CA1206281A - Tuner/converter for television signals by cable - Google Patents

Abstract

ABSTRACT
This invention relates to a tuner/converter for receiving and con-verting television signals by cable into television signals adapted to channels 2,3 or 4 of the VHF band in the RTMA standard. The tuner/converter is versatile and can be incorporated into existing converters. As opposed to such circuits currently in existence which are complicated and costly to manufacture, the design of this invention is an integral module on a single circuit plate which can be more easily and accurately manufactured and thereby provides batter performance characteristics. The intermediate frequency amplifier block employed in this invention allows for standard electronic components to be in-corporated therein through the use of printed resonant lines.

Description

I'he present invention relates to a tuner/converter for cable television signals. This tuner/converter offers a completely compact module, specially designed to form a conversion module of a television signal sent by cable to a signal compatible with channels 2, 3 or 4 of the VHF band, according to the RTMA standard. Consequently, the module which the invention presents enables a conventional tele-vision receiver, complemented with a tuning and control system, to receive television signals sent via cable, adding the possibility of remote control of the receiver, a fact from which is derived the intrinsic utility of the tuner/converter of this invention.
The tuner/converter which the invention pr~sents is widely versatile, since it can be incorporated into any type of existing converters for televisionby ca~le which use frequency synthesis, as for example, through the use of PLL or similar circuits. Likewise, the intrinsic circuit system with which the module in the invention has been carried out, enables different standards of input-output characteristics to be adapted, by merely making slight modi~ications in certain components of the circuit~
In order to appreciate the advances provided by this invention, it is use~ul to examine similar circuits currently in existence.
Current existing circuits which perform similar duties prove very complicated to manufacture, which makes them ~$

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difficult and costly to produce. This manufacturing complex ity ls derived mainly from handling the ultra-high frequeney signals which require very accurate wiring and low disper-sion and high reliability eomponents.

SU~IARY OF THE INVENTION
The objeet of the present invention lies mainly offering the design of a eonverter which, eombined with eleet-rical features suitable for its operative funetion, offers the basie advantage of enabling simple industrial manufae-ture, eombined with high operat.ivity, and in addition, offers versa-tility -la z~
features like those mentioned hereinabove.
In this connection, it should be stated that the invention has two fundamental characteristics which differentiate it with respect to other exist-ing embodiments.
The first of them lies in the integration of the whole of the tuner/
converter assembly in a single printed circuit plate, thereby improving the manufacture of this type of elements, avoiding the errors produced in the operativity of conventional tuners, as a result of assembly errors, at the same time as the dispersion of characteristics and an operative performance is obtained which coincides fully with the theoretical performance studied on the circuit, without external disturbances leading to driftage in the performance of the assembly.
Another important characteristic which the invention provides resides in the special design of the intermediate frequency amplifier block, which, taking advantage of the development of printed resonant lines, enables the incorporation of standard electronic components in a printed circuit, which provides a novel and useful feature for the manufacturing indus1:ry.
Compared with this last feature~ it should be mentioned that the intermediate frequency amplifiers normally used in known converters do not form part of the same printed circuit which houses the components making up the input and output stages and the different intermediate stages of the tuning/conversion circuits.
This implies that the conventional amplifier has to be assembled "in the open" with the use of resonant lines locating this block in a metal box which is independent of the rest of the circuit of which it forms part, and making the connections with the rest of the circuit through isolated or "passing through" connections. There is no doubt that this assembly is not 6~
going to ensure a rejection of the signal depersion, apart from involving a very great and complicated adjusting and setting operation.
Apart from these operative performance features of conventional ampli-fiers, it is observed that with the type of assembly commented on, i.e.
amplifier block independent of the printed circuit which forms the rest of the converter/tuner, a series of disadvantages are derived, from the industrial manufacturing point of view, since:
a) more interconnection components are needed, as well as more com-ponents making up each module.
b) in the assembly stage of each module, more manufacturing stages are required, and also more handling of the devlce, all of which is translated into a higher production cost of the whole, with less reliability of the device obtained, all in comparison with the results derived from the structure, whose novelty is claimed.
As mentioned hereinabove, the advan~ages which this tuner/converter offers come mainly from the intrinsic structure with which the intermediate frequency amplifier block has been designed, a structure which enables the in-clusion of all of the device in a single printed circuit plate. However, there are additional characteristics which complement the ones mentioned above, and which make this structure of tuner/converter superior over existing elements both functionally and from the commercial point of view.
In this sense, it should be mentioned that in some structures the ci:rcuitry uses a radiofrequency module in its conversion stage, with tuning through varicap diodes, varying the frequency in the range of 50-450 megahertz of the television signal by cable in an output signal varying between 5~ and 72 megahertz, compatible with channels 2, 3 and 4 of the VIIF band.
Furthermore, the tuning function can be adj~sted by means of mechanical elements provided in the device or through electronic components foreseen in the circuitry. The converter also includes a "pre-scaler" block which in the standard version offers a frequency division by the factor of 256 or 64, as the case may be, and with the output level compatible with the TTL logic or, if necessary, ECL. This prescaler stage offers an output whose frequency is obtained by the said division of the oscillation generated by the first local oscillator of the circuit, which can be used with systems provided with frequency tuners.
Thus, there is obtained a converter/tuner suitable for transforming television signals sent through a cable into signals suitable to be treated by conventional television sets in the usual channels.
In acco:rdance with the present invention, there is pro-vided a tuner/converter for cable television signals, adapted to receive and convert cable television signals into TV signals for channels 2, 3 or 4 of the VHF band in the RTMA standard, charac-terized by being built entirely on a printed circuit board having at its input, a pass-band filter adjusted between 50 and 450 MHz.
~0 preceding a first mi~ing stage, which also receives a signal from a first local oscillator and is controlled by a tuning voltage input, said fi.rst local oscillator having a resonant circuit formed by printed circuit, and controlled by varicap diodes, means for applying the additive signal resulting from the first mixing stage to an intermediate freq~ency low~pass filter in U~F, said filter generating a signal to be applied to an intermediate fre-quency amplifier comprising a resonant circuit with a double gate MOS-FET transistor and resonant lines comprising a printed circuit . ~4~

si-tuated on the same board which forms the printed circuit of the -tuner/converter assembly, said intermediate frequency amplifier is connected through an inductive coupling comprising a pass band filter, to one of the inputs of a second mixing stage, said second mixing stage receives through its other input the signal from a second local oscillator, means for appl~ing the output siynal of the econd mixing stage to the output terminal of the tuner/con-verter through a channel adapter which comprises a pass-ba.nd filter followed by a resistive attenuator~
3.0 In accordance with the present invention, there is further provided a tuner/converter for cable television signals, said tuner/converter being for receiving and converting cable television signals into television signals adapted for channels 2, 3 or 4 of the VHF band, as per RTMA standards, said tuner~conver-ter comprising: an electronic module which includes two oscilla-tors and an intermediate frequenc~ amplifier circuit, the elec-tronic module being built entirely OII a single printed circuit board, said printed circuit board having built thereon the inter-mediate frequency amplifier circuit, said intermediate freq-lency amplifier including an input filte~ having printed resonant lines and a pass~band filter made of inductive elements with silver coating, and capacitive elemen~s, the inductive and capacitive elements being positioned so that scatter0d inductance and capaci-tance are minimized.

To complement the description to be given below and in order to assist a better understanding of the characteristics of the invention, a set of drawings is attached to the present specifications, forming an integral part thereof, in which the following has been shown, with an illustrative and un:Limiting nature.
BRIEF DE RIPTION OF T~E DRAWING
Figure 1 - Corresponds to a diagrammatic cross-section view of a conventional tuner/converter, in which it can be seen how the printed circuit which houses the different stages of the converter is in-terrupted in the central area, in which the intermediate frequency amplifier is loca-ted which, necessarily, in this type of converters is mounted and wired "open".
E'igure 2 - Corresponds to a diagrammatic view, similar to that of the previous figure, but in the version which the tuner/converter of the invention offers, noticing the existence of a single printed circuit which houses all the components and stages of the device, including the said intermediate frequency amplifier.
Figure 3 - Represents a perspective view corresponding to the structure which has been shown diagrammatically in figure 1 and concerning a conventional tuner/converter.
Figure 4 - Is a similar view to the above, but corres~
ponding to the structure, shown schematically in figure 2, and concerning the tuner/converter which the invention presents.
Figure 5 - Represents the diagram of blocks correspon-ding to the functional structure of the tuner/converter shown in the invention.

-5a-Flgure 6. - Offers the theoxetical diagram making up the intermediate frequeney amplifier block.
Figure 7. - Shows a plan view of the metal housing which lodges the whole of the electronic structure of the tuner/converter andin which the different eonnection and adjustment points of the circuit can be seen.
Figure 8. - Shows a front view of the housing il-lustrated in the previous figure.
Figure 9. - Shows a profile view of the said metal housing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODI~ENT
In the light of the aforementioned figures, the tuner/converter for television signals by cable, made aecord-i,ng to the invention, is made up from an electronic circuit, whose functional structure ean ~e seen in the bloc~ diagram in figure 5 and which is housed inside a metal frame, figures 3, 7, 8 and 9, speeially designed l,o avoid radioelectrie disturbances, this circuit having :Lts different component bloc~s supported ~y a single printed circuit.
In this sense, figure 1 shows a cross~seetion of a frame which houses a eonventional tuner/eonverter, in whose figure the area intended to loeate the input stage is shown with reference number 1, while 2 shows the output stage. The intermediate frequency amplifier is located in the central area, reference no. 3. In this figure 1, the eireumstanee deserves special mention that the printed cireuit 4 is divided in-to two parts, ~ and ~', respectively, there being no printed circuit for the intermediate frequency ampliEier, which is wired independently from this printed circuit 4 and related with it through "pass-through" conneetions and direct links.
On the other hand, the -tuner/converter executed according to the lnvention is supported in a single printed circuit 5 which is common for the input 6 and output 7 stages and which likewise houses the intermediate frequency amplifier 8. From the comparison between the structure shown in figure 2 and in figure 1, we can see how a single printed circuit 5 is going to support the whole oE the tuner/converter assembly, unlike the sep~rate parts exist-ing in the structure of figures 1 and 3, which gives an idea of the assembly advantages which the structure of the inven-tion offers.
This structure can be achieved so that it is operative, thanks to the special design of the electronic circuit whlch forms the tuner/converter and, more particularly to the special design oE the intermediate frequency amplifier bloek.
If we observe the bloek diagram shown in figure 5, we ean see how the radiorequency signal accedes to the circuitry through the coaxial terminal 9, having a "pass-band"
filter stage 10 provided prior -to a mlxing stage 11, which adds to the signal ofEered by this "pass-band" filter 10, the signal reeeived from the first local oscilla-tor 12, providing ~;20~,2i 3~
the varicap diodes 13 with tuning and receiving si.gnal 14 correspondi.ng to the tuning voltage, a signal whlch accedes to the circuit from the external connection terminal 15, signal which will command the oscillation generated by this block 12.
The additive signal resulting from block 11 is applled to a pass-ba.nd filter of UHF 16 which, in turn, is attached to the input of a specially designed intermediate frequency amplifier block 17, whose output is connected to an intermediate frequency pass-band filter 18 which consti-tutes one of the signals to add by a second mixer 19 which through its other input receives the signal from a second local oscillator 20.
The output signal of the second mixer 19 is applied to a new pass-band output filter 21 wi.th which the radio-frequency output signal is determined, to apply to channels

2, 3 or 4 of the T~ channels, according to the tuning with which the second local oscillator A~O iS adjusted. The out-put signal is obtained in a new coaxial connector marked with reference number 22.

-7a-An output is connected to the first local oscillator 12, which output is associated to a divider or "prescaler" stage 23, fed at five volts from the terminal 24 and which stage 23 provides a frequency-divided signal which is obtained in terminal 25 and which can be used for those converters which employ frequency ~t~r~=~zL~Lon~
Normally, the circuit is ed at 24 volts, which are connected to the terminal marked with reference number 26, having an additional output 27 for tuning the second local oscillator 20 through electronic elements to varicap diodes or through mechanical action on an adjustment screw 28.
Regarding this structure, we can say that the input and output of frequency radio signals ~hrough connectors 9 and 22, enables direct access of the converter to the outside, thus favouring the installation, together with the return loss characteristics.
As speciied above, and as can be seen in figures 2, 4, 7 and 9, tlle electronic components are housed in the metal box; the latter is designed to avoid radioelectric disturbances and inside it has a single printed circuit 5 on which the different blocks described above are mounted, having foreseen a series of separators madc with a special layout of metal partltions ~see figure 4) which provide the characteristics necessary for the system to work correctly.
The stage marked with reference number lO, or input stage, is formed by a pass-band filter which co~ers the frequencies between 50 and 450 megahertz.
The design of this filter is formed by a multipole design filter with one high-pass filter and a trap tuned to 30 ~lz in order to shape a filter which gives a suitable reply to the radiation frequency rejection in the band under 30 Mllz.
This filter made in this way enables return losses to be as little as possible.
Ihe stage corresponding to the first mixer, reference 11, is made up of a douhly balancec. mixer, formed by four diodes with the same characteristics, fed through two transformers, one of them in the radiofrequency input made up of a toroidal symmetric transformer, and the other in the input of the local oscillator comprised by an assymmetrical toroidal transformer, whereby good radio~requency isolation is achieved between the input and the first IF stage, thereby eliminating the generation of outside harmonics which would cons-titute a parasitic signal of this stage.
The characteristics of the circuit depend basically on the response of this mixer to the work frequencies of the device, both in intermodulation and in the noise figure.
The first tunable oscillator 12, is formed by a transistor mounted on a common base with a resonant circuit made up of printed lines and variable inductances, which must cover the frequency band between 661 MHz and 1,061 M~Iz. The feature of the resonant circl.lit being formed with printed lines consititutes a difference which contrasts wi-th the structure of lines mounted in the air of two conventional circuits which perform this same task.
This resonant circuit is controlled by a varicap diode reference number 13, and has a tuning voltage variation, signal marked with number 14, obtained from the terminal 15, between 1.5 and 22 volts.
This first local oscillator 12 has the property of being polarized in a high working point, to obtain the suitable _9._ ~2~ 3~
signal levels necessary for feeding the mixer 11. I'he "noise figure" and "crossed modulation" characteristics depend basically on the oscillation level, as ~7ell as the reject-ion to second-grade beating. In this oscillator, stability with respect to ter.perature and voltage is not critical, since the latter is controlled by means of the frequency tuning system. Due to the fact that the signal level obtained is not sufficient to proceed with the mixture, the signal is amplified in two steps until a level -~a-z~

between lO and 20 dBm required is obtained.
The first amplifier step is performed with a common base transistor, which is a "specific" transistor, followed by another, formed with an MOS-FET
technology transistor. Coupling between the oscillator and the amplifier is performed through a coupling loop to avoid instabilities and i~prove its insulation. ~lso, through another inductive coupling, signal collection takes place to feed the prescaler block 23, necessary for the frequency synthesis.
At the output of the mixer block 11, ~he intermediate frequency of 612.75 MHz. corresponds to the video signal carrier and of 603.25 ~lz corres-ponding to the UHF ~udio carrier, is filtered through a low pass filter for adapting and rejecting the oscillator signal, followed by a trap at 6~0 MHz.
which prevents the frequency of the second oscillator interfering in the pre-vious stage.
The frequency signal, 612.75 MHz. is amplified through an amplifier, which includes an MOS-FET transistor.
This amplifier has the property of being an amplifier tuned to the intermediate frequency by a high Q factor resonant circuit, made with printed lines. The use of an MOS-FET transistor is the best solution for separating signals between stages, avoiding interference and intermodulations.
The IF amplifier block (intermediate frequency) 17 is so developed that in it there is the biggest difference of this converter compared to the present state of art, as it is all designed on a single printed circuit and with the resonant circuit made partly on printed resonant lines, abandoning the resonant lines traditionally mounted "in the open'l and enclosed in metal spaces.
This structure assists the introduction of the amplifier in the same printed circuit of the converter assembly, simplifying manufacturing methods, both of component mounting and in the welding and assembly process, since all GnG

the bloc~s of the converter are integrated ln a single printed cixcuit.
In addition, the adjusting operations of the circuit are simplified to the maximum, taking advantage of the in-trinsic design constituting it, whereby the result provides an entirely reliable circuit, easy to manufacture indus-trially and with the use of standard components, which is an improvement when compared with current models.
The structure of this intermediate frequency amplifier, whose circuitry can clearly be seen in figure ~
of the attached set of drawings, which is what produces the aforementioned effects, commences with a low-pass filter, with ~ structure, which receives the radiofrequency signal from the first mixer which has raised the television band signal b~ cable at higher frequencies included in the UHF
band and after a filtering and adaptation step.
This low-pass filter in ~, marked with reference number 29, includes capacitors 30 and 31 and the inductance 32, all of which aclapts the signal to -the amplifier input.
Next, a frequency trap equal to 680 r~Hz, reference 33, is intercalated in series with the input line, which prevents the frequency of the second oscillator 20, corres-ponding to the second mixer 19 f appearing in the signal applied in the input 3~ of this intermediate frequency ampli-fier. The IF signal is amplified in the stage which includes, as the main active element~ the MOS-FET double gate transistor ~2~2~

35~ and wi-th its source electrode 36 directly connected to earth, being biased so that its power gain is around 15 decibels.
The gain of t.his transistor is controlled through the bias of gate 37, polarization which determines the work point of this transistor 35.
The high quality factor and the necessary band width of the circuit are obtained -through a resonant circuit formed by printed lines 38 and 39 associated with coi].s 40 and 41 and to the capacitors 42 and 43 which are connected to the second gate 44 of transistor 35~
In these conditions, the amplifier acts as a pass-band filter, isolating the mixtures made in the converter between the :input and the output. The drain electrode of transistor 35 is connected to the second mixer 19 through a separation transformer made up of coupled coils 45 and 46, obtaining the signal which is provi.ded to mixer 19 in the ou-tput47 and through the capacitor 48. This mixer 19 also includes a ~OS-FET transistor, also receiving the signal from the second local oscillator.
Control of the local oscillator 20 can be made by mechanical adjustment, varying an inductance o:E the resonant circuit, by acting on the set screw 28 or by elec-tric action, operating on a varicap diode provided in the resonant circuit itself. This oscillator ~0 should have the property of high stability, which is why a self-oscillating two-pole circuit has been studied with a high signal level to be able to obtain the necessary signal in the mixtur~.
Its resonant circuit i9 also formed by resonant lines printed in the actual printed circuit.
In this situation, the additive mixture of the signal provided by the in~ermediate ~requency blcck and by the second local oscillator leads to the signal wanted to attac~ the TV~ in the tuning channel chosen, depending on the tuning at which the second local oscillator block 20 has been made.
The output of -the second mixer 1~, before being connected to the output terminal 22, is applied to a pass-band filter circuit which adapts the radiofrequency signal, making the signal suitable for the channel conditions desired and improving the stationary wave coefficient. This filter circuit, marked with reference number 21, also includes a resistive attenuator with a T-circuit to reduce the power gain level to the limits established by F.C~C~ an~ D.O.C.
standards inforce. The characteristic of flatness between output signal carriers is also adjusted in this filter 21, in accordance with TV quality requirements.
In this way, the structure of the tuner/converter is consolidated for television signals by cable, both from their electrical aspect, and from their mechanical aspect;
the most outstanding characteristic of this structure is that of offering the presence of a single printed circuit, which is general, and carries each and all of the component s-tages of the device, avoiding aer:Lal links which always involve heavy inter:~erence by picking up spurious radio frequency signals, apart from providing the manufacturer wi.th a delicate and meticulous industrial wiring make-up.
Finally, it should be stressed that the optimum working of the assembly and its high performance are obtained with the presence o~ exclusvi.ely standard components, without the presence oE sophisticated special or "made to measure"
components, as usually occurs in other types of tuners desi.gned to carry out the same duties.

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Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A tuner/converter for cable television signals, adapted to receive and convert cable television signals into TV signals for channels 2, 3 or 4 of the VHF band in the RTMA standard, characterized by being built entirely on a printed circuit board having at its input, a pass-band filter adjusted between 50 and 450 MHz. preceding a first mixing stage, which also receives a signal from a first local oscillator and is controlled by a tuning voltage input, said first local oscillator having a resonant cir-cuit formed by printed circuit, and controlled by varicap diodes, means for applying the additive signal resulting from the first mixing stage to an intermediate frequency low-pass filter in UHF, said filter generating a signal to be applied to an intermediate frequency amplifier comprising a resonant circuit with a double gate MOS-FET transistor and resonant lines comprising a printed circuit situated on the same board which forms the printed circuit of the tuner/converter assembly, said intermediate frequency amplifier is connected through an inductive coupling comprising a pass-band filter, to one of the inputs of a second mixing stage, said second mixing stage receives through its other input the signal from a second local oscillator, means for applying the out-put signal of the second mixing stage to the output terminal of the tuner/converter through a channel adapter which comprises a pass-band filter followed by a resistive attenuator.

2. A tuner/converter for cable television signals, said tuner/converter being for receiving and converting cable tele-vision signals into television signals adapted for channels 2, 3 or 4 of the VHF band, as per RTMA standards, said tuner/converter comprising: an electronic module which includes two oscillators and an intermediate frequency amplifier circuit; the electronic module being built entirely on a single printed circuit board, said printed circuit board having built thereon the intermediate frequency amplifier circuit, said intermediate frequency amplifier including an input filter having printed resonant lines and a pass-band filter made of inductive elements with silver coating, and capacitive elements, the inductive and capacitive elements being positioned so that scattered inductance and capacitance are minimized.

3. A tuner/converter for cable television signals, accord-ing to claim 2, further comprising a "prescaler" or division block connected to the first local oscillator block, with a division ratio of the frequency of the first local oscillator of one of 256 and 64, and an output terminal to be used in tuning systems which use frequency synthesis circuits.

4. A tuner/converter for cable television signals, accord-ing to claim 1, 2 or 3, in which frequency control of a second one of the oscillators can be performed, optionally, by one of mechanical and electronic adjustment, having an inductance in its circuit whose core is made up of a regulating screw, accessible to the user, or electrically, by variation of a voltage which con-trols the resonant circuit through the use of a varicap diode in the same local oscillator.