GB2315935A

GB2315935A - TV VHF high/low band switching

Info

Publication number: GB2315935A
Application number: GB9714465A
Authority: GB
Inventors: Masaki Yamamoto
Original assignee: Alps Electric Co Ltd
Current assignee: Alps Alpine Co Ltd
Priority date: 1996-07-31
Filing date: 1997-07-10
Publication date: 1998-02-11
Anticipated expiration: 2017-07-10
Also published as: JP3224991B2; GB9714465D0; MX9705816A; KR100292169B1; KR980012870A; GB2315935B; JPH1051332A

Abstract

A TV tuner circuit is provided which is capable of reducing the number of parts and the mounting area when a trapping circuit and a peaking circuit are formed and which is capable of improving the trapping effect. The TV tuner circuit includes a parallel-connected circuit formed of a first capacitor (11) and a first inductor (13) which is connected in parallel to the first capacitor through a switching element (14), and a series-connected circuit formed of the first inductor, a second switching element (15), and a second capacitor (16). Only when a specific channel of a VHF low band is received, the first switching element is turned on, and the parallel-connected circuit is connected in series to a signal transmission line, thereby performing trapping of the higher adjacent channel of the VHF low band. When a VHF high band is received, the second switching element is turned on, and the series-connected circuit is made to branch and connect to the signal transmission line, thereby performing peaking of the VHF high band gain.

Description

TV TUNER CIRCUIT The present invention relates to a television (TV) tuner circuit. More particularly, the present invention relates to a TV tuner circuit in which when a specific channel of a VHF low band is received, a trapping circuit for trapping signals of the higher channel adjacent thereto, and when a channel of a VHF high band is received, a peaking circuit for improvin the gain of the channel, can be structured by a small number of parts.

In the United States, for each channel (CH2 to CH6) of a VHF low band of a television broadcast and each channel (CH7 to Cm13) of a VHF high band, the following Frequency bands are assigned.

That Is, ,or the VHF low band, 54 to 64 MHz is assigned to CH2, 60 to 66 MHz is assigned to CH3, 66 to 72 MHz is assigned to CH4, 76 to 82 MHz is assigned to CH5, and 82 to 88 MHz is assigned to CH6. For the VHF high band, 174 to i80 MKz is assigned to CH7, 180 to 186 MHz is assigned to CH8, i86 to 192 MMz is assigned to CH9, 192 to 198 MHz is assigned to CH10, 198 to 204 MHz is assigned to CH11, 204 to 210 MHz is assigned to CH12, and 210 to 216 MHz is assigned to CH13.

Further, for an FM radio broadcast, a frequency band of 88 to 108 MHz is assigned. This frequency band corresponds to between CH6 of the VHF low band and CH7 of the VHF high band.

Fig. 4 is a block diagram illustrating an example of the construction of a conventional TV tuner circuit for receiving such television broadcasts, with specific circuit elements being shown for components of a part thereof.

As shown in Fig. 4, a TV tuner circuit 40 is formed of an antenna filter 41, an input tuning circuit 42, a radio frequency (RF) amplifier 43, a double-tuned circuit 44, a peaking circuit 45, a mixing circuit 46, and a local oscillation circuit 47, with these elements 41 to 47 being connected as shown in Fig. 4. The input tuning circuit 42 is formed of a trapping circuit section 48 and a tuning circuit section 49 which are cascaded. The trapping circuit section 48 is formed of a first inductor 50, a first capacitor 51, a first switching diode 52, a second capacitor 53, resistors 54 and 55, and a trapping voltagesupply terminal 56, with these elements 50 to 56 being connected as shown in Fig. 4. The tuning circuit section 49 is formed of a second inductor 57, a third inductor 58, a fourth inductor 59, a second switching diode 60, a third switching diode 61, a fifth inductor 62, a third capacitor 63, resistors 64 and 65, a low-band select voltage-supply terminal 66L, and a high-band select voltage-supply terminal 66H, with these elements 57 to 65, and 66L and 66H being connected as shown in Fig. 4. Further, the peaking circuit 45 is formed of a fourth capacitor 67, a fifth capacitor 68, a sixth inductor 69, a fourth switching diode 70, a sixth capacitor 71, resistors 72, 73 and 74, a low-band select voltage-supply terminal 75L, and a highband select voltage-supply terminal 7soh, with these elements 67 to 74, and 75 and 75H being connected as shown n Fig. 4.

The TV tuner circuit constructed as described above operates in the following way.

Television broadcasting signals received by an antenna 77 are input to the input tuning circuit 42 via the antenna filter 41. In the tuning circuit section 49, the input tuning circuit 42 tunes to a VHF low band when a low-band select voltage VL is supplied to the low-band select voltage-supply terminal 66L and tunes to a VHF high band when a high-band select voltage VH is supplied to the high-band select voltage-supply terminal 66H The input tuning circuit 42 inputs the obtained signals of the VHF low band or the VHF high band to the RF amplifier 43. The RF amplifier 43 amplifies the supplied signals of the VHF low band or the VHF high band to a predetermined level and inputs the signals to the double-tuned circuit 44. The double-tuned circuit 44 eiilnates unwanted frequency components of the signals of the VHF low band or the VHF high band and inputs the signals to the mixing circuit 46 through the peaking circuit 45. The mixing circuit 46 mixes the frequencies of the supplied signals of the VHF low band or VHF high band and a local oscillation signal from the local oscillation circuit 47 and outputs the signals as video intermediate frequency (IF) signals of a frequency 45.75 Mz and sound IF signals of a frequency 41.75 Mz.

In this case, in the trapping circuit section 48 of the input tuning circuit 42, since the trapping voltagesupply terminal 56 is normally maintained at the grunding potential, the first switching diode 52 is in an on state by the low-band select voltage VL supplied to the low-band select voltage-supply terminal 66L or the high-band select voltage VH supplied to the high-band select voltage-supply terminal 66H and the input and output terminals of the trapping circuit section 48 are short-circuitted, causing the trapping circuit section 48 not to operate. However, only when CH6 of the VHF low band is received, a trapping voltage VTR exceeding the low-band select voltage VL or the high-band select voltage VH is supplied to the trapping voltage-supply terminal 56, the first switching diode 52 is turned off, and the trapping circuit formed of a parallel-connected circuit formed of the first inductor 50 and the first capacitor 51 is connected between the input and output terminals of the trapping circuit section 48.

This trapping circuit tunes to the higher channel adjacent to CR6 of the VHF low band, i.e. the frequency band 88 to 108 MHz of an FM radio broadcast, and only when CH6 of the VHF low band is received, the frequency components of the higher channel adjacent to CH6 are trapped.

Further, in the peaking circuit 45, when a VHF low bana is received, the fourth switching diode 70 is turned off by the low-band select voltage VL supplied to the lowband select voltage-supply terminal 75L, causing the sixth capacitor 71 to be disconnected from the sixth inductor 69, and thus a peaking function for the received signals is not achieved. On the other hand, when a VHF high band is received, the fourth switching diode 70 is turned on by the high-band select voltage V:. supplied to the high-band select volt-ge-supply terminal 75H, causing the sixth inductor 59 and the sixth capacitor 71 to be connected in series, and thus a peaking function for the received signals is achievea.

In the above-described conventional TV tuner circuit 40, when CH6 of the VHF low band is received, the trapping circuit section 48 for trapping the frequency of the higher channel adjacent thereto is disposed within the input tuning circuit 42, and, when a VHF high band is received, the peaking circuit 45 for peaking signals of the VHF high band is disposed between the double-tuned circuit 44 and the mixing circuit 46, with the trapping circuit section 48 and the peaking circuit 45 being disposed separately.

As described above, the conventional TV tuner circuit 40 has problems in that since the trapping circuit section 48 and the peaking circuit 45 are formed separately, the number of parts increases, and in particular, the number of inductors, including the tuning circuit section 49, becomes as many as six, causing the mounting area of the TV tuner circuit 40 to become enlarged.

Further, the conventional TV tuner circuit 40 has problems in that since the trapping circuit section 48 is disposed within the input tuning circuit 42, trapping is performed in the circuit section having a low signal gain, noise factor (NF) deteriorates, and further, the trapping effect cannot be exhibited satisfactorily.

The present invention solves the above-described problems. An object of the present invention is to provide a TV tuner circuit capable of reducing the number of parts and the mounting area and improving the trapping effect when a trapping circuit and a peaking circuit are formed.

To achieve the above-described object, the TV tuner circuit of the present invention includes means in hic a trapping circuit section for trapping a higher channel adjacent to a specific channel (CH6) of a VHF low band, and a peaking circuit section for peaking signals of a VHF high band are shared by one circuit.

With such means, when a shared circuit of a trapping circ:it section and a peaking circuit section is formed, the number of parts can be reduced greatly, IA particular, the number of inductors which require a large amount of space when mounting can be minimized (e.g., one).

Therefore, it becomes possible to greatly reduce the number of parts and reduce the mounting area.

Further, with such means, since a shared circuit of a trapping circuit and a peaking circuit can be disposed in a portion having a large signal gain (e.g., between a double-tuned circuit and a mixing circuit), it becomes possible to improve the effect of the trapping circuit.

In an aspect of the present invention, there is provided a TV tuner circuit, comprising: a first capacitor which is connected in series to a signal transmission line; an inductor which is connected in parallel to the first capacitor with a first switching element being provided in series; and a second capacitor connected between the signal transmission line and a ground with each of the inductor and a second switching element being provided in series, wherein only when a specific channel of a VHF low band is received, the first switching element is turned on and the second switching element is turned off, causing the first capacitor and the inductor to be connected in parallel, thereby forming a parallel resonance circuit which resonates to the signals of a higher adjacent band adjacent to the specific channel, and when each channel in a VHF high band is received, the first switching element is turned off and the second switching element is turned on, causing the inductor and the second capacitor to be connected in series, thereby forming a series resonance circuit which resonates to the VHF high band.

Preferably, the parallel resonance circuit and the series resonance circuit are formed between the doubletuned circuit and the mixing circuit.

Each of the first and second switching elements may be formed of a diode.

According to the above-described TV tuner circuit in accordance with the aspect of the present invention, a trapping circuit section for trapping a higher channel adjacent to a specific channel (CH6) of a VHF low band, and a peaking circuitsection for peaking signals of a VHF high band are shared by one circuit. In this shared circuit, only when specific channel (CH6) of the VHF low band is received, trapping of the higher channel adjacent to the specific channel (cur6) is performed, and further, peaking of the signals of the VHF high band is performed when the VHF high band is received. In this case, in the shared circuit, the number of parts can be reduced greatly to less than that of this type of a conventional circuit (a circuit in which a trapping circuit section and a peaking circuit section are provided separately) , and, in particular, the number of inductors required can be minimized (e.g., one).

Thus, according to an aspect of the present invention, the number of parts can be reduced greatly, the mounting area can be reduced and, moreover, a shared circuit of a trapping circuit section and a peaking circuit section can be disposed in a portion having a large signal gain (e.g., between a double-tuned circuit and a mixing circuit). Therefore, the trapping effect in the trapping circuit section is improved.

The above and further objects, aspects and novel features of the invention will become more apparent from the following detailed description when read in connection with the accompanying drawings BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block dIagram illustrating the construction of an embodiment of a TV tuner circuit according to the present invention; Figs. 2A and 2B are equivalent circuit diagrams illustrating the operation of a peaking circuit in the TV tuner circuit shown in Fig. 1; Fig. 3 is an equivalent circuit diagram illustrating the operation of the peaking circuit in the TV tuner circuit shown in Fig. 1; and Fig. 4 is a block diagram illustrating an example of the construction of a conventional TV tuner circuit.

The preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

Fig. 1 is a block diagram illustrating the construction of an embodiment of a TV tuner circuit according to the present invention, with specific circuit elements being shown for components of a part thereof.

As shown in Fig. 1, a TV tuner circuit 1 of this embodiment is formed of an antenna filter 2, an input tuning circuit 3, a radio frequency (RF) amplifier 4, a double-tuned circuit 5-, a peaking circuit (shared circuit) 6, a mixing circuit 7, and a local oscillation circuit 8.

The antenna filter 2 is connected at its input terminal to an antenna 9 and at its output terminal to the input terminal of the input tuning circuit 3. The RF amplifier 4 is connected at ;ts input terminal to the output terminal of the input tuning circuit 3 and at its output terminal to the input terminal of the double-tuned circuit 5. The peaking circuit 6 is connected at its input terminal to the output terminal of the double-tuned circuit 5 and at its output ter;:inal to a first input terminal of the mixing circuit 7. The mixing circuit 7 is connected at its second input terminal to the output terminal of the local oscillation circuit 8 and at its output terminal to an intermediate frequency (IF) signal processing circuit (not shown) which is connected at the next stage.

In this case, the input tuning circuit 3 has the same circuit elements as those of the tuning circuit section 49 of the conventional input tuning circuit 42 shown in Fig.

4, and is formed of a second inductor 24, a third inductor 25, a third switching diode 27, a fourth switching diode 28, a fourth inductor 29, a fifth capacitor 30, resistors 31 and 32, a low-band select voltage-supply terminal 33, and a high-band select voltage-supply terminal 34. The second inductor 24 and the third inductor 25 are connected in series between the input and output terminals (signal transmission line) of the input tuning circuit 3. A fourth inductor 26, the fifth inductor 29 and the fifth capacitor 30 are connected in series between a grounding point and the connection point of the second inductor 24 and the third inductor 25. The third switching diode 27 and the resistor 31 are connected in series between the output terminal of the input tuning circuit 3 and the high-band select voltage-supply terminal 34. The fourth switching diode 28 is connected between the connection point of the fourth inductor 26 and the fifth inductor 29 and the connection point of the third switching diode 27 and the resistor 31. The resistor 32 is connected between the connection point of the fifth inductor 29 and the capacitor 30, and the low-band select voltage-supply terminal 33.

Further, the peaking circuit 6 is formed of a first capacitor 11, a second capacitor 16, a third capacitor 10, a first inductor 13, a first switching diode 14, a second switching diode 15, a fourth capacitor 12, resistors 17, 18, 19 and 20, a low-band select voltage-supply terminal 21, a high-band select voltage-supply terminal 22, and a trapping voltage-supply terminal 23. The third capacitor 10, the first capacitor 11 and the fourth capacitor 12 are connected in series between the input and output terminals (signal transmission line) of the peaking circuit 6. The first inductor 13, the second switching diode 15 and the second capacitor 16 are connected in series between the grounding point and the connection point of the first capacitor 11 and the fourth capacitor 12. The resistor 20 is connected between the connection point of the third capacitor 10 and the first capacitor 11, and the trapping voltage-supply terminal 23. The first swit -.ing diode 14 is connected between the connection point of the third capacitor 10 and the first capacitor 11 and the connection point of the first inductor 13 and the second switching diode 15. The resistor 1 is connected between the connection point of the second switching diode 15 and the second capacitor 16 and the high-band select voltagesupply terminal 22. The resistor 17 1; connected between the grounding point and the connection point of the first inductor 13 and the second switching diode 15, and in a similar manner, the resistor 18 is connected between the connection point of the first inductor 13 and the second switching diode 15, and the low-band select voltage-supply terminal 21.

The TV tuner circuit 1 of this embodiment constructed as described above operates in the following way.

Television broadcasting signals received by the antenna 9 are fed to the input tuning circuit 3 via the antenna filter 2. In the input tuning circuit 3, when a VHF low band is received, a low-band select voltage VL is supplied to the low-band select voltage-supply terminal 33, causing the third switching diode 27 and the fourth switching diode 28 to be turned off, causing the input tuning circuit 3 to tune to the VHF lc band, and signals of the VHF low band are output. On the other hand, a VHF high band is received, a oigh-band select voltage VH is supplied to the high-band select voltage-supply terminal 34, causing the third switching diode 27 and the fourth switching diode 28 to be turned on, causing the input tuning circuit 3 to tune to the VHF high band, and signals of the VHF high band are output. The RF amplifier 4 amplifies the signals of the VHF low band or the VHF high band to a predetermined level. The double-tuned circuit 5 eliminates unwanted frequency components of the amplified signals of the VHF low band or the VHF high band and inputs the signals to the peaking circuit 6.

Figs. 2A and 2B, and Fig. 3 are equivalent circuit diagrams illustrating the operation of the peaking circuit 6. Fig. 2A shows an equivalent circuit diagram when neither a trapping operation nor a peaking operation is performed. Fig. 2B shows an equivalent circuit diagram when a trapping operation is performed and a peaking operation is not performed. Fig. 3 shows an equivalent circuit diagram when a trapping operation is not performed and a peaking operation is performed.

In the peaking circuit 6, when a VHF low band is received (except when CH6 is received) , a low-band select voltage VL is supplied to the low-band select voltagesupply terminal 21 and, as shown in Fig. 2A, the first switching diode 14 and the second switching diode 15 are turned off, causing the first inductor 13 to be disconnected rom the second capacitor 16, and thus the peaking circuit formed of a series-connected circuit formed of the fIrst inductor i3 and the second capacitor 16 does n-t operate. At this time, the signals (except the signals of Cur6) of the VHF low band fed to the input terminal of the peaking circuit 6 are transmitted to the output terminal through the third capacitor 10, the first capacitor 11, and the fourth capacitor 12.

Further, In the peaking circuit 6, when CH6 of the VHF low band is received, the low-band select voltage V is supplied to the low-band select voltage-supply terminal 21, and further a trapping voltage VTR higher than the lowband select voltage Vg is supplied to the trapping voltage-supply terminal 23. As shown in Fig. 2B, the first switching diode 14 is turned on, and the second switching diode 15 is turned off, causing the first inductor 13 to be connected in parallel to the first capacitor 11, and causing the first inductor 13 to be disconnected from the second capacitor 16. In this case, the parallel-connected circuit of the first capacitor 11 and the first inductor 13 tunes to a higher channel adjacent to CH6 of the VHF low band, i.e., a frequency band 88 to 108 MHz, of an FM radio broadcast and forms a trapping circuit for trapping frequency components of the higher channel adjacent to CH6 when CH6 of the VHF low band is received. Further, the signals of CH6 of the VHF low band, fed to the input terminal of the peaking circuit 6, are transmitted to the output terminal through each of the trapping circuit formed of the third capacitor 10, the first capacitor 11 and the first inductor 13, and the fourth capacitor 13. During this transmission, the frequency components of the higher adjacent channel are eliminated by the trapping circuit.

Furthermore, in the peaking circuit 6, when a VHF hi band is received, a high-band select voltage VH is supplied to the high-band select voltage-supply terminal 22, as shown in Fig. 3, the first switching diode 14 is turned off, and the second switching diode 15 is turned on, causing the second capacitor 16 to be connected to the first inductor 13, thereby forming a peaking circuit formed of the first inductor 13 and the second capacitor 16. In this case, the~peaking circuit performs peaking of the signals of the VHF high band in order to correct the gain of the signals of the VHF high band. The signals of the VHF high band, fed to the input terminal of the peaking circuit 6, are transmitted to the output terminal through each of the third capacitor 10, the first capacitor 11 and the fourth capacitor 12. During this transmission, peaking of the signals of the VHF high band is performed by the peaking circuit in order to correct the gain of the signals of the VHF high band.

The mixing circuit 7 mixes the frequencies of the signals of the VHF low band or the VHF high band, output from the peaking circuit 6, and a local oscillation signal output from the local oscillation circuit 8 in order to form an intermediate frequency (IF) signal, and supplies the signal to an IF signal processing circuit (not shown) connected at the next stage.

As described above, according to this embodiment, in a conventional TV tuner circuit, a trapping circuit section and a peaking circuit section which are disposed individually are shared by one peaking circuit (shared circuit). Therefore, it becomes possible to share a great number of components, making it possible to reduce the number of parts and further to reduce the number of inductors which occupy a large amount of space when mounting to a minimum number (one). Thus, it becomes possible to reduce the mounting area.

Further, according to this embodiment, since the peaking circuit 6 in which a trapping circuit section and a peaking circuit section are shared is provided in a portion having a large signal gain, for example, between the double-tuned circuit 5 and the mixing circuit 7, it is possible to improve the trapping effect.

Although the above-described embodiment describes a case in which a TV tuner circuit for receiving television broadcasting signals of the United States is used as an example, the TV tuner circuit of the present invention is not limited to a TV tuner circuit for receiving television broadcasting signals of the United States and, of course, can be applied to any TV tuner circuit for receiving television broadcasting signals similar to the television broadcasting signals of the United States.

As has been described up to this point, according to the present invention, since a trapping circuit section and a peaking circuit section which are disposed individually in a conventional TV tuner circuit are shared by one peaking circuit (shared circuit), it becomes possible to share a large number of parts and reduce the number of parts. Further, since the number of inductors which occupy a large amount of space when mounting is reduced to the smallest number possible, there are advantages in that the mounting area can be reduced.

Furthermore, according to the present invention, since a peaking circuit in which a trapping circuit section and a peaking circuit section are shared can be disposed in a portion having a large signal gain, there are advantages in that the trapping effect can be improved.

Many different embodiments of the present invention may be constructed without departing from the spirit and scope of the present~invention. It should be understood that the present invention is not limited to the specific embodiment described in this specification. To te contrary, the present invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention as hereafter claimed. The scope of the following claims is to be accorded the broadest Interpretation so as to encompass ail such modifications, equivalent structures and functions.

Claims

1. A TV tuner circuit, comprising: a first capacitor which is connected in series to a signal transmission line; an inductor which is connected in parallel to the first capacitor with a first switching element being provided in series; and a second capacitor connected between said signal transmission line and a ground with each of said inductor and a second switching element being provided in series, wherein only when a specific channel of a VHF low band is received, the first switching element is turned on and the second switching element is turned off, causing said first capacitor and said inductor to be connected in parallel, thereby forming a parallel resonance circuit which resonates to the signals of the higher adjacent band adjacent to said specific channel, and when each channel in a VHF high band is received, the first switching element is turned off and the second switching element is turned on, causing said inductor and said second capacitor to be connected in series, thereby forming a series resonance circuit which resonates to the VHF high band.

2. A TV tuner circuit according to claim 1, wherein said parallel resonance circuit and said series resonance circuit are formed between a double-tuned circuit and a mixing circuit.

3. A TV tuner circuit according to claim 1, wherein said first and second switching elements are each a diode.

4. A TV tuner circuit according to claim 1, wherein said specific channel is a television broadcasting chancel whose frequency band is 82 to 88 MHz, and said higher adjacent band is an FM radio broadcasting band whose frequency band is 88 MRz to 108 MHz.

5. A TV tuner circuit substantially as hereinbefore described with reference to, and as illustrated by, the accompanying drawings.