CA1048114A - Amplifier arrangement linearised by automatic correction - Google Patents
Amplifier arrangement linearised by automatic correctionInfo
- Publication number
- CA1048114A CA1048114A CA228,923A CA228923A CA1048114A CA 1048114 A CA1048114 A CA 1048114A CA 228923 A CA228923 A CA 228923A CA 1048114 A CA1048114 A CA 1048114A
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- Prior art keywords
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- amplifier
- output
- arrangement
- signal
- Prior art date
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- Expired
Links
- 238000012937 correction Methods 0.000 title claims description 17
- 230000005540 biological transmission Effects 0.000 claims description 8
- 230000003247 decreasing effect Effects 0.000 abstract 1
- 239000003990 capacitor Substances 0.000 description 4
- 230000010363 phase shift Effects 0.000 description 4
- 230000003321 amplification Effects 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 238000003199 nucleic acid amplification method Methods 0.000 description 3
- 230000008878 coupling Effects 0.000 description 2
- 238000010168 coupling process Methods 0.000 description 2
- 238000005859 coupling reaction Methods 0.000 description 2
- 230000003534 oscillatory effect Effects 0.000 description 2
- 230000001934 delay Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000003455 independent Effects 0.000 description 1
- 238000012886 linear function Methods 0.000 description 1
- 238000000034 method Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03G—CONTROL OF AMPLIFICATION
- H03G3/00—Gain control in amplifiers or frequency changers
- H03G3/20—Automatic control
- H03G3/30—Automatic control in amplifiers having semiconductor devices
- H03G3/3036—Automatic control in amplifiers having semiconductor devices in high-frequency amplifiers or in frequency-changers
- H03G3/3042—Automatic control in amplifiers having semiconductor devices in high-frequency amplifiers or in frequency-changers in modulators, frequency-changers, transmitters or power amplifiers
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
- H03F1/32—Modifications of amplifiers to reduce non-linear distortion
- H03F1/3241—Modifications of amplifiers to reduce non-linear distortion using predistortion circuits
- H03F1/3247—Modifications of amplifiers to reduce non-linear distortion using predistortion circuits using feedback acting on predistortion circuits
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
- H03F1/32—Modifications of amplifiers to reduce non-linear distortion
- H03F1/3241—Modifications of amplifiers to reduce non-linear distortion using predistortion circuits
- H03F1/3276—Modifications of amplifiers to reduce non-linear distortion using predistortion circuits using the nonlinearity inherent to components, e.g. a diode
Landscapes
- Physics & Mathematics (AREA)
- Nonlinear Science (AREA)
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Amplifiers (AREA)
- Tone Control, Compression And Expansion, Limiting Amplitude (AREA)
Abstract
Abstract of the disclosure An arrangement comprising an amplifier having a gain G.f(ue) where G is a constant and f(ue) a function of the input voltage ue. This arrangement comprises an attenuator of gain 1/G, a comparator comparing the input signal of the amplifier and its output signal decreased by said attenuator, a circuit receiving the input signal of the arrangement and the output signal from the comparator and delivering the input signal of the amplifier.When the input signal of the arrangement is a modulated signal, two detectors are inserted before the two inputs of the comparator.
Description
~4~
The present invention relates to an amplifier arran-gsment linearised by automatic correction of the gain of an ampli~ier ~
Television transmitters and relay transmitters in the low and medium power ranges, generally comprise output sta~es in the form a~ power ampli~iers which, since they have to bs linear, are operated only over a small part of their trans-~er characteristic. The eFficiency of equipment of thi~ kind does not generally exceed 10 %.
Arrangements which make it possible to utilise a wider part of the characteristic o~ these amplifiers~ havs been proposed .
arrflngemer7ts The~e/create at the input D~ the amplifier a di tortion designed to compen~ate ~or the di3torsion producsd ~y the amplifier in the non~ ear part of its characteristic.
These arrangements require numerous adjustments which have to be carried aut frequently because the form of the ampli~ier non-linearities varies with and as a function of temperature, mean ualue of ths transmitted signal snd a number of other parameters Arrangements producing linearisation by negati~e ~eed back have also been propo6ed but the3e generally give rise to stability problcm, and they r~ult in an importan-t reduction in the amplifier gain if they affect the whole signal. If they af~ect only the difference betwesn the input and output signab of the amplifisr, there remains the drawbacks ~nherent in tha feed back pxinciple ~phasa problems and parti~l correction of the distor~ions1.
The present invention relates to an amplifier arran-gsment linearised by automatic correction of the gain of an ampli~ier ~
Television transmitters and relay transmitters in the low and medium power ranges, generally comprise output sta~es in the form a~ power ampli~iers which, since they have to bs linear, are operated only over a small part of their trans-~er characteristic. The eFficiency of equipment of thi~ kind does not generally exceed 10 %.
Arrangements which make it possible to utilise a wider part of the characteristic o~ these amplifiers~ havs been proposed .
arrflngemer7ts The~e/create at the input D~ the amplifier a di tortion designed to compen~ate ~or the di3torsion producsd ~y the amplifier in the non~ ear part of its characteristic.
These arrangements require numerous adjustments which have to be carried aut frequently because the form of the ampli~ier non-linearities varies with and as a function of temperature, mean ualue of ths transmitted signal snd a number of other parameters Arrangements producing linearisation by negati~e ~eed back have also been propo6ed but the3e generally give rise to stability problcm, and they r~ult in an importan-t reduction in the amplifier gain if they affect the whole signal. If they af~ect only the difference betwesn the input and output signab of the amplifisr, there remains the drawbacks ~nherent in tha feed back pxinciple ~phasa problems and parti~l correction of the distor~ions1.
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The feed forward arranc~ements avoid the feed back drawbacks, but require a linear power amplifier for -the amplification of the correction signalO The addition of the amplified correction signal to the main amplified signal is a delicate matter. Finally, a feed forward arrangement is rather expensive.
The object of the present invention is an amplifier arrangement for correcting non-linearities, which ~akes it possible, at modest expense, to avoid the drawbacks of the aforementioned arrangements. In particular, the arrangement in accordance with the invention which makes it possible to achieve extremely stable correction, has the advantages of loop systems without incurring their drawbacks (problems of - phase and bandwidth).
In accordance with the invention there is provided an a~plifier arrangement comprising: an amplifierp an attenuator whose input is coupled to the output of said amplifier, first and second transmission channels having respective inputs respectively coupled to the input of said amplifier and to the output of said attenuator, a comparator having two inputs respectively coupled to the outputs of said transmission channels and a correcting circuit having a correction input coupled to the output of said comparator, a signal input forming the input of said arrangement and an output coupled to the input of said amplifier, the output of said amplifier forming the output of said arrangement.
- The invention will be better understood and others of its ~~~~ ' ;~ 30 _ ~
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The feed forward arranc~ements avoid the feed back drawbacks, but require a linear power amplifier for -the amplification of the correction signalO The addition of the amplified correction signal to the main amplified signal is a delicate matter. Finally, a feed forward arrangement is rather expensive.
The object of the present invention is an amplifier arrangement for correcting non-linearities, which ~akes it possible, at modest expense, to avoid the drawbacks of the aforementioned arrangements. In particular, the arrangement in accordance with the invention which makes it possible to achieve extremely stable correction, has the advantages of loop systems without incurring their drawbacks (problems of - phase and bandwidth).
In accordance with the invention there is provided an a~plifier arrangement comprising: an amplifierp an attenuator whose input is coupled to the output of said amplifier, first and second transmission channels having respective inputs respectively coupled to the input of said amplifier and to the output of said attenuator, a comparator having two inputs respectively coupled to the outputs of said transmission channels and a correcting circuit having a correction input coupled to the output of said comparator, a signal input forming the input of said arrangement and an output coupled to the input of said amplifier, the output of said amplifier forming the output of said arrangement.
- The invention will be better understood and others of its ~~~~ ' ;~ 30 _ ~
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-Features rendered apparen-t from a consideration oF the ensuing description and related drawings in which :
- Fig. 1 illustrates an amplifier arrangement in accordance with the invention, for narrow band operation ;
- Fig. 2 illustra-tes an amplifier arrangement of wide-band design, amplifying modulated signals9 ; _ Fig. 3 i5 a detailed diagram of an element of the arrangemen-t shown in Fig. 2 ;
- Fig, 4 illustrates the attenuation charac-teristics 10 of an attenua-tor which is variable as a function of the current.
In Fig. 1, the various elements of a arrangement in accordance wi-th the invention can be seen.
The input 1 of the arrangement, designed to ~e supplied with the voltage u1(t), is connectsd to the first input of an 15 adder 2 whose output is connected to the input of an amplifier 3. This amplifier has a transfer characteristic - u (t) u (t)= 5--F~Ue(t) J whPre u (t) is the input voltage of the amplifier and u (t) is -the output voltage, G is the gain of the amplifier 3 within the linear part of its characteristic 20 and f(ue) is a non-linear function of the input voltage ue~t).
The output of tha amplifier 3 forms the output 4 of the arran gement. This output is connected to the input of an attenuator 5 whose a-ttenuation coeFficiEnt is G . The input of the ampli-; fier 3 and the output of the attenuator are connected to the 25 two inputs oF a comparator 6 whose output is connected to a J second input of the adder 2 and supplies the difference ` between the voltages applied to its two inputs.
-:;
... .
The galn of the compara-tor is e~perimentally determined so that the transfer characteris-tic between the input 1 and the output 4 oF the arrangement is such as ~e~t) = K
u1(t) k being a constant.
T~s arrangement is par-ticularly suitable in situations ; where the amplifie~ bandwidth is narrow. The limitation of the operating range is due -to the problems of phase-shiFt when the length of the leads is no-t negligible with regard to the ; wavelength9 and to the delays in the amplifiers.
This arrangement can be used to automatically correct the non-linearities in the gain of an amplifier supplied with amplitude-modulated HF signals.
A corresponding embodiment of -the arrangement in accor-; dance with the invention, has been indicated in the form of the block diagram of Fig. 2.
Elemen-ts similar to those of Fig. 1 have been designated by the same references, increased by lOo Thus the inpu-t 11 is connected to an inpu-t of a correcting circuit 12 (in broken line in the drawing). The output of circuit 12 is connected 2~ to the inpu-t of an amplifier 13 through a preamplifier 1~.
The output 14 of the power ampliFier 13 forms the output of the arrangement. This output is connected to an attenuator 15 whose a-ttenuation coefficient is G . The input of the ampli-fier 13 and the output of the attenuator 15 are respect ively connected to the inputs oF two modulation detectors S _ :
''' :
: " ' '' ' ' . ' ' ' .. ,'.,` ., ' ',...': ~, .
26 and 27 whose outputs are connected to the two inputs of a comparator 16~ The ou~put of the comparator 16 is connected to the second input of the correcting circuit 12.
The correcting circuit proper, 12, comprises two ldentical, parallel attenuators, 24 and 15, which can be modulated. The characteristic of these àttenuators as a function of the control voltage applied to them, has been shown in Fig. 4, The two attenuators have their control inputs connected to -the output of the comparator 16.
The circuit 12 furthermore comprises a first 3dB
coupler, 20, one input of which is connected to the input 11 of the circuit and the second input of which is terminated in its characteristic impedance 30. The output of the coupler .~ 20, delivering'a signal which is in-phase with the input signal, is connected to an input of a second 3dB coupler 22 whose other input is terminated i.n its own characteristic impedance 32. The in-phase and quadrature outputs of the coupler 22 are connected respectively to the inputs of the attenuators 24 and 25. These attenuators produce a small phase-shift 4 . Their outputs are connected to the two inputs of a 3dB coupler 23, the output in quadrature with the ~; input connected to the output of the attenuator 2~, being terminated in the characteristic impedance 33 of the coupler 230 That output which is in phase with the input connected.
to the output of the attenuator 24, is connected to an input . of a 3dB coupler 21, whose other input is connected to the quadrature output of the coupler 20 through a phase-shifter 28 which shifts the phase of the signal applied to it by (this is the phase-shift produced by the attenuators). The phase-shifter 28 can be constituted by a line section. The coupler 21 whose input signals are in quadrature produces no power at that of its outputs terminated in the characteristic ~ ~ .
3L~41!3~
impedance 31, while its other output forms the output of the correcting arrangement.
The operation of this system is as follows-- The input 11 of the arrangement is supplied with a modulated high-frequency signal oE low amplitude. This signal is transmitted by the correcting circuit 12 where it i6 modified by the output signal from the comparator 16 and by the transmission characteristic of said correcting circuit, in the manner explained hereinafter.
This low-amplitude signal is amplified by the pre-amplifier 18 which is perfectly linear as concerns the small signals applied to it. The power amplification!is carried - out in the amplifier 13 which is not linear for every level - of the signals applied to it, since G. f(ue) varies as a function of its input voltaged The attenuator 15 having the attenuation coefficient lG produces a signal which would be the same as the input signal to the amplifier 13 but for the non-linear gain variations. This modulated high-frequency signal is demodulated by the detector 27 while the input signal 20 to the amplifier 13 is demodulated by the detector 26. The transit time of the amplifier 13 is short (some few nanoseconds only). Moreover, the lines picking off the input signal and the output signal of the amplifier are very close to the amplifier itself and more precisely to the stage in which the signal distortion takes place. These lines, up to the detectors, are only a few centimetres in length (in practice 3 to 4 cm). Experience shows that there is consequent'ly only a very small phase-shift~
The output signal from the comparator 16 is applied to the control inputs of the two attenuators 24 and 25. The maximum permissible level of each of these attenuators is around 500 millivolts so that the use of two attenuators ,- ' , ' ', , .~ ~ ' ' . ' . ' 8~
makes it possible to apply to the input 11 of the arrangement a signal whose peak level is l V,.
The correcting circuit as described hereinbefore comprises two parallel main channels between the outputs of the coupler 20 and the inputs of the coupler 22. The first contains the phase-shifter 28 and transmits half the input power, the second contains the attenuators and modulates the signal applied to it as a function of the output signal from the comparator. ~pon this signal, there is superimposed a direct voltage which makes it possible to choose the optimum working point by adjusting the attenuation coefficient of the attenuators to a given value while the value of the output signal from the comparator is constant, this corresponding to linear amplification in the amplifier 13.
The attenuation coefficient varies between a minimum value and the aforesaid given value, in accordance with the variations in the output signal from the comparator as a -consequence of the non-linearities in the gain of the amplifier.
The attenuation characteristic of the attenuator as function of the current, shows that in the central zone the attenuation is substantiall~ linear (FigO 4).
The variations in attenuation which are produced, thus precisely follow the non-linearities in the amplified signalO The modulated signal occurring at the input 11 o~
~ the arrangement is therefore modulated by the attenuators A in accordance with the law which is a reciprocal of the varia-tions in the gain o~ the ampli~ier.
The correcting circuit is a passive system which requires no additional supply. Moreover, this system is quasi-aperiodic and simply requires phase adjustment, inde-pendent of the amplifier which is used~
The correction thus obtained is independent of the ~a8~
frequency since it acts directly upon the modulation of the signal. The length of the leads between the couplers and the comparator as well as between the output of the comparator and the correc-ting circuit, is not critical. The amplifier arrangement produces multiplication by approximately two, of the maximum output power which could be obtained without this - correcting circuit for the same criteria of linearity.
In order to improve the correction of these modulated signals, it may be useful to insert in the correction circuit a circuit having a gain varying as a function of the frequency.
An example is given hereafter where it is assumed - that the signal input is a carrier modulated by a video colortelevision signal with vestigial side-band modulation mode.
In this case, the experience shows that the amplitude of the correction signal supplied by the comparator is advantageously - increased in the color subcarrier bandwidth.
Fig. 3 illustrates the detailed diagram of the comparator 16 shown in Fig. 2, to which there has been added a circuit for effecting the aforesaid amplitude correction.
-~ 20 The comparator 16 comprises two inputs (26~ and (27) which are the outputs of the detectors 26 and 27.
These two inputs are respectively connected to the - - inputs "-" and "+" of a differential amplifier 160, the two inputs on the other hand being connected to ground through two resistors 161 and 162. The direct component required to place the output signal from the amplifier at a working point which is compatible with the characteristic (Fig. 4) of the attenua-tors 24 and 2S of FigO 2, is adjusted by means of a circuit which contains, in series, between the output of the amplifier 160 and the direct supply voltage source -V, a zener diode ' ~ , 8~
163 and a resistor 1640 A rheostat 165 and a resistor 166 in series, are arranged across the terminals of the zener diode 163. A capacitor 167 is co:nnected to the output of the amplifier 160. The second terminal of the capacitor 167 is connected to the variable term.inal of the rheostat 165.
The circuit for correcting amplitude as a function of frequency has its input connected to the variable terminal of the rheostatO
This input is connected to the base of an n-p-n transistor 171 through a resistor 172 and to the base of an n-p-n transistor 173 through two series-connected resistors 174 and 175. The collectors of the transistors 171 and 172 are respectively comlected to the direct supply voltage source +V.
The emitters of these two transistors are connected through two series-connected resistors 176 and 177. The common terminal of these two resistors is taken to the direct supply voltage source -V, through a resistor 178. This common terminal constitutes the output (17) of the amplitude correct-ing circuitO The terminal common to the resistors 174 and 175 is connected to a terminal of an oscillatory circuit comprising an inductance coil 179 and a capacitor 180~ The other terminal of this oscillatory circuit is connected to a capacitor 181 whose other terminal is grounded.
The invention is not limited to the embodiment described. In particular, in the aforesaid e~ample (concerning a high frequency modulated color television signal~ it is possible to do without the elements of the correcting circuit shown in Fig. 3 (outside block 16) provided that attenuators 24 and 25 having a gain varying as a function of ~requency are used. Moreover, in the correcting circuit 12 it is possible to utilise a single attenuator, reducing the number of couplers to 2. However, the peak permissible level o~ the input signal at 11 is then limited to 0.7 volts for an attenuator having a maximum permissible level o~ 500 milivolts.
It will be noted that, in a described example (Fig. 2 and 3), the comparison has been effected on detected signals to avoid comparing high frequency signals with the inherent phase problemsO Another solution is to effect the comparison at intermediate frequency in a transmitter comprising an intermediate frequency stage. The two detectors of Fig. 2 are then substituted by two frequency converters, and the correction, as well as the comparison, is made at intermediate.
frequency, by an adding process, as in the case of Fig~ 1.
Such a structure involves a coupling of the correction circuit to the amplifier through the frequency converter normally coupling the intermediate frequency stages to the transmission frequency stages in the transmitterO ..
0~ course, the invention i5 not limited to the embodiments described and shown which were given solely by wa9 ~f example.
'.
.
. .
.~ .
: .
\~
~41~
-Features rendered apparen-t from a consideration oF the ensuing description and related drawings in which :
- Fig. 1 illustrates an amplifier arrangement in accordance with the invention, for narrow band operation ;
- Fig. 2 illustra-tes an amplifier arrangement of wide-band design, amplifying modulated signals9 ; _ Fig. 3 i5 a detailed diagram of an element of the arrangemen-t shown in Fig. 2 ;
- Fig, 4 illustrates the attenuation charac-teristics 10 of an attenua-tor which is variable as a function of the current.
In Fig. 1, the various elements of a arrangement in accordance wi-th the invention can be seen.
The input 1 of the arrangement, designed to ~e supplied with the voltage u1(t), is connectsd to the first input of an 15 adder 2 whose output is connected to the input of an amplifier 3. This amplifier has a transfer characteristic - u (t) u (t)= 5--F~Ue(t) J whPre u (t) is the input voltage of the amplifier and u (t) is -the output voltage, G is the gain of the amplifier 3 within the linear part of its characteristic 20 and f(ue) is a non-linear function of the input voltage ue~t).
The output of tha amplifier 3 forms the output 4 of the arran gement. This output is connected to the input of an attenuator 5 whose a-ttenuation coeFficiEnt is G . The input of the ampli-; fier 3 and the output of the attenuator are connected to the 25 two inputs oF a comparator 6 whose output is connected to a J second input of the adder 2 and supplies the difference ` between the voltages applied to its two inputs.
-:;
... .
The galn of the compara-tor is e~perimentally determined so that the transfer characteris-tic between the input 1 and the output 4 oF the arrangement is such as ~e~t) = K
u1(t) k being a constant.
T~s arrangement is par-ticularly suitable in situations ; where the amplifie~ bandwidth is narrow. The limitation of the operating range is due -to the problems of phase-shiFt when the length of the leads is no-t negligible with regard to the ; wavelength9 and to the delays in the amplifiers.
This arrangement can be used to automatically correct the non-linearities in the gain of an amplifier supplied with amplitude-modulated HF signals.
A corresponding embodiment of -the arrangement in accor-; dance with the invention, has been indicated in the form of the block diagram of Fig. 2.
Elemen-ts similar to those of Fig. 1 have been designated by the same references, increased by lOo Thus the inpu-t 11 is connected to an inpu-t of a correcting circuit 12 (in broken line in the drawing). The output of circuit 12 is connected 2~ to the inpu-t of an amplifier 13 through a preamplifier 1~.
The output 14 of the power ampliFier 13 forms the output of the arrangement. This output is connected to an attenuator 15 whose a-ttenuation coefficient is G . The input of the ampli-fier 13 and the output of the attenuator 15 are respect ively connected to the inputs oF two modulation detectors S _ :
''' :
: " ' '' ' ' . ' ' ' .. ,'.,` ., ' ',...': ~, .
26 and 27 whose outputs are connected to the two inputs of a comparator 16~ The ou~put of the comparator 16 is connected to the second input of the correcting circuit 12.
The correcting circuit proper, 12, comprises two ldentical, parallel attenuators, 24 and 15, which can be modulated. The characteristic of these àttenuators as a function of the control voltage applied to them, has been shown in Fig. 4, The two attenuators have their control inputs connected to -the output of the comparator 16.
The circuit 12 furthermore comprises a first 3dB
coupler, 20, one input of which is connected to the input 11 of the circuit and the second input of which is terminated in its characteristic impedance 30. The output of the coupler .~ 20, delivering'a signal which is in-phase with the input signal, is connected to an input of a second 3dB coupler 22 whose other input is terminated i.n its own characteristic impedance 32. The in-phase and quadrature outputs of the coupler 22 are connected respectively to the inputs of the attenuators 24 and 25. These attenuators produce a small phase-shift 4 . Their outputs are connected to the two inputs of a 3dB coupler 23, the output in quadrature with the ~; input connected to the output of the attenuator 2~, being terminated in the characteristic impedance 33 of the coupler 230 That output which is in phase with the input connected.
to the output of the attenuator 24, is connected to an input . of a 3dB coupler 21, whose other input is connected to the quadrature output of the coupler 20 through a phase-shifter 28 which shifts the phase of the signal applied to it by (this is the phase-shift produced by the attenuators). The phase-shifter 28 can be constituted by a line section. The coupler 21 whose input signals are in quadrature produces no power at that of its outputs terminated in the characteristic ~ ~ .
3L~41!3~
impedance 31, while its other output forms the output of the correcting arrangement.
The operation of this system is as follows-- The input 11 of the arrangement is supplied with a modulated high-frequency signal oE low amplitude. This signal is transmitted by the correcting circuit 12 where it i6 modified by the output signal from the comparator 16 and by the transmission characteristic of said correcting circuit, in the manner explained hereinafter.
This low-amplitude signal is amplified by the pre-amplifier 18 which is perfectly linear as concerns the small signals applied to it. The power amplification!is carried - out in the amplifier 13 which is not linear for every level - of the signals applied to it, since G. f(ue) varies as a function of its input voltaged The attenuator 15 having the attenuation coefficient lG produces a signal which would be the same as the input signal to the amplifier 13 but for the non-linear gain variations. This modulated high-frequency signal is demodulated by the detector 27 while the input signal 20 to the amplifier 13 is demodulated by the detector 26. The transit time of the amplifier 13 is short (some few nanoseconds only). Moreover, the lines picking off the input signal and the output signal of the amplifier are very close to the amplifier itself and more precisely to the stage in which the signal distortion takes place. These lines, up to the detectors, are only a few centimetres in length (in practice 3 to 4 cm). Experience shows that there is consequent'ly only a very small phase-shift~
The output signal from the comparator 16 is applied to the control inputs of the two attenuators 24 and 25. The maximum permissible level of each of these attenuators is around 500 millivolts so that the use of two attenuators ,- ' , ' ', , .~ ~ ' ' . ' . ' 8~
makes it possible to apply to the input 11 of the arrangement a signal whose peak level is l V,.
The correcting circuit as described hereinbefore comprises two parallel main channels between the outputs of the coupler 20 and the inputs of the coupler 22. The first contains the phase-shifter 28 and transmits half the input power, the second contains the attenuators and modulates the signal applied to it as a function of the output signal from the comparator. ~pon this signal, there is superimposed a direct voltage which makes it possible to choose the optimum working point by adjusting the attenuation coefficient of the attenuators to a given value while the value of the output signal from the comparator is constant, this corresponding to linear amplification in the amplifier 13.
The attenuation coefficient varies between a minimum value and the aforesaid given value, in accordance with the variations in the output signal from the comparator as a -consequence of the non-linearities in the gain of the amplifier.
The attenuation characteristic of the attenuator as function of the current, shows that in the central zone the attenuation is substantiall~ linear (FigO 4).
The variations in attenuation which are produced, thus precisely follow the non-linearities in the amplified signalO The modulated signal occurring at the input 11 o~
~ the arrangement is therefore modulated by the attenuators A in accordance with the law which is a reciprocal of the varia-tions in the gain o~ the ampli~ier.
The correcting circuit is a passive system which requires no additional supply. Moreover, this system is quasi-aperiodic and simply requires phase adjustment, inde-pendent of the amplifier which is used~
The correction thus obtained is independent of the ~a8~
frequency since it acts directly upon the modulation of the signal. The length of the leads between the couplers and the comparator as well as between the output of the comparator and the correc-ting circuit, is not critical. The amplifier arrangement produces multiplication by approximately two, of the maximum output power which could be obtained without this - correcting circuit for the same criteria of linearity.
In order to improve the correction of these modulated signals, it may be useful to insert in the correction circuit a circuit having a gain varying as a function of the frequency.
An example is given hereafter where it is assumed - that the signal input is a carrier modulated by a video colortelevision signal with vestigial side-band modulation mode.
In this case, the experience shows that the amplitude of the correction signal supplied by the comparator is advantageously - increased in the color subcarrier bandwidth.
Fig. 3 illustrates the detailed diagram of the comparator 16 shown in Fig. 2, to which there has been added a circuit for effecting the aforesaid amplitude correction.
-~ 20 The comparator 16 comprises two inputs (26~ and (27) which are the outputs of the detectors 26 and 27.
These two inputs are respectively connected to the - - inputs "-" and "+" of a differential amplifier 160, the two inputs on the other hand being connected to ground through two resistors 161 and 162. The direct component required to place the output signal from the amplifier at a working point which is compatible with the characteristic (Fig. 4) of the attenua-tors 24 and 2S of FigO 2, is adjusted by means of a circuit which contains, in series, between the output of the amplifier 160 and the direct supply voltage source -V, a zener diode ' ~ , 8~
163 and a resistor 1640 A rheostat 165 and a resistor 166 in series, are arranged across the terminals of the zener diode 163. A capacitor 167 is co:nnected to the output of the amplifier 160. The second terminal of the capacitor 167 is connected to the variable term.inal of the rheostat 165.
The circuit for correcting amplitude as a function of frequency has its input connected to the variable terminal of the rheostatO
This input is connected to the base of an n-p-n transistor 171 through a resistor 172 and to the base of an n-p-n transistor 173 through two series-connected resistors 174 and 175. The collectors of the transistors 171 and 172 are respectively comlected to the direct supply voltage source +V.
The emitters of these two transistors are connected through two series-connected resistors 176 and 177. The common terminal of these two resistors is taken to the direct supply voltage source -V, through a resistor 178. This common terminal constitutes the output (17) of the amplitude correct-ing circuitO The terminal common to the resistors 174 and 175 is connected to a terminal of an oscillatory circuit comprising an inductance coil 179 and a capacitor 180~ The other terminal of this oscillatory circuit is connected to a capacitor 181 whose other terminal is grounded.
The invention is not limited to the embodiment described. In particular, in the aforesaid e~ample (concerning a high frequency modulated color television signal~ it is possible to do without the elements of the correcting circuit shown in Fig. 3 (outside block 16) provided that attenuators 24 and 25 having a gain varying as a function of ~requency are used. Moreover, in the correcting circuit 12 it is possible to utilise a single attenuator, reducing the number of couplers to 2. However, the peak permissible level o~ the input signal at 11 is then limited to 0.7 volts for an attenuator having a maximum permissible level o~ 500 milivolts.
It will be noted that, in a described example (Fig. 2 and 3), the comparison has been effected on detected signals to avoid comparing high frequency signals with the inherent phase problemsO Another solution is to effect the comparison at intermediate frequency in a transmitter comprising an intermediate frequency stage. The two detectors of Fig. 2 are then substituted by two frequency converters, and the correction, as well as the comparison, is made at intermediate.
frequency, by an adding process, as in the case of Fig~ 1.
Such a structure involves a coupling of the correction circuit to the amplifier through the frequency converter normally coupling the intermediate frequency stages to the transmission frequency stages in the transmitterO ..
0~ course, the invention i5 not limited to the embodiments described and shown which were given solely by wa9 ~f example.
'.
.
. .
Claims (4)
1. An amplifier arrangement comprising an amplifier, an attenuator whose input is coupled to the output of said amplifier, first and second transmission channels having respective inputs respectively coupled to the input of said amplifier and to the output of said attenuator, a comparator having two inputs respectively coupled to the outputs of said transmission channels and a correcting circuit having a correc-tion input couplet to the output of said comparator, a signal input forming the input of said arrangement and an output coupled to the input of said amplifier, the output of said amplifier forming the output of said arrangement.
2. An amplifier arrangement as claimed in claim 1, wherein said first and second transmission channels are cables, and wherein said correcting circuit is an adder.
3. An amplifier arrangement as claimed in claim 1, for amplifying amplitude-modulated high frequency signals, wherein said transmission channels comprise respective detectors, said correcting circuit is a variable gain circuit, and said correction input is the gain control input of said correcting circuit.
4. An amplifier arrangement as claimed in claim 3 for amplifying a carrier modulated by a video color television signal in the vestigial side band modulation mode wherein said correction input of said correcting circuit is coupled to said gain control input through a circuit increasing the signal output of the comparator in the color subcarrier bandwidth.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR7420157A FR2275065A1 (en) | 1974-06-11 | 1974-06-11 | LINEARIZED AMPLIFIER DEVICE BY AUTOMATIC CORRECTION |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1048114A true CA1048114A (en) | 1979-02-06 |
Family
ID=9139889
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA228,923A Expired CA1048114A (en) | 1974-06-11 | 1975-06-10 | Amplifier arrangement linearised by automatic correction |
Country Status (6)
| Country | Link |
|---|---|
| AR (1) | AR204865A1 (en) |
| CA (1) | CA1048114A (en) |
| DE (1) | DE2526064C2 (en) |
| ES (1) | ES438393A1 (en) |
| FR (1) | FR2275065A1 (en) |
| GB (1) | GB1491798A (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2448750A1 (en) * | 1979-02-09 | 1980-09-05 | Labo Electronique Physique | ELECTRONIC DEVICE FOR COMPENSATION FOR LINEARITY DEFECTS |
| FR2541058B1 (en) * | 1983-02-11 | 1986-01-24 | Thomson Csf | HIGH FREQUENCY AMPLIFIER LINEARIZATION DEVICE WITH COMPLEX NON-LINEARITY COEFFICIENTS |
| FR2553947B1 (en) * | 1983-10-21 | 1985-12-13 | Lgt Lab Gen Telecomm | DEVICE FOR AUTOMATICALLY PRE-CORRECTING NON-LINEARITIES IN A POWER AMPLIFIER AND TELEVISION TRANSMITTER COMPRISING SUCH A DEVICE |
| GB2164823A (en) * | 1984-09-17 | 1986-03-26 | Philips Electronic Associated | Television transmitter |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2140851B2 (en) * | 1971-08-14 | 1976-03-11 | Rohde & Schwarz, 8000 München | Compensating circuit to minimise distortion effects in HF signals - has signal transmitted through parallel circuits one with phase shift |
-
1974
- 1974-06-11 FR FR7420157A patent/FR2275065A1/en active Granted
-
1975
- 1975-01-01 AR AR25915375A patent/AR204865A1/en active
- 1975-06-10 ES ES438393A patent/ES438393A1/en not_active Expired
- 1975-06-10 GB GB2490775A patent/GB1491798A/en not_active Expired
- 1975-06-10 CA CA228,923A patent/CA1048114A/en not_active Expired
- 1975-06-11 DE DE19752526064 patent/DE2526064C2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| FR2275065A1 (en) | 1976-01-09 |
| DE2526064C2 (en) | 1984-04-12 |
| FR2275065B1 (en) | 1978-01-13 |
| GB1491798A (en) | 1977-11-16 |
| AR204865A1 (en) | 1976-03-05 |
| ES438393A1 (en) | 1977-01-16 |
| DE2526064A1 (en) | 1976-01-02 |
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