FR2491696A1 - ELECTRONICALLY CONTROLLED TRANSFER CHARACTERISTIC CIRCUIT - Google Patents

Abstract

ADJUSTMENT CIRCUIT, IN PARTICULAR TREBLE AND BASS, HAVING A PARTICULARLY LOW NOISE AND CAN BE CONTROLLED SIMPLY BY DIGITAL MEANS. THE CIRCUIT INCLUDES AN AMPLIFIER 1, TO THE OUTPUT TO WHICH IS CONNECTED THE SERIAL ASSEMBLY OF A CONDENSER 5 AND A CHAIN OF RESISTORS 41-45, WHOSE TAPS ARE CONNECTED ON THE ONE HAND, THROUGH A FIRST SWITCH 28, TO A REVERSE INPUT 11 OF THE AMPLIFIER AND, ON THE OTHER HAND, THROUGH A SECOND SWITCH 38, TO THE OUTPUT 36 OF THE TREBLE ADJUSTING DEVICE. APPLICATION: ADJUSTING THE SOUND VOLUME AND THE TONE.

Description

- "Transfer characteristic circuit controllable by

electronic way ".

  The invention relates to an electronically transferable transfer characteristic circuit, in particular an adjusting circuit, in which the input signal is

  sent to a controllable feedback amplifier.

  A circuit of this kind is known from patents

  German No. DE-PS 24 04 331 and No. DE-PS 22 62 089.

  The feedback from the amplifier and, therefore, the transfer characteristic of the circuit is varied because the current distribution of two differential amplifiers is varied in opposite directions by a DC voltage. The inputs of the two amplifiers

  differentials are coupled either through an integrated network

  Frequency dependent, so that a volume control device is obtained (No. DE-PS

  24 04 331), or through a network depending on the frequency

  quence (No. DE-PS 22 62 089) so that one obtains

  a tone control device (acute or severe).

  Circuits based on the variation of the

  current partition of two differential amplifiers

  have the disadvantage of a relatively loud noise.

  Moreover, when carrying out this circuit according to the integrated circuit technique, it is necessary to have, for the connection of the feedback network, at least three

  connections and, at least in the case of

  Positive tone adjustment, external mounting

  necessary for an integrated circuit of this kind is relative-

expensive.

  The object of the invention is to provide a circuit of the type described in the preamble so as to allow electronic control of the transfer characteristic without using current distribution circuits of the present invention.

aforementioned kind.

  The object according to the invention is achieved by the fact that a voltage divider provided with several sockets is connected to the output of the amplifier and that, through a first electronically controllable switch, the sockets are connected to an input amplifier and that, through a second electronically controllable switch, they

  are connected to the output of the circuit.

  The signal voltage has a different value at each tap of the voltage divider. If the first switch is connected to a jack having a relatively high signal voltage, the feedback

  is relatively strong and, therefore, the amplification

  is relatively low. If, on the other hand, the second

  switch is connected to a socket of this type, the am-

  plification is relatively important. A behavior

  diametrically opposite direction occurs whenever the switch is connected to a

  a relatively low voltage. In a mode of

  according to the invention, suitable for use in

  as a device for adjusting the treble, the

  Frequency dependent voltage divider is made

  so that at least part of the catch, the

  signal voltage decreases as the voltage increases

  tation of the frequency. In the structure of this circuit, it is expected that the voltage divider depending on the

  frequency is formed by the serial assembly of a condensa-

  and a chain of resistors with multiple outlets. If a circuit of this kind is realized according to the technique of the built-in cricuits, one needs only one connection which, through the chain of resistance realized according to the technique of the integrated circuits, is connected to the output of the amplifier and, through the capacitor, to a reference point

(the mass).

  In another embodiment in accordance with the

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  and appropriate to the application of the circuit as

  positive bass adjustment, it is expected that at least a portion of the taps, the signal voltage decreases as the frequency decreases. In the structure of this circuit, a resistance chain with

  several outlets are connected to the output of the amplifier.

  tor, and a capacitor is mounted between the output of the

  plifier and one of the catches. If, in this case also, the amplifier, the switch and the resistance chain are made according to the technique of the integrated circuits, it is only necessary to connect a single external component, the capacitor. For the connection of this capacitor,

  the integrated circuit must have two connections.

  In another embodiment of a provision

  such a system for the adjustment of the bass tone, that of the connections of the chain of resistors which is opposite the output of the amplifier is connected through a capacitor to a reference point (ground), and the impedance of the capacitor is low compared to the impedance of the resistor chain. Under these conditions, the capacitor connected in series with the resistor chain, preferably an electrolytic capacitor, serves to give the impedance of direct current between the tap and the reference point (for example the mass) a value so great that the

  reaction in DC voltage is important and that the

  This allows low suppression voltages at the output of the amplifier which, as known, increase

  with DC voltage amplification.

  In another embodiment of the

  According to the invention, the two switches are controlled so that one of the two switches receives

  always the full output voltage of the amplifier.

  If, for example, the resistance chain consists of n resistors and each of the two switches has n inputs, one of which can be connected each time

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  at its output, there are n combinations of switch positions, many of which are however superfluous, because, for example, a decrease in amplification

  is then compensated in whole or in part by an increase

  amplification. Thanks to the measurements according to this embodiment, the amplification range or the range of decrease and increase of acute (bass) can be obtained with only 2n-1 positions.

of switch.

  It should be noted here that the publication "Funkschau" 1980, Heft 5 already recommends a circuit for influencing audio signals, circuit in which the semiconductor switches are actuated by digital signals. The known circuit, which serves as a device for adjusting the sound volume, is relatively expensive because it requires an analog-to-digital converter with

  a resolution of 17 bits.

  The following description with regard to

  The accompanying drawings, given by way of non-limiting example, will better understand how the invention is carried out. Figure 1 is a block diagram of the

  circuit according to the invention and functioning as

Positive adjustment of the treble.

  FIG. 2 shows the shape of the frequency in different positions of the two switches according to

Figure 1.

  FIGS. 3a to 3c show equivalent diagrams of the circuit of FIG.

switch positions.

  Figure 4 shows a schematic diagram

  of a bass adjustment device in accordance with the

  vention. FIG. 5 represents the shape of the frequency of the circuits of FIG. 4 in different positions

two switches.

  Figures 6a to 6c show schemas

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  equivalents of the circuit of Figure 4 for different

switch positions.

  FIG. 1 shows a circuit which can serve as a treble control device in an audio amplifier to which a speaker for the reproduction of audio signals supplied by a radio tuner unit, a turn-on unit, is connected. disc or other such device. The circuit comprises an operational amplifier 1 having a vacuum amplification of 80 dB, an amplifier whose non-inverting input 12 receives the input signal ui. Through a chain of resistors 4, constituted by five resistors mounted in

  series 41 .... 45, the output connection 13 of the amplifier

  is connected to a capacitor 5 whose other

  end is grounded. Output 13 of the amplifier

  the four points common to the resistors 41 .... 45 are provided with five outlets 55 .... 51, which are

  connected respectively to five input connections 25 ....

  21 and 35 .... 31 of two switches-2 and 3. Depending on the position of these switches, which is indicated symbolically by a switching arm 28 or 38, one of the control inputs 21 .... 25, 31 .... 35 is connected to the output connection 26, 36 of the relevant switch 2, 3. The input to which the output 26, 36 is connected is determined by a digital information word which is applied to the five control inputs 27, 37 of the switch 2, 3. The output 26 of the switch 2 is connected to the inverting input 11 of the amplifier 1, while the output 36 of the switch 3 constitutes the output of the

  circuit from which the output signal u is taken. se-

  In the position of the switches 2 and 3, a different influence is exerted on the higher frequencies. In the switch position shown, in which, through the switch 3, the output of the

  circuit is connected directly to the output of the amplifier.

  tor, and in which the output 26 is connected to the socket

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  31 at the lower end of the chain of resistors, we obtain the equivalent diagram of Figure 3a. The value of

  the resistance R interposed between the output of the ampli-

  its inverting input corresponds to the sum of the values of the resistors 42 .... 45 of the resistor chain 4, while the value of the resistor Ro, which is small relative to R and serves to limit the increase or decrease in acute, corresponds to the value of the

  41 and is interposed, in series with the conden-

  5, between the inverting input 11 and the ground. Has

  relatively low frequencies, the impedance of

  5 is important compared to the impedance of the

  resistance R, so that the signal on the inverting input

  only 11 corresponds to the signal on the output

  of the amplifier 1. In this case, an ampli-

  voltage cation of 1 or O dB. At higher frequencies

  high, the impedance of the capacitor 5 is no longer

  glitzy in relation to the resistance R, so that the

  counter-reaction decreases, which corresponds to an increase

  amplification at higher frequencies (acute increase). The amplification as a function of the frequency then has the appearance as represented by the

  line in solid lines 121 in FIG.

  If, by not changing anything at the position of the

  3, the position of the switch 2 is varied so

  that entries 22, 23, 24 and 25 are connected successively

  at the output 26 of the switch 2 the resistance R0 increases step by step, while the resistance R decreases by the same value. As a result, at higher frequencies,

  the counter-reaction becomes stronger and stronger,

  to say that the amplification increase becomes smaller and smaller at higher frequencies, as indicated by the dotted lines 121 .... 124. If, finally, the input 25 of the switch 2 which is connected to the exit

  13 of the amplifier 1, is connected to the output of the

  26, the equivalent diagram of FIG. 3b is obtained. The value of the resistance R + R then corresponds to the

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  sum of the values of the resistors 41 .... 45. The full output voltage is then retrocoupled always at

  the input of the amplifier, so that the characteris-

  The obtained tick (line in solid lines 125) has a perfectly linear appearance if the internal resistance of the amplifier is substantially lower than the impedance.

existing on the output.

  If, as opposed to the switch position shown in FIG. 1, the input 25 of the switch 2 is connected to its output 26 and the input 31 of the switch

  3 is connected to its output 36, the equilibrium diagram

  shown in Figure 3c, the value of the

  sistance R corresponding again to the sum of the values of the resistors 42 .... 45, while the value of the

  resistance R is the value of resistance 41.

  Since, as already mentioned, at low frequencies, the impedance of capacitor 5 is high by

  ratio to the resistor R, the output signal of the amplifier

  The indicator 13 appears substantially unchanged at the output terminal 36 of the circuit. However, at higher frequencies

  the value of the resistance R is no longer neglected.

  geable with respect to the impedance of the capacitor 5,

  so that there is a decrease in the amplification

  at higher frequencies as indicated by the solid line 131 in Figure 2. In these

  conditions, the resistance R corresponding to the resistance

  this 41 of the chain of resistors 4, avoids a decrease

  too pronounced amplification at high frequencies

  Vees. If, now, switch 3 is switched from

  way that entries 32, 33 and 34 are connected successively

  at the output 36 of the switch 3 (while the input 25 of the switch 2 remains connected to its output

  26), the value of the resistance R0, in the equi-

  3c, is made larger and larger, while the value of the resistor R is decreased, which results in the decrease of amplification decreasing more and more at higher frequencies, as indicated

  by the dotted lines 132 .... 134 in FIG.

  If the switch 3 is in the upper position, the equivalent diagram as shown in FIG. 3b is again obtained as well as the independence of the amplification frequency as represented by the line 125. In addition to the switch positions described, other switch positions are possible. Thus, the inputs 23 and 33, to which the plug is connected

  53, can be linked to outputs 26, 36 of the

  2, 3, but, in this case, the decrease and increase of the treble compensate exactly, so that we obtain again a rate of linear frequency. In other switch positions, only partial compensation occurs, so that there is either an increase in the treble or a decrease in the treble, but the variation in the frequency response is between the limits 121 and 131, so these

  Switch positions are superfluous.

  For an appropriate dimensioning of the resistances

  these 41 .... 1 45 and capacitor 5, we can reach that at an upper limit frequency fg, for example at 20 kHz, the passage of one of the characteristics shown

  in Figure 2 to the adjacent feature, the amplification

  cation varies each time by 3 dB. For the variation

  quoted from the amplification of each 3 dB, it is possible to achieve with the circuit of Figure 1 increases or decreases of highs of each time about 12 dB. If it is a question of achieving even greater increases or decreases without increasing amplification variations, or the variation of the amplification at the transition from one characteristic to the other must be less than 3 dB, it is necessary to use a group of resistors with a number of resistors

even bigger.

  As already mentioned, the switches 2 and 3 are actuated by digital information words applied to their inputs 27, 37. Switches of this

  are known, for example in the form of cir-

  integrated TDA 1029, which is otherwise only suitable for switching four inputs

  two exits. We obtain a greater number of possibilities

  switching heads by cascade mounting, as described for example in the publication "Technische Informationen für die Industrie" No. 780530 (FIG. 23) of the Valvo Company. The two information words of a length of 5 bits, necessary for the control of the switches 2 and 3 are provided by a decoder circuit 6, which transforms a four-bit information word present on its input 62 into a word 10 bit positions, of which five bit positions are sent to

  the control inputs 27 and 37 of the switches 2 and 3.

  The decoder circuit may comprise a memory provided with a number of memory locations with ten bit positions corresponding to the number of possible switch positions (nine), which memory locations are addressed by the signal present on the input conductor. ; Moreover, this decoder circuit may also comprise a logic circuit consisting of gates, which circuit, for each four-position information word on the input, produces a ten-position information word on

the exit.

  The inputs 62 of the decoder circuit 6 are

  related to the output of a memory 7, whose content de-

  terminates the position of the switches 2 and 3. The memory 7 can be for example a down-counter whose counting direction can be controlled by the user through the unit 8, and which can count to nine, numbers successive ones being assigned to positions of the switches which correspond to neighboring characteristics, for example the characteristics 133 and 134 in FIG. 2, so that, during a counting cycle (down counting),

  the characteristics are covered almost continuously

  naked 121 to 131 (Figure 2) or in the opposite direction.

  It is also possible that the memory 7 is controlled by a microprocessor. If this microprocessor

  provides in series the four positions of a word of in-

  training, a record of

  who receives the information provided by the micropro-

  cessor, which is then transferred in parallel

reads to the memory 7.

  The circuit described above causes less

  noise than the known circuits, because both the amplification

  1, switches 2 and 3 can operate without the current distribution principle. The curves of increase and decrease of acute are an exact image of the other of the fact that, for the two functions, one uses the same chain of resistances and the same capacitor. If the circuit shown in FIG. 1 is produced according to the integrated circuit technique, all the elements represented, with the exception of

  capacitor 5, can be integrated on a "chip" '.

  Thus, it is sufficient to connect to such an integrated circuit only one external component (the capacitor 5) component that requires only one external connection (pin).

  At frequencies above the frequency

  the limit indicated by fg in Figure 2, and

  lifted so that the impedance of the capacitor 5 is

  low in relation to the resistance R0, and to

  In the case of higher quences than these, the transfer factor rate for a given switch position is again linear as a function of frequency - but its level is different for different switch positions. If the capacity of the capacitor 5 is so large that the "higher" frequencies, for which the amplification is a function of the frequency for a given switch position, are below the range of audiability, the circuit

  shown in FIG. 1 functions as a device

  tif adjustment of the sound volume. In this case, it is effective that the switch 2 is in a position

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  * 11 such that the inverting input 11 of the amplifier is connected to the socket 55 or 13 output of the amplifier 1, because, under these conditions, the feedback is maximum and there is the most distortions - as low as possible. For adjusting the sound volume,

  it is only the second switch 3 that must be controlled

  dice then. - If, in this case, we want to further decrease amplification jumps occurring from one switch position to another, we can go up in series with the

  resistance 41 another resistance having a value of

greater than that.

  FIG. 4 shows a so-called bass adjustment device, that is to say a circuit which

  allows you to increase or decrease

  low frequencies. The circuit of FIG. 4, which, in the same manner as the circuit of FIG. 1, can be controlled by control units 6, 7, 8 is distinguished from the latter, from the point of view of its structure, that in that the capacitor 5 is mounted between, on the one hand, the output 13 of the amplifier 1, which output is identical to the socket 55, and, on the other hand, the socket 51 provided between the two lower resistors 42 and 41 of the resistance chain, as well as the fact that the connections of the lower resistance 41 of

  the resistance chain 4 on the opposite side

  at the output 13 of the amplifier 1, is connected to ground through a capacitor 56 having a very large

  capacitance, preferably an electrolytic capacitor.

  This last capacitor serves to reduce the amplification in DC voltage of the amplifier 1 up to factor 1, so that the suppression voltages on the output

  become relatively weak. Where appropriate, this

  denser 56 can be removed if the connection of the

  41 which is connected to it, is connected in

  voltage at the same point to which is connected

  input 12 of the amplifier 1.

  If switches 2 and 3 are in the

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  position shown in Figure 4, we obtain the

  equivalent diagram shown in Figure 6a, in the

  which R1 indicates the series assembly of the resistors 42 to and the capacitor C1 corresponds to the capacitor 5, while the resistor R2 corresponds to the resistor 41

  (at all frequencies to be transferred, the impedance of

  denser 56 is negligible compared to other

  resistors). At the low frequencies of the transfer range, the impedance of the capacitor C1 is not yet negligible with respect to the resistance R2, so that, during the frequency argument, the counter-reaction stagnates and the amplification decreases until that, at medium transfer frequencies, the capacitor C 1 has, with respect to the resistor R2, substantially a short-circuit for the signal, so that the amplification takes the value 1, as indicated for the curve 221 in Figure 5. When the switch arm 28 is moved up and connects one of the jacks 52 .... 54 to the inverting input 11 of the amplifier 1, the value of which are increased the low frequencies (the bass) gradually decreases, as indicated by the amplification curves 224 in FIG. 5. If, finally, the jack, 55 of the resistance chain 4, or the output 13

  amplifier 1, is connected through the switching

  2 to the inverting input 11 of the amplifier, one

  obtains the equivalent diagram shown in Figure 6b.

  In this switching position, the chain of re-

  The sistances and the capacitor are, it is true, a charge function of the output of the amplifier, which is a function of the frequency, but the counter-action of the latter is independent of the frequency, so that the amplification, too, becomes independent of the frequency if the output resistance of this amplifier is small compared to the existing impedance on its output. We then obtain the linear appearance 225 of the amplification according to

of the frequency.

  If the switching position of the

  2 and 3 so that the inverting input 11 is connected to the socket 55 and the output is connected to the socket 51, the equivalent diagram shown on FIG.

  Figure 6c. In this case, the output voltage of the amplifier

  The indicator is divided by the voltage divider consisting of the elements R1, C1 and R2, the transfer factor

  the amplification diminishing as and when the

  frequency. This leads to the amplification curve

  231. If switch 3, instead of being connected

  at the socket 51, is connected to the sockets 52, 53 or 54, it obtains

  holds the gait of amplification 232 .... 234.

  In the bass adjustment device re-

  shown in FIG. 4, as in the device for adjusting the highs of FIG. 1, the distortions and the

  noise are significantly reduced compared to the

  known techniques for adjusting treble and bass

  electronically. In this case too, the appearance of the curves for increasing and decreasing the bass frequencies 221 .... 231 are an axial image of each other because, for the two functions, the same components are used.

Claims (11)

CLAIMS:   An electronically controllable transfer characteristic circuit, in particular an adjusting circuit, in which the input signal is sent to   a controllable feedback amplifier, characterized   in that a voltage divider (4, 5) having a plurality of   55) is connected to the output (13) of the amplifier (1) and in that, via a first switch (2) electronically controllable, the jacks (51 .... 55) are connected to an input inverter (11) of the amplifier (1) and that, through a second switch (3) controllable electronically, .. CLMF: they are connected to the output (36) of the circuit.   Circuit according to Claim 1, characterized in that the voltage divider (4, 5) has a factor of   Frequency dependent transfer.   3. Circuit according to any one of the claims   previously used, to be used as a   setting of the treble, characterized in that the division   The frequency-dependent voltage is realized so that at least a portion of the taps, the signal voltage decreases as the frequency increases. 4. Circuit according to claim 1, for use as a bass adjustment device, characterized in that the frequency-dependent voltage divider is designed so that at at least a portion of the taps the signal voltage decreases. as   and as the frequency decreases.   5. Circuit according to any one of the claims   1 to 3, characterized in that the frequency dependent voltage divider is constituted by the series circuit of a capacitor (5) and a resistor chain.   (4) having several holds (51 .... 55) (Figure 1).   6. Circuit according to any one of the claims   tions 1, 2 and 4, characterized in that a chain of   sistances with several outlets (51 .... 55) is connected   corded to the output (13) of the amplifier (1), and in that a capacitor (5) is mounted between the output   (13) of the amplifier and one of the sockets (51) (Figure 4).   7. Circuit according to claim 6, characterized in that that (51) of the connections of the resistance chain (4) which is opposite the output (13) of the amplifier (1) is connected to a reference point (the mass) through a capacitor (56), and in that the impedance of the capacitor (56) is small compared to   the impedance of the resistance chain (4).   8. Circuit according to claim 1, characterized in that, at the output of the amplifier, is connected the series circuit of a resistance chain provided with sockets and a capacitor whose impedance is low by   compared to the impedance of the chain of resistances.   9. Circuit according to any one of the claims   previous arrangements, characterized in that the two   mutators (2, 3) are controlled so that one (2 or 3) of the two switches always receive full voltage output of the amplifier (1).   Circuit according to any one of the claims   1, characterized in that as a switch (2 or 3) a semiconductor circuit is used whose switching position can be controlled by a digital information word on its control inputs (27). or 37).   Circuit according to Claim 10, characterized in that a memory circuit (7) coupled to the control inputs (27, 37) of the switches (2, 3) is provided, and in which the information words are memorized for   control inputs (23, 27) of the switches (2, 3).