first filter circuit 16, for example a high-pass filter, and to the input of the second electronic potentiometer 12 by the through a second filter circuit 17, for example a low-pass filter. Thus, depending on the setting of the electronic potentiometers 11 and 12, the input signal passes more or less through each of the high-pass and low-pass filters 16 and 17, and depending on whether the electronic potentiometers 11 and 12 vary in synchronism or in antisynchronism , you obtain a volume adjustment at a given tone or a change in tone at constant volume.

ainsi, le rapport signal/bruit est
S E
= = - (2)
B e
En comparant les formules (1) et (2), on voit que, par rapport aux circuits de l'art antérieur utilisant deux potentiomètres électroniques en série, on a gagné un facteur 2 dans le rapport signal/bruit en sortie.One of the advantages of this circuit, compared to the circuits of the prior art mentioned above, lies in the improvement of the signal / noise ratio at the output. Indeed, if there is an input signal E, that the gain of the two electronic potentiometers is equal to G and that the noise injected at their entry by each of the electronic potentiometers is equal to e, we obtain
S = 2EG

thus, the signal-to-noise ratio is
SE
= = - (2)
B e
By comparing formulas (1) and (2), we see that, compared to the circuits of the prior art using two electronic potentiometers in series, we have gained a factor of 2 in the signal / noise ratio at output.

 The invention described above consisting in using a mixer circuit preceded by filters and consisting of two electronic potentiometers in parallel can only be practically carried out with elements of the same integrated circuit, since the two electronic amplifiers should be used are as perfectly matched as possible.

 We will describe below by way of example a particular mixer circuit, forming part of the present invention, but it will be noted that the general method of using a mixer to obtain a circuit for controlling the volume and tone of signals sound is an invention regardless of the particular mixer which will be described.

 FIG. 3 represents a differential amplifier circuit used as an electronic potentiometer. This arrangement is known in itself; it will be briefly described below to define the terminology used in the present text.

This circuit includes two transistors 21 and 22 mounted as a common transmitter and whose collectors are connected to a positive supply terminal Vcc via respective resistors 23 and 24. Terminals 25 and 26 connected to the bases of transistors 21 and 22 will be called first and second command entries; terminals 27 and 28 connected to the collectors of transistors 21 and 22 will be called first and second signal outputs; and terminal 29 connected to the common transmitter connection will be called signal input.

Thus, the signal available at signal output 28 will be the signal present at signal input 29 multiplied by a factor depending on the difference between the voltages present at control inputs 26 and 25. The signal at signal output 27 is complementary to the signal at signal output 28, that is to say that, if the signal at terminal 28 increases, the signal at terminal 27 decreases correspondingly. Unless specially mounted, as will be seen below, the output signals vary logarithmically as a function of the difference between the control voltages.

 Figure 4 schematically represents a first simplified embodiment of a mixer circuit according to the present invention comprising two electronic potentiometers in parallel.

 The first electronic potentiometer comprises the transistors 30 and 31, a signal input terminal 32, a first control terminal 33, a second control terminal 34 and a first signal output 35, the other signal output being not used. The second electronic potentiometer comprises transistors 40 and 41, a signal input 42, a first control input 43, a second control input 44, and a signal output 45.

The first control inputs 33 and 43 are interconnected and receive a first control signal B.

The second control input of the first electronic potentiometer 30-31 receives a control signal A, and the second control input of the second electronic potentiometer 40-41 receives a control signal C. The signal outputs 35 and 45 are interconnected and provide an output signal sum VO. The input signals to be mixed I and II are applied to inputs 32 and 42 in the form of current sources.

To increase the value of the output signal VO without modifying the proportion of mixing or balancing of the input signals I and II, it is advisable to vary simultaneously and in the same direction the differences B-A and B-C between the control signals. To modify the mixing rate without appreciably modifying the total amplitude of the output signal, the combinations of control voltages BA and BC should be varied in opposite directions, i.e. one must increase while that the other decreases.

Figure 5 shows, also schematically, another embodiment of the mixer according to the present invention. In FIG. 5, elements identical to those of FIG. 4 are designated by the same references. The circuit of FIG. 5 has the advantage over that of FIG. 4 of carrying out DC component compensation.

Each of the input signals is in the form of an alternative component to which a DC component I1 or I2 is added. Let there be the alternative component of the first
Iî 12. the co input signal to be mixed and i2 the alternative component of the second input signal to be mixed. By appropriate and well-known circuits, the first signal to be mixed is presented to the circuit of FIG. 5 in the two forms I1 + il and Il i
Similarly, the second signal is presented in the two forms 12 + i2 and 12 - i2 *
Thus, in addition to the elements of Figure 4, the circuit of Figure 5 includes two additional electronic potentiometers. The first includes two transistors 50 and 51, a signal input 52, control inputs 53 and 54 and signal outputs 55 and 56. Likewise the second includes transistors 60 and 61, a signal input 62, inputs 63 and 64 and signal outputs 65 and 66. The second signal outputs of the electronic amplifiers comprising the transistors (30, 31) and (40,41) will be designated by the references 36 and 46 respectively (these references n 'were not shown in Figure 4 since these outputs were not used in this figure). The second control terminals 34 and 54 of the electronic potentiometers 50-51 and 30-31 are interconnected, as well as the second control terminals 44 and 64 of the electronic potentiometers 40-41 and 60-61. The first control terminals 53 and 63 of the electronic potentiometers 50-51 and 60-61 are interconnected.

The first signal outputs 55 and 65 are interconnected as are the second outputs 56 and 36 and the second outputs 66 and 46. The input terminals 32 and 52 receive signals I1-i and Il + il respectively. Input terminals 42 and 62 respectively receive signals I2-i2 and 12 + i 2
The output signal of the assembly is taken in the form of the difference between the signals at interconnection 35, 45 and the signals at interconnection 55, 65. This is achieved using a current mirror arrangement. A first transistor 71 is connected between the interconnection 35, 45 and the power source Vcc A second transistor 72 is connected between the interconnection 55, 65 and the power source Vcc. These two transistors are arranged in current mirror , their emitters both being at the supply Vcc, their bases being connected and the base and the collector of transistor 71 being interconnected. The output voltage is collected across a value resistor 73
R5 disposed between the emitter of transistor 72 and a voltage ERzf, VRf I possibly equal to Vcc. Other ways of obtaining this difference could be implemented.

 Generally with regard to FIGS. 4 and 5, in practical embodiments, these circuits will be complicated by the addition of numerous additional transistors having roles of polarization, adaptation of impedance, thermal compensation, etc. However, Figures 4 and 5 allow their simplification to better illustrate the method according to the present invention and the operation of the circuit in question.

 FIGS. 6 and 7 represent two embodiments of circuits making it possible, from two order signals corresponding respectively to a volume control order and to a balance control order, to produce the three signals A, B and C for controlling the circuits of FIGS. 4 and 5.

 The circuits of FIGS. 6 and 7 include two electronic potentiometers constituted respectively by transistors 80-81 and 90-91. The electronic potentiometer 80-81 has a signal input 82 connected to the emitters of the transistors 80 and 81 via resistors R1, control inputs 83 and 84, and signal outputs 85 and 86.

The electronic potentiometer 90-91 has a signal input 92 connected to the emitters of the transistors 90 and 91 via resistors R3, control inputs 93 and 94, and signal outputs 95 and 96.

In FIG. 6, the signal input 82 is supplied by a constant current source Io. Signal input 92 receives signal output 85 from transistor 81. Signal output 86 supplies signal B and is connected to the power terminal
Vcc via a resistor R2. Signal output 95 supplies signal C. Signal output 96 supplies signal A. These signal outputs 95 and 96 are connected to the power supply terminal Vcc via resistors R4 having a value equal to double that of R2 resistors.

The signal input 83 is connected to a reference voltage source Vî. The signal input 93 is connected to a reference voltage source V2. The signal input 84 receives a signal of order G which is varied as a function of the overall gain which it is desired to obtain (volume adjustment). The signal input 94 receives a signal of order F which is varied to determine the proportion of mixing between the two signals applied to the mixer according to the invention (balancing adjustment).

We can show by the calculation that we obtain with this circuit signals A, B and C satisfying the following conditions
RRB - C = R2 (VG - V1) - R2 (VF - V2)
R1 (VG R (VF
3
R2 R
B - A = - (VG - V1) + R (VF - V2) 1 3
With these relationships between the control signals
A, B and C, the differences BC and BA vary in the same direction when VG varies and in the opposite direction when VF varies, which is the goal. Furthermore, if we introduce these values of BC and BA to calculate the output signal VO supplied by the circuit of FIG. 5, we obtain

It can be seen that the output of the mixer is a logarithmic function of the applied volume order G and balance F signals.

FIG. 7 represents another embodiment making it possible, from volume order and balancing signals, to supply control signals A, B and C suitable for controlling the circuits of FIGS. 4 and 5. Besides common elements with those of FIG. 6, the circuit of FIG. 7 comprises the following elements and interconnections.

The signal inputs 82 and 92 are supplied by a constant current source 10. The signal output 86 supplies the signal B and is connected to a terminal 100 via a resistor R2. This terminal 100 is connected to the power supply terminal Vcc via a resistor R2 and a diode D. The signal output 95 supplies the signal C. The signal output 96 supplies the signal A.

These signal outputs 95 and 96 are connected to a terminal 101 by means of diodes D. This terminal 101 is connected to the supply terminal Vcc by means of a resistor R2. The signal input 83 is connected to a reference voltage source V1. The signal input 93 is connected to a reference voltage source V2. The signal input 84 receives a signal of order G which is varied as a function of the overall gain which it is desired to obtain (volume adjustment).

The signal input 94 receives a signal of order F which is varied to determine the proportion of mixing between the two signals applied to the mixer according to the invention. The signal output 85 is connected to the input of a device 102 with two outputs respectively connected to terminals 100 and 101. This device 102 is such that the current on each of its outputs is equal to the current at its input. I1 can be constituted in a conventional manner using circuits of the "current mirror" type.

With the circuit of figure 7, we can show that we obtain signals A, B and C whose differences obey the following relationships

If we evaluate the signal VO at the output of the circuit of figure 5 using the elements above, we obtain

There is thus a volume control which is substantially identical to that obtained with the circuit of FIG. 6, that is to say with a logarithmic variation. On the other hand, the balancing adjustment is done linearly according to the order signals.

 We can therefore choose one or the other of the two solutions described in Figures 6 and 7 depending on the results desired for the mixer according to the invention.

We have more particularly described at the beginning of this text the application of the mixer according to the invention to a circuit for adjusting the volume and the tone of a signal with a sound frequency.

Nevertheless, it is clear that this mixer can be used for all conventional applications of mixers by having means of independent volume and balancing adjustments.

It will be noted that it will be possible to use the teachings of the present patent application to make a circuit no longer comprising two electronic potentiometers in parallel but a higher number, for example 3.

 The current. invention is not limited to the embodiments explicitly described above; it includes the various variants and generalizations thereof included in the field of claims below.

Claims (10)

 1. Remote control electronic circuit for mixing two signals, characterized in that it comprises a) two differential amplifiers connected in electronic potentiometers and arranged in parallel, each comprising a signal input and output and two control inputs, - each signal input being connected to one of the signals to be mixed, - the two signal outputs being interconnected to provide an output signal, the first control inputs being interconnected and receiving a first control signal, the second control input of the first electronic potentiometer receiving a second control signal, and  - the second control input of the second electronic potentiometer receiving a third control signal ;;  b) means for supplying these three control signals in response to two order signals, the first of which acts only on the volume of the output signal and the second only on the balancing of the two input signals in the signal output, the difference between the first and the second control signal and the difference between the first and the third control signal varying by the same value and in the same direction when the volume order signal varies and by the same value but in the opposite direction when the balancing order signal varies.  2. Circuit according to claim 1, characterized in that the relation between the control signals and the command signals is such that the relation between the output signal and the command signals is logarithmic.  3. Circuit according to claim 1, characterized in that the relationship between the control signals and the order signals is such that the volume of the output signal varies logarithmically as a function of the volume order signal and that the equilibrium between the two input signals in the output signal varies linearly as a function of the balancing order signal. 4. The circuit as claimed in claim 1, characterized in that the means for supplying the control signals from the command signals themselves comprise two differential amplifiers connected as electronic potentiometers,  - the first electronic potentiometer receiving at its signal input a constant current, at its first control input a reference voltage and at its second control input the volume order signal, and supplying at its first signal output the first control signal,  the second electronic potentiometer receiving at its first control input a reference voltage and at its second control input the balancing command signal, and supplying at its first signal output the second control signal and at its second output signal the third control signal.  5. Circuit according to claims 2 and 4, charac terized in that the electronic potentiometers of the means for supplying the control signals are connected so that the second signal output of the first electronic potentiometer is connected to the signal input of the second electronic potentiometer.  6. Circuit according to claims 3 and 4, characterized in that the two signal inputs of the two electronic potentiometers of the means for supplying control signals are connected to constant current sources and in that it further comprises two intermediate terminals (100 and 101) and a device <102) supplying its two outputs connected to each of the intermediate terminals with the same current as its input connected to the second signal output of the first electronic potentiometer; the first intermediate terminal being connected to the first signal output of the first electronic potentiometer by a resistor; and the second intermediate terminal being connected to the signal outputs of the second electronic potentiometer by diodes.  7. Electronic circuit according to claim 1, characterized in that it further comprises means for compensating the continuous components included in the input signals to be mixed, these compensation means comprising two additional electronic potentiometers connected with respect to the first and second electronic potentiometers of claim 1 in the same way as these first and second electronic potentiometers together. 8. A circuit for controlling the volume and the tone of an electrical signal at a sound frequency, characterized in that it comprises a mixing circuit according to any one of claims 1 to 7 and in that the signal for which it is desired to adjust the volume and the tone is applied to each of the signal inputs of the electronic potentiometers of claim 1, at least one filtering means being provided between the terminal for supplying the signal at audio frequency and one of the input terminals.  9. Volume and tone control circuit according to claim 8, characterized in that the signal whose volume and tone are to be adjusted is connected to the signal input of the first electronic potentiometer via a filter low pass and at the signal input of the second electronic potentiometer via a high pass filter. 10. A circuit for controlling the volume and the tone of a signal at a sound frequency, characterized in that it comprises two electronic potentiometers in parallel, each receiving at their input the signal to be processed by means of at least one filtering circuit. , and whose outputs are interconnected, these two electronic potentiometers being provided with control means so that their gain varies by the same value and in the same direction in response to a signal of volume order and the same value but in direction reverse in response to a tone command signal.