FR2495407A1 - SYNTHESIZER OF TELEVISION FREQUENCIES FOR NON-STANDARD CARRIERS - Google Patents

Abstract

The present invention relates to a device for tuning to a high frequency carrier having a standard broadcast frequency associated with a selected channel or a non-standard frequency arbitrarily close to the standard frequency. According to the invention, an adjustable oscillator 50 produces a signal, which a mixer 16 combines with the high frequency carrier to derive an IF signal having an information carrier; means 26, 28, 52, 34, 36, 38, 40, 62 control the oscillator signal at a frequency shifted from its nominal frequency for the selected channel, by an amount relating to the maximum expected deviation between the non-standard and standard frequencies; and means 42, 68, 66, changes the frequency of the oscillator signal within a predetermined range from the shifted frequency to reduce the deviation between the frequency of the information carrier and its nominal value. The invention applies in particular to CATV and MATV systems. (CF DRAWING IN BOPI)

Description

The present invention relates to a device

  of television channels, and is particularly

  In the United States of America, air-television broadcasting frequency channels for very high frequencies (VHF) and ultra-high frequencies (UHF) are assigned by the United States of America. Federal Communication Commission

  (FCC). During an air broadcast, these frequencies must be

  can be maintained to a high degree of accuracy.

  Recently, frequency synthesizers include

  phase-locked loop (PLL), have been

  suggested to accurately produce oscillatory signals

  localizer at predetermined frequencies, corresponding to the various channels that a viewer may choose, For example, a tuner using a locked-in-phase loop is described in "Digital Integrated Circuits Application Note ICAN-6716" entitled "Low-Power Digital Frequency Synthesizer Utilization COS / MOS IC's "of RE FUNK, published in the Solid State Databook RCA 1972 on Digital Integrated Circuits COS / MOS (SSD-203) published

by RCA CORPORATION.

  Other types of systems are also known to tune a television receiver to standard frequencies. In one type, described in U.S. Patent No. 3,818,363 entitled "Automatic Tuning Apparatus Having Dual Frequency Sweep." at Sakamoto, published June 18, 1974, the system comprises two oscillators which are scanned alternately and in a staggered or gradual manner by a preliminary frequency over the frequency range of the local oscillator of the air diffusion channel. By counting the number of times the oscillator sweeping and stopping occurs, it is possible to determine when a preliminary control voltage of the local oscillator is close but slightly less than the

  control voltage is good for tuning a particular channel

  to bind, has been reached. Then, an auxiliary scanning circuit increases the control voltage to the correct tuning voltage. Thus, a tuner device of the frequency synthesizer type is known for the standard transmission carrier frequencies. However, not all television signals are transmitted at standard carrier air frequencies. In some television distribution systems, such as apartments and motels, television signals are applied to the receivers by cables. In these systems and others

  still using a cable (or even micro-links)

  waves), the modulated scattering carrier may arbitrarily

  to be demodulated and remodulated to a different carrier, close to the standard

  apply it to a receiver. It is therefore desirable

  to provide a device for tuning receivers

  to such non-standard carriers.

  A device that can be used to tune a television receiver at both the standard carrier frequencies associated with conventional VHF and UHF channels and non-standard carriers arbitrarily placed near the standard carrier frequencies is described. Adjusted oscillator means are included in the device

  okay, to produce a local oscillator signal.

  Mixing means combines the local oscillator signal and a received modulated carrier to derive a carrier at a modulated intermediate frequency. Programmable divider means divide the frequency of the local oscillator signal by a first number corresponding to a channel selected at that time. Phase detector means provides a first control signal for maintaining, in a predetermined phase and frequency relationship, the signal of the local oscillator whose frequency is divided and a signal at a reference frequency. The first control signal has an amplitude range between first and second amplitudes, which is sufficient to vary the signal of the local oscillator over a range of frequencies in excess of the space between adjacent channels. Frequency discriminating means produce

  a discriminator signal representing the frequency deviation

  frequencies between the carrier at an intermediate frequency and a fixed frequency (i.e. the nominal frequency of the image carrier). The discriminator signal has an amplitude range between minimum and maximum amplitudes, corresponding to the frequency differences that are

  a fraction of the frequency interval between channels.

  Means connected to the discriminator means derive a second control signal from the discriminator signal. This second control signal has an amplitude range between first and second amplitudes, which are substantially the same as the first and second amplitudes of the first control signal, and which correspond to the frequency differences of the intermediate frequency carrier, between the deviations associated with the maximum and minimum amplitudes of the

signal of the discriminator.

  Means of exploration force the local oscillator signals to be scanned or scanned over a frequency range near the frequency of a signal

  selected local oscillator. The frequency of the oscil-

  The localizer can be scanned or scanned, for example, by incrementally increasing the frequency of the signal at the reference frequency, relative to the frequency-divided local oscillator signal. Means are provided for inhibiting the scanning means when the difference between the frequency of the intermediate frequency carrier and the fixed frequency is within a predetermined range and when the magnitude of the control signal is substantially equal to the amplitude of the first control signal for the

chosen channel at that time.

  Switching means are provided for selectively applying the first and second control signals to the set oscillator means. When the scanning means is inhibited, the switching means disconnects the first control signal from the set oscillator means and, on the other hand, applies the second control signal to the set oscillator means. Then, the second control signal controls the frequency of the local oscillator signal. The invention will be better understood, and other purposes,

  characteristics, details and advantages of it appear-

  more clearly in the explanatory description

  which will follow, made with reference to the accompanying schematic drawings given solely by way of example illustrating an embodiment of the invention, and in which: - Figure 1 shows in block diagram form, a channel tuning device; constructed according to the present invention, used in a television receiver; FIG. 2 shows a logic diagram of execution of a part of the tuning device illustrated in FIG. 1; FIG. 3 shows, partly in schematic form and partly in the form of a logic diagram, the execution of other parts of the tuning device of FIG. 1; FIGS. 4 and 5 show graphical representations of the characteristics of the voltage (y-axis) as a function of the frequency (x-axis) associated with parts of the illustrated tuning device.

in Figure 1.

  FIG. 1 illustrates the general arrangement of a television receiver, employing a device

  channel tuner constructed in accordance with the present invention.

  High frequencies (RF) are received by an antenna 12,

  and are amplified by a high frequency amplifier

  The amplified high frequency signals are applied to a mixer 16 where they are combined with a local oscillator signal at the appropriate frequency, derived in a selected channel, as will be subsequently described, to form an intermediate frequency signal ( IF) The IF signals are amplified by an intermediate frequency amplifier 18 and are then applied to a video detector 20. The detector 20 extracts signals

  including, for example, chromatic components

  nance, luminance and synchronization, amplified IF signals. The video signals are applied to a video signal processing unit 22 comprising, for example, channels for processing the chrominance, luminance and synchronization components of the video signal, for

  form an image on an image tube 24.

  In the general arrangement just described, it is possible to use the components used in a CTC-68 type color television receiver, shown, for example, in RCA Color Television Service Data, FILE 1974 c-5, published by RCA Corporation, Indianapolis,

Indiana, U.S.A.

  In the illustrated device, the information of the selection of the channel is introduced by a spectator, by a channel selection keyboard 26, The keyboard 26 is composed, for example, of a keyboard of the calculator type, by which VHF channels or UHF can be chosen in a decimal format. The keyboard 26 may comprise, for example, a matrix for converting the decimal information into a binary coded decimal format (BCD). Coded signals

  binaries, representing the channel information, are

  to a register 28 of the number of the channel by a route to

multiple conductors 30.

  The register 28 converts the binary information of

  selection of the channel into other binary signals representing

  both a number "N" corresponding to the channel chosen at that time. For this purpose, the register 28 may comprise, for example, a read-only memory (ROM), in which

  information of the number "N" is stored for a recovery

  later in response to the input of the binary signals

of the keyboard 26.

  The binary signals representing the number N are applied by a multi-conductor path 32 to a programmable frequency divider 34, arranged to divide the frequency of the incoming signals by the number N.

  divider 34 is arranged in a lock loop configuration.

  In-phase (PLL), with a voltage-tuned local oscillator 50, a pre-calibrated frequency divider 52, a crystal reference oscillator 40, a programmable divider by "R" circuit 38, a phase detector 36 and a low-pass filter amplifier 46. The phase-locked loop arrangement, in combination with the channel selection device, forms a frequency synthesizer of the type described in the above-mentioned RCA application note, and allows to tune a television receiver

to standard carriers.

  Most of the rest of the block diagram shown on

  FIG. 1 relates to a device for automatically tuning

  the receiver to non-standard carriers, such as

  than those that can be encountered, for example, in CATV and MATV systems (multi-antenna and antenna array television systems). The more detailed diagram of such a device is illustrated in FIGS.

  and 3. However, we will not give a detailed description

  illustrated in Figures 2 and 3, because those skilled in the art will understand

  easily these accomplishments by reading the description

  following of the tuner of the receiver of Figure 1.

  For this purpose, the parts of the embodiments illustrated in FIGS. 2 and 3, and their interconnections have been identified by the same references as those by which they are identified in FIG. 1. Similarly, to relate the embodiments of FIGS. and 3 and

  FIG. 1, in the following description of FIG. 1,

  reference will be made to the logic signals "0" and "1" relating to the control signals associated with the tuning device. These logic signals "0" and "1" respectively correspond to voltages close to the ground of about +12 volts DC in the logic circuits of FIGS. 2 and 3, which can, for example, be formed of

  COS / MOS integrated circuits using such voltages.

  The television receiver tuning device of Figure 1 operates in two modes. Initially

  mode or mode of non-scanning, that is to say for the reception

  tion of a standard carrier frequency allocated or assigned to a selected channel, the programmable divider by N 34 and the programmable divider by R 30 are respectively set

at predetermined values.

  In the non-scanning operating mode used to tune the receiver to standard carrier frequencies, a viewer mode enable switch 54 that is operable by the viewer is placed in the open position (shown), so that a scan enable control signal (VB) (a logical "1" representing the absence or complement of a SCAN VALIDATION control signal), is applied to a logic switching unit 56 by a conductor 58 and a logic unit 62 for prepositioning the count by a conductor 60, to inhibit the device associated with non-standard carriers received in the manner

which will be described below.

  In response to the scan enable control signal, the switching logic unit 56 generates a scan stop command signal NI 1 (a logical "O") which is applied to a clock validation unit 68 by a conductor 90, to prevent the clock pulses of a divider 66 parA from reaching the clock input (to the driver 114) of a reversible counter 42. Therefore, the counter 42 will not change the number divided by R of divisor 38, as it does in the exploration mode

which will be discussed later.

  In each mode of operation, a viewer chooses a channel, by pressing or otherwise activating

  appropriate keys on the channel selection keyboard 26.

  The register 28 receives the binary signals representing the channel selection information from the keyboard 26,

  and extracts, from its memory, binary signals representing

  both the number N corresponding to the selected channel.

  The binary information representing the number N is introduced

  in the programmable N divider 34, so as to divide the frequency of the incoming signals by the number N. In addition to extracting, from its memory, binary signals representing the number N each time a new channel is chosen , whether in non-scanning or scanning mode, the register 28 also provides the start pulse control signal (ID) (a logical "1"), which is applied to the switching logic unit 56 by a conductor 78, to reset the flip-flops 5612 and 5614 (Figure 3) whose function will be subsequently described, zero. In response to the DEKURAGE IMPULSE control signal, the switching logic unit 56 outputs a control signal (a logic "O" to the driver 88) to force a switch 48 to apply the output signal (driver 122) of the amplifier unit 46 and the low-pass filter, at the control terminal of the voltage-tuned oscillator 50 by a conductor 128, to form the locked loop configuration in phase

above described.

  The START PULSE command signal is also applied to the logic unit 62, to reset it before entering a new information item.

register 28.

  The channel number register 28, in addition to deriving the appropriate number N for the programmable divider 34 and producing the start pulse control signal, provides three band switching control signals ("1s"). logic): a UHF control signal when a channel has been selected in the UHF range (i.e., channels 14-83); a LOV control signal when a channel in the low range of the very high frequencies (i.e., channels 2-6) has been selected; and an HIV command signal

  when a channel in the high range of the very high frequencies

  quences (that is, channels 7-13> has been selected.) The band switching control signals with the scan enable control signal are applied to

249,540?

  the logical unit 62, to force it to choose the appropriate number R. These band switching control signals are also applied in an appropriate known manner (not shown) to voltage tuned tuners, such as varactor diodes, in the oscillator 50 and the divider 52, to control the signal frequency at the input of the divider by N 34, according to the frequency band

of the chosen channel.

  The values of N and R for tuning the receiver to the standard carrier frequencies are shown in the columns indicated by "N scan and non-scan" and "R non-scan" in the following table. The values in the table correspond to an embodiment in which the frequency of the crystal oscillator 40 is 5 MHz and the divider 52 divides the frequency of the output signal of the oscillator set to voltage 50 by 256. Note that the values of N are equal to the frequencies, in MHz, of the output signals of the local oscillator 50 required, when they are mixed with the respective received standard carrier frequencies, to produce frequency difference intermediate frequency signals having a carrier of d. at 46.75 MHz (the standard IF image carrier in most

United States of America).

  Initially, when a channel was chosen by the viewer and the programmable divider 34 by N and the

  programmable divider 38 by R have been established, the oscilla-

  The oscillator 50 oscillates at an arbitrary frequency (i.e. at a certain average point in the chosen band). The

  operating frequency of the oscillator 50 is modified.

  in response to the dc control signal at the output of the amplifier unit and low pass filter 46, until the output error signal provided by the

  phase detector 36 shows that there is no difference

  In this case, the phase-locked loop corresponding to the oscillator 50, the divider 52 by K, the programmable divider 34 by N, the detector, or the frequency between the output signals of the divider 34 and the divider 38. of phase 36, the programmable divider 38 by R, the crystal oscillator 40 and the amplifier unit 46 and low-pass filter will produce a local oscillator signal at the output of the oscillator 50 whose frequency fLO is will report at the fxosc frequency of the output signal of the oscillator 40 by the following expression fLO = Rf XOSC (1) Note that the output signal of the unit 46 must have a range of amplitude sufficient to vary the signal of the local oscillator over a frequency range for a particular band, greater than the space between adjacent channels, and advantageously large enough to allow tuning the receiver to all channels in the particular band. Thus, for example, in the low range of the very high frequencies, the unit 46 can produce a control voltage in a range between first and second voltages, sufficient to tune the receiver

at one of the channels 2, 3, 4, 5 or 6.

  The output signal of the oscillator 50 is applied to the mixer 16 where it is combined in the conventional manner with the output signal of the RF amplifier 14 to form an intermediate frequency signal comprising an image carrier at a frequency (ie 45., 75 MHz) equal to the difference between the frequencies of the received carrier and the signal of the local oscillator. The intermediate frequency signal is amplified by the amplifier 18 and a

  video information is extracted by the video detector 20.

  The video signals are processed by the signal processing unit 22 to form an image on the face of the image tube 24. If the viewer wishes to receive signals from a

  non-standard carrier distribution system (ie

  by a CATV or MATV distribution system), the scan mode enable switch 54 is placed in the closed position, producing a scan enable control signal (a logical "0") to place the tuner in the second operating mode or scanning mode. In the second mode, during the

  reception of an arbitrary non-standard carrier frequency

  The N-programmable divider 34 is again close (i.e. in the + 2 MHz range) of the frequency of an associated standard carrier and is again set to a fixed value corresponding to the selected channel. However, the divider 38 by R is initially set to a first value or division ratio less than the value or division ratio corresponding to the associated standard carrier frequency (at which the divider 38 would have been established during the first mode), then increments it to a second ratio greater than that corresponding to the associated standard carrier frequency until agreement is obtained or until the second value

  achieved as will be explained in detail below.

  In the scanning mode (as in the non-scanning mode) of operation, a viewer selects a channel by pressing the appropriate keys on the channel selection keyboard 26, and, in response, binary information representing the number N is introduced in the programmable divider 34 by N. Furthermore, the register 28 also produces a start pulse command signal (a logic "1") which is applied to the switching logic unit 56 to reset the flip-flops. 5612 and 5614. In response to the start pulse command signal, the unit 56 generates a control signal (a logic "0" on the lead 88) forcing the switch 48 to initially connect the output terminal of the unit 46 amplifier and low-pass filter at the control terminal of the oscillator 50. In addition, the start pulse control signal also resets the logic unit 62 prepositioning account before entering new As in the non-scanning mode as well, the register 28 produces a UHF, LOV or HIV control signal, according to the frequency band

which is the chosen channel.

  According to the control signals HIV or LOV produced by the register 28 and the scan enable control signal provided by the switch 54, the logic unit 62 applies binary signals to the reversible counter 42,

  which represent the first preselected value in

  below the value at which the R number would be established

  for the same channel selected during a non-scan mode.

  The first preselected values corresponding to the various channels, which are introduced into the reversible counter 42 during the scanning mode are indicated

  in the "Start R" column of the following table.

  The logical unit 62 also produces the complements,

  HIV and WOV control signals HIV and LOV. These complements

  These elements are applied to a scanning stop logical unit 70 via a multi-conductor path 64, to set it to one of two preselected values (depending on whether the selected channel is in the high or low ranges of very high frequencies ), above the value at which the R number would be set in non-scan mode. The second preselected value corresponds to the highest value at which the number R could be incrementally increased during the scan mode. The second preselected values corresponding to the various channels are indicated in the "STOP R" column of the following table. In response to the SCAN VALIDATION control signal, the unit 56 generates a No1 scan stop control signal (a logic "1" indicating the absence or complement of the scan stop control signal N01). , to allow the clock signals of the divider 66 by A

  to reach the clock input of the reversible meter 42.

  In response to these clock signals, counter 42 increases in increments the number R from the first value

  preselected to the second preselected value.

  The second preselected values corresponding to the various channels are indicated in the "STOP R" column of the

following table.

  The operation of the phase locked loop including oscillator 50, divider 52 by K, programmable divider 34 by N, phase detector 36, crystal oscillator 40, programmable divider by R 38 and unit The amplifier and low-pass filter is identical to the non-scan mode for controlling the frequency fL0 of the local oscillator signal according to expression 1. However, as each successive clock pulse of the clock output signal of the circuit 66 divider by A reaches the reversible counter 42, the number R is incrementally incremented by a predetermined amount indicated in the "IAR" column of the following table, the magnitudes of the increments of R for

  the various channels when A is chosen equal to 2 being 2.

  As a result, the frequency of the local oscillator signal is decreased by decrements (i.e., scaled down). The starting and stopping frequencies of the local oscillator signals and the frequency increment dimensions for the various channels are indicated in the columns "fLO START", "OFF" and "A \ fLO" of the following table for an achievement in

  which A is chosen to be 2.

  The local oscillator output signal of the oscillator

  The voltage regulator 50, as in the non-sweep mode, is combined with the output signal of the amplifier 14 in the mixer 16 to produce a modulated intermediate frequency signal whose carrier frequency is incrementally increased in direct relationship to one another. an extent corresponding to the frequency range of the local oscillator signal. The scanning range for each channel is chosen large enough to include the required local oscillator signal frequency when combined with the received non-standard carrier frequency in the mixer 16 to provide a modulated intermediate frequency signal having a desired frequency. image carrier to a

  predetermined frequency, that is 45.75 MHz.

  While the intermediate frequency carrier is decremented by decrements, an automatic accurate tuning frequency discriminator 92 (AFT) connected to the output of the amplifier 18 produces a voltage which is related to the frequency difference between the frequency of the intermediate frequency carrier and 45.75 MIz. FIG. 4 shows a graphical representation of a characteristic S of the voltage as a function of frequency, associated with the circuit 92, having typical values of voltage and frequency for the embodiment illustrated in FIGS. 2 and 3. that the characteristic 412 has an amplitude range between a minimum amplitude and a maximum amplitude, which corresponds to a frequency difference (+ 25 kHz), which is a fraction of the frequency interval between channels (6 MHz). The direction in which the frequency of the modulated intermediate frequency carrier is swept

  is also illustrated by the arrow in Figure 4.

  The output signal produced at an output terminal (+) of the circuit 92 is applied to a threshold detector 82 by a conductor 104, where it is monitored. The detector 82 produces a THRESHOLD control signal (a logic "1") when the voltage at the (+) output terminal of the circuit 92 passes above a predetermined threshold 414.

  command is applied to the logical unit of communication

  56 by a driver 106, where he establishes the flip-flop

  5612 of the switching logic unit 56.

  An amplifier 94 amplifies the automatic fine tuning signal produced at a (-) terminal of the circuit 92 and applied thereto by a conductor 124. The gain of the amplifier 94 is chosen so that the amplified signal has substantially the same amplitude range, between first and second voltages, that the signal of

  output of the amplifier unit 46 and low-pass filter.

  Indeed, the amplitude range of the amplified output signal of the amplifier 94 must give substantially the

249,540?

  same voltage for a chosen channel, when it is applied

  to the oscillator 50, that the output signal of the unit 46.

  It will be noted that the first and second voltages of the amplified automatic fine tuning signal correspond to the frequency differences of the intermediate carrier frequency between the deviations associated with the maximum and minimum voltages of the characteristic of the frequency discriminator.

associate of circuit 92.

  FIG. 5 shows a graphical representation of the characteristic 512 of the voltage as a function of the

  frequency of an amplified signal at the output of the ampli-

  94, with typical values of voltage and frequency

  The direction in which the frequency of the modulated IF carrier is scanned or scanned is also illustrated by the arrow. The approximate levels of

  control voltages supplied to the oscillator 50, corresponding to

  channeling in the low range of very high frequencies are also indicated. It will be noted that a similar characteristic is associated with the channels of the high range of the very high frequencies. FIG. 5 also shows a partial graphical representation of a stepped waveform 514 similar to that of the amplifier output signal and low-pass filter 46, which causes the incremental increase of the frequency

IF carrier modulated.

  A comparator 84 compares the output signal of the unit 46 (waveform 514) which is applied thereto by a conductor 100 to the output signal of the amplifier 94 (waveform 512) supplied to it by a driver 91, and produces a COMPARISON control signal (a logical "1") when these voltages are equal. The COMPARISON control signal is applied to the switching logic unit 56 by a conductor 102, and establishes the

  flip-flop 5614 of logic unit 56.

  When the flip-flop 5612 is set in response to the THRESHOLD control signal and the flip-flop 5614 is set in response to the COMPARISON control signal, the switching logic unit 56 produces a control signal (a logical "1" on the 88), to decouple the output terminal of the amplifier unit 46 and the low-pass filter from the control terminal of the oscillator 50, and instead to couple the output terminal of the amplifier 94 to the control terminal of the oscillator 50. Next, the automatic accurate tuning signal controls the frequency of the local oscillator signal at the

output of the oscillator 50.

  If the frequency of the local oscillator signal is slipping due to temperature changes or changes in the values of the components or the like, relative to the frequency set at the time the control signal at the oscillator input 50 is switched from the output signal of the unit 46 to the precise tuning signal

  amplified automatic, the circuit 92 operates against

  reaction, to produce an automatically accurate tuning signal

  amplified tick opposing the frequency change due

to slip.

  The THRESHOLD command signal indicates that the amplified automatic accurate tuning signal changes to the right

  to provide automatic accurate tuning control.

  The threshold 414 in FIG. 4 corresponds to the threshold 516 in FIG. 5. If the switch 48 were to apply the automatic amplified accurate tuning signals of the circuit 92 to the oscillator 50 before these signals reached the threshold 516, the automatic fine-tuning control would be achieved because the control voltage applied to the oscillator 50 would change in the wrong direction, i.e., along the slope portion 518 of the feature 512 rather than along the part in

slope 520.

  The COMPARISON control signal indicates that the amplified automatic fine tuning signal produces a control voltage which, when applied to the oscillator 50, forces it to produce a local oscillator signal whose frequency is sufficiently close to the frequency of the local oscillator signal associated with the selected channel. For example, assuming that channel 4 is the chosen channel, then if switch 48 is switched to couple the output terminal of amplifier 94 to the control input terminal of oscillator 50 when the voltage the automatic amplified accurate tuning signal is at level 516, the control voltage applied to the oscillator 50 corresponds to a channel near the channel 2 rather than the control voltage required for the

channel 4.

  Thus, the control of the oscillator 50 is switched from the phase locked loop control to the automatic accurate tuning control when both the THRESHOLD and COMPARISON control signals are present. In addition, when the THRESHOLD and COMPARISON control signals have been generated, the logic unit 56 generates a SCAN STOP NO 1 control signal (a logic "0" on the conductor 90) to pock the signals. clock to reach the clock input of the

  reversible counter 42, and to prevent the further increase

  incrementalization of the programmable divider by R 38,

  and therefore terminate the scan operation.

  If no automatic precise tuning command is obtained before the number R has reached its final value ("OFF R" of the following table), the scan stop logic unit 70 produces a control signal OFF SCAN STOP 2 (a logic "0" on the conductor 108), to prevent the clock signals from reaching the clock input of the reversible counter 22 and terminating the scan. At this point, the viewer sees an image of poor quality and can choose another channel or start a new scan interval by choosing another

  channel and then rechose the original channel.

  It will be noted that the frequency of the modulated IF carrier is decreased by decrements, by decreasing the frequency of the local oscillator signal. This is desirable so that the first carrier to be reached is the desired image carrier rather than a sound carrier of a channel

  adjacent. This avoids or diminishes an erroneous agreement.

  Note that if a UHF control signal has been generated by the register 28, even if the

  sweep mode enable 54 has been closed to allow

  setting the receiver to non-standard carrier frequencies, the unit 56 will produce, in response to the UHF control signal, a SCAN STOP command signal N01 to prevent the divider clock signals from A 66 reach the clock input of the reversible counter 42 by the clock enable unit 68. Therefore, the number R in the programmable divider 38 by R is not incrementally increased when a UHF channel is selected whether or not the scan mode enable switch is pressed. This arrangement is planned because the

  most of the TV distribution systems

  Vision does not reconvert the UHF carrier frequencies for distribution at other UHF frequencies, and therefore the scan mode is not required when a UHF channel is selected. However, it will be noted that the tuning device could be modified to 1ay for carrier frequencies URF

non-standard.

  Although no detailed description of the

  FIGS. 2 and 3 have been given for the reasons mentioned above, it will be noted that with respect to the logic embodiments of FIG. 2, the integrated circuit CD4027 included as part of the programmable divider 38 by R is a flip-flop which divides the output signal frequency of the integrated circuit counter CD4059, also included in the divider 38, by 2. As a result, the numbers set in the integrated circuit meters CD4029 forming the counter reversible 42 are only half of the corresponding values of R indicated in the following table. Furthermore, only the binary signals representing "1", "2", and "4" for

  to form the largest number or digit (MSD), corresponding to

  at the position of the number of tens, and the least significant number or digit (LSD), corresponding to the position of the number of units, of a number corresponding to the values of "OFF R", are applied to the logical unit 70, because the MSD and LSD of the numbers corresponding to STOP R do not require "8" for their formation. In addition, the binary signals for forming the hundreds digit of the numbers provided by the reversible counter 42 are not applied to the logic unit 70, because the number in the hundreds digit is the same for the low to very high ranges. frequencies and high frequencies at very high frequencies, and is not

increased in increments.

  Whereas, with reference to Figure 1, the increase

  If the incremental frequency of the modulated IF carrier has been obtained by decreasing the programmable divider 38 by R, it will be noted that the frequency of the IF carrier could also be decreased by decrements by decreasing the value to be introduced into the programmable divider. 34 by N, as indicated by a multi-conductor path 126 connected between the reversible counter 42 and the divider 34. Furthermore, while the tuning device of Figure 1 has been described as decreasing by decrements the frequency of the IF carrier to avoid tuning the receiver to the sound carrier of an adjacent channel, it will be noted that the frequency of the IF carrier can be increased in increments. : I: Ia: I: I I 1 i 6:

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Claims (2)

R E V E N D I C A T I 0 N S   1.- tuning device for receiving high frequency television composite signals associated with   respective channels, each high frequency composite signal   a frequency carrier having either a standard frequency carrier or a non-standard frequency carrier, each non-standard frequency carrier being arbitrarily close to one of said respective standard frequency carriers within a first predetermined range which is less than the frequency separation between adjacent carriers of said channels, of the type comprising: a means   forming a local oscillator to produce an oscillation signal   local controller having a frequency set in response to a control signal; mixer means for combining said high frequency signals and said local oscillator signal and producing a frequency signal   intermediary comprising at least one information carrier   tion; characterized by: - a relatively stable frequency signal source (40) having a frequency substantially lower than that of said local oscillator signal; first programmable divider means (34) for dividing the frequency of said local oscillator signal by a first programmable factor (N) and producing a first frequency divided signal; second programmable divider means (38) for dividing the frequency of said stable frequency signal by a second programmable factor (R) and producing a second frequency divided signal; phase comparator means (36) for producing said control signal for said local oscillator means in response to at least one of the phase and frequency deviations between said first frequency divided signal and said second divided signal in frequency; first means (26,28) for controlling said first programmable factor and selecting one of said channels; and second means (42, 66, 68) for controlling said second programmable factor and controlling the frequency of said information carrier within a second predetermined range which is defined by said first programmable factor predetermined range.   2. Device according to claim 1, characterized in that said second control means comprises an automatic accurate tuning means (92) for producing an automatic accurate tuning signal in response to the difference between the frequency of the said information carrier and a fixed frequency, said automatic accurate tuning signal being coupled to said second programmable divider means (38) for controlling the second programmable factor (R) above.