CA1180139A - Tuner apparatus - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE:
A television tuner comprises a voltage controlled variable capacitance diode provided in common to the UHF
band, the VHF high band and the VHF low band. A tuning voltage provided from a channel selecting apparatus is applied to the variable capacitance diode as a control voltage. A relation between the tuning voltage and the receiving frequencies is selected such that the tuning voltage of the high end channel (the maximum receivable frequency) of the UHF band is higher than the tuning voltages of the respective high end channels of the remaining bands and the tuning voltage of the low end channel (the minimum receivable frequency) of the VHF' low band is lower than the tuning voltage of the resepctive low end channels of the remaining bands. The channel selecting apparatus is adapted to restrict the upper and lower limits of the tuning voltage, whereby the upper limit of the receivable frequency of the UHF band is restricted and the lower limit of the receivable frequency of the VHF low band is restricted.

Description

The present invention relates to a tuner apparatus. More specifically, the present inven~ion relates to a tuner apparatus employing a voltage controlled variable reactance device such as a voltage con-trolled variable capacitance diode for use in a television receiver, an FM receiver and the like. In West Germany, the FTZ (Fermnelde Technisches Zentralamt) has made the following proposal in the draft of January, 1979. More specifically, in West Germany the frequency range for the tele-vision broadcasting has been determined such that the Band I
10 covers 47MHz to 68MHz, the Band III covers 174MHz to 230MHz and the Bands IV and V cover 470MHz to 790MHz. A deviation allowance outside the frequency range at each of the upper and lower limits of the frequency range of each band has been determined in principle as 300 kHz. By way of an exception, as for the receiv-ing frequency band of 47 MHz to 870 MHz, a deviation allowance outside the frequency range has been determined as 7 MHz at the lower limit of the frequency range and as 8 MHz at the upper limit o-- the frequency range.
An attempt has also been made to make similar restriction in the case of the Canadian television broadcasting. According to the Canadian television broadcasting standard, the VHF low band comprises Channel Nos. 2 to 6, the VHF high band compris-s Channel Nos. 7 to 13, and the UHF band comprises Channel Nos. 14 to 84. According to the draft of October, 1978 by the Canadian DOC (Department of Communications) and the further development thereof, the following restriction has been planed. More specifically, according to the Canadian television broadcasting .39 standard, the channels for the CATV have been allotted in the region lower than Channel No. 7 and in the region higher than Channel No. 13. Therefore, a restriction has been planned in Canadian television receivers such that some of the CATV channels allotted in the region lower than Channel No. 7 and in the region higher than Channel No. 13 are made absolutely unreceiv-able. More specifically, television receivers originally not designed to receive such CATV broadcasting are sufficient enough to be capable of surely receiving only the television signal of Channel Nos. 2 to 6, Nos. 7 to 13, and Nos. 14 to 83 and there-fore a restriction has been planned to make such receivers in-capable of receiving a signal in Channels A to I of the CATV
channels in the region lower than Channel No. 7 and a signal in CATV Channels A to W in the region higher than Channel No. 13.
In making such restriction, however, one channel, i.e. Channel I
in the region immediately lower than Channel No. 7 and one channel, i.e. Channel ~ in the region immediately higher than Channel No. 13 have been considered as allowable for a deviation range.
As described in the foregoing, in some countries there have been tendencies to a strict restriction to a deviation downward or upward from the original receiving frequency band, for the purpose of effective utilization of an electric wave and observance of communication secrecy.
Under the circumstances, in order to cope with such strict frequency restriction, one might think of restriction of the upper and lower limits of the above described tuning voltage.

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However, generally tuner apparatuses involve a diversi-fied tuning voltage versus receiving fre~uency character-istic depending on each set. For example, as far as the upper ends of the UHF band and the VHF high band are concerned, it could happen that a given tuner in-volves a relation in which t,he tuning voltage of thehigh end channel of the UHF band is lower than the tuning voltage of the high end channel of the VHF high band.
The same is also true in a relation between the tuning voltage of the low end channel of the VHF high band and the tuning voltage of the low end channel of the VHF
low band. Thus, in the case where there is a diversi-fication in a relation of which is higher,and lower be-tween the tuning voltage of the high end channel and/or the tuning voltage of the low end channel among the res-pective bands, the above described restriction to thetuning voltage requires that: such tuning voltage re-stricting means be provided for each of the receiving bands. Accordingly, it becomes necessary to restrict both Ihe upper and lower limits of the tuning voltage for each of the receiving bands. Provision of such tun-ing voltage restricting means for each of the receiving bands, however, makes compli.cated the structure of the tuner apparatus and makes e~pensive the cost of the tuner apparatus.
According to the i.nvention there is provi.ded a tuner apparatus which comprises a tuning circuit in-cluding a voltage controllecl variable reactance means, ~ ~8~
the tuning circuit having a plurality of receiving bands, tuning voltage generating means, coupled to the tuning circuit for generating a tuning voltage and applying the tuning voltage to the voltage controlled variable reactance means, wherein the tuning voltage is within a single predetermined range for all of the plurality of receiving bands; and at least one of (a) and (b), where (a) comprises upper li:mit restricting means, coupled to the tuning voltage generating means, for restricting the upper limit of the tuning voltage applied ~o the voltage controlled variable reactance means; maximum receivable frequency defining means including trimmer loops and resonance conductors provided in the tuning circuit for determining the maximum receivable frequency of the tuning circuit with respect to the tuning voltage applied to the tuning circuit for all of the receiving bands such that the tuning voltage for the upper limit of the receiving band which must be restricted is greater than or equal to the tuning voltage for the upper limit of the others of the receiving bands, thereby defining the maximum receivable frequency of the plurality of receiving bands; and ~b) comprises lower limit restric-ing means including trimmer capacitors and resonance conductors provided in the tuning voltage generating means, for restricting the lower limit of the tuning voltage applied to the voltage controlled variable re-actance means; and minimum receivable frequency defining means coupled to the tuning circuit for determining the ~' ~

minimum receivable frequency of the tuning c~rcuit with respect to the tuning voltagP applied to the tuning circuit for all of the receiving bands such that the tuning voltage for the lower limit of the receiving band which must be restricted is less than or equal to the lower limit of the tuning voltage for the others of the receiving bands, thereby defining the minimum receivable frequency of the plurality of receiving bands.
In one embodiment of the present invention the tuning voltage generating means may be of a voltage synthesizer type, The tuning voltage generating means of such voltage synthesizer type comprises a switching device being rendered conductive responsive to a pulse signal and a smoothing circuit for smoo-thing the output of the switching device. In such embodiment, impedance means is interposed in a current path of the switching device for allowing a predetermined residual voltage to be applied to the smoothing circuit even when the switching device is rendered conductive. According to the above described preferred embodiment, the lower limit of the tuning voltage can be restricted with a very simple structure.
In another embodiment of the present inven-tion, the tuning voltage generating means comprises po-tentiometers each provided for each channel, so thatthe source voltage is divided by each of the potentio-meters to provide the tuning voltage corresponding to each channel. A diode is connected to a sliding contact ~L.18(~

each potentiometer, the anode of each diode being commonly connected to the input electrode of a transistor. The second electrode of the transistor is connected to the voltage source and the third electrode of the transistor is connected to the tuning voltage withdrawing terminal. A predetermined output resistor is connected between the tuning voltage withdrawing terminal and the ground potential. The source voltage is stabilized by a constant voltage diode, whereby the upper limit of the tuning voltage obtained from the tuning voltage with-drawing terminal is restricted. A predetermined resistor isconnected between the voltage source and the output resistor, so that normally a constant current is caused to 10w through the output resistor, whereby the lower limit of the voltage across the output resistor or the output voltage (the tuning voltage) obtained from the tuning voltage withdrawing terminal is restrict-ed to a predetermined value. In the above described preferred embodiment, the lower limit of the tuning voltage can be restrict-ed only by adding one resistor to a conventional tuning voltage generating means, while the upper limit of the tuning voltage can also be restricted only by using a constant voltage diode, with the result that a tuner apparatus adapted for restriction of the tuning frequency can be provided with a very simple structure.
Objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of exemplory emb~idments of the present invention when taken in conjunction with the accompanying drawings.

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Fig. 1 is a block diagram showing one example of a conventional television tuner wherein the present invention can be advantageously employed;
Fig. 2 is a graph showing a relation between the tuning voltage and the frequency (the receiving channels) of a television system proposed in West Germany for explaining the background of the present invention;
Fig. 3 is a graph showing the distribution of channels of the television broadcasting standard in Canada;
Fig. 4 is a graph showing a relation between the tuning voltage and the frequency (the receiving channels) for explain-ing the principle of the present invention;
Figs. SA and 5B are schematic diagrams of a television tuner taken as an example of the present invention, wherein Fig.
5A shows a UHF portion and Fig. 5B shows a VHF portion;

Fig. 6 is an outline view for explaining one embodiment of the present invention;
Figs. 7, 8 and 9 are outline views for depicting different embodiments of the present invention wherein different types of channel selecting apparatuses, i.e. variable tuning voltage generat~ing means are employed, respectively;
Figs. 10 to 13 are schematic diagrams of major portions of further preferred embodiments of the tuning voltage generating Cl rcult;
Figs. 14 and 15 are schematic diagrams showing examples of impedance means;

Fig. 16 is a graph showing waveforms for explaining the operation of the embodiments shown in Figs. 10 and 13;

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Fig. 17 is a schematic diagram of a major portion of a further preferred embodiment of the tuning voltage generating circuit;
Fig. 18 is a graph depicting the operation of the Fig. 7 embodiment, wherein the abscissa indicates the number of rotations of a fine tuning knob and the ordinate indicates the tuning voltage;
Fig. 19 is a block diagram showing still a further embodi-ment of the present invention; and Fig. 20 is a graph showing a relation between the tuning frequency (the receiving channel) and the tuning voltage forexplaining the Fig. 19 embodiment.
Fig. 1 is a block diagram showing one example of a tuner apparatus of a television receiver of the superheterodyne system wherein the present invention can be advantageously employed.
Since such television tuner is well-known to those skilled in the art, only those portions associated with the present invention will be briefly described. A tuner 100 comprises two input terminals 117 and 119. The input terminal 117 is connected to receive a television signal received by a VIIF antenna 1. The input terminal 119 is connected to receive a television signal received by a UHF antenna 2. The received signal from the VHF
antenna input terminal 117 is applied to a VHF high frequency amplifier 103 and is amplified and the amplified output there-25 from is applied to a VHF mixer 105.The tuner 100 also comprises a VHF local oscillator 107. The oscillation output o' the VH~ local oscillator 107 is applied to a VHF mixer 105. Accordingly, the VHF mixer 105 serves to mix the V~IF television signal with the ; ~

oscillation output from the VHF local oscillator 107, thereby to convert the VHF television signal into a VHF intermediate frequency signal. On the other hand, the received signal applied to the UHF antenna input terminal 119 is applied to a UHF high frequency amplifier 109 and is amplified and the amplified output therefrom is applied to a UHF mixer 111. The tuner 100 also comprises a UHF local oscillator 113 and the oscillation output therefrom is applied to a UHF mixer 111.

Accordingly, the UHF mixer 111 serves to mix the UHF television signal with the oscillation output from the UHF local oscillator 113, thereby to convert the UHF television signal into a UHF intermediate frequency signal. The ou~put from the UHF mixer 111, i.e. the UHF intermediate frequency signal is amplified by a UHF intermediate frequency amplifier 115 and is applied to a VHF mixer 105. On the occasion of reception of the UHF signal, the VHF high frequency amplifier 103 and the VHF
local oscillator 107 are disabled, while the VHF mixer 105 is kept enabled. Accordingly, on the occasion of reception of the UHF signal, the VHF mixer 105 serves as a UHF intermediate frequency amplifier for amplifying the UHF intermediate frequency signal. Meanwhile, on the occasion of reception of the VHF
signal, those circuits 109, 111, 113 and 115 associated with the UHF signal are all disabled, while only those circuits 103, 105 and 107 associated with the VHF signal are enabled. The VHF
intermediate frequency signal or the UHF intermediate frequency signal obtained from the VHF mixer 105 is applied from the output terminal 121 to the subsequent stage intermediate frequency circuit, not shown. These circuits 103 to 115 are housed within ~ ~81)~.3~
a shield member 101 of such as a metallic casing or frame. There-fore, any undesired radiation from those clrcuits housed within the shield member 101 toward other wireless equipment is effect-ively prevented, while any undesired electric wave or interfer-ence electric wave from other wireless equipment to thosecircuits is also effectively prevented. The above described antenna input terminals 117 and 119 and the intermediate frequency output terminal 121 are formed at predetermined posit-ions of the shleld member 101, while these terminals are electric-ally isolated from the shield member 101.
The VHF high frequency amplifier 103, the VHF localoscillator 107, the U~F high frequency amplifier 109 and the UHF local oscillator 113 each comprise a tuning circuit, not shown, for varying the tuning frequency for selection of a desired channel within a desired receiving frequency band. Each of these tuning circuits comprises a voltage controlled variable reactance device such as a voltage controlled variable capacitance diode. To that end, the -tuner 100 housed in the shield member 101 is also provided with a tuning voltage input 20 terminal 123, as electrically isolated from the shield member 101, for supply of the tuning voltage Vt~ The tuning voltage Vt from the terminal 123 is applied to the associated circuits 103, 107, 109 and 113. The shield member 101, i.e. the tuner 100, further comprises a test point (TP~ terminal 127, as electrically isolated from the shield member 101, for supply of the output from the tuner 100 to alignment equipment, not shown,for align-ment of the output waveform on the occasion of adjustment of the tuner 100. In general, the VHF band comprises a VHF low band ~.

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(the first band) of a relatively low fre~uency range and a VHF
high band (the second band) of a relatively high frequency range.
On the other hand, the UHE band may be considered as the third band of a frequency range higher than -that of the VHF high band.
Accordingly, the tuner 100 further comprises terminals 129, 131 and 133, as electrically isolated from the shield member 101~
for supply of voltage signals for selection of these frequency bands. More specifically, the terminal 129 is aimed to supply a band selection voltage BL for selection of the VHF low band, the terminal 131 is aimed to provide a band selection voltage VH for selection of the V~IF high band, and the terminal 133 is aimed to provide a band selection voltage BU for selection of the UHF band. The tuner 100 further comprises a terminal 125 for supply of an automatic gain control (AGC) voltage obtained from the intermediate frequency circuit, not shown, and a terminal 135 for supply of an automatic fine tuning (AFT) voltage, both electrically isolated from the shield member 101.
Each of the terminals 129, 131 and 133 is supplied with the band selection voltage BL, BH or BU of +15V, when the corresponding receiving frequency band is to be selected. Each of the tuning circuits included in the tuner 100 is structured to be responsive to the given band selection voltage BL, BH or BU to change the circuit constant or circuit connection of the tuning scheme so as to be adaptable to the corresponding frequency band, as well-known to those skilled in the art.
As described in the foregoing, the tuner 100 employs avoltage controlled variable capacitance diode as a tuning element of each of the tuning circuits. In such conventional 3~
tuner, the tuning voltage Vt being supplied to the variable capacitance diode was determined in accordance with a given condition. In the following, therefore, such determination of the tuning voltage will be described with reference to an example of a television tuner in ~est Germany, as shown in Fig.

2. Referring to Fig. 2, the abscissa indicates the tuning voltage and the ordinate indicates the respective channels in the VHF low band, the VHF high band and the UHF band. In West Germany, for example, the VHF low band (the first band) covers channels E2 to E4, while the VHF high band (the second band) covers channels E5 to E12. The UHF band (the third band) covers channels E21 to E69. Such tuner has been designed such that the lower limit frequency of the VHF low band may be determined so that channel E2 can be received when the tuning voltage Vt is 3V, for example. However, a television tuner must be capable of surely selecting channel E2 even in any situation and even in the worst condition. More specifically, in consider-ation of a frequency drift due to a source voltage fluctuation, an ambient temperature variation, a time dependent change and so on, a frequency deviation due to a mechanical shock, and the like, the television tuner must be designed to be capable of surely receiving channel E2 even in the worst condition which seldom occurs. Therefore, accordingly to a conventional approach, the tuner was desi~ned such that the tuning voltage Vt which is as low as 0.2 to 0.3V, for example, and is sufficiently lower than the above described 3V, may be supplied from the channel select-ing apparatus, not shown. As a result, with such a conventional television tuner, the receivable frequency range extended over L35~
the lower region beyond the necessary receivable frequency range shown by the dotted line in Fig. 2 in a normal use condition.
For example t a conventional tuner was adapted such that in the case of the VHF low band shown by the curve L in Fig. 2 the signal can be received even when the frequenry becomes lower than that of channel E2 by a frequency difference corresponding to approximately one channel. A conventional tuner was further adapted such that in the case of the VHF high band shown by the curve H the signal can be received even when the frequency becomes lower than the lower limit channel E5 by a frequency difference corresponding to approximately three channels. A
conventional tuner was further adapted such that in the case of the UHF band shown by the curve U the signal can be received even when the frequency becomes lower than the lower limit channel E21 by a frequency difference corresponding to approx-imately ten channels. A conventional television tuner was further adapted such that as for the upper limit of the respect-ive bands as well the signal of any desired receiving frequency band can be surely received with a sufficient margin in full consideration of any imaginable worst condition.
However, for the purpose of effective utilization of the electric wave and observance of secrecy of communication, in some countries there have been tendencies to restriction of reception by a tuner beyond the receivable frequency range in a 2~ television receiver, for example. More specifically, some countries have shown tendencies to legislation to restrict the receivable frequency range by a tuner in a television receiver at the upper and lower limits of the respective receiving frequency bands as shown in Fig. 2, with a margin frequency corresponding to one channel, respectively.
Referring to Fig. 2, such diversification is shown by ranges denoted as A to F in conjunction with the points a to f of the lower and upper ends of the respective receiving bands U, H and L. For example, in restricting the upper limit of the receivable frequency of the UHF band so as to be conformable to the FTZ standard, assuming such a relation as shown in Fig. 2 the upper limit of the tuning voltage ~rom the tuning voltage generating means, not shown, cannot be uniformly set to the minimum value, say 20 V,of a diversification range E. This can be substantiated by an assumption that when the high end channel of the VHF high band is receivable with the tuning voltage being say 22 V then such high end channel becomes unreceivable by such setting.
Examples of the present invention will be des~ribed by taking several examples wherein the present invention is embodied in a television tuner; however, it is pointed out that the present invention can be applied not only to a television tuner but also to an FM receiver and the like.
Fig. 4 is a graph in which the abscissa indicates the tuning voltage and the ordinate indicates the tuning frequencies tthe receiving channels) in the respective receiving bands of the VHF low band, the VHF high band and the UHF band. In the embodiment shown, it is assumed that the tuning voltage for tuning to the upper limit frequency (the maximum receivable frequency) of the UHF band is V6, the tuning voltage for tuning

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to the upper limit frequency in the VHF high band is V5, and the tuning voltage for tuning to the upper limit frequency in the VHF
low band is V4. Further, it is assumed that the tuning voltage for tuning to the lower limit frequency (the minimum receivable frequency) in the VHF low band is Vl, the tuning voltage for tuning to the lower limit frequency of the VHF high band is V2, and the tuning voltage for tuning to the lower limit frequency in the UHF band is V3. The relation of these voltages Vl to V6 is selected to be V6> V5, V6> V4, Vl~ V2 and Vl ~V3. More specifically, adjustment 3~

is made such -that in the UHF band when the tuning voltage V6 is applied the high end channel E6g can be assuredly received bu-t the channel E69 + 8 ~iHz cannot be exceeded as the upper limit value. On the other hand, adjustment is made such that in the VHF low band in the case of the tuniny voltage Vl the low end channel E2 can be assuredly received but the channel E2 - 7 MHz is e~ceeded. The lower limit ~requency of the UHF band is restricted by the tuning voltage V3 and the upper limit and the lower limit frequencies of the VHF
high band are restricted by the tuning voltages V5 and V2, and the upper limit frequehcy of the VHF low band is restricted by the tuning voltage V4. Alternatively, the tuning voltages Vl to V6 may be set in a relation of V6 = V5 = V4 and Vl =
V2 = ~3. It is pointed out that the examples of the tuning voltage generating means to be described subsequently are structured to generate the tuning voltage in common to the respective receiving bands in accordance with the last mentioned relation.
Figs. 5A and 5B are schematic diagrams of an example of a television tuner in accordance with the present invention.
Fig. 5A shows a UHF associated por~ion and Fig. SB shows a VHF associated portion. These UHF and VHF portions are implemented in a unitary tuner housed within a single shield memb~r 101; however, these portions are shown as housed in 25 separate shield members 101 in Figs. 5A and 5B for simplicity ,~
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of illustration.
Referring to Fig. 5A, first the UHF portion will be described. The shield member 101 is partitioned into suitable cells by suitable shielf plates. A UHF high frequency S amplifier 109 including an input tuning circui-t is provided within the first cell. An inter stage tuning circuit 110 is housed within the next cell and is disposed between the UHE' high frequency ampllfier 109 and a UHF mixer 111. A mixer diode Dm constituting a UHF mixer 111 is disposed within the same cell as the interstage tuning circuit 110. The UHF
high frequency amplifier 109 comprises an input tuning circuit, which comprises a resonance circui-t including a first voltage controlled variable capacitance diode Dl and a first resonance conductor Ll. The resonance circuit serves to select a desired one of the broadcasting signals in the UHF band fed from the UHF antenna input terminal 119. An amplifying transistor Tl amplifies the selected UHF television signal. The amplified television signal is applied to a primary resonance circuit o~ the interstage tuning circuit 110. The primary resonance circuit comprises a second voltage controlled variable capacitance diode D2 and a second resonance conductor L2. The primary resonance circuit is electromagnetically coupled to the secondary resonance circuit. The secondary resonance circuit comprises a third voltage controlled variable capacitance diode D3 and a third ~1 3~

resonance conductor L3. Accordingly, the television signal amplified by the transistor Tl is fed through the coupling between the primary resonance circuit and the secondary resonance circuit to the anode of the mixer diode Dm. On the other hand, the UHF local oscillator 113 comprises an oscillation transistor T2, a fourth voltage controlled variable capacitance diode D4 and a fourth resonance conductor L4. The oscillation output from the UHF local oscillator 113 is applied to the cathode of the mixer diode Dm. Accordingly, the mixer diode Dm serves to mix the two fed frequency signals, thereby to provide an UHF intermediate frequency signal, which is applied to an UElF intermediate frequency amplifier 115. The UHF intermediate frequency amplifier 115 comprises an amplifying transistor T3, the output of which is applied to a VHF mixer 105 shown in Fig. 5B. The tuning voltage Vt obtained from the tuning voltage terminal 123 of the tuner 100 is commonly applied to the first, second, third and fourth voltage controlled variable capacitance diodes Dl, D2, D3 and D4 conskituting the respective resonance circuits. The tuning voltage Vt is also applied to the VHF
portion shown in Fig. 5B. An UHF band selecting voltage BU
obtained from a terminal 133 is applied to the transistors Tl, T2 and T3. Accordingly, these transistors Tl to T3 are enabled upon application of the voltage BU from the terminal 25 133.

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Frequency adjustment of the UHF portion will be made in the following manner. For the purpose of ajusting the tuning frequency in the UHF portion, first the voltage BU is applied to the terminal 133. As the tuning voltage V-t being applied to the terminal 123, the tuning voltage V6 shown in Fig. 4, for example, is determined. Then the local oscillation frequency of the UHF local oscillator 113 is adjusted. The frequency adjustment is made with the trimmer loop TL4 coupled to the fourth resonance conductor L4. The local oscillation frequency at that time is adjusted such that the same is lower than the normal local oscillation frequency of the high end channel of the UHF band by several MHz and the same may be the frequency corresponding to one channel at the highest. Then the tuning voltage Vt obtained from the lS terminal 123 is applied as the voltage V3. The trimmer capacitor TC4 included in the UHF local oscillator 113 is adjusted at that time, so that the normal local oscillation frequency of the low end channel of the UHF band is attained with the voltage V3. After the frequenc~ of the UHP local oscillator 113 i9 thus adjusted, the input tuning circuit of the UHF high frequency amplifier 109 and the interstage tuning circuit 110 are adjusted so that the ou-tput of -the UHF mixer 111 may be the normal intermediate frequency signal. More specifically, if and when the -tuning voltage Vt is the upper limit voltage restricted by the zener diode _ ~ _ 1~

~8(~39 ZD, trimmer capacitors Tc5, Tc6 and Tc7 and the corresponding trimmer loops TLl, TL2 and TL3 are adjusted so that the normal intermediate frequency may be attained at the highest receiving frequency of the UHF band. Then the trimmer capacitors Tcl, Tc2 and Tc3 are adjusted so tha-t when the tuning voltage Vt is brought to the lower limit the normal intermediate frequency may be attained at the receiving lowest frequency of the UHF band. In general, adjustment of the diference between the local oscillation frequency and the input tuing and interstage tuning resonance frequencies to be the normal intermediate frequency is referred to as tracking adjustment. Such tracking adiustment should be made not only in the UHF high end and the UHF low end band but also in the region therebetween. Such tracking adjustment in the intermediate region is made by the trimmer loops TLl, TL2 and TL3. The characteristic of the receiving frequency with respect to the tuning voltage Vt is thus determined as shown by the curve U in Fig. 2, for example. Then the characteristic of the receiving frequency in the UHF band with respect to the tuning voltage Vt is determined through adjustment of the UHF portion.
Referring to Fig. 5B, the VHF portion of the tuner 100 is shown. The VHF portion comprises a VHF high frequency amplifier 103. The V~IF high frequency amplifier 103 comprises an input tuning circuit, which receives a VHF -television B

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signal from the VHF antenna input terminal 117. The input tuning circuit comprised inductors L5 and L6, and a voltaye controlled variable capacitance diode D5 cooperating wi-th these inductors for determining the tuning frequency of the resonance circuit. Furthermore, the VHF high frequency ampllfier 103 comprises an ampli~ying transistor T4, the output of which is applied to the primary resonance circuit constituting an interstage tuning circuit 104. The primary resonance circuit comprises a voltage controlled variable capacitance diode D6 and inductors L7 and L8 which are coupled to a secondary resonance circuit. The secondary resonance circuit comprises inductors L9 and L10 and a voltage controlled variable capacitance diode D7. Accordingly, the VHF television signal selected by the input tuning circuit of the VHF high frequency amplifier 103 is amplified by the transistor T4 and is applied through the primary resonance circuit and the secondary resonance circuit of the interstage tuning circuit 104 to a t.ransistor T5 constituting a VHF mixer 105. On the other hand, the VHF local oscillator 107 comprises an oscillation transistor T6, a voltage controlled variable capacitance diode D8, and inductors Lll and L12.
Switching diodes SDll, SD12, SD13 and SD14 are coupled to the input tuning circuit included in the VHF high frequency amplifier 103, the primary resonance circuit and the secondary resonance circuit of the interstage tuning circuit 104 and .~.--~
, ~ _ ,~ _ the VHF local oscillator 107. A V~IF low band selecting voltage BL is applied from a terminal 129 to the cathodes of these switching diodes SDll to SD14, and a VHF high band selecting voltage BH is applied from a terminal 131 to the anodes of these switching diodes SDll to SD14. Accordingly, when the VHF high band is to be selected, the inductors L6, L8, L10 and L12 are removed from the respective resonance circuits, because the corresponding switching diodes S~ll, SD12, SD13 and SD14 are rendered conductive by the band selecting voltage BH. Meanwhile, the transistor T5 of the VHF mizer 105 is supplied with the operation voltage not only on the occasion of VHF reception but also on the occasion of UHF reception, whereby the transistor T5 serves as a UHF
intermediate frequency amplifier on the occasion of UHF
reception. The otput of the VHF mixer 105 is applied to the terminal 121 as the intermediate frequency signal. Meanwhile, a terminal 127 serving as a test point is connected to -the output of the secondary resonance circuit of the interstage tuning circuit 104. A terminal 135 for an automatic fine tuning voltage is provided in association with the VHF local oscillator 107 and the UHF local oscillator 113, although not shown. A terminal 125 for an automatic gain control volgate is provided to supply an automatic gain control voltage to the transistor Tl shown in Fig. 5A and the transistor T4 shown in Fig. 5B.

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Frequency adjustment of the V~IF portion is made after the frequency adjustment of the UHF portion described previously is made. In the frequency adjustmen-t of the VHF portion, first the VHF high band is adjusted, which is followed by adjustment of the VHF low band. ~lowever, the sequential order of adjustment of the VHF high band and the VHF low band may be reversed. First the voltage BH is applied to the terminal 131, whereby the VHF portion is placed in the VHF high band mode. Then, as the tuning voltage Vt the voltage V5 shown in Fig. 4, for example, is applied. The inductor Lll included in the VHF local oscillator 107 is adjusted, whereby adjustment is made for tuning to the high end channel E12 of the VHF high band. Thereaf-ter, as the tuning voltage Vt the voltage V2 of Fig. 4 is applied and the inductor Lll is adjusted, so that the frequency is tuned to the low end channel of the VHF high band. Thereafter the inductors L5, L7 and L9 are adjusted to perform tracking adjustment.
Then, for the purpose of adjusting the VHF low band, the voltage BL is applied to the terminal 129. Then as the tuning voltage Vt the voltages Vl and V4 shown in Fig. 4 are applied and the inductance L12 is adjusted~ so that the frequency may be tuned to the low end channel and the high end channel of the VHF low band. At that time, adjustment i~ made such that the lower limit of the local oscillation B

~3 ~8~39 frequency may be lower than the normal local oscillation frequency of the low end channel E2 by several MHz, say within 7 ~Iz. On the other hand, tracking adjustment is made by adjusting the inductors L6, L8 and L10. After the above described adjustment is made in each of the frequency bands, adjustment of the VHF high band is made again to correct an influence caused by adjustment of the VHF low band.
As a matter of practice, the above described frequency adjustment is determined in consideration of a temperature drift of the locaL oscillation frequency of -the UHF local oscillator 113 and the VHF local oscillator 107, a -time dependent drift, and pull-in frequency and a holding range of an automatic frequency tuning operation.

In making frequency adjustment, consideration is given to a temperature drift and a time dependent drift of the local oscillation frequency of the UHF local oscillator 113 and a pùll-in frequency of an automatic fine tuning operation.
More specifically, the temperature drift of the local oscillation frequency of the UHF local oscillator 113 in a tuner presently available is within +1.5 MHz in the temperature variation range of -10C to +60C and a time dependent dif-t of the local oscillation frequency of the UH~ local oscillator is within +2 MUIz, while the pull-in range of the automatic fine tuning operation is +1.5 MHz. Accordingly, the highest ~80~39 receivable frequency in the UHF band rnay be determined to a frequency higher than the highest channel (E69) by 2 MHz.
By selecting the highest frequency in the above described manner, the total sum (+7 MHz) of the temperature drift (+1.5 MHz) + the time dependent drift (+2 MHz) + the pull-in range of the automatic fine tuing operation (+1.5 MHz) and the above described 2 MHz would be a frequency range which involves a possibility of deviation toward a higher frequency exceeding the above described highest receiving channel.

Since the frequency range allowed for the upper limit of the UHF channel in West Germany is 8 ~z, it follows that there is still a margin of 1 MHz even in the worst situation in consideration of the above described various drifts and the pull-in range and accordingly ~he tuner thus implemented still suffices to meet the requirement of the FTZ standard.
Even when the temperature drift and the time dependent drift have exerted an influence upon a lower frequency, such drifts would be -1.5 MHz and -2 MHz, respectively. Since adjustment has been made to a frequency higher than the normal frequency of the highest channel by 2 M~lz in making the above described adjustment, no problem is caused in reception of the highest channel.
On the other hand, the minimum receivable frequency of the VHF low band may be determined to thè frequency lower than the minimum channel (E2) by 1.5 MHz. For example, a . . .~
r-~s ~1~013~

temperature drift of the oscillation frequency of the V~F
local oscillator 107 is within +0.4 MHz in a temperature variation range of -10C to -~60C and a time dependen-t drif-t is within +1.0 MHz. A pull-in range of the automatic frequency tuning is +1.5 MHz. Accordingly, in consideration of the above described minimum receivable frequency, the total (-

4.4 MHz) of the temperature drift (-0.4 MHz) + the time dependent drift (-1 MHz) + the pull-in range of the automatic fine tuning (-1.5 MHz) + (-1.5 MHz) is a frequency range in which the frequency could drift in the lower direction to be lower than the lowest receiving channel. Since the frequency range allowed for the lower limit of the VHF low band in West Germany is 7 MHz, there is still a margin of 2.6 MHz even in consideration of the above described drifts and the pull-in range and even in the worst situation. Accordingly, the inventive tuner thus implemented can fully meet the requirement of the FTZ Standard. Even when the frequency is changed to be hiyher due to the temperature drift and the time dependent drift, such drifts are +0.4 MHz and +1.5 MHz and~ since adiustment has been made such that the frequency may be lower by 1.5 ~Hz than the normal frequency of -the lowest channel, no influence is exerted upon reception of such lowest channel (-the low end channel).
Fig. 6 is a schematic diagram showing one embodiment of the present invention. Referring to Fig. 6, the tuning B

~1~3(3~3S~

voltage generating circuit 200 is connected to provide the tuning voltage Vt to the tuner 100 described previously. It is pointed out that the circuit path including the -terrninal 137 and zener diode ZD shown by the dotted line in Fig. 6 S may be applied to the Fig. 8 embodiment to be described subsequently. Now several preferred embodiments of the tuning voltage generating circuit 200 shown in Fig. 6 will be described in the following with reference to Figs. 7 to 18.
Fig. 7 is a schematic diagram of a major por-tion of a preferred embodiment of the tuning voltage generating circuit. In the Fig. 7 embodiment the zener diode ZD is used to restrict the upper limit of the tuning voltage Vt.
The voltage being applied through the resistor R from the voltage source Vcc is made to a constan~ voltage by means of the zener diode ZD. The constant voltage thus attained by the zener diode is adjusted by means of a semifixed resistor VRl so as to attain the tuning voltage V6 only for tuning to the high end channel E69 of the UHF band. On the other hand, the tuning voltage Vl tunable to the low end channel E2 of the VHE` low band is applied through the variable resistor VR2 from the terminal 129 of the VHF low band setting voltage BL of the tuner 100. Po-tentiome-ters or variable resistors Pl to Pn are provided in parallel between the tuning voltage supplying terminal 123 and the output of ~`
~ . ~ , .

the semifixed resistor VRl so as to provide a predetermined tuning voltage in associa-tion with the respective channels.
sy closing one of the switches SWl to SWn connected to the respective sliding contacts o~-the potentiometers, the voltage of the potentiometer corresponding to the closed switch is applied from the terminal 123 through the diode D10 to the tuner 100. Even if any of the potentiometers i5 adjusted to provide a voltage lower than the lower limit Vl of the tuning voltage, since the voltage set by the variable resistor VR2 is higher than that voltage, the diode D10 is reverse biased to be turned off, so that the voltage lower than the voltage Vt is prevented from being supplied to the tuner 100. In such a case, the lower limit voltage Vl adjusted by the variable resistor VR2 is applied through the diode D9 to the tuner 100. According to the Fig. 7 embodiment, the upper limit oE the tuning voltage Vt is restricted as the voltage V6 and the lower limit of the tuning voltage Vt is restricted as the voltage Vl. Accordingly, as previously shown in Fig. 4, the maximum receivable frequency of the UHF
band and the minimum receivable frequency of the VHF low band are restricted. Meanwhile, the tuning voltage generating circuit 200 has been adapted to provide the voltage of V6 =
V5 = V4, and Vl = V2 = V3 to the -tuner 100 and the same applies to various embodiments to be described suhsequently as well as -the Fig. 7 embodiment. By doing so, an advan-tage ~ . , 3~

is brought about that the restricting means of the tuniny voltage may be adap-ted to determine only the upper limit and the lower limit. Accordingly, it is not necessary to determine the upper limit and the lower limit of the tuning voltage Vt individually for each of the receivlng bands.
Therefore, a circuit configuration may be very simple.
Furthermore~ the Fig. 7 embodiment is adapted such that the voltage BL for setting the VHF low band is used to obtain the voltage Vl. The purpose is that, since it is sufficient to define the minimum receivable frequency of at least the VHF low band with the voltage Vl, utilization of the voltage BL makes simple the structure. Accordingly, the band setting voltage BL need not be utilized for the purpose of obtaining the voltage Vl, as done in the Fig. 7 embodiment, and the voltage may be withdrawn from any other arbitrary portion. Therefore, the tuner may be structured such that the ~oltage Vl is always obtained in any of the receiving bands. Meanwhile, the semifixed resistor VRl is provided for the purpose of fine tuning and ls not necessarily required.
Fig. 8 shows a modification of the Fig. 7 embodiment.
The Fig. 8 embodiment employs the path shown by the dotted line in Fig. 6, ~or the purpose of setting the upper limi-t voltage V6 of the tuning voltage Vt. The variable resistor VR2 for the purpose of setting the lower limit voltage Vl is provided inside the tuner 100.

- ~r-~q ~01~

Fig. 9 shows a schematic diagram of a major portion of a further preferred embodiment of the tuning voltage generating circuit. Fig. 9 is of a simplest example. More specifically, the embodiment shown employs a jumper wire 201. In -the embodiment, first the jumper wire 201 is removed and the voltage of +30 V, for example, is applied to the junction 204 from an external voltage source, not shown. The minimum voltage Vl of the tuning voltage Vt is determined by adjusting the variable semifixed resistor VR3 connected between one end of each of the potentiometers Pl to Pn and the ground potential. Then the jumper wire 201 is connected between the terminals 202 and 203 and a uoltmeter, not shown, is connected to the junction 204. By looking at the voltmeter, the semifixed resistor VRl is adjusted so that the indication of the voltmeter may be +30 V, whereby the maximum voltage V6 of the tuning voltage Vt is determined. The jumper wire 201 is kept connected between the terminals 202 and 203 even when the tuner is built in a television receiver.
Figs. 10 to 13 show further preferred embodiments of the tuning voltage generating circuit and Figs. 14 and 15 are views showing one example of the impedance means for use in the above described embodiments. The embodiments shown in Figs. 10 to 13 are the tuning voltage generating circuit of the so-called voltage synthesizer type. A channel selec-ting apparatus of a voltag~ synthesizer type is disclosed in, for _ ~ _ ~,0 ~18~

example, United States Patent No. 3,968,440 issued July 6, 1976 to George John Ehni, III.
Referring to the Fig. 10 embodiment, a pulse signal as shown in Fig. 16~ is applied from the -terminal 207. The pulse width of such pulse slgnal is controlled by a control circuit, not shown, so that the same may be that associated with the designated channel. The conduction period of the switching transistor Tr included in the switching circui-t 205 is controlled as a function of the pulse signal applied from the terminal 207 and during the conduction period of the transistor Tr a current flows from the voltage source of +120 V through the resistor R3 to the transistor Tr. Accordingly, a voltage of the magnitude associated with the conduction period of the transistor Tr, i.e. the pulse width of the pulse signal thus applied appears at the junction or at the input of the smoothing circuit 206. The voltage appearing at the junction 208 is smoothed ~y the smoothing circuit 206 and is applied to the terminal 123 of the tuner 100 as the tuning voltage Vt. ~In the embodiment shown the impedance means Z is interposed in the current path of the switching circuit 205, i.e, the emitter circuit of the transistor Tr.
Furthermore, the zener diode ZD is connected between the junction ~08 and the ground. The zener diode ZD serves to restrict the input voltage of the smoothing circuit 206 and thus the upper limit of the tuning voltage Vt to the constant B

V~39 voltage (V6). On the other hand, the impedance means Z
serves to restrict the lower limit (Vl) of the tuning voltage Vt. More specifically, the voltage V on the occasion of conduction of the transistor Tr, at the junction 208 becomes V = Z X (120 - VCE)/(R3 + z) + VCE by means of the impedance means Z, where the voltage VcE ls a saturated voltage between the collector and emitter electrodes on the occasion of conduction of the transistor ~r. On the other hand, in the absence of the impedance means Z, the voltage V is equal to the voltage VcE and accordingly the voltage V in the presence of the impedance means Z is higher than that in the absence of the impedance means Z by the value (120 - VcE) x R3Z~ z Accordingly, the lower limit of the tuning voltage Vt is restricted to the constant voltage Vl (say 1.25 V). Thus, according to the Fig. 10 embodiment, the impedance means Z is in-terposed so that a given residual voltage may appear at the output point 208 even when the switching element is rendered conductive and therefore the lower limit of the tuning voltage Vt is prevented from undesirably becoming lower than the voltage Vl.
Fig. 11 shows an example in which the impedance means Z
is not connected between the emitter electrode of the switching transistor Tr and ground and the junction 208 but between the collector electrode of the switching transistor Tr and the junc-tion 208. In this case as well, a residual impedance exists in ~>'' B

~8(~

the current path on the occasion of conduction of the switchingtransistor Tr and accordingly a given residual voltage arises at the junction 208. Accordingly, the tuning voltage Vt is restricted so tha-t the same may not become lower than the constant voltage V1.
Figs. 12 and 13 show examples wherein a field effect transistor is used as the switching transistor Tr, while the remaining portions thereof are the same as those in the emboidments shown in Figs. 10 and 11.

Fig. 14 shows one example of the impedance means Z.
The Fig. 14 embodiment employs a resistor as the impedance means Z.
Fig. 15 shows another example of the impedance means Z.
The Fig. 15 embodiment employs a series connection of a plurality of diodes Dll to Dln as the impedance means Z.
Meanwhile, the connecting direction of the series connection of the diodes is selected such that ~he current flowing direction in the current path of the switching element 205 may be the forward direction of the series connection. In employing the series connection of the diodes Dll to Dln as the impedance means Z, the voltage V' of the junction 20~
becomes V' = VcE + nVak, where Vak is a forward drop vol-taye for each of the diodes Dl to Dn. Accordinyly, in the case where the impedance means Z is implemented by a series connection of the diodes, the voltage V is increased by the 3~

~ ~ ~(3~39 total nVak of -the drop vol-tages of the diodes and accordingly the tuning voltage Vt ls restricted to the constant voltage Vl.
Now representing the o-thers the operation of the Fig.
10 embodiment in combination with the Fig. 14 embodiment will be described in more detail with reference to Fig. 16.
A pulse signal (Fig-. 16A) having the pulse width corresponding to the designated channel is applied from the pulse signal circuit, not shown, to the terminal 207. The transis-tor Tr is rendered conductive as a function of the pulse width of the pulse signal. At that time, the voltage at the junction 208 remains at the voltage Vl described previously even on the occasion of conduction of the transistor Tr by means of the impedance means Z, i~e. the resistor, without becoming O(VcE). Accordingly, the voltage appearing at the junction 208 as shown in ~ig. 16B is smoothed by the smoothing circuit 206 to a direct current without including a ripple component as shown in Figs. 16C and 16D. ~he pulse width of the pulse signal at that time is ex~remely large and, even if the transistor Tr had been rendered conductive for a substantial portion of the period, the lower limit is restricted by the resistor connected to the emitter electrode of the transistor Tr and the direct current voltage, i.e. the tuning voltage Vt will neither become lower than the constant volta~e Vl 25 (say 1 25 V).

, ~

Fig. 17 is a schematic diacJram of a major portion of a further embodimen-t of the tuning voltage generating circuit and Fig. 18 is a graph explaining the operation thereof. A
characteristic feature of the embodiment shown is that the resistor R9 is connected between the collector and emitter electrodes of the transistor Trl.
In operation, a channel selecting signal is applied to any one of the input terminals al to an of -the channel setting portion 209 implemented by an integrated circuit, for example. Then one of transistors Ql to Qn corresponding to the channel selecting signal is rendered conductive and a current flows from the voltage source Vcc to the corresponding one of the variable resistors VRll to VRln corresponding to the transistor now in conduction. Accordingly, one of diodes D21 to D2n connected to the sliding contact of -the variable resistor corresponding to the transistor now in conduction is also rendered conductive and the voltage being set by the corresponding variable resistor is applied to the base electrode of the transistor Trl. The transistor Trl has the base electrode commonly connected to the anodes of the respective diodes D21 to D2n, as described previously, and also connected through the resistors R8 and R10 to the voltage source Vcc and has -the emitter electrode connec-ted to the output resistor R7 and the ripple removing capacitor C4. Meanwhile, the diode D~l is connectecl in parallel in a ~ 35 ~8~:~13~3 reverse direction between the base and emitter electrodes of the transistor Trl. The diode D~l is rendered conductive in the case where the tuning voltage Vt from the output terminal 210 changes from a high value to a low value, thereby to help a discharge of the capacitor C4. The transistor Trl is provided to compensate for a variation of the tuning voltage Vt caused by a variation of the drop voltages by the diodes D21 to D2n depedning on the temperature and such compensation is achieved by a PN junction interposed in the reverse direction with respect to these diodes D21 to D2n. The zener diode ZD is aimed to restrict the upper limit of the tuning voltage Vt at the predetermined value V6. The input terminals 211, 212 and 213 are the input terminals for the band setting voltages BL, BH and BU, respectively, and are selectively connected to the terminals bl to bn of the channel setting portion 209 by means of the selecting switches Sl to Sn. Meanwhile, the diodes D31 to D3n are aimed -to connect the terminals 211 to 213 and the terminals bl to bn only with respec-t to the selected channel and not to connect them with respect to the other channels.
In the embodiment shown the resistor R9 is connected between the voltage source line 214 and the output resistor R7. Accordingly a constant current normally flows in the output resistor R7 through the resistor R9 irrespective of conduction or non-conduction of the transistor Trl. Therefore, 13~

a constant drop voltage is obtained due to such constant current at both ends of the output resistor R7, i.e. at the output terminal 210. Accordingly, by properly selecting the ratio of the resistors R9 and R7, the lower limit of the tuning voltage Vt can be restricted to the constant voltage Vl. For example, if and when the voltage of the voltage source line 214 is 32 V, the resistor R7 is selected to be 100 kQ and the resistor R9 is selected to be approximately 2.2 MQ. Then, the lower limit of the tuning voltage Vt is restricted with the constant voltage Vl (say 1.25 V).
More specifically, referring to the Fig. 17 diagram, the voltage obtained from any one of the variable resistors VRll to VRln designated as a function of the selecting signal is applied to the base electrode of the transis-tor Trl. Then the magnitude of the voltage and thus the conductivity of the transistor Trl is determined and accordingly the capacitor C4 is charged, while the voltage at the output terminal 210, i.e. the tuning voltage Vt increases to become the voltage value of the channel associated with the channel selecting signal. If and when the tuning voltage Vt is switched from that of a higher channel to that of a lower channel, the electric charge stored in the capacitor C4 is discharged through the diode D41 and accordingly the voltage at the output terminal 210 decreases, as described previously.
However, in such a case, even if the voltage lower than the 3'1 ~ ~013~
set voltage Vl (say 1.25 V is applied from any one of the variable resistors VRl to VRn to the base electrode of the transistor Trl, no forward bias is applied between the base and emitter electrodes of the transistor Trl and therefore the transistor Trl is not rendered conductive, with the result that the tuning voltage Vt lower than the voltage Vt (say 1.25 V~ will not appear at the output terminal 210.
On the other hand, the upper limit V6 of the tuning voltage Vt is restricted to a value lower than the voltage of the voltage source line 204 by the drop voltage between the collector and emitter electrodes of the transistor Trl.
Fig. 18 shows a relation oE the tuning voltage Vt with respect to the number of rotations of a fine tuning knob, not shown, in the case where the sliding contact of any one lS of the variable resistors VRl to VRln is moved by means of the fine tuning knob in the Fig. 17 embodiment. As seen from Fig. 18, even in case where the numer of rotations of the fine tuning knob, not shown, is extremely smallr i.e.
the voltage obtained from the variable resistor is small, the minimum value of the tuning voltage Vt will not become lower than the voltage Vl (say 1.25 V). In the absence of the resistor R9, when the number of rotations of the fine tuning knob is sm~ll, as shown by the dotted line in Fig.
18, the tuning voltage Vt would become approximately 0 V, with the result -that the minimum receivable frequency of the ;`' '`' -- 4er _ V~IF low band could be off the restrlction by the FTZ standard, for example. ~nder the circumstances, the embodiments shown in Figs. 7 to 18 are adapted such that the lower limit of the tuning voltage Vt is restricted with the constant voltage Vl. On the other hand, a conventional tuner does not comprise such restriction of the lower limit of the tuning voltage Vt and accordingly the voltage could become lower than 0.3 V.
~ccordingly, in order to restrict the minimum receivable frequency in the VHF low band so as to satisfy the requirements of the FTZ standard, it is necessary to design a tuner such that the minimum channel (E2) can be received with the tuning voltage o~ approximately 0.5 V. However, reception performance of the channel E2 is degraded as compared with that of the other channels. The reason is that the lower the tuning voltage being applied the worse the quality factor of the voltage controlled variable capacitance diode.
By contrast, by restricting the lower limit of the tuning voltage Vt to the constant voltage Vl (say 1.25 V), as done in the present invention, it is sufficient to design the 2Q tuner such that the channel E2 can be received with such a relatively high tuning voltage and performance of the tuner is enhanced.
It goes without saying that the embodiments shown in Figs. 7 to 18 can be employed not only for adap-tation -to the FTZ standard but also for adaptation to other standards such .~ ~9 1~8V~ 39 as the DOC standard.
Fig. 19 is a modification of a television tuner of a double conversion type. A television tuner of such double conversion type is disclosed in, for example, United States Patent No. 3,639,840 issued February 1, 1972 to Jacob Shekel et al. In such television tuner of a double conversion type, it is necessary to change the tuning frequencyin a wide range from the VHF low band to the UHF band by the use of a single variable local oscillator. However, in achieving such a wide range of the -tuning frequency using only a single voltage controlled variable local oscillator, a difficulty is caused in the local oscillator 504 and in order to prevent such difficulty two voltage controlled variable local oscillators 504V and 504U have been employed in the Fig. 19 embodiment. More specifically, the variable local oscillator 504V is used for the VHF band and is adapted to be variable over the frequency range from 2,000 to 2,350 MHz. On the other hand, the voltage controlled variable local oscillator 504U is provided for the UHF band and is adapted to be variable over the frequency range from 2,500 to 2,900 MHz, for example. The oscillation outputs of these two variable local oscillators 504V and 504U are applied to the contacts 511V and 511U of a band selsecting swi-tch 511.
The switch 511 is switched responsive to the band selecting voltages BV and BU being applied to band selecting voltaye ~î8{~3~

terminals 531 and 533 provided in the tuner 500. More specifically, if and when the VHF band selecting voltage BV
for selecting the VHF band is applied from the channel selecting apparatus, not shown, to the -terminal 531, the switch 511 is turned to the contact 511V On the other hand, if and when the UHF band selecting voltage BU is applied from the terminal 533, the switch Sll is turned to the contact 511u. Accordingly, when the VHF band is to be selected, the oscillation output from the variable local oscillator 504V is applied to the first mixer 503. Conversely, if the UHF band is to be selected, the oscillation output from the variable local oscillator 504U is applied to the first mixer.
Fig. 20 is a graph showing a relation between the broadcasting channels (frequencies) and the tuning voltage in the case where the Fig. 10 embodiment is employed as a television tuner for the West Germany standard. Even in case of scuh modified embodiment of double conversion type, it is sufficient to supply the tuning voltage Vt having the upper limit and the lower limit restricted as shown in Figs.
7 to 18 to the terminal 523. By doing so, the maximum receivable frequency in the UHF band and the minimum receivable frequency in the UHF band are restricted with -the constant tuning voltages V6 and Vl, respectively.

Although the present invention has been described and - ~3' -~V~3~

illustrated in detall, it is clearly unders-tood that the same is by way of illustratiorl and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limi-ted only by the terms of the S appended claims.

~f~

Claims (17)

The embodiments of the invention in which an ex-clusive property or privilege is claimed are defined as follows:

1. A tuner apparatus comprising:
a tuning circuit including a voltage controlled variable reactance means, said tuning circuit having a plurality of receiving bands;
tuning voltage generating means, coupled to said tuning circuit for generating a tuning voltage and applying said tuning voltage to said voltage controlled variable reactance means, wherein said. tuning voltage is within a single predetermined range for all of said plurality of receiving bands; and at least: one of (a) and (b), where (a) comprises:
upper limit restricting means, coupled to said tuning voltage generating means, for restricting the upper limit of said tuning voltage applied to said voltage con-trolled variable reactance means;
maximum receivable frequency defining means inclu-ding trimmer loops and resonance conductors provided in said tuning circuit for determining the maximum receivable frequency of said tuning circuit with respect to said tuning voltage applied to said tuning circuit for all of said re-ceiving bands such that said tuning voltage for the upper limit of the receiving band which must be restricted is greater than or equal to said tuning voltage for the upper limit of the others of said receiving bands, thereby defin-ing the maximum receivable frequency of said plurality of receiving bands; and (b) comprises:
lower limit restricting means including trimmer capacitors and resonance conductors provided in said tuning voltage generating means, for restricting the lower limit of said tuning voltage applied to said voltage controlled variable reactance means; and minimum receivable frequency defining means coupled to said tuning circuit for determining the minimum receivable frequency of said tuning circuit with respect to said tuning voltage applied to said tuning circuit for all of said re-ceiving bands such that said tuning voltage for the lower limit of the receiving band which must be restricted is less than or equal to the lower limit of said tuning voltage for the others of said receiving bands, thereby defining the minimum receivable frequency of said plurality of re-ceiving bands.

2. A tuner apparatus comprising:
a tuning circuit including a voltage controlled variable reactance means, said tuning circuit having a plurality of receiving bands;
tuning voltage generating means coupled to said tuning circuit for generating a tuning voltage and applying said tuning voltage to said voltage controlled variable reactance means;
restricting means, coupled to said tuning voltage generating means, for restricting the limit of said tuning voltage applied to said voltage controlled variable reactance means; and receivable frequency defining means including trimmer loops and resonance conductors provided in said tuning circuit for determining the maximum receivable fre-quency of said tuning circuit: with respect to said timing voltage applied to said tuning circuit such that said tuning voltage for the upper limit of the receiving band which must be restricted is greater than or equal to said tuning voltage for the upper limit of the others of said receiving bands, thereby defining the maximum receivable frequency of said plurality of receiving bands.

3. A tuner apparatus comprising:
a tuning circuit including a voltage controlled variable reactance means, said tuning circuit having a plurality of receiving hands;
tuning voltage generating means coupled to said tuning circuit for generating a tuning voltage and applying said tuning voltage to said voltage controlled variable reactance means;
lower limit restricting means including trimmer capacitors and resonance conductors provided in said tuning voltage generating means, for restricting the lower limit of said tuning voltage applied to said voltage controlled variable reactance means; and minimum receivable frequency defining means coupled to said tuning circuit for determining the minimum receivable frequency of said tuning circuit with respect to said tuning voltage applied to said tuning circuit for all of said re-ceiving bands such that said tuning voltage for the lower limit of the receiving band which must be restricted is less than or equal to the lower limit of said tuning volt-age for the others of said receiving bands, thereby defining the minimum receivable frequency of said plurality of re-ceiving bands.

4. A tuner apparatus in accordance with claim 1, which is built in a television receiver, and which is adapted to be tunable to three receiving bands including a UHF band, a VHF high band, and a VHF low band, and wherein said maximum receivable frequency defining means comprise means for setting said tuning voltage correspond-ing to said maximum receivable frequency of said UHF band to be equal to or higher than said tuning voltage corres-ponding to the respective maximum receivable frequencies of said VHF high band and said VHF low band.

5. A tuner apparatus in accordance with claim 2, which is built in a television receiver, and which is adapted to be tunable to three receiving bands including a UHF band, a VHF high band, and a VHF low band, and wherein said maximum receivable frequency defining means comprise means for setting said tuning voltage correspond-ing to said maximum receivable frequency of said UHF band to be equal to or higher than said tuning voltage correspond-ing to the respective maximum receivable frequencies of said VHF high band and said VHF low band.

6. A tuner apparatus in accordance with claim 3, which is built in a television receiver, and which is adapted to be tunable to three receiving bands including a UHF band, a VHF high band, and a VHF low band, and wherein said maximum receivable frequency defining means comprise means for setting said tuning voltage correspond-ing to said maximum receivable frequency of said UHF band to be equal to or higher than said tuning voltage corres-ponding to the respective maximum receivable frequencies of said VHF high band and said VHF low band.

7. A tuner apparatus in accordance with claim 4, 5 or 6, wherein said receivable frequency defining means comprise means for setting said tuning voltage correspond-ing to said minimum receivable frequency of said VHF low band to be equal to or lower than said tuning voltage cor-responding to the respective minimum receivable frequencies of said UHF band and said VHF high band.

8. A tuner apparatus in accordance with claim 1, which is built in a television receiver and which is adapted to be tunable to two receivable bands including a UHF band and a VHF band, and wherein said maximum receivable frequency defining means comprise means for setting said tuning voltage correspond-ing to said maximum receivable frequency of said UHF band to be equal to or higher than said tuning voltage corres-ponding to said maximum receivable frequency of said VHF
band.

9. A tuner apparatus in accordance with claim 2, which is built in a television receiver and which is adapted to be tunable to two receivable bands including a UHF band and a VHF hand, and wherein said maximum receivable frequency defining Means comprise means for setting said tuning voltage corresponding to said maximum receivable frequency of said UHF band to be equal to or higher than said tuning voltage corresponding to said maximum receivable frequency of said VHF band.

10. A tuner apparatus in accordance with claim 3, which is built in a television receiver and which is adapted to be tunable to two receivable bands including a UHF band and a VHF band, and wherein said maximum receivable frequency defining means comprise means for setting said tuning voltage corresponding to said maximum receivable frequency of said UHF band to be equal to or higher than said tuning voltage corresponding to said maximum receivable frequency of said VHF band.

11. A tuner apparatus in accordance with claim 8, 9 or 10, wherein said minimum receivable frequency de-fining means comprise means for setting said tuning voltage corresponding to said minimum receivable frequency of said VHF band to be equal to or lower than said tuning voltage corresponding to said minimum receivable frequency of said UHF band.

12. A tuner apparatus in accordance with claim 1, wherein said tuning voltage generating means comprises switching means responsive to a given pulse sig-nal; and tuning voltage withdrawing means coupled to said switching means for withdrawing a voltage associated with a conduction period of said switching means as said tuning voltage, and said lower limit restricting means comprises im-pedance means coupled to said switching means for causing a voltage drop with a given residual voltage when said switch-ing means is rendered conductive.

13. A tuner apparatus in accordance with claim 2, wherein said tuning voltage generating means comprises switching means responsive to a given pulse sig-nal; and tuning voltage withdrawing means coupled to said switching means for withdrawing a voltage associated with a conduction period of said switching means as said tuning voltage, and said lower limit restricting means comprises im-pedance means coupled to said switching means for causing a voltage drop with a given residual voltage when said switching means is rendered conductive.

14. A tuner apparatus in accordance with claim 3, wherein said tuning voltage generating means comprises switching means responsive to a given pulse sig-nal, and tuning voltage withdrawing means coupled to said switching means for withdrawing a voltage associated with a conduction period of said switching means as said tuning voltage; and said lower limit restricting means comprises im-pedance means coupled to said switching means for causing a voltage drop with a given residual voltage when said switching means is rendered conductive.

15. A tuner apparatus in accordance with claim 12, 13 or 14, wherein said impedance means comprises re-sistive means.

16. A tuner apparatus in accordance with claim 12, 13 or 14, wherein said impedance means comprises a diode function the forward direction of which is selected to be in a current flow direction from said switching means.

17. A tuner apparatus in accordance with claim 12, 13 or 14, wherein said impedance means comprises re-sistive means and said switching means comprises a tran-sistor.