Tuner with at least a first and a second frequency band

The invention relates to a tuner having at least a first and a second frequency band and having a signal input for supplying a frequency information signal.

The invention further relates to an integrated circuit having a PLL circuit for controlling a tuner having at least a first and a second frequency band.

Such a tuner and such an integrated circuit are known for example from the tuner UV 316 from Philips. This well-known tuner is manufactured according to the WSP standard (World Standard Pinning). The WSP standard specifies the mechanical dimensions, the functions of the individual connection pins of the tuner and the antenna height. Terrestrial tuners usually have two or three frequency bands, each consisting of a tunable input filter, a controllable amplifier, a tunable bandpass filter and a mixer circuit. For controlling and selecting the frequency bands, three pins are provided in the WSP for supplying a respective control signal. The control of the tuner by means of the microprocessor of the television, which for example by means of an I²C-bus is coupled to the tuner. To select the frequency band, a table is stored in known televisions, by means of which the selectable frequencies of the television signal, the respectively associated frequency band of the tuner can be assigned. When the user of the television selects a television signal frequency, for example by means of an operating unit, the television's microprocessor uses the table to select the corresponding frequency band of the tuner and sends the control unit selection signals to the tuner.

The selection of the frequency band of the tuner by means of the microprocessor of the television has the disadvantage that only tuners can be used in the television set whose frequency bands correspond to the values ​​stored in the table of the television. A subsequent change of the tuner with regard to the characteristics of the frequency bands or the use of another tuner is no longer possible.

It is an object of the invention to provide a tuner and an integrated circuit of the type mentioned, which are universally applicable.

This object is achieved according to the invention for the tuner, that the tuner has a band selection circuit, which is provided for selecting and controlling in each case one frequency band and in that the tuner has a frequency search function for tuning to a frequency, which is provided in a first step for checking the tunability of the frequency in the first frequency band and, if tuning in the first frequency band is not possible, in a second step for checking the tunability of the frequency in the second frequency band is provided.

The tuner according to the invention thus evaluates the frequency information signal supplied to it by the microprocessor of the television set and independently selects the frequency band as a function of this frequency information signal. To enable the tuner to independently select the frequency band, it has a frequency search function. This frequency search function is intended to check in succession in at least two different frequency bands, whether a desired frequency in the respective frequency band is tunable.

Each frequency band has a mixer circuit with an oscillator for driving the mixer. The oscillator preferably has in each case a resonant circuit with a controllable capacitance. The controllable capacitance is preferably realized as a reverse biased capacitance diode (varicap diode) whose capacitance is dependent on the applied blocking voltage. By changing the reverse voltage and the associated change in the capacity, the oscillator frequency of the resonant circuit can be controlled. Terrestrial tuners are usually designed to convert input frequencies in a range of 45 MHz to 863 MHz. Since the controllable or adjustable capacitance range of the varicap diodes is limited, the tuner preferably three frequency bands each having an oscillator resonant circuit and each one provided for tuning the oscillator resonant circuit capacitance diode. Checking for tunability thus means that it is checked whether the oscillator of the respective frequency band can be tuned to the desired frequency required for mixing to the intermediate frequency of the tuner. The oscillator resonant circuits are preferably coupled by means of a programmable divider circuit with a quartz oscillator. For the synchronization of the oscillator resonant circuit with the quartz oscillator, a phase-locked loop (PLL) is preferably provided. The check as to whether a desired frequency can be tuned in one of the frequency bands can be carried out by means of a lock-in detector, which detects whether the phase-locked-loop circuit locks in, ie Whether the desired oscillator oscillation frequency of the oscillator resonant circuit is synchronized with the reference frequency of the quartz oscillator, wherein between the oscillator resonant circuit and quartz oscillator, a programmable divider circuit is provided.

The individual frequency bands usually each have a bandpass filter, which is formed by a coil and a parallel-connected capacitance diode. The junction capacitance of the capacitance diode is dependent on the applied reverse voltage and can therefore be controlled by changing the applied reverse voltage. The capacitance diodes of the bandpass filters and the capacitance diodes of the oscillator resonant circuits are preferably driven in parallel during tuning.

When a frequency information signal of a desired frequency is supplied to the tuner, in a first step, the oscillator frequency of the oscillator of the first frequency band is detuned from the lower band frequency to the upper band frequency. It is checked whether the desired frequency is tunable in the first frequency band. If the desired frequency could not be tuned in the first frequency band, it automatically switches to the second frequency band whose oscillator is now also tuned to tune to the desired frequency continuously from the lower band limit to the upper band limit.

This principle can also be applied to tuners with three or more frequency bands, wherein, for example, in three frequency bands, the tuning is first attempted in the first, then in the second and finally in the third frequency band.

The independent band selection of the tuner by means of the band selection circuit and the frequency search function has the advantage that such a trained tuner can be used in any TV. For this purpose, neither the software of the microprocessor of the TV nor the software of the tuner must be changed. Such a tuner can therefore be produced efficiently and inexpensively with very high numbers. In addition, it is possible to change the physical parameters of the individual frequency bands without requiring a change in the software of the tuner. For example, the band boundaries of the frequency bands may be shifted by using other capacitance diodes or other inductances for the respective bandpasses and oscillator circuits. In such a case, no change to the software of the tuner is required because the tuner automatically changes the switching points between the individual frequency bands.

By means of the advantageous embodiment of the invention according to claim 2, an unnecessary switching between the frequency bands can be avoided. In accordance with the difference frequency between the old and the new frequency information signals, which is supplied to the tuner by the microprocessor of the television, for example, determined by the frequency difference detection circuit, the band selection circuit determines a tune mode. This tune mode affects the further band selection, ie it determines whether and under which conditions a band switching occurs between the frequency bands.

According to claim 4, as Tune modes, for example, a renewal mode and / or an automatic frequency control mode and / or a search mode and / or a channel re-selection mode can be discriminated by means of the frequency difference detection circuit. In the refresh mode, it is recognized that the television's microprocessor has sent the same frequency information signal to the tuner again. In such a case, band switching is not desired and therefore no band switching is provided in the refresh mode. In the automatic frequency control mode, the frequency difference detection circuit detects that the frequency information signal supplied to the tuner differs only very slightly from the old frequency information signal. This is characteristic of the automatic frequency control mode of a television. In such an automatic frequency control mode, the intermediate frequency demodulator generates a fine tuning control signal which is supplied to the television's microprocessor. The television's microprocessor then provides a slightly changed frequency information signal to the tuner. By means of the frequency difference detection circuit can detect such a case and prevent disturbing band switching. As a further Tune mode is advantageously a search mode by means of the frequency difference detection circuit recognizable. Television sets have such a search mode to systematically search the individual frequency bands for receivable television channels. In such a case, the television's microprocessor continuously increases the frequency information signal supplied to the tuner in predetermined frequency steps. If a receivable channel is detected, the frequency data of this channel can be stored automatically or manually. When such search mode is performed by the television's microprocessor, frequency band switching is only desired when the end of the respective frequency band is reached. In the search mode of the tuner, therefore, a frequency band change is provided only when reaching the frequency band end. Further, by means of the frequency difference detection circuit, a channel re-dialing mode is advantageously distinguishable. In the channel re-selection mode, the band selection circuit detects that a frequency information signal corresponding to a new channel is supplied to the tuner. This is recognized by the fact that the frequency difference between the old and the new frequency information signal exceeds a predeterminable minimum distance. The frequency band adjustment takes place in the channel re-selection mode by means of the frequency search function, by means of which it is first checked whether the frequency assigned to the desired channel can be tuned in the first frequency band. If this is not possible, tuning in the second frequency band is attempted in a second step. The band switching between the first and the second frequency band takes place automatically when reaching the end of the tape. The frequency difference characteristic of the search mode is above the frequency difference of the automatic frequency control mode and below the frequency difference of the channel re-selection mode.

According to claim 3, the band selection circuit for setting a new channel, ie in channel redial mode, a band preselection circuit. This band preselection circuit divides the frequency information signals supplied to the tuner into unique and non-unique frequency information signals. In the case of unique frequency information signals, the band preselection circuit makes a definite and final decision about the frequency band associated with the frequency information signal. In the case of ambiguous frequency information signals is checked by means of the frequency search function in a first step, whether the frequency assigned to the desired channel in the first frequency band is tuned. If the desired channel is not tunable in the first frequency band, the tuner automatically switches to the second frequency band and checks to see if the desired channel in the second frequency band is tunable.

In the advantageous embodiment of the band preselection circuit according to claim 5, the band preselection circuit divides the frequency information signals of the at least two frequency bands into at least two groups. The first group comprises the frequency information signals which can be unambiguously assigned to the first frequency band and the frequency information signals whose associated received signal could be in both the first and the second frequency band. The second group includes those frequency information signals whose associated receive signal must be unique to the second frequency band. Therefore, any frequency band switching is required only in the area of ​​the first group. If the band preselection circuit determines that a frequency information signal is in the first group, it is first checked whether the frequency in the first frequency band is tunable. If the desired frequency is not tunable in the first frequency band, the tuner automatically switches to the second frequency band and tries the tuning in the second frequency band. In the second group of frequency information signals is immediately switched to the second frequency band and there is no automatic band switching provided.

An alternative division of the frequency information signals into three groups is provided according to claim 6. In this case, the first group comprises those frequency information signals which are unambiguously assignable to the first frequency band and the third group those frequency information signals which are unambiguously assignable to the second frequency band. In between, a second group of frequency information signals is provided whose associated frequency signals could be located in both the first and the second frequency band of the tuner. In the first and the third group, therefore, no automatic band switching by means of the frequency search function is provided. In the middle second group, on the other hand, it is first checked in the first frequency band whether a frequency signal assigned to the frequency information signal is tunable, and in the case of an unsuccessful attempt in the first frequency band is automatically switched to the second frequency band.

In the advantageous embodiment of the invention according to claim 7, applied to the capacitance diodes of the respective bandpass filter and the respective oscillator resonant circuits blocking voltage (Tune voltage) is evaluated by means of a tape end detector. This band-end detector compares the Tune voltage with a predefinable threshold value and supplies a control signal when this threshold value is exceeded. The tuner then automatically switches to the next frequency band and tries to tune to the desired frequency in the next frequency band.

The switching between the individual frequency bands can be advantageously realized by means of the embodiment according to claim 8. In this embodiment, the band selection circuit has a cylical shift register with n elements, where n corresponds to the number of frequency bands of the tuner. For example, in a tuner with three frequency bands, a shift register with three elements is provided. Each of these three elements contains a control information, preferably in each case one bit, which is provided for driving in each case one of the three frequency bands. For example, two of the three elements contain the control information <img file="EP1069680A2_D0001.tif" />0 ", which means that the frequency band associated with this element should not be turned on, and one of the three elements contains the control information <img file="EP1069680A2_D0002.tif" />1 ", which means that the frequency band assigned to this element is switched on and a tuning to the desired frequency is to be carried out in this frequency band. Thus, it is ensured that only one of the three frequency bands is turned on and that only in one of the three frequency bands of the tuning process is performed. When the tape end detector detects the band end of the respective frequency band, it provides a control signal to the cyclic shift register, whereby the control information is passed on to the adjacent control element. This means that the previously turned-on frequency band of the preceding control the control information <img file="EP1069680A2_D0003.tif" />0 "takes over and is switched off <img file="EP1069680A2_D0004.tif" />1 "is passed on to the following Steuerelernent, whereby the frequency band associated with the subsequent control is turned on and the tuning to the desired frequency is attempted in this frequency band.

Such organization of frequency band switching by means of a shift register is easy to realize and very reliable.

The first frequency band, which is first searched in the setting of a new channel, according to claim 9 is preferably below the second frequency band. This is particularly advantageous in tuners with three frequency bands, in which the band switching is realized by means of a shift register, since it allows a simple shift of the control information at the end of the tape.

The tuners according to the invention are preferably designed so that an overlap is provided in the boundary region between two frequency bands, so that in this overlap region a frequency is tunable both in the first frequency band and in the second frequency band. In the overlapping area, the noise is lower in the lower frequency band than in the higher frequency band, and the gain is higher in the lower frequency band than in the higher frequency band. Therefore, in ambiguous frequency information signals, it is advantageous to begin the tune operation in the lower frequency band and switch to the next higher frequency band if unsuccessful in the lower frequency band.

The tuners according to the invention can preferably be used in television sets.

The object of the invention is achieved according to the invention for the integrated circuit, in that the integrated circuit has a band selection circuit, which is provided for supplying control signals for selecting one frequency band in response to the frequency information signal, and in that the band selection circuit has a frequency search function for tuning to one frequency, which is provided in a first step for checking the tunability of the frequency in the first frequency band and, if tuning in the first frequency band is not possible, in a second step for checking the tunability of the frequency in the second frequency band is provided.

Such an integrated circuit can be used for tuners with different frequency band divisions, with no software modification required. Such an integrated circuit can therefore be produced in very large numbers.

Some schematically illustrated embodiments of the invention will be explained in more detail with reference to the drawing in FIGS. 1 to 7. Show it:<dl id="dl0001"><dt>Fig. 1</dt><dd>a schematic block diagram of a tuner with three frequency bands,</dd><dt>Fig. 2</dt><dd>the basic operation of a control mechanism for automatic band switching between the individual frequency bands by means of a shift register,</dd><dt>Fig. 3</dt><dd>the course of the tune voltages of the three frequency bands of a three-tone tuner over the frequency, wherein additionally the division of the entire frequency range of the tuner provided by means of a band preselection circuit into three unambiguous and two ambiguous frequency band ranges is shown,</dd><dt>Fig. 4</dt><dd>the Tune voltage over the frequency according to FIG. 3, wherein additionally the division of the entire frequency range of the tuner provided by means of a band preselection circuit is shown in two ambiguous and one unambiguous frequency band range,</dd><dt>Fig. 5</dt><dd>a basic functional diagram of the intended for the selection of the frequency band band selection circuit of the tuner,</dd><dt>Fig. 6</dt><dd>a flow chart of the operation of the band selection by means of the band selection circuit,</dd><dt>Fig. 7</dt><dd>a schematic block diagram of the band selection circuit.</dd></dl>

FIG. 1 shows the basic block diagram of a tuner with a first frequency band 1, a second frequency band 2 and a third frequency band. 3 The first frequency band 1, the second frequency band 2 and the third frequency band 3 are each connected in parallel and coupled to an antenna 4. The first frequency band 1 has in series a tunable input filter 10, an amplifier 11, a tunable bandpass filter 12, a mixer 13 and a tunable oscillator 14. The second frequency band 2 has in series a tunable input filter 20, an amplifier 21, a tunable bandpass filter 22, a mixer 23 and a tunable oscillator 24.

The third frequency band 3 has in series a tunable input filter 30, an amplifier 31, a tunable bandpass filter 32, a mixer 33 and a tunable oscillator 34. The reception signal received by the antenna 4 is supplied in parallel to the input filter 10 of the first frequency band 1, the input filter 20 of the second frequency band 2 and the input filter 30 of the third frequency band 3. For controlling the tuner, an integrated circuit 5 is provided which, among other things, has a PLL circuit (not shown). The integrated circuit 5 is coupled to a quartz oscillator 6. The integrated circuit 5 supplies a control signal S_PLL to the oscillator 14 of the first frequency band 1, to the oscillator 24 of the second frequency band 2 and to the oscillator 34 of the third frequency band 3. In addition, the integrated circuit 5 supplies a tune voltage V_t to the oscillator 14, the oscillator 24 and the oscillator 34. This tune voltage V_t controls as junction voltage the junction capacitance of the capacitance diodes of the tunable filters and the tunable oscillators. The integrated circuit 5 has various control inputs 7 by means of which the integrated circuit 5, for example via an I²C-Bus control signals S_TV and a frequency information signal F can be supplied from the microprocessor of a television set. The Tune voltage V_t is also supplied by the integrated circuit 5 to the input filter 10 and the bandpass filter 12 of the first frequency band 1, to the input filter 20 and the bandpass filter 22 of the second frequency band 2 and to the input filter 30 and the bandpass filter 32 of the third frequency band 3. This makes it possible to perform a parallel tuning of the input filter, bandpass filter and oscillator circuits of the respective frequency band. The integrated circuit 5 is coupled by means of a control line 8a to the integrated amplifier 11, by means of a control line 8b to the amplifier 21 and by means of a control line 8c to the amplifier 31. The control lines 8a, 8b and 8c are provided for supplying control signals for band selection of the first, second or third frequency band. By means of these control signals, the amplifier 11, the amplifier 21 and the amplifier 31 are individually switched on and off, whereby each one of the three frequency bands is selected. The mixer 13 of the first frequency band 1, the mixer 23 of the second frequency band 2 and the mixer 33 of the third frequency band 3 have a common intermediate frequency output 9. This is shown in FIG. 1 represented by the common name of the intermediate frequency output 9 for the three mixers.

For receiving a received signal supplied by the antenna 4, the tuner is supplied with a frequency information signal F by means of the control inputs 7. In response to this frequency information signal F, the integrated circuit 5 selects one of the three frequency bands 1, 2 or 3 by connecting the amplifier 11 of the first frequency band 1 or the amplifier 21 of the second frequency band 2 or the amplifier 31 of the third frequency band 3. Furthermore, one of the three oscillators 14, 24 or 34 PLL control signals S_PLL delivered. In addition, from the integrated circuit 5 Tune voltages V_t for tuning to the oscillators 14, 24 and 34, to the bandpass filters 12, 22 and 32 as well as to the input filters 10, 20 and 30. By means of the control signals S_PLL and the tune voltage Vt is attempted to tune the respective oscillator resonant circuit of the frequency band to be tuned to the resulting from the desired reception frequency and the intermediate frequency oscillator frequency. By means of the Tune voltage V_t For this purpose, the center frequency of the bandpass filter of the respective selected frequency band and the oscillator frequency of the resonant circuits of the respective oscillator shifted from the lower frequency band boundary to the upper frequency band limit and checks whether the desired frequency is adjustable by means of the oscillator of the respective frequency band. This is preferably done by monitoring by means of a PLL lock detector whether the phase control circuit of the integrated circuit 5 controlling the tuning operation engages.

The intermediate frequency output 9 is coupled to an intermediate frequency demodulator not shown via a surface acoustic wave filter. The intermediate frequency demodulator is also provided for generating an automatic gain control signal.

The integrated circuit 5 has a in Fig. 1 Band selection circuit, not shown, which is provided for independent selection of one of the three frequency bands 1, 2 or 3 as a function of the integrated circuit 5 via the control inputs 7 supplied frequency information signal F. A first possibility for realizing such a band selection circuit in a simple manner is shown as a schematic operating principle in FIG. 2 shown. According to FIG. 2 are for selecting the first frequency band 1, the second frequency band 2 or the third frequency band 3, a first control bit D0, a second control bit D1 and a third control bit D2 provided. The first control bit D0 is for transmission via the control line 8a to the amplifier 11 of the first frequency band 1, the second control bit D1 for transmission via the control line 8b to the amplifier 21 of the second frequency band 2 and the third control bit D2 for transmission via the control line 8c the amplifier 31 of the third frequency band 3 is provided.

For the present example, the first frequency band 1 should be the lower frequency band of the tuner. This is referred to below as lower frequency band LB (low band). The second frequency band 2 is to be the middle frequency band of the tuner below. It is referred to below as the middle frequency band MB (mid-band). The third frequency band 3 is to be the upper frequency band of the tuner below. It is referred to below as the upper frequency band HB (high band). FIG. 2 shows the allocation table between the values ​​of the control bits D0, D1 and D2 and the respectively selected frequency band LB, MB or HB. Is the first control bit D0 <img file="EP1069680A2_D0005.tif" />1 "and the second control bit D1 and the third control bit D2 <img file="EP1069680A2_D0006.tif" />0 ", then the lower frequency band LB is selected, and accordingly, only the lower frequency band amplifier 11 is turned on, and the second control bit D1 takes the value <img file="EP1069680A2_D0007.tif" />1 ", the middle frequency band MB is selected, if the third control bit D2 is the value <img file="EP1069680A2_D0008.tif" />1 ", the upper frequency band HB is selected. The band switching between the lower frequency band LB, the middle frequency band MB and the upper frequency band HB can be preferably according to FIG. 2 realized by means of a shift register 40, which has a first memory array 41, a second memory array 42 and a third memory array 43. The first memory field 41 is provided for storing the first control bit D0, the second memory field 42 for storing the second control bit D1 and the third memory field 43 for storing the third control bit D2. The first memory field 41 has the control information <img file="EP1069680A2_D0009.tif" />1 ", the second memory field 42, the control information <img file="EP1069680A2_D0010.tif" />0 "and the third memory field 43, the control information <img file="EP1069680A2_D0011.tif" />0 "up. This configuration is in the simplified band selection circuit of FIG. 2 set at the beginning of a tune process. Therefore, if the tuner is supplied with a new frequency information signal at the control inputs 7, the lower frequency band LB is first switched on by means of the band selection circuit and the tuner attempts to tune the desired frequency in the lower frequency band LB. If this is not possible, the information stored in the shift register 40 is in each case pushed further onto a memory field, as a result of which the second memory field 42 contains the control information <img file="EP1069680A2_D0012.tif" />Subsequently, the tuner attempts to tune the mid frequency band oscillator MB to the desired frequency, if this is not possible, the shift register control information is again shifted one space at a time, causing the shift register to shift third memory field 43, the control information <img file="EP1069680A2_D0013.tif" />Finally, an attempt is then made in the upper frequency band HB to tune the oscillator of this frequency band to the desired frequency: the successive check of the lower frequency band LB, the middle frequency band MB and the upper frequency band HB for tunability of the desired frequency causes relatively long tuning or seek times for the frequencies that are in the upper frequency band HB.

An advantageous embodiment for shortening these search times is shown in FIG. Fig. 3 shows the Tune voltage V_t, by means of which the capacitance diodes of the bandpass filters 12, 22 and 32 and the oscillators 14, 24 and 34 of the tuner according to FIG. 1 are tunable over the frequency. The area I shows the course of the Tune voltage V_t of the first frequency band 1 over the frequency, the range II the course of the Tune voltage V_t of the second frequency band 2 over the frequency and the range III the course of the Tune voltage V_t of the third frequency band 3. The region I and the region II overlap in a region IV. The region III and the region II overlap in a region V. In the overlap region IV, a frequency in both the first frequency band 1 and in the first second frequency band 2 are tuned. In the overlap region V, a frequency in both the second frequency band 2 and in the third frequency band 3 can be tuned.

The entire frequency range of all terrestrial tuners, ie the range encompassing the individual frequency band ranges of the tuners of all television standards ranges from 45.25 MHz to 863.25 MHz. According to FIG. 3 this entire frequency band range is determined by means of a in Fig. 3 Band selector circuit not shown in a first group 50, a second group 51, a third group 52, a fourth group 53 and a fifth group 54 divided. The band preselection circuit is preferably incorporated in the integrated circuit 5 according to FIG. 1 integrated. The first group 50 comprises the frequency band range from 45.25 MHz to 126.25 MHz, the second group 51 the frequency band range from 126.25 MHz to 175.25 MHz, the third group 52 the frequency band range from 175.25 MHz to 399.25 MHz, the fourth group 53 the frequency band range from 399.25 MHz to 471.25 MHz and finally the fifth group 54 the frequency band range from 471.25 MHz to 863.25 MHz. If the tuner is supplied by the microprocessor of the television with a new frequency information signal for setting a new receiving channel, then the band preselection circuit makes a preselection of the frequency band on the basis of FIG. 3 represented groups 50 to 54. The first group 50 is clearly the lower frequency band LB, the second group 51 is ambiguously the lower frequency band LB or the middle frequency band MB, the third group 52 clearly the middle frequency band MB, the fourth group 53 ambiguous the middle frequency band MB or the upper frequency band HB and the fifth group 54 assigned the upper frequency band HB. If the frequency information signal supplied to the tuner is in the first group 50, the third 52 or the fifth group 54, the band preselection circuit makes a final decision about the frequency band assigned to this frequency information signal. In the case of frequency information signals of the first group 50, the tuner is switched to the lower frequency band LB, in the third group 52 the tuner is switched to the middle frequency band MB and in the fifth group 54 the tuner is switched to the upper frequency band HB. In the second group 51, the tuner is first switched to the lower frequency band LB and it is tried to tune in the lower frequency band to the desired frequency. If the tune attempt in the lower frequency band LB is unsuccessful, the tuner automatically switches to the middle frequency band MB and tries to tune it to the desired frequency in the middle frequency band MB. In an analogous manner, for frequency information signals of the fourth group 53, it is first attempted to tune the desired frequency in the middle frequency band. If this is not successful, the tuner automatically switches to the upper frequency band HB and tries to tune to the desired frequency in this frequency band.

The software and the control electronics of a tuner according to FIG. 3 can be used for all tuners whose switching points lie between the lower frequency band LB and the middle frequency band MB within the second group 51 and whose switching points between the middle frequency band MB and the upper frequency band HB are in the range of the fourth group 53. The boundaries of the second group 51 and the fourth group 53 are designed to include the switching points between the individual frequency bands of all commercially available tuners. The frequency band boundaries of groups 50 to 54 may be modified accordingly for other applications. By means of the division of the entire frequency band range into the groups 50 to 54, the tune time can be significantly shortened since the frequency band range to be searched is significantly reduced.

FIG. 4 shows an alternative division of the frequency band range of the terrestrial tuner, which also as a band preselection circuit in the integrated circuit 5 of FIG. 1 is integrable. According to FIG. 4 the entire frequency band range is divided into a first group 55, a second group 56 and a third group 57. The first group 55 comprises the frequency band range from 45.25 MHz to 175.25 MHz, the second group 56 the frequency band range from 175.25 MHz to 471.25 MHz and the third group 57 the frequency band range from 471.25 MHz to 863.25 MHz. In the case of frequency information signals of the first group 55, it is provided to first switch to the lower frequency band LB in the case of a reception channel to be newly set and to attempt to tune the desired frequency in this lower frequency band LB. If this is not possible, then the medium frequency band MB is automatically switched over and the tune process is repeated there. In the case of frequency information signals of the second group 56, it is provided to first try to tune a frequency to be newly set in the middle frequency range MB. If this is not possible, the tuner automatically switches to the upper frequency band HB and tries to tune the desired frequency in the upper frequency band HB. For frequency information signals of the third group 57, the tuner immediately switches to the upper frequency band HB. An automatic frequency switching is not provided. This embodiment has the advantage that the band preselection circuit has to divide the frequency information signals into only three groups. This simplifies the decoder. The limits of the first, second and third groups can be changed depending on the application. The software and control electronics of a tuner with a band preselection circuit according to FIG. 4 can be used for all tuners whose switching points between the lower frequency band LB and the middle frequency band MB are within the first group 55 and whose switching points between the middle frequency band MB and the upper frequency band HB are in the second group 56.

In the overlapping area IV, a frequency can be tuned in both the lower frequency band LB and the middle frequency band MB. Since in the overlapping area IV the noise and the gain in the lower frequency band LB are more favorable, it is advantageous to receive a received signal located there in the lower frequency band LB. In an analogous manner, it is better to receive a receive signal located in the overlap region V in the middle frequency band MB. Therefore, in the second group 51, it is better to start the Tune operation first in the lower frequency band LB, and in the third group 53, it is better to start the Tune operation in the middle frequency band MB. This ensures that in the overlapping areas IV and V is preferably received in the respective lower frequency band

FIG. 5 shows a functional diagram of the intended for the selection of the frequency band band selection circuit of the tuner, which preferably in the integrated circuit 5 of FIG. 1 is integrated. According to FIG. 5 The band selection circuit comprises a frequency difference detection circuit 60 which, when a new frequency information signal is supplied to the tuner, determines the frequency difference between the old frequency information signal and the new frequency information signal. By means of the frequency difference determination circuit 60, the frequency difference between the old and the new frequency information signal is divisible into a first frequency difference range 60a, a second frequency difference range 60b, a third frequency difference range 60c and a fourth frequency difference range 60d. In the first frequency difference area 60a, the old and the new frequency information signals are identical, and the band selection circuit is in the renewal mode 61. In the renewal mode 61, the band selection circuit has recognized that the same frequency information signal has been supplied to the tuner again. In such a case, no frequency band switching is provided.

Therefore, the band selection circuit transitions to the end mode 65 where it waits to supply a new frequency information signal. In the second frequency difference range, the new frequency information signal differs only slightly from the old frequency information signal, preferably only one bit for digitally supplied frequency information signals. In such a case, the band selection circuit is in an automatic frequency control mode 62, ie the band select circuit detects that the TV is performing a fine-tuning of the received channel. In such a case as well, no frequency band switching is desired, and accordingly, the band selection circuit is also transferred to the end mode 65. The third frequency difference range 60 c is associated with a search mode 63. Television sets have such a search mode to systematically search the individual frequency bands for receivable remote channels. In such a case, the television's microprocessor continuously increases the frequency information signal supplied to the tuner in predetermined frequency steps. The size of these frequency steps is typically in a frequency range of 62.5 kHz to 1 MHz. If such a search mode is performed by the television's microprocessor, frequency band switching is only provided when the end of the respective frequency band has been reached. In the search mode, it is therefore checked by means of a band detector 66 whether the band end of the respective frequency band in which the search mode is currently being executed has been reached. This can be done for example by monitoring the Tune voltage. If the tape end detected by the tape end detector 66, the tuner switches to the next higher frequency band. This is indicated by block 67 in FIG. 5 shown. As the fourth frequency range, the frequency difference detection circuit 60 discriminates a frequency difference range 60d, thereby converting the tuner into a channel re-selection mode 64. In this channel re-selection mode, the frequency difference detection circuit 60 detects that a frequency information signal corresponding to a channel to be re-tuned is supplied to the tuner. This recognition is realized in that the frequency difference between the old and the new frequency information signal must exceed a predetermined minimum distance. For terrestrial transmitters, the distance between the individual channels is usually 7 MHz. The threshold value for the fourth frequency difference range 60d is therefore to be selected slightly below this channel spacing, preferably at approx. 5 MHz. This means that the tuner transitions to the channel re-selection mode 64 for newly supplied frequency information signals which are at least 5 MHz away from the old frequency information signal. In the channel re-election mode 64, a preselection of the frequency band is first made by means of a channel preselection circuit 68. The channel preselection circuit 68 has an example according to FIGS. 3 or 4 trained assignment function, which either uniquely assigns the supplied frequency information signal to one of the frequency bands or only makes a preselection and optionally performs a band switching. If the channel preselection circuit 68 is, for example, as shown in FIG. 3 formed, frequency information signals which are in the first group 50, the third group 52 or the fifth group 54, a unique and final band selection is made. This is represented by block 69. Thereafter, the band select circuit enters the end mode 65 and waits for a newly supplied frequency information signal. However, if the frequency information signals supplied to the tuner are in the second group 51 or the fourth group 53, only a pre-selection of the frequency band is made in the block 70, ie in the second group 51 is switched to the lower frequency band LB and the fourth group 53 to the middle frequency band MB. If it is not possible to tune in the second group 51 in the lower frequency band LB, this is detected by means of the band end detector 66 and in block 67, a band switching to the middle frequency band MB is performed. In an analogous manner, the fourth group 53 first attempts to tune in the middle frequency band MB. If this is not possible, it is detected by means of the tape end detector 66 and switched in the block 67 to the upper frequency band HB.

FIG. 6 FIG. 12 is a principle flowchart showing the process of band selection when a new frequency information signal is supplied to the tuner. Block 70 represents the start, ie, the tuner is supplied with a new frequency information signal. In the following block 71, the frequency information signal newly supplied to the tuner is compared with the old frequency information signal and the frequency difference is determined. Thereafter, it is checked in the block 72 whether the determined difference frequency must be assigned to the renewal mode or the automatic frequency control mode on the one hand, or to the search mode or the channel re-selection mode on the other hand. This is realized by means of a threshold check, ie It is checked whether the frequency difference is below a first threshold or above this first threshold. The first threshold value should be set so that the frequency differences of the automatic frequency control mode are below this threshold value and the frequencies of the search mode and the channel re-selection mode are above the threshold value. If it is detected in block 72 that the frequency difference information signal is below the first threshold value, then the system changes to block 73, which represents that no band switching is provided. If it is determined in block 72 that the supplied frequency difference signal is above the first threshold value, it is checked in block 74 whether the frequency difference lies below or above a second threshold value. This second threshold is chosen to allow discrimination between the search mode and the channel re-selection mode. If the frequency difference signal is below the second threshold, then the tuner is in the search mode and it is passed directly to the block 75, in which it is checked whether the band end of each frequency band is reached. If this is the case, then in block 76, the system switches to the next higher frequency band. Otherwise, no frequency band switching is provided. If it is determined in block 74 that the frequency difference signal is above the second threshold, then the tuner is in the channel re-selection mode and in block 77 a band preselection is made by means of a band preselection circuit, ie for example, in a preselection circuit according to FIG. 3 the frequency difference signal is assigned to one of the five groups 50 to 54 and the frequency band assigned to this group is switched on. In the following block 78 it is checked whether the group determined in block 77 is a unique or ambiguous group, ie whether the frequency information signal is within the first group 50, the third group 52 or the fifth group 54, each uniquely associated with a frequency band, or if the frequency information signal is within the second group 51 or the fourth group 53 ambiguously associated with two frequency bands , In the former case, ie in the case of the unique groups 50, 52 and 54, no further band switching is provided and it is transferred directly to the block 79. In block 79 it is checked whether the PLL oscillator of the tuner is locked to the desired reception frequency. If this is not the case, an error message is output in block 80. If the locking to the desired reception frequency was successful, then in block 81 the tuning process is ended successfully. If it is determined in block 78 that the frequency information signal in the example according to FIG. 3 is in the second group 51 or the fourth group 53, so in the block 82 is first switched to the lower of the two frequency bands, ie in the second group 51 on the lower frequency band LB and in the fourth group 53 on the middle frequency band MB. Thereafter, a check is made in block 75 as to whether the frequency band end has been reached. If this is not the case, then no band switching is provided. If the frequency band end detected in block 75, then in the following block 76 is switched to the next higher frequency band, ie in the second group 51 on the middle frequency band MB and in the fourth group 53 on the upper frequency band HB. Thereafter, it is checked in block 79 whether the PLL oscillator is locked to the desired reception frequency. In the affirmative case, the tune operation is successfully completed with the block 81. In the negative case, an error message is output in block 80.

Fig. 7 shows a hardware implementation of a band selection circuit 90. The band selection circuit 90 has an input register 91 on which a frequency information signal F is provided in digital form via, for example, an I²C-bus of the TV can be fed. The input register 91 has 14 memory locations for digital storage of the frequency information signal F. The input register 91 is coupled on the one hand with a band preselection circuit 92 and on the other hand with a frequency difference determination circuit 93. The frequency information stored in the input register 91 is supplied in parallel to the band preset circuit 91 and the frequency difference detection circuit 93. In the band preselection circuit 92, a frequency allocation table is implemented, as shown for example in FIGS. 3 and 4 is described. The frequency band selected by the band preselection circuit 92 is written in a shift register 94 in digital form. The shift register 94 has a first memory array 94a, a second memory array 94b and a third memory array 94c. The memory array 94a is provided as control information for the lower frequency band LB, the second memory array 94b as control information for the middle frequency band MB and the third memory array 94c as control information for the upper frequency band HB. The shift register 94 is cyclical, ie the memory information of the first memory array 94a is written in the third memory array 94c at the next shift clock. The frequency difference detection circuit 93 detects the frequency difference between the old and the new frequency information signal F. The control of the shift register 94 via a control line 95, which is coupled to the output of an AND circuit 96 and to the output of an AND circuit 97. The band selection circuit 90 has as a band end detector a tune voltage comparator 98, which compares the tune voltage, by means of which the bandpass filter and the oscillator of the respective frequency band is controlled, with a reference voltage. If the Tune voltage is above this reference voltage, then the Tune voltage comparator 98 generates a positive control bit <img file="EP1069680A2_D0014.tif" />1 "and supplies this via a control line 99 on the one hand to the input of the AND circuit 96 and on the other hand to the input AND circuit 97th The frequency difference detection circuit 93 supplies a positive control bit "1" to the AND circuit 96 via a control line 100 when the detected frequency difference signal is in a range of 2 to 16 digital frequency steps, for example. This corresponds to the search mode. The frequency difference detection circuit 93 provides a positive control bit <img file="EP1069680A2_D0015.tif" />1 "to the AND circuit 97 when the frequency difference detected by the frequency difference detection circuit is, for example, greater than 80 digital frequency steps, in this case, a new channel to be reset The band preselection circuit 92 provides a positive control bit through a control circuit 102 <img file="EP1069680A2_D0016.tif" />1 "to the AND circuit 97 when the frequency of the supplied frequency information signal is in a non-unique group, ie For example, in a band preselection circuit according to FIG. 3 in the second group 51 or in the fourth group 53. In such case, if unsuccessful, it may be necessary to switch to the next higher frequency band in the first selected frequency band. The AND circuit 96 only supplies a control signal for band switching to the shift register 94 when the tape end is signaled by means of the Tune voltage comparator via the control line 99, ie when the end of the respective frequency band is reached, and when the frequency difference determination circuit 93 signals via the control line 100 that the newly supplied frequency signal is assigned to the search mode, ie that the TV successively searches the frequency bands for receivable channels.

The AND circuit 97 only supplies a band switching control signal to the shift register 94, if the tape end is signaled by means of the Tune voltage comparator via the control line 99, when the frequency difference detection circuit 93 signals via the control line 101, that the newly supplied frequency signal corresponds to a new receiving channel and when at the same time signals the band preselection circuit 92 via the control line 102, that the newly supplied frequency information signal is in an ambiguous range, in which possibly a band switching is required.