KR920002761B1 - Tuning system for a multiband tv receiver - Google Patents

Abstract

No content.

Description

Tuning System for Multiband TV Receivers

1 is a schematic diagram in block diagram form of a tuning system in accordance with one embodiment of the present invention;

2 is a graph of amplitude variation versus frequency characteristics associated with the embodiment of FIG.

3 and 4 are schematic diagrams of circuitry including embodiments of the invention useful in the tuning system of FIG.

* Explanation of symbols for main parts of the drawings

10: UHF receiving antenna 12: IF trap

14 UHF-Band Tuning Filter 15 UHF-Band Filter Controller

16: UHF Amplifier 20: Deplexer

30A: VHF receiving antenna 32: filter

36 high band tuning filter 40 VHF amplifier

44 low band tuning filter 50 mixer

52 amplifier 56 local oscillator

60 IF tuning amplitude 62 mixer

64: 370MHz Oscillator 66: IF Filter

70: tuning controller

The present invention relates to a tuning system for a television receiver, in particular a system in which tuning of the tuning preference path can be varied for certain conditions.

Television (TV) tuning systems select as many TV radio frequencies (RFs) as desired at different frequencies received from broadcast or cable TV signal sources to generate intermediate frequencies from which display and sound information are obtained. In a dual (modified) tuning system, two frequency conversions (moves) are performed to transform the first received RF signal into a first IF signal, a second IF signal, and a last IF signal.

It is common for signals of different channels to interfere with each other, leading to degradation of the TV picture or sound that is ultimately reproduced. The degree of interference depends on the frequency selection characteristics of the filter, the operation of the local oscillator of the mixer, and the choice of the intermediate frequency range.

For example, consider that VHF channel 5 having an RF image carrier is selected at 77.25 MHz by a dual conversion tuning system having a first IF passband around the first image carrier frequency of 415.75 MHz. A local oscillation frequency of 493 MHz is generated so that the first mixer converts the 77.25 MHz image carrier to 415.75 MHz. If the signal of UHF channel 31 with an RF image carrier at 573.25 MHz was mixed with the local oscillating signal, a signal at a different frequency of 80.25 MHz would be generated. Since 80.25 MHz is within the frequency band of VHF channel 5 (ie, 76 to 82 MHz), disturbance conditions may occur. Similarly, there are UHF RF carriers that can create disturbance conditions for each of the low band VHF channels 2 through 13 as well as many cable TV channels.

Typically, placing a switch, such as a PIN diode or transistor switch, in the signal path between the RF signal source and the mixer can prevent the generation of disturbance signals, thereby preventing potential disturbance signals in the unselected band from reaching the mixer. do. However, at the UHF frequency, switches are configured in a non-capacitive manner, such as by shockstrip capacitances, which cause signals to leak through or around these switches, which may cause unwanted interference. Have a sufficiently strong strength. The present invention attenuates unwanted signals so that any disturbance signals generated are weakened so that they cannot be detected in a TV picture or sound.

To this end, the tuning system of the present invention corresponds to the first and second tuning bands and has a first and second signal path having a frequency selection characteristic controlled in response to the tuning signal generated by the tuning controller. It is composed. The signals generated in the first and second signal paths are combined in a common signal path. The tuning control device also generates a band indicative signal for modifying the tuning signal applied to the first signal path when the channel is selected within the second band.

Hereinafter, with reference to the accompanying drawings, the present specification will be described in more detail.

In the dual conversion tuning system of FIG. 1, the television signal received at the UHF antenna input 10, the VHF antenna input 30A, and the CATV input 30B is connected to the deplexer 20 as described below. In the United States, this television signal includes a channel number and is present in the frequency bands shown in the following table.

TABLE 1

Each channel is assigned a bandwidth of about 6 MHz in the frequency spectrum and has an image carrier at a frequency of 1.25 MHz which is higher than the frequency at the lower limit of the assigned channel. The frequencies described above correspond to the frequencies of the picture carriers PIX of the selected television channel.

The frequency spectrum for the channel frequency (k f) in the various TV frequency bands in the United States is shown in FIG. For the L-VHF band 202, the H-VHF band 206, and the UHF band 210, the amplitude of the received signal is shown at a number of levels, where the level of the broadcast signal is wide, for example. , And may vary in size over a range between 10 microvolts and 100 millivolts. On the other hand, the received CATV signal exhibits very little change between 1 millivolt and 6 millivolts in signal strength, as shown for the MB-CATV band 204 and the SB-CATV band 208.

FIG. 2 (b) defines the low band, high band and UHF band of radio frequency (RF) in combination with the filters 44, 36 and 14 of FIG. 1 to be described below. The image carrier of the first intermediate frequency (IF) signal is selected at 414.75 MHz between the SB-CATV and UHF-TV bands. The video carrier of the second IF signal is selected at the standard frequency 45.75 MHz used in the United States. The bandwidth of the desired TV signal at each IF frequency is 6 MHz and the center of the bandwidth is 414 MHz for the first IF and 44 MHz for the second IF.

While the present invention is only described with variable broadcast bands and cable bands currently used in the United States, it should be understood that they are not really limited to those bands.

For example, an off-the-air broadcast band signal may be supplied from a cable TV signal source in fact and may exist within a TV frequency band used in Europe or Japan.

As shown in FIG. 1, when the selected TV channel is in the UHF band, it is connected from the UHF antenna 10 to the first input terminal of the deflector 20 via the UHF band frequency selection tuning filter 14. . The filter 14 is tuned to pass a signal at a frequency corresponding to the frequency of the TV channel selected between the connections 14c.

The UHF filter 14 exhibits a tuning lowpass frequency selection characteristic in response to the tuning voltage VT. This characteristic represents attenuation of a signal having a frequency lower than the frequency of the selected channel and showing a relatively larger attenuation for frequencies higher than the frequency of the selected channel. Filter 14 exhibits a maximum amplitude response (i.e., maximum pass band with minimum attenuation) at the frequency of the selected channel. The lowest bandwidth is about 25 MHz when tuned near UHF channel 14 and increases to about 40 MHz when tuned near UHF channel 83. Specific embodiments of the filter 14 will be described below with reference to FIG.

IF trap 12 reduces the level of any signal at a frequency close to the first IF received by UHF antenna 10. This reduction in signal level is desirable because the first IF frequency of 415.75 MHz is close to the lower end of the UHF band. For example, radio or radar signals may be generated, radiated or conducted externally from the first IF portion. The trap 12 suppresses the unwanted signal near the first IF frequency, otherwise the signal may be applied to the IF circuit. For this purpose the trap 12 attenuates the signal between 411 MHz and 417 MHz.

The UHF amplifier 16 couples the signal between the output 14 of the filter 14 and the first input of the deplexer 20. Amplifier 16 exhibits a gain of about 14 to 15 dB over the UHF frequency range and has an input and output impedance of about 50 ohms to match the impedance of filter 14 and deplexer 20. This amplifier 16 is provided only when a channel is selected within the UHF band, because its operating voltage, i.e., the band switch voltage VB3 (about 18 volts), is provided as indicated by level 260 of FIG. Operates when a channel is selected in band. Since the amplifier 16 does not operate when a signal other than the UHF band is selected to be received, attenuation occurs in the path between the antenna 10 and the deplexer 20 at that time.

TV signals in the VHF and CATV bands (54 to 402 MHz) are divided into a low tuning band and a high tuning band because their frequency bandwidth is well over the 7: 1 range. Tuning in the range greater than 3: 1 is not practical due to the limited range of variable voltage capacitance diodes. Accordingly, the tuning device of FIG. 1 for the VHF and CATV bands is divided into the low-tuning band and the high-tuning band separated in the MB-CATV band, that is, the frequency of only 150 MHz, as shown in FIG. As a result, each of the high and low tuning bands includes a signal having a range smaller than the 3: 1 frequency range.

The TV signals in the VHF and CATV frequency bands are connected to the deplexer 20 of FIG. The switch SIA may be switched to the position BC-A to apply a signal from the VHF antenna 30A to the input of the filter 32, and apply a CATV signal from the input terminal 30 to the filter 32. Can be connected to location CA-A. Filter 32 is a high pass filter that attenuates signals at frequencies below about 40 MHz, slightly below the lowest frequency to be received (ie, VHF channel 2 at 54 to 60 MHz). Filter 32 passes signals in the low band (54-150 MHz) and high band (150-402 MHz). If the selected channel is in the high band, VB2 is applied to the switches 34 and 38 to conduct them (the switch is closed) to connect the high band filter 36 between the filter 32 and the VHF amplifier 40. . However, when the selected channel is in the low band, VB1 is applied to the switches 42 and 46 to conduct these switches to connect the low band filter 44 between the filter 32 and the VHF amplifier 40.

The high band tuning filter 36 exhibits a tuning highpass frequency selection characteristic in response to the tuning voltage VT. This characteristic shows a relatively large attenuation of the signal with a frequency lower than the frequency of the selected high band channel of the signal with a frequency higher than the frequency of the selected channel. Minimal attenuation occurs in the maximum passband, including the frequency of the selected channel. As a result, the filter 36 not only selects the RF carrier for the selected channel, but also rejects signals at relatively low frequencies, especially those in the low band.

The low band pass filter 44 is tunable in response to VT similar to that described above with respect to the UHF filter 14 except that the bandwidth of the maximum amplitude response pass band increases significantly as the high frequency channel is selected. Low pass frequency selection characteristics. The filter 44 not only selects the RF carrier of the selected channel but also removes the signal at a relatively high frequency, in particular the signal at the high band and the first IF frequency.

The VHF amplifier 40 in FIG. 1 connects the signal generated by the filter 36 or 40 to the second input of the deplexer 20. The operating potential VB 12 is applied to the VHF amplifier 40 whenever a channel in the low or high tuning band is selected, but not in the UHF band when this channel is selected. Thus, when the VHF channel is selected, the VHF and CATV signal paths are separated from the deplexer 20. The operating potential VB12 is generated from the band switch voltages VB1 and VB2 by a diode " OR " circuit including the diodes D12 and D14.

The diplexer 20 of FIG. 1 receives an RF signal from the UHF band signal path at the first input connection, receives an RF signal from the VHF and CATV band signal path at the second input connection, and receives the received RF signal at the output connection. Connect to common signal path. Therefore, the deplexer 20 may be referred to as a passive element signal combiner.

The mixer 50 receives the RF signal from the output of the deplexer 20, receives a local oscillation frequency signal from the amplifier 52, and converts the RF signal into an IF signal having an image carrier at a first IF frequency of 415.75 MHz. .

Tuning voltage controlled local oscillator (VCO) 56 generates a local oscillation frequency signal for each of the three tuning bands. The VCO frequency tunes to the appropriate one of the bandpass filters 14, 36 and 44 in response to the tuning voltage VT. The VCO frequency range is shown in the following table.

TABLE 2

The amplifier 52 may amplify the signal from the VCO 56 so that the RF signal from the deplexer 20 has a relatively large intensity so that no additional distortion occurs in the mixer 50.

The first IF signal from the mixer 50 is then amplified by the tuned IF amplifier 60. Amplifier 60 includes a two-section input filter tuned to a first IF image carrier frequency of 415.75 MHz and having a bandwidth of about 12 MHz, and a three-section output filter tuned to 415.75 MHz and having a bandwidth of 10 MHz. In fact, the IF signal amplified from 60 of these filters is mixed with the 370 MHz frequency signal from the second local oscillator 64 by the mixer 62 to generate a second IF signal with an image carrier at 45.75 MHz. The second IF signal is coupled to the IF output 68 via an IF filter 66.

The tuning controller 70 responds to the selection of the channel to generate the tuning potential VT and the band switch potentials VB1, VB2 and VB3. The tuning potential VT shown in FIG. 2C typically varies between a low level of about 1.5 volts indicated by the imaginary line 220 and a high level of about 24 volts indicated by the imaginary line 222. When the selected channel is in the low tuning band, the VT is a low value of point 224 if the VHF channel is selected as 2 and a high value if the MB-CATV channel E is selected. When the selected channel is within the high-tuning band, the VT is the low value of point 228 if MB-CATV channel F is selected and the high value of point 230 if W-17 is selected for SV-CATV channel. In a similar manner, VT is the low value of point 232 when UHF channel 14 is selected and the high value of point 234 when UHF channel 83 is selected.

The band switch signals VB1, VB2 and VB3 are represented by the characteristic curves 240, 250 and 260 of Figs. 2, d, e and f only when channels in the corresponding bands are selected. Likewise, it is at a high level of about 18 volts and is at zero volts when a channel outside of a particular band is selected. A U.S. Patent Application No. 271,742 filed by DJ Carlson et al. On June 5, 1981, a phase locked loop tuning system comprising a prescaler adjusted to oscillate at frequencies outside the band is transferred to the same assignee as the present invention. And a tuning control device suitable for generating a tuning and band switch potential of the same kind as generated by the controller 70 is referred to for the purpose of explanation.

The UHF band filter controller 15 receives the band signal VB12 which exists at a high level whenever the selected channel is in the high band or the low band. In such a case, the selected low band RF signal is passed by one of the band filters 36 and 44. The UHF RF signal is then attenuated by the UHF amplifier 16, which is not connected at this time and is not operated because the UHF band signal B3 is at a low level. However, a strong UHF RF signal may be shorted around or through amplifier 16 because of the inevitable eddy current capacitive coupling path due to the physical configuration. These unwanted UHF RF signals can be mixed with the signal from the VCO 16 by the mixer 50 to be a disturbing signal at the IF frequency as described above.

This undesired UHF RF signal is typically attenuated by the filter 14 tuned to track the tuning of the bandpass filters 36 and 44 because all three filters are tuned by the same tuning voltage VT (i.e. filter controller). (15) is not).

In order to reduce this disturbing signal to a level that cannot be discerned by television viewers, the Peter controller 15 responds to the band signal VB12 to change the tuning voltage VT in the band filter 14 via the connection 14D. do. As such, filter 14 is detuneed to attenuate the UHF signal passing through it to UHF amplifier 16. As described below, two pairs of filters 14 are achieved as the tuned circuit receives the converted tune voltage, so that this frequency is referenced to a frequency that is substantially different from the frequency of the potential disturbance channel.

As shown in FIG. 3, the UHF band filter 14 is inductively coupled between the input 14A and the output 14B of the filter by inductors L402, L406, L408, L410 and L414 connected in series. It is a double-tuned low pass filter provided with high-side inductive couplong. Capacitance C408 acts as a DC shielding capacitor with negligible AC impedance at UHF frequency.

Inductors L404 and L406 operate as tapped inductors to maintain the impedance of input 144 at about 50 ohms. Likewise, inductors L410 and L414 operate as tap-type inductors to maintain the output impedance at about 50 ohms. Input and output inductors L402 and L414 help maintain a nearly constant bandwidth over the wide tuning range of filter 14. Capacitor C404, which includes capacitance combined with conductors on a printed board, is connected in parallel with inductor L408. (C404 and L408) are chosen to resonate at about 1,000 MHz. Variable frequency tuning is provided by variable capacitance diodes (CD42 and CD44), which are connected to ground from the ends of the tuning circuit (C408-C404) via coupling capacitors C402 and C406, respectively. do. C402 and C406 exhibit very low impedance at the frequency of the UHF television signal passed by the filter 14. The anodes of (CD42 and CD44) are connected to the ground potentials through inductors L404, L406, L408, L410 and L412. Connected.

Tuning potential VT is applied to terminal 14c to change the capacitance of diodes CD42 and CD44 through isolation resistors R402, R404 and R406. VT may vary between about 1.5 and 24 volts for UHF channels 14-83, as shown in FIG. Negligible d.c. Since the current is conducted by the capacitance diodes CD42 and CD44, any d.c. No voltage drop occurs, so a full magnitude tuning voltage VT is applied to the cathodes of CD42 and CD44.

The filter control circuit 15 changes the voltages applied to (CD42 and CD44) to synthesize the filter 14 when the selected channel is not in the UHF band as follows. then. The band representing the voltage VB12 is at a high level of about +18 volts in order to apply a forward bias to the base of the switch transistor TS via the resistors R410 and R41. Thus, the TS becomes conductive to conduct between the cathode of CD44 and the collector-emitter path of TS and the ground potential comprising connection 14D. As a result, the resistors R406 and TS operate as a single voltage divider to the VT between the connection portion 14C and ground, supplying the modified same tuning potential to each of the cathodes of (CD42, CD44).

Since the voltages appearing at each end of (CD42 and CD44) are reduced, each of them exhibits a larger capacitance, thereby reducing the resonant frequency of each circuit to which they are connected. Since this voltage is reduced by about the same amount, each resonant circuit is tuned to a lower frequency to shift the peak passband of filter 14 near or below the lowest frequency in the UHF TV band.

4 is a plan view of the FIG. 3 apparatus in which the filter control circuit 15 changes the voltage applied to (CD42 and CD44) to assist the filter 14 when the selected channel is not in the UHF band as follows. To show. The band representing the voltage VB12 then becomes a high level of about +18 volts to apply a forward bias to the base of the switch transistor TS via the resistors R410 and R412. The TS is thereby conductive to conduct between the cathode of CD44 and the ground potential comprising the collector-emitter path of TS, the connection 14B and resistor R414. As a result, resistors R406, R404 and R414 act as voltage dividers for VT between connection 14C and the ground point, thereby supplying differently modified tuning potentials to each of the cathodes of CD42 and CD44.

Since the voltages appearing across each of (CD42 and CD44) are reduced, each of them exhibits greater capacitance, thereby reducing the resonant frequency of each circuit to which they are connected. As these voltages are reduced by different amounts, each resonant circuit is tuned to a different frequency to make the filter 14 operate as a broadband attenuator.

Additionally, VB12 may be applied to CD42 to increase the modified tuning voltage appearing across CD42 via series connected resistor R420, diode D420 and connection 14F. Accordingly, the resonance frequency of the circuit including (CD42) is tuned to a higher frequency than that combined with (VT). Therefore, these two resonant circuits are synthesized differently by the respective tuning voltages being modified differently. That is, the portion (CD41) is synthesized at a relatively high frequency while the portion (CD44) is composed at a relatively low frequency. This variant has the advantage that known circuits, including (CD42 and CD44), cause the widest separation within the tuned frequency.

It should be noted that the present invention may reduce the potential disturbances as described above. For example, VCO 56 generates a component signal at the second harmonic of the desired local oscillation frequency for the selected VHF TV channel, and the signal from the unselected UHF channel is caused by mixer 50 responsive to the second harmonic signal. Can move to the first IF signal band. One such case is when VHF channel 4 is selected. The second harmonic (966 MHz) of the local oscillator 56 frequency (483 MHz) may move the signal on UHF channel 27 (549.25 MHz PIS) to 416.75 MHz, approaching the first IF signal frequency 415.75 MHz.

Modifications to the mentioned configurations are intended to be within the scope of the invention as defined by the following claims. For example, when the transistor TS of FIG. 3 or the resistor RA206 of FIG. 4 is connected, it must be satisfied that the tuning voltage becomes large enough to shift the highest pass band of the filter 14 to a higher frequency upon deformation. do. In addition, it may be satisfactory that an arbitrary resistor is inserted into the collector of the switch transistor TS at the junction of the resistors R402 and R404 by the resistor R414 (shown in phantom) as shown in FIG. be worth. The dashed lines around the filter 14 here represent a radio frequency shielding membrane, and the embodiment described herein preferably minimizes the number of feedthrough capacitors required to make a connection through the shielding membrane.

Claims (11)

First and second signal paths 12, 14, 16, 30, 34, 36, 40, 42 adapted to be tuned by the tuning voltage VT to move the radio frequency signals to the first and second frequency bands, respectively. 44 and 46, a tuning signal circuit 70 for generating the tuning signal VT and the band signals VB1, VB2, VB3, and VB12 for a desired frequency band, and the first and second signal paths. RF coupling means (deplexer 20) for coupling a signal from the common signal paths 50, 60 and a tuning signal couple for applying the tuning signal VT to the first and second signal paths. A television receiver tuning system comprising ring means (14c, R406), wherein the first signal when the radio frequency signal selected by the first signal path (12, 14, 16) is included in the second frequency band. The first signal in response to the band signal VB12 to shift the path to a frequency outside the first frequency band. Water appointed television synchronization system, characterized in that connected to the potential transition circuit (15,14D) to change the tuning signal (VT) applied to the path. 2. The apparatus of claim 1, wherein the first signal paths (12, 14, 16) comprise a filter (14) having variable capacitance diodes (CD42, CD44) to which the tuning signal (VT) is applied. 14c) includes a resistor R406 through which the tuning signal VT is applied to capacitance diodes CD42 and CD44, the means of change being in response to the band signal VB12. And means (14D) connected to a circuit connection point (R402, R404, 14D) between the resistor (R406) and the capacitance diode (CD42, CD44) to change the voltage. 3. A television receiver according to claim 2, characterized in that said potential change means (15) comprises switch means (TS) for selectively conducting a potential source (ground V) in response to said band signal (VB12). Synchronization system. 4. The switch according to claim 3, wherein said switch means (TS) is an output electrode (TS collector) connected to said circuit point (14D), a common electrode (TS emitter) connected to said potential source (ground point ∇), and said band. A tuning system for a television receiver, characterized in that the signal (VB12) comprises a transistor (TS) having an input electrode (TS base) applied to cause the transistor to conduct between its output and the common electrode. The signal path of claim 1, wherein the signal paths (12, 14, 16) comprise a filter (14) having first and second resonant circuits (L406, L406, L410, C404, CD42, CD44). And the second resonant circuit includes first and second variable capacitance diodes CD42 and CD44 to which the tuning signal is applied, respectively, wherein the applying means 14c and R406 include at least one resistor R406. Through this resistance, the tuning signal VT is applied to the first and second capacitance diodes CD42, CD44, and the changing means 15, 14D are used to change the potential there. And means connected to circuit connection points (R402, R404, 141) between the first and second capacitance diodes (CD42, CD44). 6. The tuning system for a television receiver according to claim 5, wherein said changing means (15, 14D) change respective potentials in said first and second capacitance diodes (CD42, CD44) in a similar manner. 2. The first and second resonant circuits (L406) according to claim 1, wherein the first signal paths (12, 14, 16) have first and second variable capacitance diodes (CD42, CD44) to which the tuning signal is applied, respectively. , L408, L410, L404, CD42, CD44, wherein the applying means 14c, R406 comprise at least one resistor R406 through which the tuning signal VT is applied to the first and the first and second resistors. The circuit point R404 is applied between the second capacitance diodes CD42 and CD44, and the changing means 15 and 14D are used to change the potential therein and between the resistor R406 and the first capacitance diode CD42. And the band signal for changing the tuning signal VT applied to the second capacitance diode CD42 in a direction opposite to the potential change at the circuit point, the first means 15 and 14E connected to CD44. Copper for a television receiver, characterized in that it comprises second means (D420, R420, 14F) responsive to VB12. Jaw system. The method of claim 7, wherein the second means (D420, R420, 14F) for changing the tuning signal (VT) applied to the second capacitance diode (CD42) is the band signal to the second capacitance diode (CD42). And a diode (D420) and a resistor (R420) for connecting the VB12. 2. The first and second resonators of claim 1, wherein the first signal paths (12, 14, 16) have first and second variable capacitance diodes (CD42, CD44) to which the tuning signal (VT) is applied, respectively. Circuits (L406, L408, L410, C404, CD42, CD44), wherein the applying means (14C, R406) comprises a first resistor (R404) and a second resistor (R404) through the first resistor. The tuning signal is applied to the first capacitance diode CD44 and the tuning signal is applied to the second capacitance diode CD42 through the second resistor, and the changing means 15, 14D, 14E are there. For first television (14E) connected to circuit points (R404, CD42) between the first resistor (R404) and the first capacitance diode (CD44) to change the potential of Synchronization system. The switch means (TS) according to claim 7 or 9, wherein said first means (15, 14E) causes said first means (15, 14E) to selectively conduct a potential source (ground point ∇) in response to said band signal (VB12). A tuning system for a television receiver. 11. The switch according to claim 10, wherein the switch means (TS) causes the output electrode (TS collector) connected to the circuit points (15, 14E), the common electrode (TS emitter) connected to the potential source (ground point), and a transistor. And a transistor (TS) having an input electrode (TS base) to which said band signal (VB12) is applied for conducting between its output electrode and a common electrode.

Images