DE2738905C3 - Tuning device for a television receiver - Google Patents

Description

- H ± nV

where m is an integer factor of L and / 743 "- is an integer.

3. Tuning device according to claim 1 or 2, characterized in that the predetermined Direction is essentially horizontal.

4. Voting device according to at least one of the> o Claims 1 to 3, characterized in that the arrangement (38, 40) for generating the control signal a circuit arrangement (38) for generating a reference frequency sequence of pulses with a Property of the phase and frequency relationship between the local oscillator signal and depends on the reference frequency signal.

5. Tuning device according to claim 4, characterized in that the arrangement (38, 40) for Generating the control signal contains a circuit arrangement (40) for integrating the pulse train.

6. Tuning device according to at least one of the preceding claims, characterized in that the arrangement (34, 36) for generating the Reference frequency signal a source (34) for a * -, Fixed frequency signal and a circuit arrangement (36) for dividing the fixed frequency signal by a Factor/? contains.

7. Tuning device according to at least one of claims t to 4, characterized in that the signal from the local oscillator (42) is coupled to a circuit arrangement (44) which divides the frequency of the local oscillator signal by a scaling factor K and generates a pre-divided local oscillator signal , and that the pre-allocated local oscillator signal is fed to the arrangement (38, 40) for generating the control signal via a circuit arrangement (46), which divides the frequency of the pre-allocated local oscillator signal by a factor N which depends on the selected channel

8. tuning device according to claim 6 and 7, characterized in that / Cgieich R is

9. Tuning device according to claim 8, characterized in that the circuit arrangement (46) for dividing the frequency of the pre-divided local oscillator signal by the factor N contains a programmable counter, and that the factor K is chosen so that the frequency of the pre-divided local oscillator signal is smaller or equal to the highest frequency that the programmable counter can process.

10. Tuning device according to claim 9, characterized indicated that ^ is an integer

11. Tuning device according to claim 10, characterized in that the circuit arrangement (36) for dividing the frequency of the fixed frequency signal by the factor R contains a first counter circuit; that the circuit arrangement (44) for dividing the frequency of the local oscillator signal by the factor K contains a second counter circuit and that the factors K and R are equal to 240.

The invention relates to a tuning device as it is assumed in the preamble of claim 1 In particular, it is an electronic tuning device for television receivers, which with a phase control work.

Phase-locked circuits can be used to advantage in many applications because they provide a signal to synthesize which has a fairly accurate and stable frequency that is easy to control leaves. Such circuits typically include a reference frequency signal source, a controlled oscillator, a programmable counter for dividing the Frequency of the oscillator output signal by an adjustable factor, a phase demodulator for Generation of a signal corresponding to the phase or frequency relationship between the reference frequency signal and the oscillator signal and a low-pass filter for generating a direct current control signal for the oscillator from the output signal of the phase demodulator. Examples of such phase locked loops and its applications are set out in the RCA Digital Integrated Circuits User Notice, Application Note ICAN 6101 »The RCA COS / MOS Phase-Locked Loop - A Versatile Building Block for Micro-Power Digital and Analog Applications «which z. B. in the RCA data book SSD-203 B (COS / MOS Digital Integrated Circuits) from 1974, pp. 471-478.

Because of the advantages that result from programmability, accuracy and stability, has recently been concerned with the use of phase regulators in tuning devices for radio and televisions. Descriptions relating to this can be found in DE-OS 26 51 297, 27 08 232 and 27 22 659.

The components of phase-locked tuners must be carefully chosen so there are no problems in the recipient. For example, phase-regulated voting devices work generally with a phase detector of the type specified in the above-mentioned user communication Type that generates pulses at the frequency of the reference frequency signal, the duration of which is the Phase and frequency relationships between the reference frequency signal and the local signal Represent oscillator. Because the low-pass filter, which the control signal for the oscillator from the output signal of the phase detector, this output signal may not be sufficiently filtered, this can Control signal may be modulated in an undesirable manner with pulses of the reference frequency. That depends The local oscillator signal generated by the amplitude of the control signal can then be a frequency-modulated Contain components which, when processed by the recipient, may cause undesired interference in the audio or video output signals of the receiver

For example, frequency-modulated components of the local oscillator signal that are generated by a with Phase control working tuning device of an FM radio receiver are generated according to Demodulation by the demodulator of the receiver generates audible interference signals that disturb the listener. The generation of such audible interference signals in FM radio or radio frequency receivers that use a phase-locked tuner work can be reduced by changing the reference frequency the phase control higher than the highest frequency in the audio frequency range selects the disruptive Components of the reference frequency that are generated by the phase-controlled tuning device, is then outside the audio frequency range and is therefore normally no longer audible.

The use of a similar measure in a television receiver, namely cie reference frequency the phased tuner higher than the highest used to generate the image Signal frequency to choose in order to avoid visible effects of frequency-modulated components caused by the phase-controlled tuning device are generated, is not possible without further ado, since one then would have to use a reference frequency which is much higher (e.g. higher than 4.5 MHz) than that of the for Phase regulator currently available digital circuits can be easily processed.

It is also desirable to have parts of the phase-locked tuner simultaneously to use for other parts of the television receiver to save costs, but you have to care carefully that the cost savings do not adversely affect the operating characteristics of the recipient as a whole. It is Z. B. in the publication "A Frequency Synthesizer for Televi- ^ sion Receivers "by Eric Breeze and colleagues in the" IEEE Transactions on Broadcast and Television Receivers «Band BRT 2ü, t-'t. 4, Nov. 1974, pp 259 to 263 and US-PS 39 80 951 have been suggested to generate a signal with the frequency of 3.58 MHz, i. H. the Color carrier frequency according to the US standard, which is determined by a crystal oscillator of a color demodulator part of a television receiver, a phase detector in a phase regulator of a tuner of the recipient to reduce the cost to the recipient by having a saves a separate crystal oscillator for the generation of the reference signal To divide the frequency of the 3.58 MHz signal down to a sufficiently low frequency that corresponds to the The operating frequency range of the digital circuit used in the phase regulator is compatible that the 3.58-M Hz signal is divided should expediently can also be chosen so that visible effects of modulation components of the local Oscillator at the reference frequency are suppressed if possible. It is true in the above Publication from IEEE Transactions ... on page 262 mentions that an additional advantage of the use of the 3.58 MHz color subcarrier signal as the reference signal consists in the fact that any digital interference signals that arise are coherent with the 15.75 kHz grid frequency and are therefore less annoying when they are visible on the screen, which still needs to be explained For reasons, however, the reference signal frequencies, which are determined by dividing the integer numbers, are suitable Have a 3.58 M Hz reference color subcarrier frequency generated, not for extensive suppression of interfering images, the pulse components of the control signal of a non-filtered out reference signal frequency phase-regulated tuning device are generated.

The invention is based on the object in a television receiver with a phase-locked loop Use a phase detector to keep superimposition effects to a minimum, resulting in modulations of the Express the local oscillator signal by the reference frequency signal.

This object is achieved by the features cited in the characterizing part of claim 1.

It is from DE-OS 24 03 367 a tuning system that works with phase control (for short as PPL tuning system referred to) for a television described in which the phase-locked loop is interrupted when changing channels. The phase detector contains its input signal there directly from a stable frequency oscillator, which oscillates at 45.75 MHz. From a certain one However, there is a relationship between the reference frequency and the scanning frequencies for the electron beams nothing said

In the following, the invention is based on an exemplary embodiment and its special features are discussed explained in detail. The accompanying single figure shows a block diagram of a television receiver with a phase-regulated tuning device designed according to the invention.

The television receiver shown in the drawing contains an antenna 12 for receiving high frequencies Television signals and an RF part 14 for amplifying and otherwise processing the received. Signals. The amplified RF signals are in a mixer 18 with generation of an intermediate frequency signal (IF signal) mixed with a local oscillator signal, r / elches through a phase-controlled Tuning device 16 is generated. The ZF Signa! is amplified and filtered in an IF part 20

as well as otherwise processed and then another Circuit part 22 is supplied, which generates color, luminance, synchronization and color signal components. That The color signal and the luminance signal are fed to corresponding electrodes of a picture tube 24, -> while the audio signal is fed to a loudspeaker 26.

The synchronizing signal component of the output signal of the IF part 20 is fed to a synchronizing signal separating part 28, which separates horizontal and vertical synchronizing pulses from the signal mixture. The horizontal synchronization pulses are fed to a Ηοιϊ zontal deflection circuit 30 which controls the horizontal deflection of the electron beams in the picture tube 'M. The horizontal deflection circuit 30 also supplies a signal to a high-voltage unit 31, which generates a high voltage for operating the picture tube 24. The vertical synchronization pulses are a Ver tilcalahlpnkcrhajtuncr 32 »•! •» 'leads, d'P di? Vp.rtilcajah- lenkunj! the electron beams in the picture tube 24 controls.

The parts of the television receiver described so far can be constructed in a known manner, for. B. like the receiver mentioned in the publication "RCA Television Service Data, File 1975 C-10", publisher 2> RCA Corporation, Indianapolis, Indiana, V.St.A. for the CTC-74 device.

The phase-locked tuner 16 includes an oscillator 34, e.g. As a crystal oscillator! Xtal provides a signal with a stable and well-defined frequency m. The frequency of this fixed frequency signal is divided by the factor R by means of a divider 36. The divider 36 can e.g. B. contain a counting circuit and supplies a reference frequency signal of the frequency / Wequality f _x tal / R- The value js of the factor R is selected so that the reference frequency fnEF is sufficiently low to be compatible with the operating frequency range of other parts of the phase-controlled tuning device 16 . Furthermore, the value of the factor R, as will be explained in more detail below, is selected with respect to the value of the fixed frequency fx tal se that the reference frequency generated is in a very specific relationship to the horizontal and vertical scanning frequencies // or. V of the receiver is stationary, so that visible effects of undesired frequency-modulated components of the local oscillator signal, which can arise from the phase control, are largely suppressed.

The reference frequency signal is applied to an input of a phase detector 38 directly, i. H. without further Frequency division, supplied. The output signal of a programmable divider 46 is fed to the other input of the phase detector. The phase detector 38 generates a signal which shows the phase and / or Frequency deviation between the two input signals represents a typical phase detector, which for the phase-locked loop or the phase comparator or phase regulator 16 provides a series of pulses whose repetition frequency is equal to the reference frequency and whose duration is the phase and frequency deviation between the two input signals depends on A phase detector of this type is described in the already mentioned user notification RCA ICAN 6061 and in that of the Integrated circuit CD 4046 available from RCA Corporation Somerville, New Jersey.

The output signal of the phase detector is fed to a low-pass filter 40, which it under formation of a DC voltage signal, the amplitude of which fluctuates in accordance with the phase and frequency deviations between the input signals of the phase detector 38. This variable DC voltage signal is fed to a voltage-controlled oscillator, which serves as a local oscillator 42, to control its oscillation frequency. The output signal of the local oscillator 42 is fed to the mixer 18 and a prescaler 44 which has the division factor K.

The prescaler 44 with. the division factor K contains z. B. a counting circuit which divides the frequency of the local oscillator signal by a factor K , which is chosen so that the divided output signal has a frequency compatible with the operating frequency range of the other components of the phase controller 16 frequency. The value of the factor K is selected in particular so that that which is supplied to the programmable divider 46 pin code? Fr? " ¹ .!?" »Na» _; dip klpjnpr jet aU Hip hftrhctp

Frequency that the programmable divider can process.

The programmable divider 46 divides the frequency of the output signal of the prescaler 44 by a programmable factor N, which depends on the channel that a user of the television set has set by means of a channel selection unit 48. The programmable divider 46 can e.g. B. contain a counter that generates one cycle of the output signal per A / cycle of the input signal. The factor N is z. B. controlled by binary coded decimal number signals which are supplied by the channel selection unit 48. The output signal dps programmable divider 46 is fed to the phase detector 48 in order to close the phase locked loop of the phase controller 16.

In operation, the control signal emitted by the low-pass filter 40 adjusts the frequency of the local oscillator signal until the frequency and the phase of the output signal of the divider 36 dividing by the factor R and the divider 46 dividing by the factor N are in a predetermined relationship, ie in are essentially the same. If this is the case, the phase regulator 16 can be described as "kicking in" or synchronized and the local oscillator signal then has a frequency 4o according to the following equation:

NK

JLO = - £ -} XTAL = NKF _REF .

(1)

In the United States of America, the values of the frequencies of the local oscillator signal calculated in MHz for the channels selectable by a television subscriber contain prime numbers in a range between 101 and 931, i.e. numbers whose smallest common divisor is 1. It is therefore desirable that for each Channel that can be set by a television participant N is equal to the frequency, calculated in MHz, of the corresponding local oscillator signal Under these conditions, equation (1) can be written as follows:

1 MHz = Kf _REf .

Theoretically, according to equation (2), the frequency of the local oscillator is as stable as the reference frequency. However, if a phase detector of the

The above-mentioned RCA user notification ICAN 6061 is used as the phase detector 38, residues of the error signal pulses, which represent the phase and frequency deviation between the output signals of the divider 36 dividing by the factor R and the divider 46 dividing by the factor W, and with the reference frequency fg £ F occur, cause a frequency modulation of the frequency Λ.ο of the local oscillator. The reason for this is that in practice it is difficult to use the low-pass filter 40 to suppress all traces of the error signal pulses in the generated DC voltage control signal. The control signal fed to the local oscillator 42 is therefore amplitude-modulated with the error signal pulse components that occur at the reference frequency far. The amplitude modulation components of the control signal result in a corresponding frequency modulation of the local oscillator signal.

If a local oscillator signal, which contains frequency-modulated components, is mixed with a high-frequency carrier in mixer 18, an IF signal is produced which can also contain a frequency-modulated component. Since the conventional IF circuits, as they are normally used in the IF amplifier 20, an unbalanced, z. B. falling amplitude / frequency characteristic with respect to the video carrier frequency (z. B. 45.75 MHz), IF signal components whose frequency is above that of the video carrier are attenuated more than IF signal components whose frequency is below that of the video carrier . The video signal generated by the IF part 20 can thus have an amplitude modulation with a frequency corresponding to the reference frequency. After processing by the video part 22, this amplitude modulation of the output signal from the IF part 20 usually generates a visible interference pattern in the picture displayed by the picture tube 24, which disturbs the viewer. As already mentioned, the visible effects of the frequency modulation of the local oscillator signal with the reference frequency far are thereby eliminated or at least considerably reduced formed in that three substantially converging, intensity-modulated electron beams which the three primary colors, d. H. Red, green and blue correspond, in a grid pattern over a fluorescent screen -, the inside of the piston of the picture tube 24 are deflected. The electron beams are deflected horizontally along alternating lines, while a vertical deflection takes place at the same time. Two Vertical deflections or partial images are for one

in full picture required. During the one The odd-numbered lines are used during the partial image and the even-numbered lines during the next partial image Lines scanned. This type of raster scan is commonly referred to as "interlace scan",

r, since when scanning the lines of a partial image every other line of the image is skipped as a whole. According to the television standard in the United States of America, a complete picture has a total of 525 lines with a frequency H equal to

: i) The frequency of the line sync pulses, ie about 15 734 kHz, are sampled. Two fields are scanned per image with the vertical or field frequency V , which is equal to the frequency of the vertical synchronization pulses, namely 2 (H / 525) or about 60 Hz

r> is.

Compatible with the transmission and reception of color television signals for black and white televisions to make, signal groups, which represent the color formation, are frequency-wise between signal groups,

κι represent the brightness information, nested. As a result, they take the color information signals representing the same frequency band as the signals representing the brightness information. So that the color signals do not have any disturbing patterns on the

j-, screen of a black-and-white receiver, the carrier assigned to the color signals has a frequency which is equal to an odd multiple of half the line frequency H , while the carrier assigned to the luminance signals is a Fre quency that is equal to a whole multiple of Line frequency / - / is. Because of these relationships to the horizontal or

Relationship to the horizontal and vertical scanning frequency Hbzw. K is chosen. The reference frequencies that can be used for this purpose are specifically given by the equation

f _REF = - H ± nV

(3)

given, where η is an integer and m is an odd integer. This equation thus defines a group of frequencies, all of which are the sum of a -, -, odd-numbered sub-multiple (sub-harmonics) of the horizontal scanning or line frequency and a whole multiple (harmonic) of the vertical scanning frequency or screen frequency. Under these circumstances, Amplitudenmodulationskompo- lift _b0 components of the video signal, which occur at the reference frequency frequency-modulated components of the local oscillator signal corresponding to when the image formation on.

The equation (3) can be determined by a short _6A description of certain aspects of the operation of the receiver 10 better understood when generating a color image. The image generated by the receiver 10 is In relation to the vertical or field frequency V , a signal which represents brightness information passes through a whole number of periods during the scanning of each given line or each given field. This means that changes in brightness either recur in the next line or in the next partial image and are thus amplified. In the case of the signal representing the color information, however, the opposite relationships exist. Since the frequency of a signal representing color information is an odd multiple of half the line frequency H , a signal representing color information passes through a certain number of cycles plus half a cycle during one line period. When the next line of the relevant partial image is scanned, the signal representing the color information reappears with a phase shifted by 180 °. It also appears out of phase when the same line of the following partial image is scanned. As a result of this antiphase, a cancellation effect occurs and the human eye cannot easily perceive a disturbance pattern based on brightness fluctuations which are generated on the screen of a black-and-white receiver by a signal representing color information. One can

So a color television signal can be received satisfactorily even with a black-and-white receiver.

In the United States of America, the color subcarrier has a frequency of 3.5795 ... MHz, so about 3.58 MHz. The color subcarrier frequency is equal to 455 times half the line frequency according to FIG US standard, i.e. H. 15 / 34.26573 ... Hz (about 15734 Hz). The image disturbances generated by the path auxiliary carrier occur therefore during each line very often and they will, as mentioned, compensated or canceled from line to line. The image disturbances that occur in a particular Lines are generated by the color subcarrier, are thus compensated by the out-of-phase image disturbances, which the color subcarrier erases in the next line (in numerical order) in the next partial image. Thus, for example, the color subcarrier image disturbances in line 1 of partial image 1 are caused by the Antiphase color subcarrier image interference in line 3 of sub-image 1 is eliminated.

In order to understand equation (J), it is important to remember that the reference frequency / j? / Tf for phase-regulated television tuning equipment is limited in frequency by the highest frequency, the relevant circuit parts, in particular the programmable divider circuits, such as the divider 36, of the phase regulator. The circuit units currently available for phase regulators should the reference frequency can be considerably less than 3.58 MHz. The periods are subject to these conditions the interference images associated with the reference frequency so long that several Lines are scanned. In other words, those related to the color subcarrier would Noise signals cause disturbing patterns in the line direction if they are not compensated, while the interference associated with the reference frequency signal leads to disruptive image patterns in the vertical or picture direction of the television picture if they are not eliminated.

So in order to keep the visibility of interference patterns low, which originate from a reference frequency signal, that is compatible with components as they are currently

If available, the image interference caused by the reference frequency signal should cancel each other out from field to field and not from line to line like the image interference caused by the color subcarrier. This means that the picture disturbances caused by the reference frequency signal in one field should be out of phase with the picture disturbances caused by the reference signal in the next field. This can be expressed mathematically by the following equation:

(4)

where j is any integer. The term V72 corresponds to the phase inversion required for the cancellation of vertical interference patterns.

Since every integer j can always be expressed as the sum of the difference between two other integers η and ρ , equation (4) can be rewritten as follows:

(5)

Since V = 2Α / Λ25 according to the television standard in the United States, equation (5) can be written as follows:

./REf= t Ml · '+ ( ^P} l) 52 I.
St. + (2p r * 525 Power man (6) (2p t 11
525 (71

where / n is an integer, the equation (6) write as follows:

which corresponds to the calibration (3). From the Equation (7) can be seen that

(2p rl) =

525

Since (2p ± 1) is always an odd number, m must be an integer factor of 525, so m must be one of the odd numbers 1,3,5.7,15,21,25,35. 75,105,175 or 525.

The values of m, η and K. which satisfy the equation (3) are given by the expression

I MHzOK

(10)

given, which results from the union of equations (2) and (3). Taking into account the fact that V = 2 (H / 525) , equation (10) can be written as follows:

525

(H

If possible , K should be an integer, since dividers that divide by a non-integer divisor are relatively complex and therefore relatively expensive. Unfortunately, however, there are no exact solutions to equation (11) for which K is an integer. However, there are a number of solutions for which K is an integer and which give a reference frequency within ± 1 Hz of a frequency-exact solution. By such an inexact solution, a complete elimination of the interfering signals, which are based on a frequency modulation of the local oscillator signal and recur with the period of the reference frequency, cannot be achieved. B. to be expected between 15 and 20 dB.

An inexact solution of equation (11), which ensures a considerable reduction in the undesired interference signal, is given by the values m = 5, η - 17 and K = 240. With this solution, the use of a 1 MHz crystal oscillator and the choice of R = K, the result is a reference frequency of 4166.66667 Hz, which deviates by 0.8325 Hz from the corresponding exact solution of equation (11). This solution is out The following reasons are particularly useful: Counters that are used to divide the frequency of relative

serve high-frequency signals, e.g. B. the oscillator signal for channel 82, which has a frequency of 931 MHz in the United States, should contain as large a number of binary or flip-flop stages as possible, which without feedback from the output of one stage to the input of a second stage through the the second level is reset after a certain number of counting scripts are connected in series. Resetting a binary divider stage takes a certain amount of time, which considerably limits the maximum operating frequency of a counter. If you choose the number 240 for K , you can use a counter that contains four binary levels connected in series without feedback, which divide by 16 and are followed by the four binary levels with feedback ι which divide by 15. Since the first four stages of the counter operate without feedback, they can easily divide the relatively high input frequency (by 16) and provide a relatively low frequency which can be divided by the last four stages (by i5), whose operating frequency is fed back Is limited.

In the following, examples of other solutions will be discussed which enable the use of the last two binary stages connected in series: or flip-flops without a feedback circuit. These solutions can be implemented in the form of a tuning device containing a phase-locked loop with a 1 MHz crystal oscillator and a value of R which is equal to that of K. If you choose m - 5, η = -5 and K - 344, you get a reference frequency of 2906.97674 Hz, which deviates by 0.11616 Hz from the corresponding exact reference frequency. For the division by 344, a counter can be used that contains, for example, 3 binary divider stages connected in series without feedback, which cause a division by 8 and follow the 6 binary divider stages connected in series with feedback, which cause a division 43. If one chooses m equal to 5, η equal to -1 and K 324, one obtains a reference frequency of 3085.41975 Hz, which is 0.4933 Hz from the exact one given by equation (5)

with 324, for example, a counter can be used that has two binary Divider stages without a feedback circuit, which divide by a factor of 4, to the 7 in a row switched binary divider stages with feedback that divide by 81 follow.

With regard to the above-mentioned publication by Eric Breeze in the "IEEE Transactions" November 1974, where it is suggested that the reference frequency for a phase-locked tuner should be derived from the 3.58 MHz color subcarrier frequency, it should be noted that there is no integer divider with which the Color subcarrier frequency can be converted into an odd submultiple of the line frequency H , as required by equation (3). According to the US television standard, the color subcarrier frequency is deliberately chosen to be an odd multiple of half the line frequency so that signal components with the frequency of the color subcarrier are not visible in the image are. In other words, 3.57954 ... MHz divided by 15734.26573 ... Hz equals 222.5, which is not an integer. In the aforementioned Breeze publication, two reference frequencies derived from the 3.58 MHz color subcarrier frequency are mentioned: a reference frequency of 10 kHz for VHF channels is obtained by taking 3.58 MH '. by 358 (ie 179 χ 2) and a reference frequency of 2.5 kHz for UHF channels is generated by dividing 3.58 MHz by 1432 / 179x8). The reference frequency, which is closest to the known reference frequency of 10 kHz for the VHF channels and which represents an exact solution to equation (3), is 9.98001982 kHz (equation (3) with m = 3 and η = 79). The reference frequency suggested in the Breeze publication for the VHF channels is 18.7 Hz from the nearest reference frequency, which is an exact solution of equation (3). In a corresponding way it can be shown that the known reference frequency of 2.5 kHz for the UHF channels is 12.2 Y \ l vuii uci nuiiMen cxakicn reference frequency that corresponds to equation (3) (equation (3) with m = 7 and η = 4. Since the solutions of the equation (3) so reference frequencies according to the invention only mutual distances of 59.95 Hz (ie equal to the Vertikalablenk- or field frequency according to the US standard), have the known reference frequencies mentioned in the foregoing provide fairly represent poor solutions with regard to the compensation of video signal components that arise from reference-frequency amplitude modulation components of the phase-regulated control signal.

By using a phase-locked tuner with a reference frequency that is in the is substantially equal to one of the frequencies defined by equation (3), not only are undesirable Interference patterns avoided from a reference frequency frequency modulation of the local oscillator signal originate, but this is also achieved without additional circuitry. In practice you can even simplify the circuit arrangement for the phase-controlled tuning device. For example, the requirements for the

The elimination of interference effects through reference-free frequency modulation is no longer exclusively through the low-pass filter must be effected. So you can use a simpler and therefore cheaper low-pass filter use. In addition, the synchronization time of the phase control, i. H. the Period of time that is required before the fully synchronized state occurs in the case of a phase-regulated Tuners whose frequency is substantially equal to that given by equation (3) Frequencies is shortened compared to the known phase regulators. The reason for this is that with a phase-regulated tuning device, the reference frequency thereof is essentially the same one of the frequencies represented by equation (3), use a low-pass filter with a higher cutoff frequency can than must be used in the known phased tuners. around a to achieve sufficient high frequency attenuation.

1 sheet of drawings

Claims (2)

Patent claims: 1. Tuning device for a television receiver with an image display device which can be scanned line by line by s a scanning device in a predetermined direction with a first scanning frequency H , a predetermined number L of scanned lines resulting in a raster and each pair of successive ι ο rasters in a second scanning frequency V / 2 are sampled, with a controllable oscillator for generating a local oscillator signal for tuning the television receiver to a selected channel according to the amplitude of a control signal, and a divider to which the oscillator signal! is supplied for division by a predetermined amount, further with a reference frequency signal generator, and with a control signal generator, which is coupled to the reference frequency signal generator sövie the divider for the oscillator signal and generates a control signal that the frequency and phase relationships between the oscillator signal and the reference frequency signal represents and contains amplitude components occurring with the reference frequency, characterized in that the frequency of the reference frequency signal is related to the sampling frequencies in such a way that when the image display device is scanned, visible influences of video components, which are caused by the amplitude-modulated components of the control signal, from raster to raster in substantially cancel out and also lower than / or equal to the next frequency which the control signal generator (38,44,46, 48) is able to process, and practically equal to jV ± 1/2 V, where j denotes an integer is 2. Tuning device according to claim 1, characterized in that the reference frequency im essentially the same