GB1590400A

GB1590400A - Television tuning device

Info

Publication number: GB1590400A
Application number: GB4444177A
Authority: GB
Original assignee: Indesit Industria Elettrodomestici Italiana SpA
Current assignee: Indesit Industria Elettrodomestici Italiana SpA
Priority date: 1976-10-25
Filing date: 1977-10-25
Publication date: 1981-06-03
Also published as: IT1074274B; FR2368827B1; FR2368827A1; DE2747681A1

Description

(54) TELEVISION TUNING DEVICE (71) We, INDESIT INDUSTRIA ELET TRODOMESTICI ITALIANA S.p.A., an Italian Body Corporate of, Str. Piossasco Km. 17, Rivalta, Turin, Italy, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a device for tuning a television receiver.

Televisions contain circuits for selecting the required television channel and converting the received signal from the frequency of the selected channel to the fixed frequency at which the signal amplifier circuits of the television operate. This selection and conversion circuit arrangement is commonly known as a "tuner". There are many different types of tuners available on the market which, though they differ as to circuit arrangement, have one thing in common: they are usually very complicated especially with regard to component assembly and adjusting of the finished circuit.

Another feature common to known types of tuners is that they offer very little versatility and differ considerably from one another as regards operation.

In fact, there is such a wide range of tuners available on the market that they can be classified, for example, according to the television channels they are designed to receive. If classified in this way, we find there are tuners for receiving channels on the VHF + UHF bands or only UHF or CATV or combinations of CATV + VHF or CATV +VHF +UHF bands. Obviously, the tuners in each group differ considerably with regard to design. Such a wide range of tuners is inevitable, however, if it is considered that the same television set has to be marketable in countries broadcasting over different bands.

In Great Britain, for example, it is sufficient for the tuner to receive signals transmitted on the UHF band whereas, in Italy, a tuner also has to be designed to receive VHF band signals and, in some countries, such as Belgium, where cable broadcasting has become widespread, also CATV band signals.

Given the complexity of the device and the difficulties encountered both with regard to manufacture and design, it has not yet been found possible to produce a single tuner which is both economical and capable of meeting all demands.

According to the present invention, there is provided a tuning device for use in a television receiver to tune the receiver to a selected one of a number of receivable television channels and for converting a selected received signal to a predetermined lower frequency band, the tuning device comprising a plurality of modules each comprising an electrical circuit performing a single elemental function in the tuning device, separate ones of the modules including radio frequency attenuating circuit, a radio frequency amplifier circuit, an oscillator circuit and/or a mixer circuit; and supporting and connecting means for the modules.

The invention will be further described, by way of a non-limiting example, with reference to the attached drawings in which: Figure 1 is a block diagram of one embodiment of tuner according to the present inven tion: Figure 2 is a circuit diagram of specific circuits which can be used in the embodiment of Figure 1;and Figure 3 shows one possible arrangement of the parts of a tuning device according to the present invention.

One embodiment of tuning device according to the present invention includes a number of circuits each of which performs a definite function and which can be represented by the blocks in Figure 1. As far as actual manufacture is concerned (see Figure 3), each block consists of a small board on which an electric circuit with a given function is assembled and which is in turn, assembled, using the module method, on a rack which serves both to support and connect the modules together to form a single, compact tuning device.

In Figure 1, number 1 indicates an antenna connected to the input of a signal attenuating circuit 2 fitted with a terminal 3 for controlling signal attenuation. The output of circuit 2 is connected to the input of three radio-frequency amplifiers 4,5 and 6 having different pass-band Amplifier 4, for example, has a pass-band from 470 Mitt to 900 Mitt and is suitable only for amplifying signals in the UHF band. Amplifier 5 has a pass-band ranging from 47 Mitt to 139 MHz for amplifying signals on bands I and II and for CATV channels Sl to Ss. Finally, amplifier 6 has a passband ranging from 139 Mitt to 300 Mitt for amplifying singals on CATV channels S6 to S19 and band III. All three amplifiers 4, 5 and 6 have traps tuned for cutting out unwanted frequency ranges within the above bands as well as a respective terminal (7, 8 and 9) for switching amplifier operation according to the desired channel. The outputs of amplifiers 4, 5 and 6 are connected to the input of a signal attenuating circuit 10 with two terminals 11, 12 for controlling the degree of attenuation of the signal by the circuit. The output of circuit 10 is connected to the first input of a mixer circuit 13 which also has a second input connected to a variable-frequency oscillator 14. The output of mixer circuit 13 is connected to a first input of mixer circuit 15 which also has a first output terminal to which the received television signal is sent, converted to the intermediate fixed frequency at which the signal amplifier circuits downstream from the tuner operate. Mixer circuit 15 also has a second output terminal to which a control signal is sent for controlling the amplitude of the signal processed by mixer 15 and which is sent to terminal 12 of circuit 10 to prevent distortion or intermodulation caused by excessive amplitude of the processed signal.

Finally, a fixed-frequency oscillator circuit 16 is connected to a second input of mixer circuit 15.

The circuit operates as follows: The radiofrequency signal received by antenna 1 is sent to attenuating circuit 2, which can be a normal PIN diode attenuator circuit, which receives the control signal coming from the signal processing circuits connected to the video detector downstream in the circuit. The function of this circuit is to prevent the amplifier stages downstream from becoming saturated when very strong signals are received. Depending on whether the signal being received is in the pass-band of one of amplifiers 4, 5 and 6, the appropriate one of the amplifiers will be activated by a signal received at one of the activating terminals 7, 8,9 which is sent out by the operator selecting the desired channel on the keyboard. If necessary, the received signal is also attenuated by circuit 10.

When control terminal 12 of circuit 10 receives the signal of mixer circuit 15, it operates an automatic gain control device in the tuner to provide a better, quicker amplitude check of the signals processed inside the tuner so as to give added protection against distortion and intermodulation as compared with that provided by an automatic gain control device which acts on all the receiver amplifying circuits between the antenna and the video detector.

The signal is then converted in the first mixer circuit 13 to a first intermediate frequency of 426 Mitt and then, in the second mixer circuit 15, to an intermediate frequency of 36 Mitt which is the normal frequency used in television receivers. In this way, there is no longer any need for a variably-tuned band filter at the input of mixer 13. As the first intermediate frequency is 426 MHz, the image frequency produced during conversion falls outside the reception band and is automatically cut out.

No image frequency problems arise during the second conversion by mixer 15 which receives the signal converted to the first intermediate frequency and a fixed-frequency (390 MHz) reference oscillation from oscillator 16.

By keeping to a fixed-frequency signal, the image frequency produced during the second conversion can easily be cut out by means of a highly selective fixed-frequency filter. In this way, only one circuit operates at variable frequency, that is, oscillator 14, and a single varicap can be used instead of the three used on known tuners.

Figure 2 shows one possible circuit arrangement of the invention, shown in block form in Figure 1. Numeral 19 indicates an input terminal corresponding to the input terminal of the attenuating circuit 2 shown in Figure 1. The signal coming from the antenna passes through capacitor 21 to a normal attenuator circuit consisting of three PIN diodes 22, 23 and 24, then through capacitor 25 to be made available at the output of signal attenuating circuit 2.

Attenuating circuit 2 consists of five resistors 26, 27, 28, 29 and 30 and an inductor 34 which act as a biasing and control network for the PIN diodes and four capacitors 31,32,33 and 36 which act as a by-pass. Attenuating circuit 2 also consists of a high-pass filter LC composed of inductor 20 and capacitor 21 which, together with the trap filter composed of inductor 35 and capacitor 37, serves to provide the correct pass-band to the circuit 2. The output of the latter is connected directly to the three input terminals of band-pass amplifiers 4, 5 and 6 shown in Figure 1 and which, in Figure 2, consists of transistors 38, 39 and 40 and associated parts.

Each of these transistors is connected in common-base configuration (capacitors 41,42 and 43 can be regarded as short-circuits at the frequencies in question) and has a resistive biasing network consisting of three resistors 44, 45,46;47,48,49;and 50,51,52. Capacitors 53, 54 and 55 are also short-circuits at the frequencies in question. Connected to the input and output of the three amplifiers comprising the transistors 38, 39 and 40, are: ahigh-pass filter LC 56, 57, 58 at the input of transistor 38; a high-pass filter LC 59, 60, 61, 62 at the output of transistor 38; aband-pass filter LC 63, 64 at the input of transistor 39; a band-pass filter LC 65, 66, 67, 68 at the output of transistor 39; a band-pass filter LC 69, 70 at the input of transistor 40; and a band-pass filter LC 71,72, 73,74, 75 at the output of transistor 40.

The outputs of the three amplifiers are therefore connected to the input of the signal attenuating circuit 10 shown in Figure 1 which comprises PIN diode 76 which receives a first control signal from the video detector via inductor 77 and a second control signal through resistor 78. Attenuating circuit 10 also includes two filter capacitors 79 and 80 and a biasing resistor 81. Attenuating circuit 10 sends the signal to the first mixer circuit 13, comprising common base-connected transistor 82, which also receives the signal coming from the variablefrequency oscillator on the emitter through capacitor 83. The mixer circuit also comprises three bias resistors 84, 85 and 86, two filter capacitors 87 and 88, a high-pass output filter LC 89, 90 and a twin-tuned band-pass circuit tuned to the first intermediate frequency 426 Mitt comprising capacitors 91, 94, 95 and 96 and two resonant lines 92 and 93.

The variable-frequency oscillator 14 shown in Figure 1 comprises transistor 97, biasing resistors 98, 99 and 100 and filter capacitor 101,102,103 and 138. The oscillator circuit also includes a positive feedback capacitance 104 and a varicap diode 105 which, together with a resonant line 106, fixes the frequency of the oscillator. The capacitance of varicap diode 105 and, consequently, the frequency of oscillator 14, is controlled by means of d.c.

biasing received from a + V voltage source through resistor 107. The oscillation produced in the oscillator circuit is then applied, via capacitor 108 and resistor 109, to the first mixer circuit (circuit 13 in Figure 1).

The signal converted to the first intermediate frequency (426 MHz) and available at the output of the first mixer is fed to the second mixer (circuit 1 5 in Figure 1) comprising transistor 110, filter capacitors 111, 112, 113 and 114 and biasing resistors 115,116,117 and 118.

The second mixer also comprises two LC filters composed of inductors 119 and 120 and capacitors 121 and 122, respectively. The former filter, 119, 121 is tuned to the second intermediate frequency, that is, 36 Mitt (the standard intermediate frequency used on television receivers) and the latter filter 120, 122 is tuned to a frequency forbidden for radiation (eg. the frequency of fixed oscillator 16). The collector of transistor 110 is connected to a diode 123 which detects the amplitude of the signal at the collector and, by means of the low-pass filter consisting of capacitor 124 and resistor 125, produces a d.c. signal for controlling the attenuation introduced by circuit 10.

The converted signal is finally made available at the output terminal 126 from which it is sent to the I.F. amplifiers downstream in the receiver.

The 390 Mitt reference oscillation required for the second conversion is supplied to transistor 110 via capacitors 127 and 128 by a fixed-frequency osicllator (oscillator 16 in Figure 1) comprising transistor 129, filter capacitors 130 and 131 and bias resistors 132, 133 and 134. The fixed-frequency oscillator also includes a feed-back capacitor 135 and a resonant circuit tuned to 390 Mitt frequency comprises capacitor 136 and resonant line 137.

All the circuits mentioned up to now are supplied from the terminals marked +B. In the case of the three band-pass amplifier circuits, the supply terminal +B can also act as the activating terminal which is 7, 8 or 9 in Figure 1.

Transistors 38, 39,40, 82, 97, 110 and 129 are conveniently all the same type and identical to one another (eg. BF 479).

For an explanation of the operation of the circuits shown in Figure 2, see the explanation given for block diagram 1. The Figure 2 circuits have been enclosed by dotted lines to show the corresponding Figure 1 blocks.

Figure 3, as mentioned previously, shows a practical arrangement of the parts making up the present tuning device, in particular the arrangement of the modules (which are printed circuit boards). Numeral 200 is a rack which serves both to support and connect the modules to one another. The rack also includes a terminal board with input and output terminals for connecting the tuner to the remaining television circuits and control keys. The modules and terminals numbered from 202 to 216 perform the same functions as the blocks and terminals numbered 2 to 16 in Figure 1.

Numeral 300 indicates three connecting terminals, which are easily connected and disconnected, for connecting module 216 to rack 200. Identical terminals are provided for each module in varying numbers according to the connection requirements and operation of each individual module assembled vertically on the rack.

Rack 200 comprises a support 400, in the form of a printed circuit for connecting the modules and terminals, with copper tracks, which contains part of the above-mentioned terminals 300 and acts as a support for metal screens 500 for screening and supporting the modules.

The whole module assembly making up the tuner is, of course, covered with two lids not shown in the Figure.

The symbol +B indicates the electric circuit supply terminals, +V indicates the biasing voltage for the varicap diode in variablefrequency oscillator 214 and numerals 219 and 226 indicate the tuner input and output terminals respectively.

A number of the parts shown in Figure 2 are not assembled inside the modules but are used for module connection, such as inductors 230, 231,232 and 233 and condensers 234 and 235 shown in Figure 3.

Another point to notice is that the second signal attenuator circuit represented by block 10 in Figure 1 has not been used in the Figure 3 arrangement.

For an explanation of how the device works, see the description given above, bearing in mind that the exclusion of circuit 10 has no effect on the operation of the device as a whole.

The advantages of the above device will be seen clearly from this description, in particular, the flexibility of the system afforded by the use of modules which can be added or removed to provide various solutions according to requirements. Arranged as described, the device can receive and select all the television channels on the VHF, UHF, and CATV bands. However, if the set the tuner is assembled on does not require such a wide reception range, the cost can be reduced by excluding one of the modules, for example, one of the three radiofrequency amplifiers marked 4, 5 and 6 in Figure 1. A further saving, as shown in Figure 3, could be the exclusion of the attenuating circuit indicated by number 10 in Figure 1.

The use of modules enables substantial changes to be made to the circuit arrangement of a given block without affecting the rest of the circuits.

For example, attenuating circuits 2 and 10 of Figure 1 could be built using controlled (bipolar or FET) transistors instead of PIN diodes. In the same way, mixer circuits 13 and 15 could be built using FET's or diodes instead of bipolar transistors.

The value of the first intermediate frequency can also be changed, for example, in areas disturbed by a signal of roughly 426 MHz, by merely replacing module 13 and readjusting module 16.

Yet another advantage of the device is the ease with which individual modules can be assembled on the rack. The whole assembly process is simplified even further if, instead of discreet circuits, some of the modules are built using film or even integrated circuits.

The module system also simplifies repair work, by making fault detection and part replacements both quick and easy.

Another advantage is the reduction in rejects during manufacture and the fact that the finished product requires a minimum amount of adjusting which is both trouble-free and independent. The use of a single varicap and the second conversion of the received signal frequency means that parts with real values differing considerably from nominal ones can be used with no risk of jeopardizing operation.

Another advantage is that by using the circuits mentioned in the description a single tuner can be used for receiving all types of television channels regardless of the band. Yet another advantage of the tuner described is that it enables a much higher rejection of image frequency than has been pcssible up to now as well as a reduction of intermodulation and distortion in the case of very strong signals or signals very near another strong station being received.

To those skilled in the art, it will be clear that variations can be made to the circuits described by way of example without, however, departing from the scope of the present invention as defined in the appended claims.

One of the many variations, for example, could be the selection of the first intermediate frequency and fixed-frequency oscillator. It has no effect on the operation of the circuit if a first intermediate frequency other than 426 MHz is used. Any one of the frequencies between the last television channel on band III and the first on the UHF band or one even higher than the last channel on the UHF band (roughly 1 GHz) can be used.

Attention is drawn to our co-pending applications Nos. 43318/77 (Serial No 1584737) and 44442/77 (Serial No 1584738) which describe and claim features of the above described apparatus.

WHAT WE CLAIM IS: 1. A tuning device for use in a television receiver to tune the receiver to a selected one of a number of rceivable television channels and for converting a selected received signal to a predetermined lower frequency band, the tuning device comprising a plurality of modules each comprising an electrical circuit performing a single elemental function in the tuning device, separate ones of the modules including a radio frequency attenuating circuit, a radio frequency amplifier circuit, an oscillator circuit and/or a mixer circuit; and supporting and connecting means for the modules.

2. A device according to claim 1, and including a rack for supporting, shielding and inter-connecting the said modules.

3. A device according to claim 2, wherein the rack can accommodate N such modules and the arrangement is such that in use the device comprises less than N modules.

4. A device according to any one of claims 1 to 3, wherein the arrangement is such that a selected signal is frequently converted twice to obtain an intermediate frequency signal.

5. A device according to claim 4, which has a plurality of separate radio frequency amplification modules having different pass bands such that it is capable of receiving all the television channels on one or more of the VHF, UHF and CATV television bands.

6. A device according to claim 4 or 5, wherein a single variable-capacity device is used to select the required channel.

7. A device according to claim 4, 5 or 6 and including at least one circuit for attenuating the received signal, at least one band-pass amplifier for the received signal, a first mixer circuit for receiving the received signal and a first reference oscillation from a variablefrequency oscillator, and a second mixer circuit for receiving a signal from the output of the first mixer circuit and a second reference oscillation from a fixed frequency oscillator.

8. A device according to claim 7, and includ

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

3 arrangement.

For an explanation of how the device works, see the description given above, bearing in mind that the exclusion of circuit 10 has no effect on the operation of the device as a whole.

The advantages of the above device will be seen clearly from this description, in particular, the flexibility of the system afforded by the use of modules which can be added or removed to provide various solutions according to requirements. Arranged as described, the device can receive and select all the television channels on the VHF, UHF, and CATV bands. However, if the set the tuner is assembled on does not require such a wide reception range, the cost can be reduced by excluding one of the modules, for example, one of the three radiofrequency amplifiers marked 4, 5 and 6 in Figure 1. A further saving, as shown in Figure 3, could be the exclusion of the attenuating circuit indicated by number 10 in Figure 1.

The use of modules enables substantial changes to be made to the circuit arrangement of a given block without affecting the rest of the circuits.

For example, attenuating circuits 2 and 10 of Figure 1 could be built using controlled (bipolar or FET) transistors instead of PIN diodes. In the same way, mixer circuits 13 and 15 could be built using FET's or diodes instead of bipolar transistors.

The value of the first intermediate frequency can also be changed, for example, in areas disturbed by a signal of roughly 426 MHz, by merely replacing module 13 and readjusting module 16.

Yet another advantage of the device is the ease with which individual modules can be assembled on the rack. The whole assembly process is simplified even further if, instead of discreet circuits, some of the modules are built using film or even integrated circuits.

The module system also simplifies repair work, by making fault detection and part replacements both quick and easy.

Another advantage is the reduction in rejects during manufacture and the fact that the finished product requires a minimum amount of adjusting which is both trouble-free and independent. The use of a single varicap and the second conversion of the received signal frequency means that parts with real values differing considerably from nominal ones can be used with no risk of jeopardizing operation.

Another advantage is that by using the circuits mentioned in the description a single tuner can be used for receiving all types of television channels regardless of the band. Yet another advantage of the tuner described is that it enables a much higher rejection of image frequency than has been pcssible up to now as well as a reduction of intermodulation and distortion in the case of very strong signals or signals very near another strong station being received.

To those skilled in the art, it will be clear that variations can be made to the circuits described by way of example without, however, departing from the scope of the present invention as defined in the appended claims.

One of the many variations, for example, could be the selection of the first intermediate frequency and fixed-frequency oscillator. It has no effect on the operation of the circuit if a first intermediate frequency other than 426 MHz is used. Any one of the frequencies between the last television channel on band III and the first on the UHF band or one even higher than the last channel on the UHF band (roughly 1 GHz) can be used.

Attention is drawn to our co-pending applications Nos. 43318/77 (Serial No 1584737) and 44442/77 (Serial No 1584738) which describe and claim features of the above described apparatus.

WHAT WE CLAIM IS: 1. A tuning device for use in a television receiver to tune the receiver to a selected one of a number of rceivable television channels and for converting a selected received signal to a predetermined lower frequency band, the tuning device comprising a plurality of modules each comprising an electrical circuit performing a single elemental function in the tuning device, separate ones of the modules including a radio frequency attenuating circuit, a radio frequency amplifier circuit, an oscillator circuit and/or a mixer circuit; and supporting and connecting means for the modules.
2. A device according to claim 1, and including a rack for supporting, shielding and inter-connecting the said modules.
3. A device according to claim 2, wherein the rack can accommodate N such modules and the arrangement is such that in use the device comprises less than N modules.
4. A device according to any one of claims 1 to 3, wherein the arrangement is such that a selected signal is frequently converted twice to obtain an intermediate frequency signal.
5. A device according to claim 4, which has a plurality of separate radio frequency amplification modules having different pass bands such that it is capable of receiving all the television channels on one or more of the VHF, UHF and CATV television bands.
6. A device according to claim 4 or 5, wherein a single variable-capacity device is used to select the required channel.
7. A device according to claim 4, 5 or 6 and including at least one circuit for attenuating the received signal, at least one band-pass amplifier for the received signal, a first mixer circuit for receiving the received signal and a first reference oscillation from a variablefrequency oscillator, and a second mixer circuit for receiving a signal from the output of the first mixer circuit and a second reference oscillation from a fixed frequency oscillator.
8. A device according to claim 7, and includ

ing a second attenuating circuit between the output of the said band-pass amplifier and the input of the said first mixer circuit and an automatic gain control which, depending on the signal present at the output of the said second mixer circuit, acts on the said second attenuating circuit to keep the amplitude of the output signal constant.
9. A device according to claim 7 or 8, wherein the or each attenuating circuit include, at least one PIN diode.
10. A device according to claim 7 or 8, wherein the or each attenuating circuit includes a transistor.
11. A device according to claim 7,8,9 or 10, wherein at least one mixer circuit includes a transistor.
12. A device for tuning a television receiver according to any one of claims 7 to 11, wherein at least one of the said mixer circuits includes a diode.
13. A device according to any one of the preceding claims, wherein the circuitry of at least one of the modules is in thin or thick film form.
14. A device according to any one of the preceding claims, wherein the circuitry of at least one of the said modules is made using semi-conductor monolithic integrated circuit techniques.
15. A tuning device for a television, such device being constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.
16. A television receiver incorporating a tuning device according to any one of the preceding claims.