CA1175505A - Circuit arrangement with electronically controllable transfer characteristic - Google Patents
Circuit arrangement with electronically controllable transfer characteristicInfo
- Publication number
- CA1175505A CA1175505A CA000387125A CA387125A CA1175505A CA 1175505 A CA1175505 A CA 1175505A CA 000387125 A CA000387125 A CA 000387125A CA 387125 A CA387125 A CA 387125A CA 1175505 A CA1175505 A CA 1175505A
- Authority
- CA
- Canada
- Prior art keywords
- circuit arrangement
- circuit
- output
- amplifier
- capacitor
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 239000003990 capacitor Substances 0.000 claims abstract description 39
- 230000007423 decrease Effects 0.000 claims description 11
- 230000001419 dependent effect Effects 0.000 claims description 8
- 239000004065 semiconductor Substances 0.000 claims description 2
- 238000010586 diagram Methods 0.000 description 12
- 230000009467 reduction Effects 0.000 description 10
- 238000006722 reduction reaction Methods 0.000 description 10
- 230000006870 function Effects 0.000 description 7
- 230000000875 corresponding effect Effects 0.000 description 5
- 230000004044 response Effects 0.000 description 4
- 238000012886 linear function Methods 0.000 description 2
- 230000005236 sound signal Effects 0.000 description 2
- 230000002238 attenuated effect Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 229910052729 chemical element Inorganic materials 0.000 description 1
- 230000001276 controlling effect Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- QHGVXILFMXYDRS-UHFFFAOYSA-N pyraclofos Chemical compound C1=C(OP(=O)(OCC)SCCC)C=NN1C1=CC=C(Cl)C=C1 QHGVXILFMXYDRS-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03G—CONTROL OF AMPLIFICATION
- H03G5/00—Tone control or bandwidth control in amplifiers
- H03G5/02—Manually-operated control
- H03G5/04—Manually-operated control in untuned amplifiers
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03G—CONTROL OF AMPLIFICATION
- H03G3/00—Gain control in amplifiers or frequency changers
- H03G3/001—Digital control of analog signals
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03G—CONTROL OF AMPLIFICATION
- H03G5/00—Tone control or bandwidth control in amplifiers
Landscapes
- Tone Control, Compression And Expansion, Limiting Amplitude (AREA)
- Amplifiers (AREA)
- Networks Using Active Elements (AREA)
Abstract
ABSTRACT:
The invention relates to a control device cir-cuit, specifically a low-noise treble or bass-control device, which is digitally controllable in a simple man-ner. It comprises an amplifier, whose output is connected to the series arrangement of a capacitor and a tapped resistor chain, the taps of said resistor chain being con-nected to an inverting input of the amplifier via a first switch and to the output of the control device via a second switch.
The invention relates to a control device cir-cuit, specifically a low-noise treble or bass-control device, which is digitally controllable in a simple man-ner. It comprises an amplifier, whose output is connected to the series arrangement of a capacitor and a tapped resistor chain, the taps of said resistor chain being con-nected to an inverting input of the amplifier via a first switch and to the output of the control device via a second switch.
Description
1175505 ~
PHD 80141C 1 10.9.1981 Circuit arrangement with electronically controllable transfer characteristic.
The invention relates to a circuit arrangement with an electronically controllable transfer characteris-tic, specifically a tone or volume control circuit, the input signal being applied to an amplifier having con-trollable negative feedback.
Such a circuit arrangement is known from DE-PS
24 04 331 and DE-PS 22 62 089. The negative feedback of the amplifier, and consequently the transfer characteris-tic of the circuit arrangement, is varied in that the cur-rent distribution between two differential amplifiers is varied in an opposite sense by a direct voltage. The in-puts of the two differential amplifiers are coupled to each other either via a frequency-independent network so that a volume control device is obtained (DE PS 24 04 331), 15 or via a frequency-dependent network (DE-PS 22 62 o89), so that a tone control device (treble or bass control) is ob-tained O
A disadvantage of circuit arrangements which are based on the variation of the current distribution between two differential amplifiers is that they exhibit a compa-ratively large amount of noise. Moreover, if such a cir-cuit arrangement is constructed as an integrated circuit there need be provided at least three external connection terminals for connection of the negative feedback network and the external connections to such an integrated circuit are comparatively intricate, at least when said circuit is used as a tone control device.
It is an object of the present invention to de-sign a circuit arrangement of the type mentioned in the opening paragraph in such a way that the transfer charac-teristic can be controlled electronically without the useof current distribution circuits of the said type.
PHD 80141C 2 10.9.1981 According to the invention this object is ~ achieved in that a voltage divider circuit having a plu-rality of taps is connected to the output of the amplifier and in that the taps are connected to an inverting input of the amplifier via a first electronicall~ controllable switch and to the output of the circuit arrangement via a second electronically controllable switch.
The signal voltage on each tap of the voltage divider circuit has a different value. If the first switch is connected to a tap carrying a comparatively high signal voltage, the negative feedback will be comparatively strong nd the gain will consequently be comparatively low. However, if the second switch is connected to such a tap, the gain will be comparatively high. The situation is exactly reversed when the switch is connected to a tap carrying a comparatively low voltage. In a further embodiment of the invention, intended for use as a treble control device, the frequency-dependent voltage divider circuit is designed so that the signal voltage on at least 2Q some of the taps decreases at increasing frequency. In one embodiment of this circuit arrangement the frequercy-de-pendent voltage divider circuit comprises the series ar-rangement of a capacitor and a resistor chain with a plu-rality of taps.
When such a circuit arrangement is constructed as an integrated circuit only a single connection is re-quired, which via the integrated resistor chain is con-nected to the amplifier output and via the capacitor to a reference point (earth).
In a further embodiment of the invention, which is suitable as a base control device, the signal voltage on at least some of the taps decreases as the frequency decreases. In an embodiment of this circuit arrangement a resistor chain comprising a plurality of taps is con-nected to the amplifier output and a capacitor is arrang-ed between the amplifier output and one of the taps. If the amplifier, the switches and the resistor chain are PHD 80141C 3 10.9.1981 again constructed in an integrated form only one external component, the capacitor, needs to be connected, For the connection of this capacitor the integrated circuit should comprise two connections.
In a further embodiment of such a bass control device the terminal of the resistor chain which is remote from the amplifier output is connected to a reference point (earth) via a capacitor and the impedance of the capacitor is low relative to the-impedance of the resis-tor chain. The capacitor in sëries with the resistor chain, which capacitor is suitably an electrolytic capaci-tor, serves to make the d.c. impedance between the tap`and the reference point (for example, earth) so high that the d.c. negative feedback is strong and the d.c. gain is unity.
This minimizes offset voltages on the amplifier output, which voltages as is known increase as the d.c. gain in-creases.
In a further embodiment of the invention the two switches are controlled in such a way that one of the two switches always conveys the full output voltage of the amplifier. If, for example, the resistor chain com-prises n divider resistors and each of the two switches has n inputs, with one input at any time being connected to its output, this yields n combinations of switch po-sitions, some of which are redundant, because, for exam-ple, a treble reduction is fully or partly compensated for by a treble boost. Owing to the steps in accordance with this embodiment the entire treble (bass) control range re-quires only 2(n-1) switch positions.
In this respect it is to be noted that from the magazine "Funkschau" 1980, Vol. 5, a circuit arrangement is known for influencing audio signals, in which circuit arrangement the semiconductor switches are actuated by digital signals. However, the known circuit arrangement, which serves as a volume control device, is comparatively expensive, because it requires the use of an analog-to-digital converter with a resolution of 17 bits.
117S50s PHD 80141C 4 10.9.1981 The invention will now be described in more ~ detail with reference to the drawings. In the drawings Fig. 1 is a circuit diagram of the circuit ar-rangement in accordance with the invention, which func-tions as a treble control device, Fig. 2 represents the frequency response forvarious positions of the two switches in the arrangement of Fig. 1, Fig. 3a to 3c represent equivalent diagrams of the circuit arrangement of Fig. 1 for various switch po-sitions, Fig. 4 is a circuit diagram of a bass controldevice in accordance with the invention, Fig. 5 represents the frequency response of the circuit arrangement of Fig. 4 for various positions of the two switches, Figs. 6a to 6c-represent equivalent diagrams of the circuit arrangement of Fig. 4 for various switch posi-tions.
Fig. 1 shows a circuit arrangement, which may be used as a treble control device in an audio amplifier to which a loudspeaker is connected, which loudspeaker serves for the reproduction of audio signals supplied by a radio tuner, a record player or the like. The circuit arrangement comprises an operational amplifier 1 with an open-loop gain of 80 dB, whose non-inverting input 12 re-ceives the input signal ui. The output terminal 13 of the amplifier is connected to a capacitor 5 via a resistor chain 4 comprising five series-connected resistors 41 ... 45, the other end of said capacitor being connected to earth. The output 13 of the amplifier and the four junction points between the resistors 41 ... 45 are pro-vided with five taps 55 ... 51, which are connected to the five input terminals 25 ... 21 and 35 .~.. 31 respec-tively of two switches 2 and 3. Depending on the positionsof said switches, which are symbolically represented by a switch arm 28 and 3B respectively, one of the control in-PHD 80141C 5 10.9.1981 puts 21 ... 25 or 31 ... 35 is connected to the respective output terminal 26 or 36 of the relevant switch 2 or 3.
Which input is connected to the output 26 or 36 is deter-mined by a digital data word applied to the five control inputs 27 or 37 of the respective switches 2 and 3.
The output 26 of the switch 2 is connected to the inverting input 11 of the amplifier 1, whilst the out-put 36 of the switch 3 constitutes the output of the/-cir-cuit arrangement, on which output the output signal uO is 10 available. The higher frequencies are then influenced in different ways depending on the switch positions of the switches 2 and 3.
In the switch position shown, in which the out-put of the circuit arrangement is connected directly to 15 the output of the amplifier via the swi~ch 3 and in which the output 26 is connected to the tap 31 at the lower end of the resistor chain~ the equivalent diagram of Fig. 3 is valid. The resistance R between the output of the ampli-fier and its inverting input corresponds to the sum of 20 the values of the divider resistors 42 45 of the re-sistor chain 4~ whilst the resistance Ro~ which is low in comparison with R and which serves to limit the treble boost or reduction~ corresponds to the value of the resis-tor 41 and, in series with the capacitor 5, is included 25 between the inverting input 11 and earth. At comparatively low frequencies the impedance of the capacitor 5 is high in comparison with the impedance of the resistance R~ so that the signal on the inverting input 11 substantialIy corresponds to the signal on the output of the amplifier 30 1. In this case a voltage gain of 1 or 0 dB is obtained.
At higher frequencies the impedance of the capacitor 5 may no longer be ignored in comparison with the resistance R, so that the negative feedback decreases, which corres-ponds to an increase of the gain at higher frequencies 35 (treble boost). Thus, the gain as a function of the fre-quency will vary as represented by the uninterrupted line 121 in Fig. 2.
PHD 80141C 6 10.9.1981 If~ with the same position of the switch 3, the position of the switch 2 is changed so that the inputs 22~
23, 24 and 25 are consecutively connected to the output 26 of the switch 2, the resistance Ro will increase stepwise, - 5 whilst the resistance R will decrease by the same amount.
Thus~ at the higher frequencies the negative feedback will increase continually, that is, the boost at the higher frequencies will be reduced continually, as is represented by the broken lines, 122.... 124. If finally the input 25 of the switch 2, which input is connected to the output 13 of the amplifier 1, is connected to the switch output 26, the equivalent diagram shown in Fig. 3b is valid. The resistance Ro + R then corresponds to the sum of the values of the resistors 4t ...45. The full output voltage is then always fed back to the amplifier input, so that the re-sulting characteristic (continuous line 125) is perfectly linear if the internal resistance of the amplifier is sub-stantially smaller than the impedance existing at the out-put.
If, in contradistinction 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 to the output 36, the equivalent diagram of Fig. 3c is valid, the resistance R again corresponding to the sum of the values of the resistors 42....45 and the resistance Ro corres-ponding to the value of the resistor 41. Since, as already stated, the impedance of the capacitor 5 at low frequenci~
is high in comparison with the resistance R, the output signal of the amplifier 13 appears substantially unchanged on the output terminal 36 of the circuit arrangement. At higher frequencies, however, the resistance R is no longer negligible in comparison with the impedance of the capaci-tor 5, so that the gain decreases towards the higher fre-quencies, as represented by the uninterrupted line 131 in Fig. 2. The resistance Ro~ which corresponds to the divider resistor 41 of the resistor chain 4, then prevents an ex-cessive reduction of the gain at high frequencies. If the PHD 80141C 7 10.9,1981 switch 3 is now changed over, so that consecutively the inputs 32~ 33, 34 are connected to the output 36 of the switch 3 (the input 25 of the switch 2 remaining connected to its output 26), the resistance Ro in the equivalent diagram of Fig. 3~ increases continuously, whilst the resistance R is reduced, so that the gain reduction at higher frequencies decreases continuously, as is represent-ed by the broken lines 132...134 in Fig. 2. In the upper position of the switch 3 the equivalent diagram of Fig. 3b and the frequency-independence of the gain as represented by the line 125 are obtained again.
In addition to the switch positions described, other positions are possible. For example, the inputs 23 and 33~ to which the tap 53 is connected~ may be connected 15 to the outputs 26 and 36 of the respective switches 2 and 3, but the treble reduction and treble boost then exactly compensate for each other so that again a linear frequency response is obtained. In other switch positions only a partial compensation is obtained, so that either a treble boost or treble reduction is obtained, but the variation of the frequency response still varies between the limits 121 and 131, so that these switch positions are super-fluous.
When the divider resistors 141...45 and the ca-pacitor 5 are suitably dimensioned, it can be achieved that the gain for an upper limit frequency fg, for exam-ple at 20 kHz, between adjacent characteristics shown in Fig. 2 varies by, for example 3 dB. For the specified gain variation steps of 3 dB, overall treble boosts or reductions of + 12 dB can be obtained with the circuit arrangement of Fig. 1. If even greater boosts or reduc-tions are required without the gain variations being increased, or if the gain variation between adjacent characteristics should be smaller than 3 dB~ a resistor chain with even more divider resistors should be employed.
As already stated~ the switches 2 and 3 are changed over by digital data words on their respective PHD 80141C 8 10.9.1981 inputs 27 and 37. Such switches are known, for example in the form of the integrated circuit Philips TDA 1029, which, however~ is designed for switching over from four inputs to two outputs. A greater number o~ switching pos-sibilities is obtained by cascading, as is for exampledescribed in the Magazine "Technische Informationen f~r die Industrie~ no. 780530 (Fig. 23) published by Valvo.
The two 5-bit data words required for controlling the switches 2 and 3 are supplied by a code converter circuit 6~ which converts a four_bit data word appearing on its input 62 into a ten-bit data word~ of which five bits are each applied to the control inputs 27 and 37 of the switches 2 and 3. The code converter circuit may comprise a memory having a number of ten-bit storage locations corresponding to the number of possible switch positions (nine), which locations are addressed by the signal on the input line 62; it may alternatively comprise a logic circuit comprising gates~ which circuit produces a ten-bit data word on the output for each four-bit data word on the input~
The inputs 62 of the code converter circuit 6 are connected to the output of a memory 7, whose content determines the position of the switches 2 and 3. The me-mory 7 may for example be an up-down counter~ which can count to nine and whose counting direction can be con-trolled by the user via the unit 8, consecutive countsbeing assigned to the switch positions which correspond to adjacent characteristics, for example the characteris-tics 133 and 134 in Fig. 2, so that during a count-up (down) cycle the characteristics 121 to 131 (Fig. 2) are covered quasi-continuously in the one or the other direc-tion.
However, the memory 7 may also be controlled by a microprocessor. If said microprocessor serially supplies the four bits of a data word~ a shift register is required into which the data supplied by the microprocessor is load-ed, which data is then transferred in parallel to the me-PHD 80141C 9 10.9.1981 !mory 7.
The circuit arrangement described produces a smaller amount of noise than the known circuit arrange-ments, because the operation of both the amplifier and the switches 2 and 3 is not based on the current distribution principle. The treble boost and reduction curves are exactly mirror-inverted relative to each other, because for both functions the same resistor chain and the same capacitor are used. If the circuit arrangement shown in Fig. 1 is manufactured as an integrated circuit, all the elements shown, except for the capacitor 5~ can be in-tegrated on one chip~ Thus, only one external circuit ele-ment (the capacitor 5) must be connected to such an in-tegrated circuit and for this purpose only one external connection (pin) is needed.
For frequencies above the limit frequency fg in Fig. 2 which are so high that the impedance of the capa-citor 5 is low in comparison with the resistance Ro and for frequencies higher than the first-mentioned frequen-cies the transfer characteristics is again in a linearfunction of the frequency for a specific switch position~
but it is situated at different levels for different switch positions. If the capacitance of the capacitor 5 is now made so high that the "higher" frequencies, for which the gain is frequency-dependent for a specific switch position, are situated beyond the range of audi-bility, the circuit arrangement shown in Fig. 1 will function as a volume-control device. Suitably, if the switch 2 is in such a switch position, the inverting in-put 11 of the amplifier then remains connected to the tap55 or the output 13 of the amplifier 1, because in that case the negative feedback is a maximum and the distor-tion is minimal. Then, only the second switch 3 needs to be controlled for adjusting the volume. - If the gain variation steps for different switch positions should be further reduced, a further resistor having a value higher than the resistor 41 may be arranged in series with said ~175SO~i PHD 80141C 10 10.9.1981 last-mentioned resistor.
~ Fig. 4 represents a so-called bass-control de-vice~ that is a circuit arrangement by means of which the lower frequencies can be boosted or attenuated at option.
The circuit design of the circuit arrangement of Fig. 4~
which arrangement can be controlled by the control units 6, 7, 8 in the same way as the circuit arrangement of Fig.
1, dlffers from t~e last-mentioned circuit arrangement only in that the capacitor 5 between the output 13 of the amplifier 1, which output corresponds to the tap 55, and the tap 51 is arranged between the two lower resistors 42 and 41 of the resistor chain, and in that the terminal of the lower resistor 41 of the resistor chain 4 which is remote from the output 13 of the amplifier 1 is connected to earth via a capacitor 56 with a very higher capacitance~
suitably an electrolytic capacitor. The function of the last-mentioned capacitor is to reduce the d.c. gain of the amplifier 1 to unity, so that the offset voltages on the output become comparatively small. Said capacito 56 may be dispensed with if the terminal of the resistor 41 which is connected to said capacitor is d.c. coupled to the point to which the input 12 of the amplifier 1 is con-nected.
In the switch position of the switches 2 and 3 as shown in Fig. 4 the equivalent diagram of Fig. 6a is valid for the circuit arrangement, R1 representing the series arrangement of the resistors 42 to 45, the capaci-- tor C1 corresponding to the capacitor 5, and the resistor R2 corresponding to the resistor 41 (for all the frequen-cies to be transmitted the impedance of the capacitor 56is negligible relative to the other resistances). For the lower frequencies of the transmission range the impedance of the capacitor C1 is not yet negligible relative to that of the resistor R2, so that the negative feedback in-creases and the gain decreases at increasing frequency,until at the mid-range frequencies the capacitor C1, in comparison with the resistor R2, substantially presents PHD 80141C 11 10.9.1981 a short-circuit to the signal, as a result of which the gain assumes the value 1, as is represented by the gain cur~e 221 in Fig. 1. If the switch arm 28 is set to the upper position and one of the taps 52 . . . 54 is connected to the inverting input 11 of the amplifier 1, the extent to which the low frequencies (bass tones) are boosted de-creases continually, as is represented by the gain curves 224 in Fig. 5. If finally the tap 55 of the resistor chain 4, or the output 13 of the amplifier 1, is connected to the inverting input 11 of the amplifier via the switch 2, the equivalent diagram of Fig. 6b will be valid.' In this switch position the resistor chain and the capacitor function as a frequency-dependent load of the amplifier output, but its negative feedback is frequency-independent, so that the gain also becomes frequency-inde~endent if the output resistance of said amplifier is low in comparison with the impedance acting on its output. The gain then varies as a linear function of the frequency, as is re-presented by 225.
If the switch position of the switches 2 and 3 is changed in such a way that the inverting input 11 is connected to the tap 55 and the output to the tap 51, the equivalent diagram shown in Fig. 6c is obtained. The out-put voltage of the amplifier is then divided by the vol-tage divider comprising the elements R1, C1 and R2, thetransfer coefficient or the ga~n then being reduced at decreasing frequency. This results in the gain curve 231.
If the switch 3 is connected to the taps 52, 53 or 54 instead of to the tap 51, the gain characteristics 232 30 . . .234 are obtained.
For the bass-control device shown in Fig. 4 and the treble-control device shown in ~ig. 1 the distortion and noise are reduced substantially in comparison with the known electronically controllable treble and bass-control devices. The bass-boost and reduction curves 221 .. 231 are then again strictly mirror-inverted relative to each other~ because the same components are utilized for both functions.
PHD 80141C 1 10.9.1981 Circuit arrangement with electronically controllable transfer characteristic.
The invention relates to a circuit arrangement with an electronically controllable transfer characteris-tic, specifically a tone or volume control circuit, the input signal being applied to an amplifier having con-trollable negative feedback.
Such a circuit arrangement is known from DE-PS
24 04 331 and DE-PS 22 62 089. The negative feedback of the amplifier, and consequently the transfer characteris-tic of the circuit arrangement, is varied in that the cur-rent distribution between two differential amplifiers is varied in an opposite sense by a direct voltage. The in-puts of the two differential amplifiers are coupled to each other either via a frequency-independent network so that a volume control device is obtained (DE PS 24 04 331), 15 or via a frequency-dependent network (DE-PS 22 62 o89), so that a tone control device (treble or bass control) is ob-tained O
A disadvantage of circuit arrangements which are based on the variation of the current distribution between two differential amplifiers is that they exhibit a compa-ratively large amount of noise. Moreover, if such a cir-cuit arrangement is constructed as an integrated circuit there need be provided at least three external connection terminals for connection of the negative feedback network and the external connections to such an integrated circuit are comparatively intricate, at least when said circuit is used as a tone control device.
It is an object of the present invention to de-sign a circuit arrangement of the type mentioned in the opening paragraph in such a way that the transfer charac-teristic can be controlled electronically without the useof current distribution circuits of the said type.
PHD 80141C 2 10.9.1981 According to the invention this object is ~ achieved in that a voltage divider circuit having a plu-rality of taps is connected to the output of the amplifier and in that the taps are connected to an inverting input of the amplifier via a first electronicall~ controllable switch and to the output of the circuit arrangement via a second electronically controllable switch.
The signal voltage on each tap of the voltage divider circuit has a different value. If the first switch is connected to a tap carrying a comparatively high signal voltage, the negative feedback will be comparatively strong nd the gain will consequently be comparatively low. However, if the second switch is connected to such a tap, the gain will be comparatively high. The situation is exactly reversed when the switch is connected to a tap carrying a comparatively low voltage. In a further embodiment of the invention, intended for use as a treble control device, the frequency-dependent voltage divider circuit is designed so that the signal voltage on at least 2Q some of the taps decreases at increasing frequency. In one embodiment of this circuit arrangement the frequercy-de-pendent voltage divider circuit comprises the series ar-rangement of a capacitor and a resistor chain with a plu-rality of taps.
When such a circuit arrangement is constructed as an integrated circuit only a single connection is re-quired, which via the integrated resistor chain is con-nected to the amplifier output and via the capacitor to a reference point (earth).
In a further embodiment of the invention, which is suitable as a base control device, the signal voltage on at least some of the taps decreases as the frequency decreases. In an embodiment of this circuit arrangement a resistor chain comprising a plurality of taps is con-nected to the amplifier output and a capacitor is arrang-ed between the amplifier output and one of the taps. If the amplifier, the switches and the resistor chain are PHD 80141C 3 10.9.1981 again constructed in an integrated form only one external component, the capacitor, needs to be connected, For the connection of this capacitor the integrated circuit should comprise two connections.
In a further embodiment of such a bass control device the terminal of the resistor chain which is remote from the amplifier output is connected to a reference point (earth) via a capacitor and the impedance of the capacitor is low relative to the-impedance of the resis-tor chain. The capacitor in sëries with the resistor chain, which capacitor is suitably an electrolytic capaci-tor, serves to make the d.c. impedance between the tap`and the reference point (for example, earth) so high that the d.c. negative feedback is strong and the d.c. gain is unity.
This minimizes offset voltages on the amplifier output, which voltages as is known increase as the d.c. gain in-creases.
In a further embodiment of the invention the two switches are controlled in such a way that one of the two switches always conveys the full output voltage of the amplifier. If, for example, the resistor chain com-prises n divider resistors and each of the two switches has n inputs, with one input at any time being connected to its output, this yields n combinations of switch po-sitions, some of which are redundant, because, for exam-ple, a treble reduction is fully or partly compensated for by a treble boost. Owing to the steps in accordance with this embodiment the entire treble (bass) control range re-quires only 2(n-1) switch positions.
In this respect it is to be noted that from the magazine "Funkschau" 1980, Vol. 5, a circuit arrangement is known for influencing audio signals, in which circuit arrangement the semiconductor switches are actuated by digital signals. However, the known circuit arrangement, which serves as a volume control device, is comparatively expensive, because it requires the use of an analog-to-digital converter with a resolution of 17 bits.
117S50s PHD 80141C 4 10.9.1981 The invention will now be described in more ~ detail with reference to the drawings. In the drawings Fig. 1 is a circuit diagram of the circuit ar-rangement in accordance with the invention, which func-tions as a treble control device, Fig. 2 represents the frequency response forvarious positions of the two switches in the arrangement of Fig. 1, Fig. 3a to 3c represent equivalent diagrams of the circuit arrangement of Fig. 1 for various switch po-sitions, Fig. 4 is a circuit diagram of a bass controldevice in accordance with the invention, Fig. 5 represents the frequency response of the circuit arrangement of Fig. 4 for various positions of the two switches, Figs. 6a to 6c-represent equivalent diagrams of the circuit arrangement of Fig. 4 for various switch posi-tions.
Fig. 1 shows a circuit arrangement, which may be used as a treble control device in an audio amplifier to which a loudspeaker is connected, which loudspeaker serves for the reproduction of audio signals supplied by a radio tuner, a record player or the like. The circuit arrangement comprises an operational amplifier 1 with an open-loop gain of 80 dB, whose non-inverting input 12 re-ceives the input signal ui. The output terminal 13 of the amplifier is connected to a capacitor 5 via a resistor chain 4 comprising five series-connected resistors 41 ... 45, the other end of said capacitor being connected to earth. The output 13 of the amplifier and the four junction points between the resistors 41 ... 45 are pro-vided with five taps 55 ... 51, which are connected to the five input terminals 25 ... 21 and 35 .~.. 31 respec-tively of two switches 2 and 3. Depending on the positionsof said switches, which are symbolically represented by a switch arm 28 and 3B respectively, one of the control in-PHD 80141C 5 10.9.1981 puts 21 ... 25 or 31 ... 35 is connected to the respective output terminal 26 or 36 of the relevant switch 2 or 3.
Which input is connected to the output 26 or 36 is deter-mined by a digital data word applied to the five control inputs 27 or 37 of the respective switches 2 and 3.
The output 26 of the switch 2 is connected to the inverting input 11 of the amplifier 1, whilst the out-put 36 of the switch 3 constitutes the output of the/-cir-cuit arrangement, on which output the output signal uO is 10 available. The higher frequencies are then influenced in different ways depending on the switch positions of the switches 2 and 3.
In the switch position shown, in which the out-put of the circuit arrangement is connected directly to 15 the output of the amplifier via the swi~ch 3 and in which the output 26 is connected to the tap 31 at the lower end of the resistor chain~ the equivalent diagram of Fig. 3 is valid. The resistance R between the output of the ampli-fier and its inverting input corresponds to the sum of 20 the values of the divider resistors 42 45 of the re-sistor chain 4~ whilst the resistance Ro~ which is low in comparison with R and which serves to limit the treble boost or reduction~ corresponds to the value of the resis-tor 41 and, in series with the capacitor 5, is included 25 between the inverting input 11 and earth. At comparatively low frequencies the impedance of the capacitor 5 is high in comparison with the impedance of the resistance R~ so that the signal on the inverting input 11 substantialIy corresponds to the signal on the output of the amplifier 30 1. In this case a voltage gain of 1 or 0 dB is obtained.
At higher frequencies the impedance of the capacitor 5 may no longer be ignored in comparison with the resistance R, so that the negative feedback decreases, which corres-ponds to an increase of the gain at higher frequencies 35 (treble boost). Thus, the gain as a function of the fre-quency will vary as represented by the uninterrupted line 121 in Fig. 2.
PHD 80141C 6 10.9.1981 If~ with the same position of the switch 3, the position of the switch 2 is changed so that the inputs 22~
23, 24 and 25 are consecutively connected to the output 26 of the switch 2, the resistance Ro will increase stepwise, - 5 whilst the resistance R will decrease by the same amount.
Thus~ at the higher frequencies the negative feedback will increase continually, that is, the boost at the higher frequencies will be reduced continually, as is represented by the broken lines, 122.... 124. If finally the input 25 of the switch 2, which input is connected to the output 13 of the amplifier 1, is connected to the switch output 26, the equivalent diagram shown in Fig. 3b is valid. The resistance Ro + R then corresponds to the sum of the values of the resistors 4t ...45. The full output voltage is then always fed back to the amplifier input, so that the re-sulting characteristic (continuous line 125) is perfectly linear if the internal resistance of the amplifier is sub-stantially smaller than the impedance existing at the out-put.
If, in contradistinction 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 to the output 36, the equivalent diagram of Fig. 3c is valid, the resistance R again corresponding to the sum of the values of the resistors 42....45 and the resistance Ro corres-ponding to the value of the resistor 41. Since, as already stated, the impedance of the capacitor 5 at low frequenci~
is high in comparison with the resistance R, the output signal of the amplifier 13 appears substantially unchanged on the output terminal 36 of the circuit arrangement. At higher frequencies, however, the resistance R is no longer negligible in comparison with the impedance of the capaci-tor 5, so that the gain decreases towards the higher fre-quencies, as represented by the uninterrupted line 131 in Fig. 2. The resistance Ro~ which corresponds to the divider resistor 41 of the resistor chain 4, then prevents an ex-cessive reduction of the gain at high frequencies. If the PHD 80141C 7 10.9,1981 switch 3 is now changed over, so that consecutively the inputs 32~ 33, 34 are connected to the output 36 of the switch 3 (the input 25 of the switch 2 remaining connected to its output 26), the resistance Ro in the equivalent diagram of Fig. 3~ increases continuously, whilst the resistance R is reduced, so that the gain reduction at higher frequencies decreases continuously, as is represent-ed by the broken lines 132...134 in Fig. 2. In the upper position of the switch 3 the equivalent diagram of Fig. 3b and the frequency-independence of the gain as represented by the line 125 are obtained again.
In addition to the switch positions described, other positions are possible. For example, the inputs 23 and 33~ to which the tap 53 is connected~ may be connected 15 to the outputs 26 and 36 of the respective switches 2 and 3, but the treble reduction and treble boost then exactly compensate for each other so that again a linear frequency response is obtained. In other switch positions only a partial compensation is obtained, so that either a treble boost or treble reduction is obtained, but the variation of the frequency response still varies between the limits 121 and 131, so that these switch positions are super-fluous.
When the divider resistors 141...45 and the ca-pacitor 5 are suitably dimensioned, it can be achieved that the gain for an upper limit frequency fg, for exam-ple at 20 kHz, between adjacent characteristics shown in Fig. 2 varies by, for example 3 dB. For the specified gain variation steps of 3 dB, overall treble boosts or reductions of + 12 dB can be obtained with the circuit arrangement of Fig. 1. If even greater boosts or reduc-tions are required without the gain variations being increased, or if the gain variation between adjacent characteristics should be smaller than 3 dB~ a resistor chain with even more divider resistors should be employed.
As already stated~ the switches 2 and 3 are changed over by digital data words on their respective PHD 80141C 8 10.9.1981 inputs 27 and 37. Such switches are known, for example in the form of the integrated circuit Philips TDA 1029, which, however~ is designed for switching over from four inputs to two outputs. A greater number o~ switching pos-sibilities is obtained by cascading, as is for exampledescribed in the Magazine "Technische Informationen f~r die Industrie~ no. 780530 (Fig. 23) published by Valvo.
The two 5-bit data words required for controlling the switches 2 and 3 are supplied by a code converter circuit 6~ which converts a four_bit data word appearing on its input 62 into a ten-bit data word~ of which five bits are each applied to the control inputs 27 and 37 of the switches 2 and 3. The code converter circuit may comprise a memory having a number of ten-bit storage locations corresponding to the number of possible switch positions (nine), which locations are addressed by the signal on the input line 62; it may alternatively comprise a logic circuit comprising gates~ which circuit produces a ten-bit data word on the output for each four-bit data word on the input~
The inputs 62 of the code converter circuit 6 are connected to the output of a memory 7, whose content determines the position of the switches 2 and 3. The me-mory 7 may for example be an up-down counter~ which can count to nine and whose counting direction can be con-trolled by the user via the unit 8, consecutive countsbeing assigned to the switch positions which correspond to adjacent characteristics, for example the characteris-tics 133 and 134 in Fig. 2, so that during a count-up (down) cycle the characteristics 121 to 131 (Fig. 2) are covered quasi-continuously in the one or the other direc-tion.
However, the memory 7 may also be controlled by a microprocessor. If said microprocessor serially supplies the four bits of a data word~ a shift register is required into which the data supplied by the microprocessor is load-ed, which data is then transferred in parallel to the me-PHD 80141C 9 10.9.1981 !mory 7.
The circuit arrangement described produces a smaller amount of noise than the known circuit arrange-ments, because the operation of both the amplifier and the switches 2 and 3 is not based on the current distribution principle. The treble boost and reduction curves are exactly mirror-inverted relative to each other, because for both functions the same resistor chain and the same capacitor are used. If the circuit arrangement shown in Fig. 1 is manufactured as an integrated circuit, all the elements shown, except for the capacitor 5~ can be in-tegrated on one chip~ Thus, only one external circuit ele-ment (the capacitor 5) must be connected to such an in-tegrated circuit and for this purpose only one external connection (pin) is needed.
For frequencies above the limit frequency fg in Fig. 2 which are so high that the impedance of the capa-citor 5 is low in comparison with the resistance Ro and for frequencies higher than the first-mentioned frequen-cies the transfer characteristics is again in a linearfunction of the frequency for a specific switch position~
but it is situated at different levels for different switch positions. If the capacitance of the capacitor 5 is now made so high that the "higher" frequencies, for which the gain is frequency-dependent for a specific switch position, are situated beyond the range of audi-bility, the circuit arrangement shown in Fig. 1 will function as a volume-control device. Suitably, if the switch 2 is in such a switch position, the inverting in-put 11 of the amplifier then remains connected to the tap55 or the output 13 of the amplifier 1, because in that case the negative feedback is a maximum and the distor-tion is minimal. Then, only the second switch 3 needs to be controlled for adjusting the volume. - If the gain variation steps for different switch positions should be further reduced, a further resistor having a value higher than the resistor 41 may be arranged in series with said ~175SO~i PHD 80141C 10 10.9.1981 last-mentioned resistor.
~ Fig. 4 represents a so-called bass-control de-vice~ that is a circuit arrangement by means of which the lower frequencies can be boosted or attenuated at option.
The circuit design of the circuit arrangement of Fig. 4~
which arrangement can be controlled by the control units 6, 7, 8 in the same way as the circuit arrangement of Fig.
1, dlffers from t~e last-mentioned circuit arrangement only in that the capacitor 5 between the output 13 of the amplifier 1, which output corresponds to the tap 55, and the tap 51 is arranged between the two lower resistors 42 and 41 of the resistor chain, and in that the terminal of the lower resistor 41 of the resistor chain 4 which is remote from the output 13 of the amplifier 1 is connected to earth via a capacitor 56 with a very higher capacitance~
suitably an electrolytic capacitor. The function of the last-mentioned capacitor is to reduce the d.c. gain of the amplifier 1 to unity, so that the offset voltages on the output become comparatively small. Said capacito 56 may be dispensed with if the terminal of the resistor 41 which is connected to said capacitor is d.c. coupled to the point to which the input 12 of the amplifier 1 is con-nected.
In the switch position of the switches 2 and 3 as shown in Fig. 4 the equivalent diagram of Fig. 6a is valid for the circuit arrangement, R1 representing the series arrangement of the resistors 42 to 45, the capaci-- tor C1 corresponding to the capacitor 5, and the resistor R2 corresponding to the resistor 41 (for all the frequen-cies to be transmitted the impedance of the capacitor 56is negligible relative to the other resistances). For the lower frequencies of the transmission range the impedance of the capacitor C1 is not yet negligible relative to that of the resistor R2, so that the negative feedback in-creases and the gain decreases at increasing frequency,until at the mid-range frequencies the capacitor C1, in comparison with the resistor R2, substantially presents PHD 80141C 11 10.9.1981 a short-circuit to the signal, as a result of which the gain assumes the value 1, as is represented by the gain cur~e 221 in Fig. 1. If the switch arm 28 is set to the upper position and one of the taps 52 . . . 54 is connected to the inverting input 11 of the amplifier 1, the extent to which the low frequencies (bass tones) are boosted de-creases continually, as is represented by the gain curves 224 in Fig. 5. If finally the tap 55 of the resistor chain 4, or the output 13 of the amplifier 1, is connected to the inverting input 11 of the amplifier via the switch 2, the equivalent diagram of Fig. 6b will be valid.' In this switch position the resistor chain and the capacitor function as a frequency-dependent load of the amplifier output, but its negative feedback is frequency-independent, so that the gain also becomes frequency-inde~endent if the output resistance of said amplifier is low in comparison with the impedance acting on its output. The gain then varies as a linear function of the frequency, as is re-presented by 225.
If the switch position of the switches 2 and 3 is changed in such a way that the inverting input 11 is connected to the tap 55 and the output to the tap 51, the equivalent diagram shown in Fig. 6c is obtained. The out-put voltage of the amplifier is then divided by the vol-tage divider comprising the elements R1, C1 and R2, thetransfer coefficient or the ga~n then being reduced at decreasing frequency. This results in the gain curve 231.
If the switch 3 is connected to the taps 52, 53 or 54 instead of to the tap 51, the gain characteristics 232 30 . . .234 are obtained.
For the bass-control device shown in Fig. 4 and the treble-control device shown in ~ig. 1 the distortion and noise are reduced substantially in comparison with the known electronically controllable treble and bass-control devices. The bass-boost and reduction curves 221 .. 231 are then again strictly mirror-inverted relative to each other~ because the same components are utilized for both functions.
Claims (11)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A circuit arrangement with an electronically controllable transfer characteristic, specifically a tone or volume control circuit, the input signal being applied to an amplifier having controllable negative feedback, characterized in that a voltage divider circuit having a plurality of taps is connected to the output of the ampli-fier and in that the taps are connected to an inverting input of the amplifier via a first electronically control-lable switch and to the output of the circuit arrangement via a second electronically controllable switch.
2. A circuit arrangement as claimed in Claim 1, characterized in that the voltage divider circuit has a frequency-dependent transfer characteristic.
3. A circuit arrangement as claimed in Claim 2, intended for use as a treble control device, character-ized in that the frequency-dependent voltage divider cir-cuit is designed so that the signal voltage on at least some of the taps decreases as the frequency increases.
4. A circuit arrangement as claimed in Claim 1, intended for use as a bass-control device, characterized in that the voltage divider is frequency-dependent and is designed so that the signal voltage on at least some of the taps decreases as the frequency decreases.
5. A circuit arrangement as claimed in Claim 2 or 3, characterized in that the frequency-dependent voltage divider circuit comprises the series arrangement of a capacitor and a resistor chain with a plurality of taps.
6. A circuit arrangement as claimed in Claim 1, characterized in that a resistor chain comprising a plur-ality of taps is connected to the output of the amplifier and in that a capacitor is arranged between the amplifier output and one of the taps.
7. A circuit arrangement as claimed in Claim 6, characterized in that the terminal of the resistor chain which is remote from the output of the amplifier is con-nected to a reference point (earth) via a capacitor and in that the impedance of the capacitor is low relative to the impedance of the resistor chain.
8. A circuit arrangement as claimed in Claim 1, characterized in that the series arrangement of a tapped resistor chain and a capacitor is connected to the ampli-fier output, the impedance of said series arrangement being low relative to the impedance of the resistor chain.
9. A circuit arrangement as claimed in Claim 1, 2 or 3, characterized in that the two switches are controlled in such a way that one of the two switches always conveys the full output voltage of the amplifier.
10. A circuit arrangement as claimed in Claim 1, characterized in that each switch is formed by a semi-conductor circuit, whose switching state can be controlled by means of a digital data word applied to its control input.
11. A circuit arrangement as claimed in Claim 10, characterized in that there is provided a memory circuit which is coupled to the control inputs of the switches, the data words for the control inputs of the switches being stored in such memory circuit.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP3037986.3 | 1980-10-08 | ||
| DE3037986 | 1980-10-08 | ||
| DEP3132402.9 | 1981-08-17 | ||
| DE19813132402 DE3132402A1 (en) | 1980-10-08 | 1981-08-17 | CIRCUIT ARRANGEMENT WITH ELECTRONICALLY CONTROLLABLE TRANSMISSION BEHAVIOR |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1175505A true CA1175505A (en) | 1984-10-02 |
Family
ID=25788351
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000387125A Expired CA1175505A (en) | 1980-10-08 | 1981-10-01 | Circuit arrangement with electronically controllable transfer characteristic |
Country Status (6)
| Country | Link |
|---|---|
| CA (1) | CA1175505A (en) |
| DE (1) | DE3132402A1 (en) |
| ES (1) | ES506051A0 (en) |
| FR (1) | FR2491696A1 (en) |
| GB (1) | GB2085686B (en) |
| IT (1) | IT1138934B (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL8201376A (en) * | 1982-04-01 | 1983-11-01 | Philips Nv | CIRCUIT FOR AMPLIFYING AND / OR ATTENUATING A SIGNAL. |
| US4490843A (en) * | 1982-06-14 | 1984-12-25 | Bose Corporation | Dynamic equalizing |
| DE3222607A1 (en) * | 1982-06-16 | 1983-12-22 | Philips Patentverwaltung Gmbh, 2000 Hamburg | CIRCUIT ARRANGEMENT WITH SEVERAL SIGNAL PATHS, MADE BY ACTIVE CIRCUITS |
| GB2217539B (en) * | 1988-04-14 | 1992-09-23 | Plessey Co Plc | Prescaler output filter |
| DE4015019A1 (en) * | 1990-05-10 | 1991-11-14 | Philips Patentverwaltung | Audio circuit with electronically controlled transmission - has feedback amplifier followed by voltage divider with controlled tap-off switching |
| DE4114364A1 (en) * | 1991-05-02 | 1992-11-12 | Sgs Thomson Microelectronics | DEVICE FOR APPROPRIATE VOLUME CONTROL |
| DE4431481A1 (en) * | 1994-09-03 | 1996-03-07 | Philips Patentverwaltung | Circuit arrangement with controllable transmission behavior |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2262089C3 (en) * | 1972-12-19 | 1975-10-30 | Philips Patentverwaltung Gmbh, 2000 Hamburg | Circuit arrangement for electronic frequency influencing, in particular electronic sound adjuster |
| DE2332211C3 (en) * | 1973-06-25 | 1978-12-14 | Siemens Ag, 1000 Berlin Und 8000 Muenchen | Device for evaluating electrical signals |
| DE2629701A1 (en) * | 1976-07-02 | 1978-01-05 | Licentia Gmbh | AMPLIFIER WITH CONTROLLABLE TRANSMISSION MEASUREMENT AND SWITCHABLE CONTROL CHARACTERISTIC |
| DE2647602A1 (en) * | 1976-10-21 | 1978-04-27 | Licentia Gmbh | Band pass filter with variable attenuation in pass band - has differential amplifier with feedback circuit to inverting input |
| JPS54114159A (en) * | 1978-02-27 | 1979-09-06 | Mitsubishi Electric Corp | Automatic gain control circuit |
| DE2847363C2 (en) * | 1978-10-31 | 1982-06-09 | Matth. Hohner Ag, 7218 Trossingen | Transistor amplifier |
| DE2920056A1 (en) * | 1979-05-18 | 1980-11-27 | Blaupunkt Werke Gmbh | Audio amplifier with frequency-dependent feed-back - has two feedback networks leading from output to inputs of pre-amplifying and output stages |
-
1981
- 1981-08-17 DE DE19813132402 patent/DE3132402A1/en active Granted
- 1981-10-01 CA CA000387125A patent/CA1175505A/en not_active Expired
- 1981-10-05 IT IT24315/81A patent/IT1138934B/en active
- 1981-10-05 GB GB8130003A patent/GB2085686B/en not_active Expired
- 1981-10-06 ES ES506051A patent/ES506051A0/en active Granted
- 1981-10-07 FR FR8118876A patent/FR2491696A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| GB2085686B (en) | 1985-04-17 |
| IT8124315A0 (en) | 1981-10-05 |
| GB2085686A (en) | 1982-04-28 |
| FR2491696A1 (en) | 1982-04-09 |
| DE3132402C2 (en) | 1988-06-01 |
| ES8301400A1 (en) | 1982-11-16 |
| FR2491696B1 (en) | 1984-06-08 |
| ES506051A0 (en) | 1982-11-16 |
| DE3132402A1 (en) | 1982-05-27 |
| IT1138934B (en) | 1986-09-17 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4598252A (en) | Variable gain power amplifier | |
| US5351030A (en) | Variable attenuator for attenuating gain of analog signal in accordance with digital signal | |
| US5995817A (en) | Device for varying the cutoff frequency of a low-pass filter | |
| US4509021A (en) | Circuit for amplifying and/or attenuating a signal | |
| US5574792A (en) | Volume and tone control circuit for acoustic reproduction sets | |
| US4439739A (en) | Circuit arrangement with electronically controllable transfer characteristic | |
| US6442281B2 (en) | Loudness volume control system | |
| CA1175505A (en) | Circuit arrangement with electronically controllable transfer characteristic | |
| JPH0511450B2 (en) | ||
| US4002994A (en) | Tone control circuit | |
| US4451795A (en) | Circuit arrangement with controllable transfer characteristic at higher frequencies | |
| US4055818A (en) | Tone control circuit | |
| US4544912A (en) | Scale switchable digital-to-analog converter | |
| US4883991A (en) | Circuit arrangement for adjusting a reference level in a periodic signal | |
| GB2074409A (en) | Variable load impedance gain-controlled amplifier | |
| US4176329A (en) | Tone control circuit | |
| US4929908A (en) | Gain controllable amplifier circuit | |
| US6339356B1 (en) | Variable attenuator | |
| US4432097A (en) | Tone control circuit | |
| US4994770A (en) | Tone control device | |
| US4500932A (en) | Signal processing circuit | |
| US4583050A (en) | Gain control circuit | |
| US4710962A (en) | Signal control apparatus | |
| US3829626A (en) | Telephone line equalizer | |
| US4611179A (en) | Wide-band type high-frequency amplifier circuit |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |