DE1122578B - Circuit arrangement for the stereophonic reproduction of signals - Google Patents

Description

The patent application N18053 Villa / 21a ² relates to a circuit arrangement for the stereophonic reproduction of signals which, in the form of the sum signal A + B of the associated, stereophonic signals A and B and the difference signal A ~ B modulated in amplitude onto a subcarrier frequency, are mutually exclusive belonging signals A and B are supplied to the input circuit of the circuit arrangement, the stereophonic reproduction apparatus is provided with separate playback channels, which are fed by the coherent stereophonic signals A and B, and wherein the low-frequency sum signal A + B and to the subcarrier frequency in the amplitude modulated differential signal A - B are fed jointly to two amplitude demodulators which are polarized in opposite directions with respect to the low-frequency sum signal A + B and whose outputs are each connected to the input of one of the separate channels. As described in detail in the main patent application, particular advantages are achieved with the relevant circuit arrangement for the stereophonic reproduction of signals; the described arrangement is characterized, among other things, by a simple design, good playback quality and favorable crosstalk properties, the crosstalk between the channels being reduced to a minimum by simple means, e.g. B. to less than 30 to 40 db.

The invention aims at a further improvement of a circuit arrangement of the type mentioned at the beginning, whereby the reproduction quality can be increased even further by simple means, in particular in arrangements for stereophonic reproduction of signals in which the low-frequency sum signal A + B has a higher level than that the subcarrier frequency modulated on the difference signal A - B.

The circuit arrangement according to the invention is characterized in that a frequency-dependent attenuator is switched on between the input of the stereophonic playback device and the two amplitude demodulators, which in each case has an essentially constant attenuation in the frequency bands of the low-frequency sum signal A + B and the difference signal AB modulated onto the subcarrier frequency which is greater for the sum signal A + B lying in the low frequency band than for the difference signal A-B modulated onto the subcarrier frequency.

To the improvement achieved in the transmission circuitry

for stereophonic reproduction

of signals

Addition to patent application N 18053 VIII a / 21a ^s
(Interpretation document 1100 086)

Applicant:

NV Philips' Gloeilampenfabrieken,
Eindhoven (Netherlands)

Representative: Dipl.-Ing. E. Walther, patent attorney,
Hamburg 1, Mönckebergstr. 7th

Claimed priority:
Netherlands of March 2, 1960 (No. 248 992)

Frans Louis Henri Marie Stumpers

and Rudolf Schutte, Eindhoven (Netherlands),

have been named as inventors

To fully utilize quality are, according to a further feature of the invention, the separate ones Channels of the stereophonic reproduction device through a frequency-dependent compensation network to compensate for that caused by the frequency-dependent attenuator in the separate channels Crosstalk coupled with each other. The invention and its advantages are set out in the Drawing explained in more detail, for example.

Fig. 1 shows a stereophonic radio receiver with a circuit according to the invention;

Fig. 2 shows a frequency attenuation characteristic curve for explaining the circuit according to the invention, and FIG. 3 shows a variant of the stereophonic receiver illustrated in FIG. 1.

The stereophony receiver shown in Fig. 1 is suitable for receiving stereophony signals modulated on the same carrier frequency in frequency, which are derived from the sum signal A + B of the coherent stereophony signals A and B, z. B. in the band from 30 to 15,000 Hz, and a subcarrier frequency modulated in amplitude by the difference signal A - B of 35 kHz, the modulation signal formed in this way in the band

109 787/290

From 30 to 50000Hz the carrier frequency is frequency-modulated with a frequency of about 100 MHz with a stroke of 75 kHz. The low-frequency sum signal A + B with a z. B. by 6 db higher level than the modulated on the subcarrier frequency difference signal A-B emitted.

The stereophonic receiver is equipped with a receiving antenna 1 and an intermediate frequency stage 2 provided with a mixer stage and an oscillator 3 connected thereto, whose obtained by mixing Intermediate frequency oscillations in the band of 10 700 kHz after amplification and any limitation are fed to an output band filter in the intermediate frequency stage 2, which is through two coupled circles 4 and 5 is formed.

The band filter 4, 5 forms part of a per se for the demodulation of normal frequency modulation transmissions known type of frequency modulator and contains two connected to the ends of the circuit 5, in the opposite direction for current permeable rectifiers 6, 7, which have an output impedance 8 are connected, with an intermediate tapping point of the circle 5 at the end a coupling coil 9 coupled to the circular coil 4 is connected. The output impedance 8 of the frequency demodulator consists of a resistor 10, which is created by connecting two capacitors in series 11, 12 is bridged with a grounded connection point and a smoothing capacitor 13, wherein the output voltage of the frequency demodulator is a center tap of the output resistor 10 is taken.

An output voltage occurs at the output of a frequency demodulator, which is formed by the sum signal A + B in the band from 30 to 15,000 Hz and the difference signal A - B in the frequency band from 20 to 50 kHz, modulated on the subcarrier frequency in amplitude. This output voltage is fed via the separating capacitor 14 to a device 16 to be discussed further below in order to recover the coherent stereophony signals A and B , which are fed to playback devices 19, 20 after low-frequency amplification in separate low-frequency amplifiers 17, 18.

The low-frequency amplifiers 17 and 18, which are of identical design, are formed by triodes with grid leakage resistors 21 and 22 and non-bridged cathode resistors 23, 24 or 25 and 26, which cause negative feedback of the triodes 17, 18. The amplified, coherent stereophonic signals A and B are taken from the output resistors 27, 28 in the anode circuits of the triodes 17, 18, which, as shown schematically in the figure, are connected to the playback devices 19, 20 via isolating capacitors 29, 30 .

In order to recover the coherent stereophonic signals A and B from the output voltage of the frequency demodulator in a simple manner, this output voltage is supplied to the device 16 from the sum signal A + B and the differential signal A-B modulated on the subcarrier frequency in amplitude polarized amplitude demodulators, the input circuits of which are connected in parallel to the output circuit of the frequency demodulator 4 ... 9. Each of these amplitude demodulators is provided with a rectifier cell 31, 32 and an output impedance connected to it, which is formed by the parallel connection of a resistor 33 or 34 and a capacitor 35 or 36. The output voltages of the amplitude demodulators 31, 32 are fed via isolating capacitors 37 and 38 to the control grids of the triodes 17 and 18, which are connected as low-frequency amplifiers. With the exception of the opposite current flow directions of the rectifier cells 31, 32, the amplitude demodulators are of identical design.

If the output voltage of the frequency demodulator 4 ... 9 consisting of the audio-frequency sum signal A + B and the differential signal AB modulated on the subcarrier frequencies in the amplitude occurs at the input of the demodulators 31, 32, then each of the amplitude demodulators 31, 32 leads

ao an amplitude demodulation of the difference signal AB modulated onto the subcarrier frequency, the audio-frequency sum signal A + B being effective as a threshold voltage for the two oppositely polarized rectifier cells 31, 32 and thus an operating point shift of the two rectifier cells 31, 32 in the rhythm of the sum signal A in opposite directions + B accomplished. In addition to the amplitude demodulation of the enveloping signal formed by the difference signal A-B , there is thus a sum and a difference formation of the audio-frequency difference and sum signals A-B and A + B , which is why the output circuits 33, 35 and 34, 36 of the amplitude demodulators 31, 32, the coherent stereophony signals A and B can be taken, which are fed to the two playback devices 19, 20 via the two low-frequency amplifiers 17 and 18, respectively.

In addition to a good playback quality and a frequency-independent phase curve, the crosstalk between the two channels, the z. B. due to mutual coupling or to an unequal level between the (A + ß) signal and the 04 - B) signal in the entire audio frequency band of 15 kHz is reduced to less than 30 to 40 db. The result is that frequency-independent crosstalk occurs, the crosstalk voltages having a fixed phase relationship with the stereophonic signals A and B ; these crosstalk voltages are either in phase or out of phase with the stereophonic signals A and B. The voltages in the two channels can in particular with a good approximation by A + aB

and

B + aA

are shown, where aB and aA denote the crosstalk voltages and α denote the crosstalk factors, the size and phases of which are the same and which can have both a positive and a negative value.

As is described in more detail in the main patent application ben, with a positive value of the frequency- independent crosstalk factors α, so that the signals in the two channels are represented by A + nB and B + aA , a compensation of

Crosstalk between the channels is achieved by inserting a resistor 41 between the cathode resistors 23, 24 and 25, 26. If the frequency-independent crosstalk factors have negative polarity, with the signals in the two channels being denoted by A - aB and B - aA , the crosstalk is compensated for by the parallel connection between the two output impedances 33, 35 and 34, 36 of the amplitude demodulators a resistor 40 and a capacitor 15 is switched on, which parallel circuit 40, 15 is dimensioned such that the time constant of the network 40, 15 is equal to the time constant of the output impedance 33, 35 and 34, 36 of the amplitude demodulators 31 and 32, respectively. As is explained in more detail in the main patent, the network 40, 15 also leads to an improvement in the reproduction quality.

In this way, a very good reproduction quality and a fixed phase progression achieved and the crosstalk between the two channels in the entire audio frequency band from 30 to 15,000 Hz to less than 30 to 40 db. In addition, the shown Receivers can be made suitable in a simple manner for the usual frequency modulation reception, by connecting the output circuits of the amplitude demodulators 31, 32 to one another by means of a switch 42 get connected.

According to the invention, a further improvement in the transmission quality is obtained by placing a frequency-dependent attenuator 43 between the separating capacitor 14 and the two amplitude modulators 31 and 32 with in the frequency bands of the audio-frequency sum signal A + B (30 to 15,000 Hz) and the subcarrier frequency modulated difference signal AB (20,000 to 50,000 Hz) is switched on with essentially constant attenuation, the attenuation for the sum signal A + B lying in the audio frequency band being greater than for the difference signal A-B modulated onto the subcarrier frequency. In the embodiment shown, the frequency-dependent attenuator 43 is formed by a voltage divider with a series resistor 45 and a cross resistor 46, and the series resistor 45 is bridged by a capacitor 47 to form a high-pass filter that is permeable to the difference signal A-B modulated to the subcarrier frequency is; the cutoff frequency of the high-pass filter is z. B. 10,000 Hz. Fig. 2 shows the attenuation characteristic of the frequency-dependent attenuator 43; the attenuation of the element 43, measured in db, is given as a function of the frequency.

In this way, the output signal of the frequency demodulator 6 ... 9, which consists of the sum signal A + B in the band from 30 to 15,000 Hz and from the difference signal A-B modulated onto the subcarrier frequency of 35 kHz in the band from 20 to 50 kHz is fed via the frequency-dependent attenuator 43 to the amplitude demodulators 31, 32, the low-frequency sum signal A + B experiences greater attenuation in the frequency-dependent element 43 than the difference signal A - B modulated onto the subcarrier frequency. In the exemplary embodiment shown, the greater attenuation of the low-frequency sum signal z. B. 6 db. This measure leads to a further improvement in the transmission quality; In particular, nonlinear distortions still present in the two amplitude demodulators 31, 32 during the amplitude demodulation and during the formation of the sum and difference are substantially reduced. However, this improvement in quality cannot yet be fully exploited with the circuit described, because frequency-dependent crosstalk occurs simultaneously in the mutually separated channels, but this can be easily compensated for by coupling the separate channels of the stereophonic playback device to one another by means of a frequency-dependent compensation network is used.

This is a frequency-dependent cross-talk at the higher frequencies of the coherent, stereophonic signals A and B. As seen from the attenuation characteristic curve of Fig. 2 shows the signal frequencies experienced in the low-frequency sum signal A + B of about 10 kHz, and the signal frequencies of the difference signal modulated onto the subcarrier frequency in the vicinity of 20 kHz, which thus correspond to the higher frequencies of the stereophonic signals A and B , a frequency-dependent attenuation, while the frequency-dependent phase shifts occurring in the network 43 further contribute to the frequency-dependent crosstalk.

The crosstalk between the two stereophonic channels is of such a nature as itself can be determined mathematically and experimentally that the signals in these channels by the formula

Α + γΒ Β + γΑ

can be represented, the frequency-dependent crosstalk factors; ■ in the two channels being the same, while the crosstalk factors γ also have a simple, frequency-dependent course. These two properties of the frequency-dependent crosstalk brought about by the frequency-dependent attenuator 43 enable this crosstalk to be precisely compensated for in a surprisingly simple manner. This is achieved in that the resistor 41 lying between the cathode circuits of the low-frequency amplifiers 17, 18 is bridged by a member 44 which consists of the series connection of a resistor 48 and a capacitor 49, which elements are dimensioned such that the time constant of the elements 41, 48, 49 with the cathode resistors 23, 24, 25 and 26, which together form a frequency-dependent network, is practically equal to the time constant of the frequency-dependent attenuator 43. In practice it turns out that good results are also achieved if the resistor 48 in the network 44 is omitted. By surprisingly simple means in this way, while maintaining a favorable crosstalk, the z. B. between the two stereophonic channels in the entire frequency band is less than 30 to 40 db, a significant improvement in playback quality is achieved, which is particularly important for stereophonic playback of signals in which the low-frequency sum signal A + B has a higher level, e.g. in the illustrated embodiment 6 db than that on the

Subcarrier frequency modulated difference signal AB.

If a precisely balanced frequency response is required in the stereophonic playback device described, the higher signal frequencies of the stereophonic signals A and B should be weakened somewhat, since the higher frequencies of the attenuator 43 and the compensation of the frequency-dependent crosstalk by means of the network 44 Signals A and B are somewhat preferred at the same time. This can be achieved in a simple manner in that in series with each of the anode resistors 27, 28 of the low-frequency amplifiers 17, 18 a capacitor 50 or 51 bridged by a resistor 52 or 53 is attached; the time constant of these networks 50, 52 or 51, 53 is approximately equal to the time constant of the frequency-dependent element 43.

Some data of a circuit that has been extensively tested in practice is mentioned below Specified type:

Resistance 45 10 kOhm

Resistor 46 10 kOhm

Capacitor 47 1500 pF ^a5

Capacitor 50, 51 390 pF

Resistance 41 80 kOhm

Resistor 48 7.5 kOhm

Capacitor 49 27OpF

Resistance 52.53 lOOkOhm

These measures can easily be implemented even if the stereo receiver is fitted with transistors be performed. If z. B. the low frequency amplifier in the separate channels transistors in have a common emitter circuit with unbridged emitter resistors, so this can be achieved the frequency-dependent attenuator 43 brought about crosstalk in a simple manner be compensated that a network between the emitter electrodes of the transistors in the emitter circuit is attached, which consists of a series circuit bridged by a resistor Resistance and a capacitor of appropriate size exists and that again with the unbridged Emitter resistors form the frequency-dependent compensation network.

Both the frequency-dependent attenuator 43 and the compensation network to compensate for the frequency-dependent crosstalk can also trained in other ways. It is advantageous that the frequency-dependent attenuator 43 has a simple embodiment. This not only enables easy assembly, but also by simple means a practically accurate one in the whole frequency band to be reproduced Compensation of the frequency-dependent crosstalk between the channels.

Fig. 3 shows a variant of the receiver illustrated in Fig. 1, which is also a simple one frequency-dependent attenuator has. Corresponding elements have the same reference numbers designated.

In this embodiment, the frequency-dependent attenuator is through a series resistor 54 and a transverse resistor 55 formed, with an inductance in series with the transverse resistor 55 56 is turned on, which together with the resistors 54, 55 a high-pass filter for the the subcarrier frequency forms the modulated differential signal. The attenuation characteristic of the frequency-dependent Attenuator 54, 55, 56 has the same course as in the diagram of FIG. 2, and the crosstalk between the channels has the same frequency-dependent profile as that in FIG. 1 illustrated facility.

This embodiment results in a significant simplification in that the elimination of the frequency-dependent crosstalk as well as the achievement of a flat frequency characteristic can be brought about by a single network which, as can be seen from the figure, is connected as a common output impedance in the output circuit of the low-frequency amplifiers 17, 18 . The network consists of a parallel circuit of a capacitor 57 and a resistor 58, wherein said time constant is made 56 approximately equal to the time constant of the frequency dependent element 54, 55th In exactly the same way as was described with reference to FIG. 1, the reproduction quality is significantly improved while maintaining a favorable crosstalk ratio between the channels.

The data of a circuit of the type mentioned that has been extensively tested in practice are:

Resistor 54 10 kOhm

Resistance 55 10 kOhm

Inductance 56 150 mH

Resistance 58 200 kOhm

Capacitor 57 68 pF

Resistance 41 8 kOhm

Similar to the circuit according to FIG. 1, the circuit described with reference to FIG. 3 is for transistor assembly suitable. In this case, the compensation network that consists of the parallel connection of the capacitor 57 and the resistor 58 exists as a common output impedance in the Collector circuit of the emitter-operated transistors of the low-frequency amplifier inserted will.

For the sake of completeness, it should be mentioned here that the frequency-dependent attenuator 45, 46, 47 according to Fig. 1 in conjunction with the correction network 57, 58 in Fig. 3 and that the frequency-dependent Attenuator 54, 55, 56 of FIG. 3 in combination with the correction network 41, 48, 49 of FIG. 1 can be used.

Claims (11)

PATENT CLAIMS: 1. Circuit arrangement for the stereophonic reproduction of signals which are fed to the input circuit of the circuit arrangement in the form of the sum signal A + B of the coherent stereophonic signals A and B and the amplitude-modulated difference signal A - B of these coherent signals and B, wherein the stereophonic playback device is provided with separate playback channels, which are fed by the coherent stereophonic signals A and B , and wherein the low-frequency sum signal A + B and the difference signal AB modulated in amplitude on the subcarrier frequency together have two amplitude demodulators are supplied which are polarized in opposite directions with respect to the low-frequency sum signal A + B and whose outputs are each connected to the input of one of the separate channels, according to patent application N 18053 VIII a / 21 a ² , characterized in that between the input of the stereophonic playback device and the two amplitude demodulators (31, 32), a frequency-dependent attenuator (43) is switched on, which has an essentially constant attenuation in the frequency bands of the low-frequency sum signal A + B and the η difference signal A-B modulated onto the subcarrier frequency, which is greater for the sum signal A + B lying in the low frequency band than for the difference signal AB modulated onto the subcarrier frequency. 2. Circuit arrangement according to claim 1, characterized in that the separate channels of the stereophonic playback device to compensate for the frequency-dependent crosstalk caused by the frequency-dependent attenuator (43) in the separate channels are coupled to one another by a frequency-dependent compensation network. 3. Circuit arrangement according to claim 1 or 2, characterized in that the frequency-dependent attenuator (43) consists of a series resistor (45) and a transverse resistor (46) and that the series resistor (45) is bridged by a capacitor (47), which together with these resistors, a high-pass filter which is permeable to the differential signal A - B modulated onto the subcarrier frequency is formed. 4. Circuit arrangement according to claim 1 or 2, characterized in that the frequency-dependent attenuator consists of a series resistor (54) and a transverse resistor (55) in series with an inductance (56) which, together with these resistors, is a modulated onto the subcarrier frequency Difference signal A-B forms high-pass filter permeable. 5. Circuit arrangement according to claim 3 or 4, in which the amplitude demodulators extracted, stereophonic signals in the separate channels existing tube amplifiers are supplied, characterized in that the tube amplifiers (17, 18) are not bridged Cathode resistors (23, 24 or 25, 26) included and that between the cathode circuits the tube amplifier a frequency-dependent network (44) is switched on, the consists of the parallel connection of a capacitor (49) and a resistor (41) and with the non-bridged cathode resistances form a frequency-dependent compensation network, which compensates for the frequency-dependent crosstalk caused in the channels will. 6. Circuit arrangement according to claim 3 or 4, in which the amplitude demodulators extracted stereophonic signals in the separate channels lying transistor amplifiers are supplied in emitter circuit, characterized in that the transistor amplifiers emitter resistances not bridged in a common emitter circuit in the emitter circuit contain and that between the emitter circuits of the transistor amplifier a frequency-dependent Network is switched on, which consists of the parallel connection of a resistor and a capacitor exists and with the unbridged emitter resistances a frequency-dependent Compensation network forms which the frequency-dependent generated in the channels Crosstalk compensated. 7. Circuit arrangement according to claim 5 or 6, characterized in that in series a resistor (48) is connected to the capacitor (49) of the frequency-dependent network (44) is. 8. Circuit arrangement according to claim 5, 6 or 7, characterized in that in the Output circuit of each of the low-frequency amplifiers for linearizing the frequency response, the parallel connection a resistor (52 or 53) and a capacitor (50 or 51) is inserted. 9. Circuit arrangement according to claim 3 or 4, in which the amplitude demodulators extracted stereophonic signals in the separate channels lying tube amplifiers are supplied, characterized in that the frequency-dependent compensation network to compensate for the evoked in the channels frequency-dependent crosstalk due to a common anode impedance in the anode circuit of the two tube amplifiers (17,18) formed from the parallel connection of a resistor (58) and a capacitor (57) consists. 10. Circuit arrangement according to claim 3 or 4, in which the amplitude demodulators taken, stereophonic signals in the separate channels lying transistor amplifiers are fed in emitter circuit, characterized in that the frequency-dependent Compensation network to compensate for the frequency-dependent caused in the channels Crosstalk is formed by a common collector impedance in the collector circuit of the two transistor amplifiers, which from the parallel connection of a resistor and a capacitor. 11. Circuit arrangement according to one of the preceding claims, characterized in that that the time constant of the frequency-dependent compensation network is practically equal to the Is the time constant of the frequency-dependent attenuator. 1 sheet of drawings 109 787/290 1.62