Tuning system for a television receiver

Tuning system for a television receiver for which

RCA ^ CDRPDRATION seeks to obtain the privilege of invention in Portugal.

This invention relates to television receiver tuning systems for selecting one of several channels arranged in a plurality of frequency bands.

Commercially distributed television (TV) receiver tuning systems usually use a plurality of tuners, each including its own mixer, for receiving signals on a plurality of TV frequency bands. For example, a first tuner selects channels in the VKF-TV (54-88 MegaHertz (MHz) and 174-216 MHz) frequency bands while a second tuner selects channels in the UHF-TV (470-890 MHz) frequency bands. ). When you want the TV receiver to speed up too. With cable TV (CATV) signals, your tuning system may require the addition of a third tuner and mixer.

Dual conversion tuning systems to avoid the complexity and expense inherent in a plurality of tuners are built to receive atmospheric VHF-TV and UHF-TV signals as described by DL Ash, High Performance TV Receiver, IEEE Transactions on Consumer Electronics, Volume CE-24, No. 1, February 1978, Pages 39-46, However, the need continues to exist for a low cost simple tuning system for receiving VHF-TV, UHF-TV, and CATV signals.

In the present invention, a multi-band tuning system produces an IF signal from RF signals residing in, in said order, a first broadcasting band, a first cable band, a second broadcasting band, and a second cable band. .

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-2 TABLE 1

<td>TU range</td><td>Frequency Zone (MegaHertz)</td><td>Number in channel</td>

<td>Low UHF Broadcasting (L-UHF)</td><td> 54-88</td><td> 2-6</td>

<td>Cable Medium Range (MB-CATU)</td><td> 90-174</td><td>A-5 to I</td>

<td>High UHF Broadcasting (H-UHF)</td><td> 174-216</td><td> 7-13</td>

<td>Cable underbody (SB-CATU)</td><td> 216-402</td><td>0 to W + 17</td>

<td>UHF Broadcasting (UHF)</td><td>470-B90</td><td> 14-83</td>

Each channel is assigned about 6 MHz of bandwidth in the frequency spectrum and each has an image carrier at a frequency 1.25 MHz greater than the frequency at the lower end of the band segment assigned to it. Where reference is made to specific channel frequencies in the following descriptions, that frequency will correspond to the frequency at which the television channel image carrier selected is translated into the particular portion of the tuning system being described.

Frequency spectrum for channel frequencies in the various TU frequency bands in the United States is shown in FIGURE 2 (a). For band L-UHF 202, band H-UHF 206 and band UHF 210, the amplitude of the received signals is presented as a plurality of levels indicating that broadcast signals can vary in intensity over a wide range, for example from 10 microvolts and 100 millivolts.

The received CATU signals, on the other hand, exhibit much less variation in signal strength, typically between 1 and 6 millivolts, as illustrated for MB-CATU 204 and SB-CATU 208 bands.

FIGURE 2 (b) defines the low range, high range, and UHF range of radio frequencies (RF) associated with filters 44, 36, and 14, respectively, of FIGURE which will be described below, The first intermediate frequency60. 825

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A control device generates a tuning signal of a magnitude determined by the frequency of a selected channel. A first filter selects color RF signals responsive to channels selected in a first tuning range including the first broadcasting range and a lower frequency portion of the first cable band in response to the tuning signal. A second filter selects RF signals corresponding to channels selected in a second tuning range including a higher frequency portion of the first cable band, the second broadcasting and cable bands in response to the tuning signal. A selection device allows the first filter to operate when the selected channel is in the first tuning range and allows the second filter to operate when the selected channel is in the second tuning range.

In the drawings ·

FIGURE 1 is a schematic diagram under the force; A block diagram showing an embodiment of the present invention.

FIGURES 2, 3, 5 and 6 are graphical representations of various response frequency versus amplitude characteristics associated with the embodiment of FIGURE 1j and

FIGURES 4, 7, and 8 are schematic circuit diagrams useful in the tuning system of FIGU RA 1.

In the dual conversion tuning system of FIGURE 1, the television signals received at the UHF antenna input, UHF antenna 30A and CATU input 3GA are coupled to diplexor 20 as shown below. This system is a dual conversion tuning system because two frequency conversions (transfers) are performed. · In the United States, these television signals include the channel numbers and are in the frequency bands shown in the following table.

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day (IF) is selected to be at 415.75 MHz, which is between the SB-CATU and UHF-TU bands. It is also without the radar range of about 420-450 MHz and is therefore unlikely to interfere or be interfered with by other signal sources. The second IF is the standardized IF TU frequency of 45.75 MHz.

It is implied that although the present invention is described in terms of the various broadcast and cable bands used in the United States, it is not limited to that scope. For example, fused radio band signals could in fact be transmitted over a cable.

When the selected TU channel is in the UHF band, it is coupled to the UHF antenna 10 at the diplexor input 20A via the tunable UHF 14 band frequency selection filter of Fig. 1. Filter 14 receives UT tuning potential at link 14P so that it preferably passes frequencies corresponding to the TU channel selected between its input 14A and its output 14B.

FIGURE 3 shows the frequency selective attenuation characteristic 300 corresponding to TU channel selection at the relatively low UHF frequency ft. Filter 14 exhibits a low pass generic characteristic characterized by lower attenuation at the lower frequency portion 302 of curve 300 and relatively higher attenuation at the upper frequency portion 304. 0 filter 14 preferably passes signals at the chosen channel frequency ft as indicated by the near peak of that frequency range 306. The width of the frequency range is defined between the intersection of characteristics 300 and ghost lines 308 indicating an attenuation of 3 more B than in passabanda. Feature 300 'corresponds to feature 300 when the frequency of the chosen channel f_t is situated at a higher frequency f '_t· For filter 14, the 306 bandwidth is 25 MHz when the frequencies f. correspond to UHF channel 14 while the bandwidth 306 'increases to 40 MHz when frequency f'_t corresponds to UHF channel 83 for the circuit described below with respect to Figure 4. A specific embodiment of filter 14 is described below.

buffer 12 reduces the level of any of the 416 MHz signals received by UHF antenna 10 since the first 416 MHz IF frequency is close to the UHF band. These undesirable signals can be either externally developed or extracted from the first IF section. This tends to reduce the possibility of

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undesirable signals at the first IF frequency are appended to the IF circuits. Buffer 12 exhibits a high pass frequency characteristic 500 shown in FIGURE 5 since it shows a slight attenuation in its pair.

504 at frequencies greater than f corresponding to ~ c lower frequency in the UHF band (about 470 MHz) and greater attenuation in portion 502 at lower frequencies. Around the frequency IF f_i (416 MHz), 12 exhibits higher attenuation as indicated by part 506 of feature 500.

UHF amplifier 16 couples signals between output 140 of filter 14 and input 20A of diplexor 20, displays 14-15 dB of gain over the UHF frequency set, and has input and output impedances of about 50 ohms. 0 amplifier 16 is operative only when the UHF band channel has been chosen in terms of its operating voltage, UB3 switching band voltage (about 18 volts), is present only when channels in the UHF frequency has been ”chosen by level 260 of FIGURE 2 (f).

Signals in the TU and CATU bands are divided between low and high tuning bands as follows. These signals cover a frequency zone in excess of seven-by-one; tuning over a zone larger than three-by-one is not feasible due to the limited zone of varying voltage diodes and capacity. The breakdown of the 54-402 MHz zone between the MB-CATU and H-UHF bands (at about 174 MHz) would further percale a 3 1/4 to one tuning zone for the lower band.

In the present equipment the tuning bands are divided into a band within the MB-CATU band of about 150 MHz, as shown in FIGURE 2 (b). Thus, each of the low and high tuning ranges includes frequencies in a zone smaller than the three to one ratio.

The choice of frequencies in the low and high tuning ranges is also influenced by design considerations for filters 36 and 44. In filter design, it is more difficult to achieve narrow bandwidth at high frequencies than at low frequencies; It is also more difficult to obtain a constant bandwidth in a tunable filter over a wide frequency range. To minimize distortion and interference from the adjacent channel, narrower filter bandwidth is required when channel signal amplitudes vary widely (as for UHF-TU broadcasting signals) than when there is a smaller zone. amplitude (as for CA-TU signals). Since the boundary between the lower and upper bands has been set at 150 MHz within the MB-CATU range, the widely varying L-UHF and H-UHF TU broadcast signals are both at the low frequency extremes of the

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tuning system ranges and the more controlled MB-CATV and SB-CATV signals are at the upper ends of these ranges. Thus, the frequency distribution of the filters employed in the present tuning system gives rise to satisfactory performance while solving the difficulty of design requirements for tunable filters embedded therein.

TV signals at VHF and CATV frequencies are coupled to diplexor 20 as described below. In Figure 1, the SIA switch may be switched to position BC-A to apply signals from VHF antenna 30A to input 32A of buffer 32 or may be connected to position CA-Α to apply CATV signals from its terminal 30B.

Buffer 32 is similar to Buffer 12 described above with respect to Fig. 5 except that its maximum attenuation level 502 is at the second IF (about 46 MHz) which is close to the frequency (about 54 MHz) corresponding to at the lowest frequency to be received (VHF, channel 2). The filter couples signals in both the lower (54 to 150 MHz) and higher (150 to 402 MHz) bands to the 32B swim. If the chosen channel is in the high range then VB2 is applied to make the switches 34 and 38 conductive (closed) to thereby engage the high range filter 36 between nodes 32B and 4QA. If the chosen channel is in the low range, however, then VB1 is applied to switches 42 and 46 which are then made conductive to connect low range filter 44 between nodes 32B and 40A.

High band tunable filter 36 shows the selective feature of the high pass frequency 600 shown in FIGURE 6 wherein the greatest attenuation occurs more at the relatively lower frequency portion 602 than at the relatively higher frequency portion 604. As a result, filter 36 not only chooses the frequencies corresponding to the chosen channel f1, but also tends to handle the lower frequency signals, particularly those in the low tuning frequency range. The width of fai. xa is indicated for curve 600 relative to the -3 dB line 608. When higher frequency channels are chosen the filter bandwidth 36 increases.

Feature 600 'corresponds to feature 600 when the frequency of the chosen channel f' is at a relatively higher frequency f '^. When filter 36 is tuned such that f1 corresponds to MB-CATV channel F, the bandwidth 606 is about 18 MHz; when f '_x corresponds to the W + 17 SB-CATV channel, the 606 'bandwidth is about 40 MHz.

tunable lower range filter 44

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6 shows a low pass frequency selective feature 300 represented in FIGURE 3 and described above with respect to the UHF filter 14 except that said bandwidth is increased to a substantially greater degree when higher frequency channels are selected. The bandwidth 306 is about 8 MHz when it corresponds to channel 2 UHF, and the bandwidth 306 'is about 20 MHz when it corresponds to channel E MB-CATU, filter 44 does not only select frequencies. corresponding to the chosen channel of f_t but it also tends to reject signals at higher frequencies, especially those in the high tuning range and the first IF frequency.

UHF amplifier 40 of FIGURE 1 couples node signals 40A to input 20B of diplexor 20 and is substantially the same as UHF amplifier 16 above ≤ credit. It differs, however, in that its operating potential UB12 is applied across a 0R audio circuit consisting of diodes D12 and D14 such that amplifier 40 receives as operating potential the voltage UB1 or VB2 when a channel within low or high range tuning is chosen, but receives no operating potential when a channel of the UHF band is chosen. Node 40 can thus be disconnected from diplexor input 20B when a UHF channel is chosen.

diplexor 20 of FIGURE 1 receives RF signals from the UHF lane signal pathway at its input link 20A, receives RF signals from the UHF lane signal pathways and CATU at its input link 20B, and combines these pathways signals to transmit RF signals to your 20C output connection. Within diplexor 20, the pathway comprises a high pass filter 22 coupling input 20A to a loop point 24 followed by a low pass filter 26 coupling this loop point to outlet 20C. Interlace 20B is connected to loop 24 by a series of cascaded low-pass filters 28.

The mixer 50 receives RF signals from the output of diplexor 20C and frequency signals from the 1 call oscillator of amplifier 52 through point 52A. In response, the mixer 50 translates the RF signal on the selected frequency channel into a first IF signal of about 416 MHz (i.e. the first frequency conversion).

Serial Patent Application No. 2. 294 131 US titled Diplexor for TV Tuning Systems, was completed by G, E, Theriault on Aug 19 £

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1981 to describe the appropriate implementations of diplexor 20 and mixer 50.

amplifier 52 provides a relatively higher frequency level signal in a 10-18 dBm zone to the frequency mixers 50 and maintains an impedance of about 50 ohms at point 52A. When the mixer 50 is driven by such a high frequency signal level, the RF signal from diplexor 20 may also be of a higher relative strength without introducing additional distortion.

It is preferable to choose a relatively higher IF, for example 416 MHz, a high level of mixer 50 driving for the reason described above. It is also preferable to minimize distortion in the mixer 50 by choosing circuit gain between antennas 10 and 50A and mixer to be just sufficient to obtain an acceptable noise value at the receiver. In this case, the bandwidths of the filters 14, 56 and 44 may be relatively larger for the double conversion syntony system as compared to the narrower bandwidths that would be required in a single conversion tuning system to obtain the same. equivalent distortion and noise values. This advantage allows the filter bandwidth to be increased with the frequency of the chosen channel as described above.

The first IF signal is then amplified by the FI amplifier 60. 0 amplifier 60 may include a 2-section input filter tuned to 416 MHz IF about 12 MHz bandwidth, and a three-section output filter also tuned to 416 MHz IF frequency about 10 MHz bandwidth, 0 The IF signal at the output 62A of the IF amplifier is then mixed with a 570 MHz frequency signal from the local oscillator 64 to the frequency mixer 62 in a second frequency conversion to produce the conventional 46 MHz IF signal. FI is then coupled to IF outlet 68 via IF filter 66.

tuning control 70 responds to a channel selection to develop tuning potential

UT and switching range potentials UB1, UB2 and UB5.

UT tuning potential shown in FIGURE 2 (c) typically ranges from a lower value of about 1.5 volts indicated by the dashed line 220 to a higher value of about 24 volts indicated by the dashed line 222. When the channel chosen is in the lower tuning range, UT tends to a lower value at point 224 when UHF channel 2 is chosen and tends

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-860,825 RCA 77024 to a high value at point 226 when MB-CATU channel E is chosen. When the chosen channel is in the high tuning range, UT also tends to a low value at point 228 when the F MB-CATU channel is chosen and tends to a high value at point 230 when the SB-CATU channel W + 17 is chosen. Similarly, UT tends to a low value at point 232 when UHF channel 14 is chosen s to a high value at point 234 when UHF channel 83 is chosen. Switching band signals UB1, UB2 and UB3 are at a high level of about 1B volts as indicated by the features 240, 250 and 260 of Figures 2 (d), 2 (e) or 2 (f) only when a channel in the range to which they correspond has been chosen, and are at zero volts when a channel outside this special range is chosen.

Three tunable voltage controlled local oscillators (UCO) are considered to develop the local oscillator frequency signals in the three tuning ranges. This is done in such a way that the frequency of a particular oscillator (54, 56, 58) can be conveniently chosen to follow the frequency tuning of its associated filter (14, 36 and 44 respectively) that responds to the same UT tuning potential. . The frequency zone from which frequency signals are to be supplied to amplifier 52 at 52B can be seen in the following table.

TABLE 2

<td>Banner</td><td>Channel Number</td><td>Local Oscillator Frequency (MegaHertz)</td>

<td>Low range</td><td>2 (L-UHF)</td><td> 471</td>

<td>(UCO 58)</td><td>6 (L-UHF)</td><td> 499</td>

<td></td><td>A-5 (MB-CATU)</td><td> 507</td>

<td></td><td>E (MB-CATU)</td><td> 561</td>

<td>High range</td><td>F (MB-CATU)</td><td> 567</td>

<td>(UCO 56)</td><td>I (MB-CATU)</td><td> 585</td>

<td></td><td>7 (H-UHF)</td><td> 591</td>

<td></td><td>13 (L-UHF)</td><td> 627</td>

<td></td><td>the (sb-catu)</td><td> 633</td>

<td></td><td>W + 17 (SB-CATU)</td><td> ' 813</td>

<td>UHF range</td><td>14 (UHF)</td><td> 887</td>

<td>(UCO 54)</td><td>83 (UHF)</td><td> 1301</td>

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Oscillators 54, 56 and 58 respectively receive potentials V81, UB2 and UB5 as their operational potentials, so that they become operative only when the chosen channel falls within the frequency range with which the specific oscillator is associated.

Appropriate embodiments of the filters 14, 56 and 44, shown in FIGURES 4 and 7, will now be described. The UHF 14 strip filter shown in Fig. 4 is a dual-tuned low pass filter with a high side inductive coupling introduced between its input 14A and its output 14B by the serial connection of the induction coils L402, L406. , L408, L410 and L414. The C408 serves as a color locking capacitor.

current continues with an alternating current impedance at UHF frequencies. Coils L404 and L406 serve as a shunt induction configuration to maintain input impedance 14A at about 50 ohms.

Similarly, coils L410 and L412 serve as inductive shunt configuration to maintain impedance at output 14B at about 50 ohms. Input and output coils L402 and L414 help maintain a substantially constant bandwidth over the wide tuning zone of filter 14. Condenser C404 is connected in parallel with coil L408 for a resonance at about 1000 Hz. Variable tuning frequency is obtained by variable capacity diodes CD42 and CD44, respectively connected to the ends of the tuned circuits L408-C404 via coupling capacitors C402 and 406, which show very low impedance to the frequencies of the signal. televisions passed by filter 14. 0 UT tuning potential at the 14C terminal is applied to vary the capacity of the CD42 and CD44 diodes across the insulation resistors R402 and R404, respectively, UT may vary between about 1.5 and 24 volts for UHF channels 14-58.

Figure 7 is a detailed diagram of switches 54, 58, 42 and 44 and tunable filters 56 and 44. Switch 54 conducts TU signals from nodes.

528 to input 56A via the bio-capacitors C7D2 and C704 when the PIN diode SD72 is dimmed by applying the band switching voltage U82 across the RF coil L702. Resistance R7D2 controls the current flowing through SD72 when a channel in the high range is chosen. During this time the PIN diode SD74 'is held in reverse by potential through resistor R702. When the channel is. harvested is from a different range from the high range, the SD47 diode is kept forward biased either by UB1 applied via diode D84 or by UB5 applied via diode D78. The current in the front direction that

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The circle in 5D74 is determined by resistance R702 and the potential therethrough applies a reverse bias to SD72. Resistance 704 provides a return path when the SD 74 is maintained and biased, capacitor C706 is a direct current blocking capacitor. providing a low impedance connection at TU frequencies between □ cathode SD72 and ground when SD74 conductor »switch 38 is of the same type as switch 34, and are made conductive and nonconductive together. Switches 42 and 46 are also of the same type as switch 34, however, they are made conductive only when the chosen channel is in the low range. Corresponding elements that perform similar functions on switches 34, 38, 42 and 46 are listed in the same row as the following table.

TABLE 3

<td>Switch 34</td><td>Switch 38</td><td>Switch 42</td><td>Switch 46</td>

<td>L702</td><td>L714</td><td>L720</td><td>L732</td>

<td>C7D2</td><td>C714</td><td>C720</td><td>C734</td>

<td>C704</td><td>C712</td><td>C722-</td><td>C732</td>

<td>C706</td><td>C716</td><td>C724</td><td>C736</td>

<td>R702</td><td>R712</td><td>R72Q</td><td>R728</td>

<td>R704</td><td>R710</td><td>R722</td><td>R73D</td>

<td>SD72</td><td>5D78</td><td>SD82</td><td>SD88</td>

<td>SD74</td><td>SD76</td><td>3D84</td><td>5D86</td>

<td>D78</td><td>D82</td><td>D76</td><td>D80</td>

<td>D84</td><td>D86</td><td>D72</td><td>D74</td>

The high-range tunable filter 36 shows a high-pass characteristic due to the serial connection of capacitors C708, C710 and capacitors diodes CD72 and CI3? 4 between input 36A and output 36B and inductive coupling on the side. low in the bypass inductances L706, L708 and L71D. The section including capacitors C7D8, C71D and L7D8 shows a high-tuned feature tuned for low band rejections. Variable tuning is obtained by varying the respective capacity of the variable capacity diodes CD72 and CD74 responding to the applied reverse trend respectively.

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through resistors R706 and R708 of the VT tuning potential at the 36C terminal. The capacity of the CD72 resonates with coils L704 and L706, while CD74 resonates with L710 and L712.

Low range tunable filter 44 is inductively coupled to the high side and is similar to the UHF filter 14 described above. The induction coil L726 and capacitor C728 are tuned to the resonant frequency of about 200 MHz to block high-range signals. This frequency is then tuned to lower values ​​by applying the 44T terminal VT tuning potential to the variable potential diodes CD76 and CD78 through resistors R724 and R726. Condensers C726 and C730 provide relatively low impedance pathways at the frequencies between their respective CD76 and CD78 cathodes. Coils L722 and L724 serve as an inductive shunt configuration as with L730 and L728 coils.

Modifications to the present invention are contemplated, and the present invention should be limited only by the following claims. For example, the switch SL was represented as a mechanical switch, as it was assumed that a television receiver would normally be used with either a 3DA VHF antenna or a CATV 30B connection but not both since VHF channel programming is usually also provided in front of CATV. However, if fully automatic reception is desired, S14 may be replaced by a relay or PIN diode switch controlled by a switched band voltage or diplexor.

In addition, the UHF amplifier 16 and VHF amplifier 40 may be removed and switch-type PIN diode switches 34 placed in place if a single amplifier is inserted into connection 20C between diplexor 20 and mixer 50.

A specific desirable modification when the first IF frequency is about 416 MHz is shown in FIGURE 8. TV broadcast signals for VHF channel 12 have an image carrier at about 205 MHz and a sound carrier at about 205 MHz. As the second harmonic of these carriers, as well as the signals in the sum of their frequencies, are close to the IF frequency, it is desirable to provide for the attenuation of these carriers. To this end, L706, described above with respect to FIGURE 7, is selectively coupled to constitute a buffer except sometimes when channel 12, or adjacent channels 11 and 13, are chosen.

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12A coil L0O6 is situated such that its winding is mutually coupled with the two coils of coil L706 closest to ground G, As a result, capacitor C801 is reflected by the transformer coupling between coils L806 and L706 to be effectively in series with the farthest part of L706 from ground G, The combination serves as a serial buffer and is tuned to channel 12 achieving about 20 dB attenuation at 210 MHz and about 10 dB at 205 MHz. A portion of the + V operating voltage developed by the voltage divider including resistors R801 and R802 is applied to the anode of the SD801 switch diode. C802 Lead Conductor couples the top of the C801 or L806 interconnect to ground at TU frequencies for which it exhibits a small impedance; capacitor 805 similarly mates the cathode coupling of 3D801 to ground.

For broadcast reception switch 51B, which is a second pole of switch S1A described above with respect to Figure 1, is in position BC-B to apply voltage + U to cathode 5DB01 through switch S2 and resistor R8D5 to make the reverse of SD 801.

With SDB01 in reverse position, C801 is coupled as described above. When each of channels 11, 12 or 13 is chosen, 52 moves from IN position to IN position to forward SD801 by grounding the respective cathode. As a result, C801 is coupled to ground via small impedances of SD801, C803 and C802 essentially shorting C801 and thus disabling the above described C801-L706 buffer circuit.

For CATU reception, S1B is moved to the CA-B position to similarly disable the C801-L7Q6 buffer circuit.