FR2532502A1 - TELEVISION SOUND DETECTION DEVICE WITH FREQUENCY TRANSLATION PHASE LOCKED LOOP - Google Patents

Abstract

THE INVENTION CONCERNS A TELEVISION SOUND DETECTION DEVICE WITH A FREQUENCY TRANSLATION PHASE LOCKING LOOP. THE DEVICE MAINLY INCLUDES A CONTROL OSCILLATOR 50, A MIXER 44, A PHASE DETECTOR 48 AND A LOW PASS FILTER 52 AT THE OUTPUT OF WHICH SOUND INFORMATION APPEARS. THE INVENTION APPLIES IN PARTICULAR TO STEREOPHONIC TELEVISION RECEIVERS.

Description

2532-502

  The present invention relates to the treatment

  sound signals in television, and concerns more

  particularly a phase locked loop with trans-

  Frequency detection to detect sound information.

  The transmission of multi-channel sounds for

  Stereophonic and bilingual broadcasting involves the use of

  be one or more subcarriers of sound, these sub-

  carriers increasing the bandwidth of

  television sound from 15 kHz to about 90 kHz or more.

  As a result, the snoring that is produced in the

  Sound signal processing channel is becoming more pronounced.

  Snoring that can be defined as the result of

  state of the image-related modulation transferred to the sound signals has always been present to a certain degree in a television signal processing circuit but has

  always been kept within tolerable limits by different

various circuit techniques.

  In the early days of television, image sound signals were processed in separate channels that were located behind the tuning circuits.

  separation avoids any significant mutual action in the reception

  carrier between image and sound carriers and thus virtually eliminates the snoring produced at the receiver But

  unfortunately, the frequency variations of the oscilla-

  the local agreement partner resulting from a drift of the

  Accurate autonhetic cord are applied to the intermediate frequency sound carrier as well as to the intermediate frequency image carrier and are detected as spurious interference (humming) by the sound frequency modulation detector. the sound channel has a much narrower bandwidth than that of the picture channel, the receiver must be tuned for better sound and not for a better picture. The modern television receivers almost universally implement the method of processing sound signals between the carriers According to this method

  the image carriers 7 th sound processed after the

  cooked in a common intermediate frequency channel

  which has a particular intermediate frequency bandwidth response which (1) attenuates the sound carrier by about 20dB more than the image carrier and (2) decreases the image carrier by 6dB on

  the high frequency slope of the frequency bandwidth

  Then, the larger image carrier is processed in the video channel to detect the video information and, to recover the sound information, the two intermediate frequency carriers are mixed to form a sound signal.

  intermediate carrier having a frequency corresponding to

  unlike the intermediate carrier frequencies

  For example, in the NTSC system, an image carrier of 45.75 M Hz is mixed with a 41.25 M Hz sound carrier to produce a 4.5 sound signal.

  M Hz between carriers The detection process between

  This is particularly advantageous because common-mode frequency modulation in the sound and picture carriers (caused for example by variations of the local tuning oscillator in the receiver itself and in the attached devices to which

  the receiver can be connected, for example a converts

  TV target) is canceled by the mixing of the intermediate frequency signals when the carrier-to-carrier sound signal is developed.

  between the carriers is not free of snoring.

  Although the response of the intermediate frequency bandwidth between the carriers is necessary to

  correct detection of the image carrier, its use

  the use tends to significantly increase snoring on

  sound compared to the separate channel process of

  ge and sound, (1) by a notable attenuation of the

  and a resulting reduction in the ratio of

  signal-sound signal, and (2) attenua-

  unequal intermediate frequency image carrier sideband which applies an accidental phase modulation to the image carrier, often called Nyquist modulation, introducing a distortion of the sound signal during mixing between the carriers; in the carrier-to-carrier system, a high degree of modulation or over-modulation of the picture drummer (which is frequently caused by overlapping local neighboring stations) may eliminate the image carrier signal and cause snoring at the frequency of lines and frames (i.e. 15,734

  Hz and 60 Hz in the NTS Co system The problem of snoring

  between carriers is described in more detail in an article entitled Intercarrier Bèzz Phenomena Analysis

  and Cure 'by P Foekens and Co Go Ellers in IEEE Trans-

  shares on Consumer Ele 6 tronicsv Acit 1981, pages 381 to

  Snoring on the sound produced by a system

  between carriers (although present) can be tolerated in monophonic television receivers because of the relatively narrow bandwidth of the receiver's sound channel But with the greater bandwidth of its n-channel devices Ultimate snoring

  is also increased and is no longer in all-

  lerableso A sound detection device has been developed, combining the separate and between carrier and

  can be called 'carrier separation'.

  This position is described in the aforementioned article by P Fockens and C G Eilers. According to this arrangement 9 after the tuning circuit 9 the image carrier signal is treated separately =

  the sound carrier signal to extract sound information.

  However, the image and sound carriers in intermediate frequency are processed together in a carnelal of sound to detect the information of sound according to the system between porteussdecorit above As in this arrangement, the frequency filter response Intermediate required to detect the video signal in the sideband is not included in the sound channel, the Nyquist-effect snoring is virtually eliminated. However, since the carrier-to-carrier methods are now the carriers of sound,

  intermediate frequency image are processed together

  in the inter-frequency amplification channel

  Thus, the distortion associated with the timing of the signal of

  sound, caused by nonlinear effects in the ampli-

  intermediate frequency indicator and the degree of modula-

  video are two sources of snoring associated with

  the system between carriers that are not eliminated.

  In addition, circuits: additional as amplifi-

  between carriers, circuits granted and a

  Criminator are also necessary.

  The invention therefore relates to a device for detecting

  sound signal that combines the advantages of

  separation and carrier processes without their

  individual convenients and with a minimum of complexity

  In accordance with the invention, a device for

  perceiving sound information from a television signal including sound carrier signals and

  of intermediate frequency image comprises an oscilla-

  controlled transmitter producing a frequency output signal

  controlled and a phase locked loop to trans-

  frequency converter with a frequency mixer and a phase detector The mixer receives the oscillator output signal at one input and the intermediate frequency image carrier signal at the other input The phase detector receives the signal of its intermediate frequency has an input and the output of the mixer to the enbreed A low-pass filter connected between the output of the phase detector and a control input of the oscillator completes the locking loop of

  phase by producing a control signal for the oscilla-

  The detected sound information appears at the output of the low-pass filter. In the present phase-locked loop device, it is necessary to provide with the television sound signal detection device a device for indicating the presence of

rasites in the video signal.

  Other features and advantages of the

  will be better understood when reading the description of

  following example of embodiments and with reference to the accompanying drawings in which:

  Fig 1 is a simplified diagram of a receiver

  television transmitter comprising a sound detection device according to the invention,

  Figure 2 is a simplified diagram of a

  television receiver concerning another way of reali-

  tion of a loop-type sound detection device

  phase shifting with frequency translation according to the

  Figure 3 is a schematic diagram of another embodiment of a sound detection device.

  with phase-locked loop with frequency translation

  quence for the television receiver of Figure 2, also according to the invention, and

  Figure 4 is a simplified schematic diagram of a

  television receiver including another mode yet

  embodiment of the invention with a device for

  give a signal indicating spurious pulses.

  According to Figure 1, a broadcast signal of

  television received by an antenna e is applied to a cir-

  cooks lo ok which includes a high amplifier

  frequency 12, a mixer 14 and a local oscillator 16.

  The tuning circuit 10 selectively converts the signals

  image carrier and high frequency sound of a

  particular television in carriers of frequency

  intermediate frequency such as 45.75 M Hz and 4-1.35 MH Hz

  in the NTSC system Frequency carriers

  quence appear at the output terminal

  of the tuning circuit 18 The image carrier of frequency

  45.75 M Hz intermediate frequency is an amplitude modulated signal which contains the composite image information The 41.25 EM Hz intermediate frequency sound carrier is a frequency modulated signal A common signal processing cir- cuit television in

  colors comprising a channel 20 for filtering and amplifying

  intermediate frequency, an imaging detector

  Ge 22 and an image signal processor 24 react to the intermediate frequency image carrier at terminal 18, producing the color video signals of red R, green V and blue B for a cathoscope (not shown). ) that produces a color image of a

  television scene In addition, a tuned floor 26 of

  and amplifier delivers a filtered version, am-

  folded and limited frequency carrier signal

  intermediate stage at the image detector 22 for the de-

  synchronous recording of the composite video signal of the

  of intermediate frequency image The output of

  It is also applied to an accurate autotune detector 28 via a phase shift circuit 90 which produces a signal of

  precise automatic tuning control at the exit of

  28, this signal being applied to the oscillator

  In this manner, the frequency and phase of the local oscillator signal applied to the mixer 14 are aligned with the frequency and phase of the received high frequency image carrier.

  operation of the image detector 22, the limiter / am-

  26, the automatic tuning detector 28 and

  depondator 30 are described in more detail in the

  of United States of America No. 4,263,611.

  The intermediate frequency channel 20 has a current bandwidth response 32 in which

  the intermediate frequency image carrier P is des-

  from 6 d B on the higher frequency slope of 7 - the bandwidth response 32 and the intermediate frequency sound carrier S is located at about 25 d B

  lower on the lower frequency slope of the

  Thus, the residual sideband video information can be detected without significant interference.

  of the carrier band of sound in intermediate frequency.

  Unfortunately, the bandwidth response 32 produces what is called a Nyquist carrier phase modulation on the intermediate frequency image carrier

  because of the asymmetrical attenuation of the ban-

  Laterals of the Interval Frequency Image Carrier

  In a common sound detection device

  between carriers, this Nyquist distortion of the

  Intermediate frequency image distortion causes carrier-to-carrier sound distortion due to mixing of sound carriers and intermediate frequency images This distortion of the carrier-to-carrier sound signal causes humming of the sound. the effect of Nyquist increases in direct relation with the increase of bandwidth of the sound signal Thus, if we consider that the lare

  bishop of a signal of his omposite containing

  subcarriers for the transmission of, for example, monophonic, stereophonic and second program signals, is significantly smaller than the bandwidth of a monophonic signal usually handled by a carrier-to-carrier device and thus appears

  that the process between carriers of sound detection

  than not to be satisfactory because snoring produces

3 u is significantly increased.

  According to the invention, the carrier of sound at frequency

  intermediate quence is treated in a separate circuit

  image carrier processing circuits in frequency

  intermediate quence and the composite signal of his is

  detects by a phase lock loop 53 to trans-

  Accordingly, for detecting the sound information, the image and sound carriers at terminal 18 produced at the terminal 18 are applied to low-band image and sound filters 36 and 38 by a buffer amplifier 34. and a terminal Ao A picture-in-picture filter 36 has a symmetrical, narrow and relatively narrow bandwidth response (e.g. 11 Hz) centered on the intermediate frequency image carrier frequency (e.g. 75 I Hz

  in the NTSC system) to select only the sig-

  Intermediate Frequency Image Carrier Image A

  Intermediate 40 frequency amplifier and a limit

  42 and 42 respectively amplify and appropriately limit the intermediate frequency image carrier signal and apply the resultant limited image carrier and substantially unmodulated dono to an input of the frequency converter.

frequency 44.

  A band-pass filter 38 has a relatively narrow symmetrical bandwidth 39 (for example 1 M Hz) centered on the frequency of the intermediate frequency sound carrier (for example 41.25 M Hlz

  in the NTSC system) to select only the

  carrier of intermediate frequency sound which is

  applied after appropriate amplification by an

  intermediate frequency multiplier 46, at an input

  of a phase detector 48 Frequency amplifiers

  intermediate 40 and 46 can be configured

  similar, each including for example an amplifier.

  Integrated Circuit Intermediate Frequency Factor Such as G 2 e TA 6707 Manufactured by Tokyo Shibaura Electrie Co., Ltd. Limiter 47 may simply consist of polarized Schottky barrier diodes in opposition

  and connected in parallel A current circuit 47 of

  automatic gain control responds to the output of the amplifier.

  intermediate frequency indicator 46 (or alternatively

  at the output of the amplifier 40) to deliver

  automatic gain control of intermediate frequency amplifiers 40 and 46 to conmend their gain and to establish their output signals at levels

: 2532502

  predetermined. A voltage controlled oscillator 50

  diode with a variable capacitance, having a frequency of os-

  nominal oscillation equal to the difference in frequency (eg 4.5 M Hz in the NTSC system) between

  and intermediate-frequency image

  touch a second mixer inlet 34 The latter

  may consist of a double multiplier circuit

  A balanced model such as the MC 1486 model produced by Motorola Semiconductors Products, Inc. operates in switch mode in response to the limited amplitude intermediate frequency image carrier (which behaves like the switching control signal) for

  mixing the inter-frequency image carrier signal

  middle and the output signal of the controlled oscillator

  by voltage and it delivers at its output a signal representing

  both the differences in frequency and phase between

  input signals The difference in frequency between the

  This 41.25 MHz output signal from the mixer 44 is applied to a second input of the phase detector 48 which may also consist of an integrated circuit MC 1496. phase 48 produces an output signal whose amplitude varies

  in direct relation to the phase difference of its

  input and so it works as a demodulator

  of frequency modulation for the sound carrier of frequency

  frequency modulated intermediate frequency applied to its first input by the amplifier 46 and it delivers at its output a baseband composite sound signal (with the unwanted signals that result from the operation of

  detection) For a more detailed description of the

  analog multipliers as well as

  modulators of frequency modulation, there is reason to

  refer to an article entitled "Application of a Mono-

  thic Analog Multiplier ", by A Bilotti, IEEE Journal of

  Solid State Circuits, December 1968, pages 373 to 380.

  A low-pass filter 52 connected to the output of the de-

  phase detector 48 filters its output signal for

  to obtain a control signal of the oscillation frequency

  Voltage Controlled Meter 50 The mixer 44, the

  The low-pass filter 52 has a bandwidth sufficient to select the signal of its composite in banana, and the low-pass filter 52 constitutes the phase-locked loop 53 with frequency translation. (rejecting the unwanted signals at a higher frequency) and

  provide the composite sound signal, for example, to a

  If a stereophonic program is provided in the composite sound signal, the decoder 54

  decodes this composite signal and delivers stereo signals

  left and right phonics to loudspeakers 56 and 58 respectively If stereo programming does not

  is not provided, the decoder 54 delivers the monopho-

to the speakers.

  In operation, the mixer 44 converts the

  frequency of the image carrier signal in frequency

  medial applied to its input and delivers an output signal whose frequency corresponds to the difference of

  frequencies of these input signals, for example 41.25 M Hz.

  Unwanted output signals corresponding to the

  wise of input signals and sum of input signals

  are attenuated by the low-pass filter 52 of bank width.

  The amplitude of the output voltage

  48 phase detector is a measure of the phase shift between the input signals This output voltage is

  filtered or applied to the low-pass filter 52 as a

  Controlled oscillator control voltage 50 Frequency

  output of the controlled oscillator 50, and by

  from the converted signal of 41.25 1 Mz from the

  44 varies in direct relation to the amplitude of

  the control voltage and in a sense that reduces the de-

  phasing between the signals at the inputs of the phase detector 48 When the phases of the detector input signals 48

  quadrature (900), the amplifier control voltage

  minimal study is applied to the controlled oscillator 50.

  Therefore, because of the reactive nature of the loop 53 when it is locked, the voltage

  control at the output of the filter 52 corresponds to the in-

  sound and this tension is such that the frequency

  the difference signal converted at the output of the

  mixer 44 is equal to the average frequency of the carrier

  In this case, the phase detector 48 contains a frequency modulation detector for frequency demodulation of the intermediate frequency sound carrier.

  frequency modulation in common mode which can be

  to the sound and image carriers, for example by the local oscillator 16-or television accessories such as a cable television converter which can precede the tuning circuit 10 is transferred to the converted difference signal and therefore , canceled

in the phase detector 48.

  The present phase detection device

  advantageous because it uses a predefined frequency space

  between the carriers of sound and the image of

  intermediate, allowing a simplified tuning of the receiver and canceling the common mode frequency modulation of the IF carrier. In addition, the Nyquist modulation of the image carrier due to

  upper frequency bandwidth in inter-

  median does not produce any snoring sound in the pre-

  More particularly, the detection devices

  image and sound processing channels are separated

  after the chord circuit 10 o In the chord channel

  sound processing 9 the image bandpass filter 36 attenuates

  symmetrically nudges the sidebands of the intermediate frequency image carrier and eliminates the snoring type of 'V 9 yquist' In addition, the filter response 37

  bandpass is narrow enough to cancel practically

  the components of the video signal which are at one of the frequencies corresponding to second and third subharmonic frequencies of 4.5 Mf Hz (for example 2.25 M Hz and 1.5 l M Hz respectively from the carrier of intermediate frequency image at 45.75> Ez in the NTSC system) Since the frequency of the output signal of the control oscillator 50 is also 1.5 M Hz, sound frequency bursts of sound are avoided at the output of the mixer 44 Therefore another source

  of snoring on the sound related to the image that is inherent

  the inter-carrier detection system is practically

eliminated.

  Moreover, comparing with the system between

  carriers, in which the bandwidth of the frequency channel

  the intermediate frequency sound carrier, which adversely affects the signal-to-noise ratio in the sound channel, in the system according to the invention, the band-pass filter of its sound practically without attenuation applies the intermediate frequency sound carrier to the amplifier 48. Thus, the amplitude level of the sound carrier is approximately 25 dB above that in the carrier-to-carrier system, and the signal ratio sound of the detected sound signal is therefore improved for a high frequency signal of a given level It should also be noted that, since the signal of sound between carriers is not produced, there is no need for a carrier amplifier, of a discriminator between carriers and circuits acr

* associated ropes.

  It should be noted that the amplitude levels of the input signals to the mixer 44 and the detector of

  phase 48 as long as their input circuits react

  This is mainly because of the frequency and phase of the input signals. Thus, an i-hierarchical rejection of the amplitude modulation of the intermediate-frequency image carrier modulation is obtained in addition, although a frequency signal is obtained. (ie 82.5 MD: z) is also produced at the output of the phase detector 48, its modulation envelope is substantially symmetrical and therefore has no noticeable effect on the basic frequencies of its Therefore, the effect of

  limiter 42 does not have to be as strong as the one needed

  This lower degree of limitation further reduces: (1) the possibility of image-related snoring at the line and frame rate caused by a limited degree of image carrier modulation intermediate frequency and; (2) the production of harmonics that can mix with the output of the controlled oscillator 50 and generate a

  distortion of the audible frequency band.

  In another embodiment, the intermediate frequency image carrier at the output of the amplifier limiter 26 can be applied to the mixer 44 at the

  pdrnt B and be used as a switching input signal

  The circuit between points A and B can be eliminated

  However, since the intermediate frequency amplification channel is included in the sound detection device, the modulation produced by the Nyquist effect is not eliminated and this embodiment may not be acceptable for detecting a composite signal of broadband sound But since the carrier-of

  its intermediate frequency is produced with an atten-

  relatively low, there is still an improvement

  Significant ration of the signal-to-noise ratio by detecting sound signals of relatively narrow bandwidth,

  such as a monophonic sound signal.

  Intermediate frequency amplifiers

  40 and 46 are used in the mode of

  Fig. 1, but a common amplifier could be used to amplify the intermediate frequency image and sound carrier signals at the output of

  buffer 34, as will be described later.

  According to Fig. 2, a broadcast signal of

  vision received by an antenna 108 is applied to a television tuning circuit 110 which includes an amplifier

  high frequency 112, a mixer 114 and an oscillator

  The tuner circuit 110 convertselectrically

  the high-frequency image and sound carrier signals of a selected television channel, at intermediate carrier frequencies at, for example, 75 14 Ez and 41.25 M Hz respectively in the system.

  NTSC Intermediate Frequency Carriers Appear

  at the output terminal 118 of the tuning circuit The 45.75 M Hz intermediate frequency image carrier is essentially an amplitude modulated signal which contains the composite image information The intermediate frequency 41 frequency carrier , 25 M Hz is by

  against a frequency-modulated signal A processing circuit

  color television signal

  comprising a middle frequency filtering and amplifying channel 120, a video detector 122 and a video signal processor 124 receiving the intermediate frequency image carrier of the terminal 118 to produce the red color (R) video signals. , green (V) and blue (B) for a cathoscope (not shown) that reproduces the color image of a television scene in

  In addition, a shelf connected to the amplifier-amplifier 126 pro-

  duit a filtered, amplified and limited version of

  of the frequency-carrier image carrier signal

  intermediate for the video detector 122 for the purpose of

  Synchronous recording of the composite video signal of the intermediate frequency image carrier The carrier output

  intermediate frequency image of the limiter / amplifier

  126 is also applied to a chord detector

  3 u automatic accurate through a network de-

  Phaser 130 to 90 for producing an automatic tuning control signal at the output of the detector 128, this signal being applied to the local oscillator 116. In this manner, the frequency and phase of the local oscillator signal applied to the mixer 114 follow the frequency and

  the pnase of the received high frequency image carrier.

  The construction and operation of the video detector 122, amplifier limiter 126, tuning auto-tuning detector 128 and phasor array 130 are described in more detail in U.S. Patent No. 4,263,611. I 120 of the intermediate frequency has a current bandwidth response 132 in which the intermediate frequency image carrier P is located 6 d B down on the upper frequency slope of the bandwidth response 132 and the

  sound carrier is in intermediate frequency is

  killed about 25 d B down the slope of

  inference of the response 132 Thus, the information

  residual side-band video can be detected without significant interference with the carrier of

  intermediate frequency sound As has been explained

  the response to a bandwidth of inter-

  mediator 132 contains a phase modulation of the carrier

  get "Nyquist" on the frequency carrier.

  Due to the asymmetrical attenuation of the sidebands of the image carrier in frequency in the middle of the present sound detection device, the intermediate frequency carrier is processed in a separate circuit of the signal carrier. image carrier processing in intermediate frequency and signal

  Composite sound is detected by a lock loop.

  frequency translation phase 157 of Fig. 2 o

  According to the invention, appropriate amplification of the

  image and sound in intermediate frequency

  suitable for application to the lock loop.

  Phase 157 is provided by a common amplifier.

  More particularly, the intermediate frequency image and sound carriers produced at terminal 118 are supplied by a buffer ampli fi er 134 and an amplifier.

  filter 136 at the same frequency amplifier inter-

  The filter 136 has a frequency response

'3250 2'

  bandwidth with two bumps (two ctetes)

  a portion of bandwidth 137 symmetrical and

  relatively narrow (eg from 1 to 3 d B)

  frequency on the intermediate frequency image carrier frequency P and a symmetrical and relatively narrow portion of the bandwidth 137b (e.g.

  3 d B) centered on the frequency of sound carrier at frequency

  intermediary to select and pass relatively smoothly the image carriers and

  sound to the intermediate frequency amplifier 138.

  The filter 136 maintains the relative amplitudes of the picture and sound carriers and consists of a current tuned circuit in discrete elements or a surface acoustic wave filter such as the filter F 1322

  manufactured by Tokyo Shibaura Electric Company LTD The

  intermediate frequency indicator 138 linearly amplifies the image and sound carriers and includes a

  automatic gain control circuit of the amplifier

  138 to establish output signals to

predeterminated calves

  From the output of the frequency amplifier

  intermediate frequency 138, a buffer amplifier 140 and

  limiter 142 apply an amplifier image carrier

  limited study and therefore practically without modulation to a

  input 143 of a mixer 144 A filter 146, an amplifier

  Buffer 148 and a limiter 50 apply only

  the carrier of intermediate frequency sound at the

  The limiters 142 and 150 may simply be diodes with

  Schottky of opposite polarities connected in parallel.

  The filter 146 may consist of a plug circuilt in

  discrete elements with a center frequency tuned to give a frequency response 147 with a maximum attenuation at the intermediate frequency image carrier frequency and a minimum attenuation at the frequency of the sound carrier S. A voltage controlled oscillator 154, tuned 253250 a diode with variable capacity, with a nominal modulation frequency equal to the frequency difference, for example 1.5 MHz for the NTSC system between the

  image carrier and the carrier of frequency sound

  Intermediate produces a second input signal at the terminal 145 of the mixer 144. The mixer 144 may consist of

  for example in a double analog multiplier circuit

  that balanced, for example the MC 1496 circuit produced by Motorola Semiconductor Praducts Inc., operating in switching mode in response to the image carrier

  intermediate frequency of limited amplitude

  The mixer 144 mixes the intermediate frequency image carrier signal and the output signal of the controlled oscillator to produce at its output a converted frequency signal representative of the frequency limiter 142 (which acts as a switching control signal). the frequency and phase difference between the input signals The frequency difference between the input signals of the mixer 144 is 41.25 M Hz. This 41.25 M Hz output signal of the mixer 144 is applied to a

  second input of the phase detector 152 which can also

  consist of an integrated circuit MC 1496 The detection

  phase converter 152 produces an output signal whose output

  plitude varies as a direct function of the phase difference of these input signals and therefore behaves as

  a frequency modulation demodulator for the por-

  intermediate frequency modulated frequency sound

  quence applied and it delivers at its output a signal

  composite of sound in baseband (with the signals

  desirable that result from the detection process).

  A low-pass filter 156 connected to the output of the phase detector 152 filters the output signal of this

  last to produce a control signal of the frequency

  quence of the voltage-controlled oscillator 154 The

  144, the phase detector 152, the controlled oscillator 154 and the low-pass filter 156 constitute the id phase-locked loop 157 in frequency translation The low-pass filter 156 has a bandwidth sufficient to select the signal composite of sound

  baseband (while rejecting unwanted signals

  higher frequency) and it delivers the signal

  composite sound, for example to a stereophonic decoder

  If a stereo program is provided in the composite sound signal, the decoder 158 decodes the composite signal and provides the stereo signals.

  from left and right to 160 and 162 speakers.

  If a stereophonic program is not planned, the deco-

  Deur 158 delivers the monophonic signal to the loudspeakers.

  In operation, the limiter 142 reacts to the

  signal of higher amplitude applied to its input.

  In television broadcasting and in television distribution

  cable, the transmitted sound carrier is attenuated by at least 8 d B with respect to the amplitude of the image carrier.

  relative magnitudes, the indicator 142 selects

  the image carrier alone at the output of the amplifier.

  138 and applies it without modulation to the mixer 144.

  On the other hand, a band pass filter or a plug circuit filter could be used in place of the limiter 142 but it could not be incorporated in an integrated circuit chip as easily as for example a

  diode limiter circuit and could not extract the

  amplitude modulated video training.

  As indicated, the mixer 144

  converts the frequency of the image carrier of frequency

  intermediate quency applied to its input and delivers an output signal having a frequency corresponding to the difference of the input signal frequencies (for example 41.25 ± 1 Hz) to the input terminal 153 of the detector

  The undesirable output signals correspond to

  spanning the input signals and the sum of the frequencies of the input signals are also produced

  at the output of the mixer 44, but these signals can not be

  to reach the decoder 158 due to the relatively narrow bandwidth of the low-pass filter 156 o The filter 146 attenuates the image carrier

  compared to the sound carrier and the limiter 150

  to the sound carrier of greater amplitude and practically only applies the sound carrier to the input 151 of the phase detector 152 The amplitude of the voltage

  output of the phase detector 152 is a measure of the

  phasing between input signals This output voltage is filtered and applied by the low-pass filter

  156 as a control voltage of the oscillator com-

  The output frequency of the oscillator com-

  1549 and therefore the signal converted to 41925 M Hz from the mixer 144 varies in direct relation to the magnitude of the control voltage and in a

  meaning that reduces the phase shift between signals to

  When the phases of the input signals of the detector 52 are in quadrature (900), a minimum amplitude control voltage is applied to the controlled oscillator 154.

  nature of reaction of the loop 157, when it is ver-

  rusted, the control voltage at the output of the low-pass filter 156 corresponds to the information of her and she

  is such that the frequency of the difference signal con-

  verti at the output of the mixer 144 is equal to the frequency

  average frequency of the carrier of sound in inter-

  mediates and its phase is in quadrature with that of the carrier of sound in intermediate frequency Thus the phase detector 152 behaves like a frequency modulation detector to demodulate in frequency

  the carrier of intermediate frequency sound.

  Common mode frequency modulation can

  be applied to image and sound carriers, for example

  by the local tuning oscillator 116 or the

  television accessories as a converter

  cable television that may precede the provision of

  daccordance 110, and this modulation is transferred to the

  nal difference converted and then canceled in the

pnase detector 152.

  Since only one frequency amplifier

  intermediate level is used to produce

  amplified sound and image carriers for the

  phase lock key 157 with frequency translation

  the complexity of the circuit and consequently its price are also reduced compared to the

already described.

  It should be noted that the amplitude levels of the input signals of the mixer 144 and the phase detector 148 are such that their input devices react mainly to the frequency and phase of the input signals and not to their amplitudes. Thus, an inherent rejection of amplitude modulation of the modulation of

  the intermediate frequency image carrier is obtained.

  Thus, although a sum frequency signal (i.e.

  82.5 M Hz) is also produced at the output of the

  phase detector 152, its modulation envelope is es-

  sensibly symmetrical and therefore has only an insignificant

  relying on the baseband frequencies of his

  the effect of the limiter 142 need not be so im-

  that necessary in a system between carriers

  This lower degree of limitation reduces: (1) the possibility of

  unrestricted noise on the line frequency and the frequency of -frame causes a high degree

  of modulation of the image carrier in inter-frequency

  mediator, and; (2) the production of harmonics that can mix with the output of the controlled oscillator 154 and produce a distortion in the frequency band

  audible The detection device described in

  above, from the intermediate frequency amplifier 138 to the decoder 158 (excluding the filter 146) can advantageously be made on the same integrated circuit The limiters 142 and 150 may consist of diode circuits. and 146 can be implemented using relatively inexpensive tuned circuits because of the attenuation they must provide.

is limited.

  But in another embodiment, the

  miter 150 can be eliminated in order to compensate for the

  addition of the signal which has already been produced by the limiter 150, the filter 146 having to produce a

  corresponding increase in attenuation at the frequency

  image carrier B This can be done easily

  by adjusting the tuning circuit components.

  In addition, the filter 146 can be made in the form

  a relatively narrow bandpass filter (eg

  peak 50 kHz) with a frequency response 154 centered on the sound carrier frequency S and providing substantial attenuation to the frequency of the image carrier P.

  The various embodiments described below

  above describe various techniques for attenuating the sound carrier and preventing them from reaching the input 151 of the phase detector 152. If the image carrier is not attenuated appropriately at the input 151,

  the passage of the image carrier between the output of the

  144 and the input 153 of the detector 152 mixes with the image carrier at the input 151 and produces a zero beat output signal which could be in

  the audible frequency range and thus distort

sound formation.

  FIG. 3 represents another embodiment of

  of a sound detection device of the

  television of Fig 2 The elements whose realization

  tion and operation are the same are designated

  by references identical to those of Figure 2.

  A filter 166 is provided between the output of the mixer 144 and the input 153 of the phase detector 152 to attenuate

  the image carrier and let the

  Thus, a device for providing the

  sound processor at the input 151 of the phase detector 152,

  since the filter 146 and / or the limiter 150 is not

  The filter 166 may be of the plug circuit type having a response frequency 167 providing maximum rejection of the signal at the image carrier frequency P and a minimum attenuation at the frequency of the sound carrier S Envariante, the filter 166 can be of the band-pass type with a relatively narrow frequency bandwidth response 168 (for example, ok Hz) with a frequency centered frequency

  carrier of its S and providing attenuation suostan-

  In the embodiments already described, the intermediate frequency image carrier produced at the same time

  the output of the television tuner is processed

  in a separate intermediate frequency channel for developing the video information The sound information is detected by a frequency translation phase locked loop comprising a mixer and a phase detector respectively responsive to

  Frequency and Image Frequency

  medial, appearing at the output of the tuning circuit.

  According to another embodiment, the invention relates to a device which detects parasitic defects of the video signal and which restores the information of its

  from a television signal with a single

  phase locked loop and that can be easy-

  made in the form of an integrated circuit.

  According to FIG. 4, a broadcast television signal

  is received by an antenna 208 e t applied to a circuit

  The latter selectively converts

  high-frequency image and sound sources of a selected television channel into respective intermediate frequency carriers, for example at 45.75 -ffz and 41.25

  M Hz in the NTSC system Inter Frequency Carriers

  mediate appear at the output of the tuning circuit 212.

  The intermediate frequency image carrier is essentially

  tally an amplitude modulated signal which contains the composite image information On the other hand, the intermediate frequency image carrier is essentially

  an amplitude modulated signal that contains the ini'orma-

  However, the sound carrier

  intermediate frequency is a frequency-modulated signal

  quence A current signal processing circuit

  color television system comprising a channel 214 of

  and intermediate-frequency amplification and an image detector 216 responds to the intermediate-frequency image carrier at terminal 212 by detecting a composite video signal in baseband. The video signal in a band

  base is applied to an input 217 of a filter eliminating

  218 which separates the chromium subcarriers

  of the C and Y luminance of the composite and

  signals 219 and 220 respectively.

  more detailed description of the band eliminator filter

  The luminance and chrominance signals are processed in the usual manner to develop color signals which are applied to respective guns of a cathoscope (not shown). The resulting electron beams are deflected by successive horizontal lines to produce an image on

  the catheter screen in the usual way.

  Intermediate frequency channel 214 has a current bandwidth response 221 in which

  the intermediate frequency image carrier P is

  at 6 d B down on the slope of the higher frequencies

  bandwidth response 21 and the intermediate frequency sound carrier S is located at about d 13 down the lower frequency slope of the bandwidth response 221 o It follows that the video information of the sidebands -residuals can be detected without significant interference with the carrier

  of intermediate frequency sound As this has been explained

  that, the intermediate frequency bandwidth response 221 contains a carrier phase modulation

  intermediate of Nlyquist of the image carrier in frequency

  this intermediate because of the dissvmetric attenuation of the sidebands of the intermediate frequency image carrier.

  In the present receiver, a loop in

  Frequency translation pnase 222 treats the intermediate frequency sound carrier in a separate circuit of the intermediate frequency image carrier processing circuit to detect sound information and substantially reduce the Nyquist modulation. A buffer amplifier 224 couples the intermediate frequency sound and image carriers to terminal 212 with image and sound bandpass filters 226 and 228 respectively. The image bandpass filter 226 a

  a symmetrical response, relatively narrow (for example,

  a bandwidth of 1 M Hz to 3 d B) centered on the intermediate frequency image carrier frequency

  (eg 45.75 M Hz in the NTSC system) to leave

  The intermediate frequency image carrier signal 230 and the limiter 232 amplify and limit

  appropriately the carrier image signal of frequency

  intermediate and apply to one input a

  signal carrier 234, the carrier of frequency in-

* The result is a limited result and, therefore,

unmodulated.

  The band pass filter of its 228 has a pas-

  relatively narrow (e.g. 1 4 Hz to 3 d B) symmetrical health center centered on the intermediate frequency carrier frequency S (for example 41.25 Mhz in the NTSC system) to let practically only the signal of carrier of intermediate frequency sound and these

  immediate lateral hinges that are applied, after am-

  multiplication by an intermediate frequency amplifier

  236 to an input of a phase detector 238 The amplifiers

  Intermediate frequency drivers 230 and 236 may be similarly constructed and may each consist of, for example, an integrated circuit amplifier such as the TA 7607 model manufactured by Tokvo Shibaura Electric Co. LTD. The limiter 232 may consist simply of gate diodes. Scllottky of opposite polarities connected in parallel A current automatic gain control circuit 240 can at the output of the intermediate frequency amplifier 236 (or alternatively to

  the output of the amplifier 230) to deliver

  automatic gain control units to intermediate frequency amplifiers 230 and 236 to control

  their gain and establish their output signals to

predetermined calves.

  A voltage controlled oscillator 242

  diode with a variable capacitance having a frequency of os-

  nominal cillation equal to the frequency difference,

  (eg 4.5 Ez in the NTSC system) between

  image and intermediate frequency sound produces a second input signal for the mixer 234.

  can for example consist of a double circuit multiplica-

  Analog balanced transmitter such as the MC 1496 model produced by Motorola Semiconductor Products, Inc. which operates in a switching mode in response to an amplitude-limited intermediate frequency image carrier (which behaves as a switching control signal) to mix the image carrier signal in frequency

  intermediate and the output signal of the oscillator com-

  sent and obtain at the output a frequency signal con-

  vertie representing the differences in frequency and phase between the input signals In the NTSC system, the

  frequency difference between the input signals of the

  234 is 41.25 M Hz This output signal at 41.25 ± 4 Hz

  mixer 134 is applied to a second input of the de-

  phase detector 238 which may also consist of a circuit

  integrated bake MC 1496 The phase detector 238 produces an output signal whose amplitude varies in direct relation to the input phase difference and therefore functions as a frequency modulation demodulator for the intermediate frequency signal frequency modulated applied at its first input by the amplifier 136, and it delivers at its output a signal of its composite in

  baseband (with the unwanted signals that result

  the detection process). A low-pass filter 244 connected to the output of phase detector 238 filters its output signal for

  produce a control signal of the frequency of the os-

  Controlled spark generator 242 The mixer 234, the phase detector 238, the controlled oscillator 242 and the filter

  low-pass 244 constitute the phased-in loop.

  Frequency translation 222 The low pass filter 244 has sufficient bandwidth to select

  the composite sound signal in the base band, but suffi-

  narrowly rejecting unwanted higher frequencies, and applies the composite sound signal,

  for example to a stereo decoder 246 If a pro-

  stereo program is provided in the composite sound signal, the decoder 246 decodes the signal and delivers the

  stereophonic signals from left and right to

  248 and 250 respectively.

  re-phonogram is not provided, the decoder 246 delivers a

  monophonic signal to the speaker.

  In operation, the mixer 234 converts the frequency of the intermediate frequency image carrier signal applied to its input and delivers an output signal of a frequency corresponding to the difference

  frequency of the input signals (for example 41.25 N Hz).

  The unwanted output signals corresponding to the

  of the input signals and the sum of the input signals are attenuated by the relatively narrow bandwidth

  the low-pass filter 244 The amplitude of the output voltage

  The phase detector 238 is a measure of the phase shift between these input signals. This output voltage is filtered and applied by the low pass filter 244 as a

  Controlled oscillator control voltage 242 Frequency

  quence of the output signal of the controlled oscillator 242

  and therefore the signal converted at 41.25 N Hz from

  mixer 244 varies in direct relation with the am-

  of the control voltage and in a way that

  the phases of the input signals of the detector 238 are in quadrature (90) a phase-to-phase voltage

  minimum amplitude command is applied to 1-'oscilla-

  As a result, because of the feedback nature of the loop-222, when latched, the control voltage at the output of the filter 244 is such that the frequency of the difference signal converted at the output of the mixer 234 is equal to the average frequency of the intermediate frequency sound carrier and its phase is

  in quadrature with the phase of the carrier of sound in frequency

  Thus, the phase detector 238 functions as a frequency modulation detector for frequency demodulating the intermediate frequency sound carrier and producing a signal which, when it is filtered by the filter 244, matches the sound information. .

  Since the mixer 234 also reacts

  to the image carrier signal, frequency modulation

  common mode which can be applied both to

  2 D the carrier of sound and that of image, for example by los-

  local tuner tuner 210 or television accessories like a TV converter by

  cable which can precede the tuning circuit 210, is

  operated by the mixer 234 to the converted frequency signal

  and therefore, canceled in phase detector 238.

  As already mentioned, the carrier of his

  frequency modulated is selected at the output of the

  cooks 710 tuned by a bandpass filter 228 and amplified

  236 This latter, controlled by the cir-

  Baked Automatic Gain Control 140 conditions the

  sound carrier so that it has a moderate amplitude

  long-term stant, and tends to eliminate normally occurring amplitude fluctuations, which are not associated with parasites. Time constants

  of the automatic gain control circuit are sufficient

  short to limit the appearance of fluctuations

  Because amplitude fluctuations are caused by spurious pulses, the amplitude of the modulated sound carrier is practically constant. Since phase locked loops are relatively insensitive to amplitude, no limiter is necessary

  between amplifier 236 and detector 238 for eliminating

  fluctuations due to parasitic impullsions.

  Therefore, the output of amplifier 236 is an advantageous point for detecting fluctuations

  amplitude of the modulated carrier in order to

  to create a fault control signal and to reduce

  defects in the video signal produced by pulses

  In addition, since the bandwidth of the filter 238 is wide enough to pass the sound carrier and part of its sidebands, it introduces a relatively shorter signal delay than the delay in the signal circuit. video and a

  sufficient time to compensate for the defect in this

  nal video A circuit 252 control signal generator 8

  of defects comprising a synchronous detector 254 which de-

  the fluctuations produced by pulses which

  The sites can be advantageously incorporated in the structure of the phase-locked loop already described, with the addition of a minimum number of emitters, and in a manner easily incorporated into the structure of the interlocking loop. phase of the sound detector, prefereerence in the form of a circui-r integro Fêtant given that the output signal of the nélaneeur

  2: 4 has a frequency equal to the average frequency of the

  frequency-modulated sound but in phase quadrature, a phase shift network 256 of 900 shifts the signal of

  mixer output 234 of 900 and applies it to a

  synchronous detector 254 So when the carrier

  of its frequency modulated is applied to the other

  detector 254, the phases of the input signals are in synchronism (i.e. in phase) with each other.

  and therefore the synchronous detector 254 of a machine

  well-known detects the amplitude variations of the frequency-modulated sound carrier.

  can also consist for example of a double multiplication

  balanced, as in the MC 1496 integrated circuit

  city. The amplitude variations produced at the output of the detector 254 are applied to a first input of a comparator circuit 258. A continuous threshold signal

  from a source 260 is applied to a second

  comparator 258 The comparator produces a change

  output state when the output signal of the

  254 goes through the threshold level The output signal

  detector 254 may be an alternating signal

  sluggishness with a relatively low amplitude except

  in the presence of spurious pulses or other

  in which case, there appears a relatively large and fast variation of the output signal which can be positive or negative due to the oscillation associated with

  example with the mutual action of the parasitic pulse.

  with the high frequency circuit of the tuning circuit 210.

  It may therefore be desirable to include a second comparator circuit arranged with a threshold of opposite polarity to detect synchronous excursions of the output signal of the detector of one polarity or the other or the two comparators can be interconnected substantially for

  produce an output signal only for a response

  in correlation with a parasitic pulse oscillation characteristic

  The output signal of the comparator is condition-

  born by the addition generator 262 and applied to the 3 o terminal 253 to allow or inhibit a switch 264

  which modifies the substitution of the video signal in the

  The pulse generator 262 may be a monostable multivibrator which produces a pulse of prescribed amplitude and duration (generally

  typically of the order of 1 to 10 microseconds).

  tests indicate that the duration of the impulse

  site is usually grouped in the range of 1 to 3

  microseconds and a control pulse of 3 micro-

  l O second is sufficient to compensate for the majority of

  However, it may be desirable to

  to terminate the video substitution at a particular time.

  each interval, for example during the period

  in this case, the generator of

  pulses can be a toggle circuit triggered by

  transition, set to "1" by the output signal of the

  and "O" by a separate delay pulse.

  example, the horizontal sync pulse

  tale. The band eliminator filter 218 is made according to the technology of charge transfer components

  and has a charge coupled device (CCD)

  taking a 1-H delay line (a horizontal image line) with CCD summation sections and a sampling and holding circuit to perform the desired cross-filter function for video signal band elimination and separation interleaved luminance (Y) and chrominance (C) signals as described in U.S. Patent No. 4,158,209. The charge-coupled delay line is in fact a series of stored storage elements connected to each other. series by which the sampled data is selectively transferred

  cb 4 one element to the next at a predetermined frequency.

  The signal can be nondestructively sampled at one or more of the storage positions to realize

  a particular delay of the signal An adder 266

  kills the average of two image signal samples that are taken at half of a subcarrier cycle

  chrominance and after a delay of 1 hour

  raised and delayed is conditioned in the adder 266 for its chrominance signal to be out of phase by 180 (half of a chrominance subcarrier cycle) relative to the non-sampled delayed signal remaining in the charge-coupled component. so that the sampled signal and the delayed signal are in the correct chrominance phase to serve as a substitution signal A delayed signal of a horizontal line is available at the output of the adder 266 and

  is applied to the terminal 269 by an amplifier 268.

  The signal at terminal 269 is then applied to an

  filter eliminator filter 270 For a

  For a more detailed description of the phase inversion circuit of the chrominance signal, reference should be made to US Pat. No. 4,272,585.

  for example, a band eliminator filter 218 is pro-

  issued by Tokyo Shibaura Co, -Ltd, 9 Japan, in the form

of an integrated circuit T 3928.

  The real-time video signal is applied to terminal 217 of the band-eliminating filter, and then

  the input connection 271 of the CCD register by the

  264 If the presence of a signal fault, for example a parasite, has been determined in the real-time signal, the delayed signal of a horizontal line

  from terminal 269 momentarily replaces the sig-

  Real-time signal provided by the video detector 2169 by positioning the switch 264 to access the delayed signal of a line applied to the input 270 of the filter

  Thus, the signal previously referred to

  delayed by a horizontal line of image is recycled into the register CC Do

  The above description demonstrates the advantage

  of the technique of substituting a delayed signal for the real-time signal in a video signal processing circuit of a color receiver using

253250 2

  a particular t-pe band eliminator filter.

  Another provision for use in black and white television receivers may

  consist of a single line of delay of one

  In this case, the input of the delay line is connected to receive a signal

  video in real time and the comni 3ateur selects

  the real-time signal or the delayed signal from the delay line directly to the other

  processing circuits In this provision, the sign

  The video is not recycled in the delay line but traverses it simply after being delayed by an image line. For a color signal, a delay corresponding to an integer of horizontal line periods can also be used for To obtain the same basic result For example, for an NTSC color signal, the delay circuit may consist of

  in a line of delay of two horizontal lines,

  which case it is useful to reverse the phase of the com-

  chrominance component of the video signal so that this chrominance component is in the appropriate phase

  to serve as a substitution signal.

  Thus, this embodiment which has just been described constitutes a device in which the detection of a parasitic implosion or a defect in the signal

  image is advantageously performed with a de-

  phase-locked loop sound signal detector which detects P sound iniormations Although separate intermodal frequency amplifiers 230 and 236 are used in the embodiment of FIG.

  In Fig. 4, a common user could be used.

  se to amplify Ima Re's Dorteuse signals

  and intermediate frequency sound produced on the

  buffer 224, as already described.

  In addition, the pitch lock loop 122 is shown with a mixer 234 for drifting

  the frequency signal converted to 41.25 14 U {z for

  to the phase detector 238 and a synchronous detector 254, but the nominal frequency of the signal

  output of the controlled oscillator could be

  at the same frequency as that of the sound carrier and applied directly to detectors 238 and 254

  as shown by the dotted line in FIG.

  Of course, in this variant, the mixer 234 would be suppressed and could not eliminate the frequency modulation by

  common mode of image and sound carriers.

  It is furthermore understood that in the embodiment described, the fault control signal is used to control the substitution of the delayed image signal, but the fault control signal

  could be used in conjunction with another

  baked suppression or pest compensation.

  For example, the fault control signal could be used to make the automatic gain control circuit of the television receiver insensitive to

  spurious pulses in the video signal.

  Finally, it is clear that the NTSC frequencies mentioned above are only exemplary and can be modified appropriately to adapt the operation to other frequencies.

  in NTSC, PAL and SECAM television systems.

  Of course, various modifications can

  be brought by the person skilled in the art to the modes of

  described in Figures 1 and 1, illustrated by way of examples

  menswear-and without departing from the scope of the invention.

Claims (12)

REVENDICATIOI NS   1 Apparatus for detecting sound information in a television device comprising a   source of an intermediate frequency signal which   holds image and sound carriers modulated with image and sound information respectively, camera   characterized in that it comprises a control oscillator   (50; 154; 252) responsive to a control signal   plicated to a control input and whose output de-   delivers a controlled frequency output signal, a   positive (44; 144; 234) having first and second inputs and an output for producing a signal   converted into frequency, said first input being   connected to react to said image carrier and the se-   an input terminal being connected to react with said output signal of the oscillator, a phase detector (48; 152; 238) with first and second inputs and an output, said first input being connected to react to said sound carrier and said second entry being   connected to react to said convergent frequency signal   and a low-pass filter (52; 156; 244) with an input connected to the output of said phase detector (48,152;   238) and an output which produces said communication signal   control input to said controlled oscillator (50, 154, 252) and producing the said information of his.   Apparatus according to claim 1 in the   which said controlled frequency output signal has   a nominal frequency equal to the difference in frequency   between said image carriers and sound carriers,   characterized in that said device (44; 144;   234) which produces a signal converted into a frequency   carries a mixer (44; 144, 234) including a first   trea (B) is connected to receive said carrier   image, of which a second input is connected for re-   cevoir said output signal of the oscillator and whose output produces said frequency converted signal '   at a nominal frequency equal to the frequency of called carrier of sound.   Apparatus according to claim 2, characterized   characterized in that it comprises an amplifier (34, 36, 40, 42) responsive to said image carrier by applying a substantially unmodulated carrier to said mixer (44) or   Apparatus according to claim 3, characterized   risé in that it comprises a first filter circuit   (38) with symmetrical bandwidth centered on lm.   sound-bearing frequency, having a connected input   to receive said intermediate frequency signal and an output, and a first frequency amplifier   intermediate (46) connected between the output of the first   first filter circuit (38) and the first input of said pnase detector (48).   Apparatus according to claim 41, characterized in that said amplifier comprises a second filter circuit (36) with a symmetrical bandwidth centered on the image carrier frequency, having an input connected to receive said intermediate frequency signal and a output, and a second intermediate frequency amplifier (4 o) connected between the output   said second filter circuit (36) and the first mixer (44).   Apparatus according to claim 5, characterized   characterized in that it includes an amplitude limiter con-   between the output of said second frequency amplifier   intermediate quency (40) and the first input of said mixer (44)   Apparatus according to any one of the   1, 2 and 6, wherein said in'ormations   Several channels of sound are   characterized in that it includes a decoder circuit with   multiple channels (54) having an input connected to the output of said low-pass filter (52) and an output which   or produces one or more of said sound channels.   Apparatus according to claim 2, characterized   in that said phase detector and said mixer   consist respectively of a double multiplication balanced analogue transmitter.   Apparatus according to claim 2, characterized   in that it comprises a first filter (156) comprising   an input connected to receive said intermediate frequency signal and an amplitude response characteristic as a function of the two-bump frequency (137a, 137b) with peak amplitude portions (S, P) centered at the frequency of said image and sound carriers respectively to produce at its outputs said   image and sound carriers, an amplifier (138) omitted   taking an input connected to the output of said first filter (136) for amplifying said image and sound carriers and producing said ampolified carriers at the output of said amplifier (138) and a second filter   (146) connected to one of said first and second   said second filter (146) having an amplitude response characteristic as a function of frequency producing a predetermined attenuation at the frequency of 1: d of the carrier.   image and significantly less than said attenuation pre-   determined at the frequency and said carrier of sound.   Apparatus according to claim 9,   characterized in that said second filter (146) is connected   between the output of said amplifier (138) and   3 C O first input of said phase detector.   Apparatus according to claim 9, characterized   in that said second filter (1-46) is connected between the output of said mixer (144) and said second   input of said phase detector (152).   12-Apparatus according to any one of the claims   9 to 11, characterized in that it comprises a   positive selection (140, 142) coupled between the output of said amplifier (138) and the input of said mixer (144)   to produce at its output said image carrier.   Apparatus according to claim 12, characterized   in that said selection device (140, 142) consists of a diode limiter circuit (142) for producing a substantially unmodulated image carrier to the inlet of said mixer (144).   Apparatus according to claim 12, characterized   in that it comprises a first selection device   connection (148, 150) connected between the output of said second   (146) and said first input of said detector of   phase (152), said selection device (148, 150) pro-   providing additional attenuation of said image carrier thereby enabling said filter (146) to produce less than said predetermined frequency attenuation of said image carrier.   Apparatus according to claim 14, characterized   in that it includes a second selection device   (140, 142) connected between the output of said amplifier (138) and the input of said mixer (144) to provide said   mixer (144) said image-only carrier -   Apparatus according to claim 14, characterized   characterized in that said first and second selection devices (148, 150, 14 o, 142) consist of limiters with diodes (148; 150).