DE1080614B - Circuit arrangement for compensating for amplitude compression or expansion of an alternating current signal - Google Patents

Description

GERMAN

The invention relates to a circuit arrangement for compensating for amplitude compression or expanding an AC signal with a first transmission channel and a second Transmission channel whose input is connected to the first channel at points whose Phase difference is 180 °.

A color television signal contains the so-called luminance signal, that controls the intensity or brightness, and a color carrier signal, its amplitude determines the saturation or purity of the color. Any change in the amplitude of this color carrier occurs Reason for a change in the amplitude of the luminance signal, what is commonly referred to as differential gain causes distortion in the color saturation.

In single-color or multi-color television systems, the luminance signal can be caused by the non-linear characteristic the devices used in generating, transmitting and receiving the signal and also in the conversion from electrical to optical energy or vice versa. This distortion exists usually in a compression or expansion of the positive or negative signal amplitudes, which are accordingly the one in USA. the standard used to identify the light and dark areas of the image. One such distortion is known as grayscale distortion, when it occurs in a single color system or as luminance or saturation distortion Color television signals.

The distortions discussed here can relate to an electrical transmission path in a Compression of both the white image parts and the black image parts of the signal or in an expansion both parts consist or in a compression of one and an expansion of the other part. Of the Synchronization pulse, which is used in television broadcasts, is in the blacker-than-black range, and the percentage of this impulse is a sensitive criterion for the compression or Expansion in this area.

A similar type of electrical waveform distortion can be caused by non-linear switching elements in an electrical transmission path or a non-linear transducer. Examples such distortions are provided by modulation or demodulation processes, loudspeakers, electron tube or transistor amplifiers, microphones, electrical transmitters, or other devices.

For example, an electron tube amplifier with only one output tube normally produces distortions of the even-numbered harmonics, preferably with the 2nd harmonic, resulting in an expansion of the signal amplitudes of one polarity and circuit arrangement
for compensation, an amplitude compression or expansion
an AC signal

Applicant:

Western Electric Company, Incorporated, New York, N, Y. (V. St. A.)

Representative: Dr.-Ing. K. Boehmert

and Dipl.-Ing. A. Boehmert, patent attorneys,

Bremen 1, Feldstr. 24

Claimed priority:
V. St. v. America December 17, 1956

Jean Harold Clark, Covina, Calif. (V. St. Α.),

has been named as the inventor -

consists in a compression of the signal amplitudes of the other polarity. This can be compensated for or compensate by introducing an equal and oppositely directed distortion, which restores the original waveform, provided that this equalization or equalization either immediately before or immediately after the source of the distortion in the Transmission path is arranged. If this is not done, a delay equalization is provided, so that with an electrically long transmission circuit the transit time of the fundamental wave and that of its essentials Harmonics are essentially the same. There are no noticeable differences in the speed of propagation or in the transmission time between the fundamental wave and the essential ones Harmonics, then no delay equalization is required, regardless of the bridged one Distance.

Distortions of a similar kind are also found in teletransmission or facsimile transmission.

There is already an equalization circuit known that represents a frequency-dependent network and thus a desired dependence of the amplitude on the Frequency results. The known circuit contains a branch circuit bridging the transmission channel with non-linear switching elements from which an adjustable voltage is derived and the transmission channel can contact forwarded. The setting

009 507 / 284-

this tapping can be achieved by changing the DC control voltage of the non-linear elements will. With the known circuit, however, a differential, i. H. nonlinear gain is not balance. S.

The new circuit arrangement is intended to compensate for the distortion by providing the same and introduces an oppositely directed distortion signal for correction. This equalizer is common the electrical part of the signal transmission path assigned and provides a correction for this part of the system. The circuit arrangement can of course also be designed to compensate for any nonlinear distortion resulting from a Conversion of optical into electrical and electrical into optical energy result. The compensation can be done either before or after the distortion, and it can be of various types Distortions can be corrected by one or more equalizers so that all sections of the Can turn the transmission path made linear.

The new circuit arrangement for equalization is constructed according to the invention in such a way that one the channels contains switching means for changing the signal amplitude and two bridging one of the channels Branch circuits are present, each with two non-linear switching elements and one in between The resistor is switched on, and that the other channel is also connected on the output side to each of the resistors and that the characteristics of the non-linear switching elements of the two branch circuits run in such a way that through one branch circuit the distortions of the positive and through the other the distortions of the negative signal components are compensated.

Rectifiers are provided as non-linear switching elements. To change the signal amplitude an attenuator is provided in one channel. The arrangement can also be made that to change the signal amplitude in one channel, an amplifier with an adjustable gain factor is provided.

It is advisable to have a phase shift network in one channel to correct the phase shift of the amplifier arranged in this channel at the operating frequency of the circuit arrangement to be provided. The entire circuit can be constructed either symmetrically or asymmetrically and then be grounded with one side.

The non-linear switching elements are advantageously included in the two branch circuits opposite polarity switched on. Preferably there is a resistor with an adjustable, with the resistors in the two branch circuits connected tap parallel to the output side Arranged at the end of that channel which contains the amplifier. There are also switching means for setting the characteristic of the non-linear switching elements provided.

In a particular embodiment of the invention, the first channel contains two amplifiers in Series connection, with a resistor with an adjustable tap connected across the output of this channel is, and this tap is connected to the resistors «of the two branch circuits that between the ungrounded input terminal and the ungrounded output terminal of one amplifier lie.

In another embodiment are a main channel 'And a control channel with common input terminals and provided with an amplifier in the control channel, which is provided by a voltage divider with an adjustable tap is completed. The arrangement is such that the two branch circuits a resistor between the two non-linear switching elements with an adjustable Tap included and between the tap of the voltage divider at the amplifier output and the Low potential side of the main channel are connected that the non-linear switching elements in one branch circuit in the opposite direction to the non-linear switching elements of the other branch circuit are connected and that the taps of the resistors in the branch circuits with the side higher potential of the main channel are connected.

The circuit can also be constructed in such a way that at Using a main channel with an attenuator, the two branch circuits across the output terminals of the main channel and a resistor between the two contain non-linear switching elements with a tap, the non-linear switching elements in each branch circuit are polarized opposite to each other and a connection between the taps and the ungrounded input terminal of the attenuator.

The principle on which the operation of the equalizing circuit arrangement is based should now to be considered. First off the distorted input signal that will be equalized should derive two partial signals. These signals have unequal amplitudes and are either in phase or have a phase shift of 180 ° from one another. The unequal amplitude can can be achieved by amplifying or attenuating one of the two signals, or by doing the one signal amplifies and the other attenuates. One of these partial signals is a differential, i. H. subjected to amplitude dependent treatment, and then the two signals are combined again. This differential treatment can be achieved, for example, in that one of the signal paths is bridged by one or more controllable, non-linear switching elements or by the fact that one mixes the two signals with one another via one or more such switching elements. These elements also speak essentially to the instantaneous value of the current or the voltage in the circuit at. Therefore the amplitude of the smaller signal is influenced by that part of the larger signal which can pass through the non-linear device so that the output signal im essentially a function of the instantaneous voltage or the instantaneous current applied to the equalizer will. Furthermore, switching means are provided in order to change the shape of the current-voltage characteristic curve of the set non-linear switching elements and also to a different response for currents or Obtain voltages of different polarity. A plurality of such nonlinear ones can also be used Use devices to make a simultaneous correction for different polarities of the signal and for different curve shapes. aside from that bias currents or voltages can be used which are suitable for the generation of Curve shapes to correct the various distortions are suitable.

The invention and its features and advantages are better understood from the following individual description

Practice of exemplary embodiments in context with the figures. It shows

Fig. 1 is a schematic circuit of a symmetrical Circuit arrangement according to the invention,

Fig. 2 schematically shows an unbalanced circuit * arrangement with two amplifiers in the signal transmission path,

3 shows an asymmetrical circuit arrangement with an amplifier in the control channel and a phase shift network in the main channel and

4 shows an asymmetrical circuit arrangement using an attenuator.

Let us now consider the figures in detail.

The symmetrical circuit arrangement according to FIG. 1 contains a first transmission channel 9 which is connected between a pair of input terminals 5 and 6 and a pair of output terminals 7 and 8. The transmission channel 9 contains an amplifier 11 and a phase shift network 12, which are connected in series. The network 12 is provided to compensate for any phase distortion of the amplifier 11 in the frequency band of interest. In some cases this network can be omitted. The combined phase shift of the amplifier 11 and the network 12 can be either 0 or 180 ° at the selected working frequency f of the equalizer. This frequency can, for example, coincide with that of the color carrier if the circuit arrangement is to be used in a color television transmission system.

The two current branches 83 and 84 form parts of a branch circuit 13. The channel 9 and the branch circuit 13 are parallel with respect to the input terminals 35. The current branches 83 and 84 are connected to one another at their output ends via a resistor or a voltage divider with an adjustable tap 21, which is connected to the displaceable tap 16 of a voltage divider 17 lying transversely to the output end of the transmission channel 9. The branches 83 and 84 each contain non-linear switching elements 18 and 19. The branches 85 and 86 form parts of a further branch circuit 14 which is also connected in parallel to the input ends of the transmission channel 9. The output ends of these current branches 85 and 86 are also connected to point 16 via a voltage divider with an adjustable tap 26. Non-linear switching elements 22 and 23 are arranged in the branches 85 and 86, respectively.

The switching elements 18, 19, 22 and 23 can, for example Crystal diodes, copper oxide, selenium or electron tube rectifiers, neon tubes or similar Gas discharge tubes, as well as non-linear resistors, capacitors or inductors. she are shown here as rectifiers. Each of these switching elements can be replaced by two or more non-linear Switching elements are replaced, and there can be 6σ for biasing currents or voltages or additional Use series or shunt resistors to obtain the required characteristics necessary to correct the distortion of the input signal.

Are the tapping points 16, 21 and 26 in its middle position, then the circuit arrangement delivers no correction whatsoever. The branch circuit 13 otherwise results in a correction of the positive deviations of the output signal. If you move the tap 21, you can thereby expand the amplitude and -set compression. The branch circuit 14 results in a correction of the negative signal parts of the output signal. By adjusting the tap 26 one can adjust an expansion or a compression. The setting of the tap 16 and the selection of the gain factor of the amplifier 11 'determine the size and the range of the correction. the Gain the amplifier 11 can be made adjustable and then adjust so that there is no overall attenuation or that in the circuitry there is even some amplification.

If only an expansion of the signal amplitude is required, two of the non-linear switching elements, for example 19 and 23 are omitted. If only compression is required, the non-linear switching elements ^ and 22 can be omitted. FIG. 2 shows an asymmetrical circuit arrangement according to the invention, the two being connected in series Amplifiers 28 and 29 ″ in the transmission channel 27 between the input terminals 5, 6 and the output terminals 7, 8 contains. One side of the transmission channel is grounded at points 31, 32 and 33. Each of the amplifiers 28 and 29 has a phase shift of 180 ° at the frequency /, Die Current branches 34 and 35 are connected to the upper input terminal 5 at their input sides. the Input ends of current branches 88 and 89 are at an ungrounded point 38 between the amplifiers 28 and 29 connected. The branches 34 and 88 form parts of one branch circuit and are at their output ends via a voltage divider with an adjustable tap 39 with each other tied together. The output ends of branches 35 and 89 are also through a voltage divider with a adjustable tap 40 connected to one another. Points 39 and 40 are on an adjustable tap 36 of a voltage divider 37 which is parallel to the output terminals 7 and 8. Therefore bridge the current branches 34 and 35 both amplifiers 28 and 29, while the current branches 88 and 89 only the bridge the second amplifier. The non-linear switching elements 90, 91, 92 and 93, which are used here as rectifiers are shown in each case in the branch circuits 34, 88 and 35, 89. If the taps 36, 39 and 40 in their middle position, then the circuit arrangement does not provide any correction. The rectifiers 90 and 91 result in a correction of the amplitude for the positively directed parts of the input signal, while the rectifiers 92 and 93 equalize the amplitude of the negative signal parts. the Rectifiers 90 and 92 result in an expansion of the signal amplitude, while rectifiers 91 and 93 provide compression. The settings of the taps 39 and 40 determine the proportion of the equalizer characteristics between expansion and compression. The setting of the tap 36 and the gain of the Amplifiers 28 and 29 determine the size of the individual corrections.

Fig. 3 shows an unbalanced circuit arrangement with a single amplifier in a Control channel is arranged. The one between the input terminals 5, 6 and the output terminals 7, 8 Main channel 42 contains a phase shift network 43 and is grounded at points 44 and 45. The control channel 47, which is connected in parallel to the main channel 42 at its input terminals, contains an amplifier 48, the output of which is passed through a voltage divider 49 with an adjustable tap 50

is completed. One side of the control channel 47 is grounded at point 52.

The parallel combination of the two branch circuits 53 and 54 is in Reite with the control channel 47 switched. The branch 53 contains a series combination of two non-linear switching elements 55 and 56 and an intermediate resistor 57 with an adjustable tap 58. In the same way The branch 54 includes non-linear switching elements 60 and 61 and a resistor 62 with an adjustable Tap 63. The non-linear switching elements are shown here as rectifiers. The rectifiers are polarized in one direction in branch 53 and in the opposite direction in branch 54. The input ends of the branches 53 and 54 are connected to the tap 50, and the output ends are connected to the earthed output terminal 8. The taps 58 and 63 are at the output terminal 7. The size of the correction achieved is through the setting of the tap 50 and the Gain of amplifier 48 is determined. The division of the correction between the positive signal amplitudes and the negative signal amplitudes depend on the setting of taps 58 and 63.

The network 43 has a phase shift chosen to compensate for the phase shift of the amplifier 48 at the frequency f. The circuit arrangement therefore only provides loss compensation. In some cases, however, the network 43 can be omitted.

Fig. 4 shows an unbalanced circuit arrangement which does not require an amplifier of its own, although such can be placed in series with it if so desired. An attenuator 65 is in Main channel 66 connected between the input terminals 5, 6 and the output terminals 7, 8. One Side is grounded as shown at points 67 and 68. Two impedance branches 70 and 71 are parallel connected to the output ends of the channel 66. Branch 70 contains a series combination two non-linear switching elements 72 and 73 and a resistor 74 arranged between them with adjustable tap 76. In the same way, branch 71 contains non-linear switching elements 77 and 78 and a resistor 79 with a tap 80. 4-5 The switching elements 72, 73, 77 and 78 are used as rectifiers shown. The rectifiers in branch 70 are polarized in opposite directions to those in branch 71 and are also polarized opposite to one another, so that they are connected to one another in a branch with the anodes while they are connected to their cathodes in the other branch. A line 81 connects the input terminal 5 to the taps 76 and 80, creating a second channel.

The attenuator 65 is preferably made adjustable, either continuously or in steps so that the output voltage of the main channel 66 can be adjusted so that the required Waveform to compensate for amplitude compression or expansion results. The setting of tap 76 determines the correction of the positive signal amplitude, and the setting of the Point 80 controls the correction of the negative signal amplitude.

In all of the arrangements described here, DC circuits or DC earth connections are used for the pulsating and rectified currents generated in the rectifiers as being present accepted. These DC circuits should be used in the phase shifter networks, amplifier inputs, Attenuators or in the subsequent devices with which the circuit arrangement is connected is to be present. If this is not the case in a special case, then the necessary circuits can for the return to earth can be inserted through appropriately arranged resistors. In the circuit arrangement according to the invention, for example, if the type of distortion is such that one or more non-linear switching elements are seldom or never needed, In order to achieve sufficient equalization, these switching elements are omitted. Also can the circuit arrangement also has an amplifier in the first transmission channel and an attenuator in the second, parallel transmission channel included.

Claims (13)

Patent claims: 1. Circuit arrangement for compensating for an amplitude compression or expansion of a AC signal with a first transmission channel and a second transmission channel, which has its input to the first channel is connected to points whose phase difference is 180 °, characterized in that one of the channels contains switching means for changing the signal amplitude and two one of the channels Bridging branch circuits are present, each with two non-linear switching elements and each contain a resistor connected in between, and the other channel on the output side is connected to each of the resistors and that the characteristics of the non-linear switching elements of the two branch circuits run in such a way that the Distortion of the positive and by the other the distortion of the negative signal components be compensated. 2. Circuit arrangement according to claim 1, characterized in that the non-linear switching elements Rectifiers (18,19,22,23) are provided (Fig. 1). 3. Circuit arrangement according to claim 1 or 2, characterized in that to change the Signal amplitude in the one channel (66) an attenuator (65) .provisions (Fig. 4). 4. Circuit arrangement according to claim 1 or 2, characterized in that to change the Signal amplitude in one channel (9,27,47) an amplifier with an adjustable gain factor (11, 29, 48) is provided (Fig. 1, 2 and 3) 5. Circuit arrangement according to claim 4, there-. characterized by 'that the ein.Kanal (9) a Phase shift network (12) for correcting the phase shift of the amplifier (11) in this Contains channel at the operating frequency of the circuit arrangement (Fig. 1). 6. Circuit arrangement according to one of claims 1 to 5, characterized in that it is constructed symmetrically (Fig, I). 7.. Circuit arrangement according to one of the claims 1 to 5, characterized in that they are constructed asymmetrically and one side is earthed (Figs. 2, 3 and 4). 8. Circuit arrangement according to one of the preceding Claims, characterized in that the non-linear switching elements (18, 19 or 22, 23) in each of the two branch circuits are switched on with opposite polarity (Fig. 1). 9. Circuit arrangement according to claim 4 to 6, characterized in that a resistor (17) with an adjustable one connected to the resistors (21 and 26) in the two branch circuits Tap (16) arranged parallel to the output-side end of that channel (9) containing the amplifier (11) (Fig. 1). 10. Circuit arrangement according to claim 9, characterized in that switching means for adjustment the characteristic of the non-linear switching elements are provided. 11. Circuit arrangement according to claim 1, 2 and 7, the first channel of which contains two amplifiers in series, characterized in that a resistor (37) with an adjustable tap (36) is connected across and this tap with the resistors to the output of this channel (27) (39 or 40) of the two branch circuits (34, 90, 39, 91, 88 and 35, 92, 40, 93, 89) connected between the non-earthed input terminal (5) and the non-earthed output terminal (38) of the an amplifier (28) (Fig. 2). 12. Circuit arrangement according to claim 1, 2 and 7 with a main channel and a control channel with common input terminals and with an amplifier in the S expensive channel, which is completed by a voltage divider with an adjustable tap, characterized in that the two branch circuits (53 and 54) each contain a resistor (57 or 62) between the two non-linear switching elements (55, 56 or 60, 61) with an adjustable tap (58 or 63) and between the tap (50) of the voltage divider (49) on the Amplifier output and the low potential side (8) of the main channel (42) are connected so that the non-linear switching elements (55, 56) in one branch circuit (53) are opposite to the non-linear switching elements (60, 61) of the other branch circuit (54) are connected and that the taps (58 and 63) of the resistors (57 and 62) in the branch circuits with the side (7) of higher potential of the main channel (42) are connected (Fig. 3). 13. Circuit arrangement according to claim 1 and 2 with a main channel with an attenuator, characterized in that the two branch circuits (70 and 71) are connected transversely to the output terminals (7, 8) of the main channel (66) and each have a resistor (74 or 79) between the two non-linear switching elements (72, 73 or 77, 78) with a tap (76 or 80) contain that the non-linear switching elements in each branch circuit are polarized opposite to one another and that a connection between the taps (76 or 80) and the ungrounded input terminal (5) of the attenuator (65) is provided (Fig. 4). Considered publications:
German patent specification No. 866 054. 1 sheet of drawings © 009 507/28 * 4.