MXPA00011629A - Switchable band filter - Google Patents

Abstract

In a secondary tuning circuit, a capacitor (40) is provided between a connection point between a direct-current blocking capacitor (33) and a tuning coil (34) and a connection point between a varactor diode (37) and another direct-current blocking capacitor (38). The capacitor (40), another tuning coil (32) and the varactor diode (37) form a trap circuit. As a result, it is possible to prevent a frequency selection characteristic of the multiple-tuning circuit from deteriorating due to an undesired new tuning circuit formed by a static capacitance generated in a non-conductive state of the switch diode (41).

Description

MULTI-TUNING CIRCUIT FOR A TUNER CAPABLE OF PREVENTING THE DETERIORATION OF THE CHARACTERISTIC OF SELECTION BACKGROUND OF THE INVENTION FIELD OF THE INVENTION In general, the present invention relates to a multiple tuning circuit used in a tuner capable of changing a tuning frequency between a variety of frequency bands by switching a switch diode on and off. More particularly, the present invention relates to a multiple tuning circuit used in a tuner capable of preventing the frequency selection characteristic thereof from deteriorating due to a new unwanted tuning circuit formed by a static capacitance generated in a non-conducting state of a switch diode.

DESCRIPTION OF THE RELATED ART 20 A multiple tuning circuit used in the conventional tuner is explained by referring to Figures 4, 5, 6 and 7. As shown in Figure 5, the tuning circuit comprises a circuit of fcSi »3 - h ---« Í - 3 »» primary tuning 51 and a secondary tuning circuit 52. The first tuning circuit 51 includes a series circuit of a direct current blocking capacitor 53 and a diode varactor 54. The first tuning circuit 51 also includes another series circuit of a tuning coil 55 for high band reception, a tuning coil 56 for lower band reception, a resistor 57, a coupling coil 58 and a capacitor Direct current blocking 59, which are connected to each other in the order shown in the figure. The series circuit and the other series circuit form a parallel circuit. The anode and the cathode of the varactor diode 54 are connected to ground and to the direct current blocking capacitor 53 respectively. The other terminal of the direct current blocking capacitor 59 is also connected to ground. The connection point between the direct current blocking capacitor 53 and the tuning coil 55 for high-band reception serves as the input terminal of the multi-tuning circuit. This input terminal is connected to a high frequency amplifier 60 in the next step. A series circuit comprising a direct current blocking capacitor 61, a switching diode 62 and a direct current blocking capacitor 63 is connected between the connection point between the tuning coil 55 for high-band reception and the coil of tuning 56 for receiving lower band and ground. In this series circuit, the anode and cathode of the switch diode 62 are connected to the direct current blocking capacitor 61 and the direct current blocking capacitor 63 respectively. The connection point between the direct current blocking capacitor 61 and the switch diode 62 is connected to a switching terminal 65 for high-band reception via a power-supply resistor 64. The connection point between the switching diode 62 and the direct current blocking capacitor 63 is connected to a switching terminal 67 for lower band reception through a power supply resistor 10 66. In addition, the connection point between the switching diode 62 and the current blocking capacitor direct 63 is connected to ground through a bias resistor 68. The connection point between the varactor diode 54 and the direct current blocking capacitor 53 is connected to a tuning voltage terminal 70 through a feeder resistor of power 69. The second tuning circuit 52 includes a parallel circuit comprising a varactor diode 71 and a series circuit. The series circuit comprises a tuning coil 72 for high band reception, 20 a tuning coil 73 for receiving lower band, a resistor 74, a direct current blocking capacitor 75, the coupling coil 58 and the capacitor direct current blocking 59, which are connected to each other in the order shown in the figure. The anode and the cathode of iiuiÉliaiwiifc varactor diode 71 are connected to ground and to the tuning coil 72 for high band reception respectively. The connection point between the varactor diode 71 and the tuning coil 72 for high-band reception is connected to a series circuit of a varactor diode 76 and a direct current blocking capacitor 77. The anode and the cathode of the varactor diode 76 are connected to the direct current blocking capacitor 77 and the tuning coil 72 for high-band reception respectively. The other end of the direct current blocking capacitor 77 is connected to an output terminal of the multiple tuning circuit. The output terminal is connected to a mixer 78 in the next step. In the mixer 78, an oscillation signal generated by an oscillator that is not shown in the figure is mixed with a signal output from the multiple tuning circuit to produce an intermediate frequency signal. A series circuit of a direct current blocking capacitor 79 and a switching diode 80 are provided between the connection point of the tuning coils 72 and 73 and the connection between the intercurrent diode 62 and the direct current blocking capacitor. 63. The anode and cathode of the switch diode 80 are connected to the direct current blocking capacitor 79 and to the direct current blocking capacitor 63. The connection point between the direct current blocking capacitor 79 and the switching diode 80 is connect to the switch terminal 65 for high band reception through a power feeder resistor 81.

----- • '--- On the other hand, the connection point between the direct current blocking capacitor 63 and the switch diode 80 is connected to a switching terminal 67 for receiving lower band through a feeder resistor 66. The connection point between the tuning coil 72 for high-band reception and the varactor diode 71 is connected to the tuning voltage terminal 70 via a power-supply resistor 82. In the configuration described above, when a voltage is applied to the terminal 65 for high band reception, the switching diodes 62 and 80 are put in the conductive state. When a voltage is applied to the terminal 67 for lower band reception, on the other hand, the switching diodes 62 and 80 are put in a non-conductive state. In this way, the multiple tuning circuit can be changed from a high band reception state to a lower band reception state or vice versa. It is worth mentioning that, in order to change the multiple tuning circuit of a tuner shown in Figure 5 to a state of reception of high-band television signals each having, for example, a frequency on the scale of 170 MHz to 222 MHz, a generally 5V voltage is applied to terminal 65 for high band reception and voltage is not applied to terminal 67 for lower band reception. With a voltage of 5V applied to terminal 65 for high band reception, a voltage is applied to the switching diodes 62 and 80 in the forward direction, connecting both switching diodes 62 and 80 in a conducting state. In this -i-i-i-i-i-i - ^. i - ^^ - M- -ÍBJHWllM ^ - - ™ llll I '- - - • - - - - • - - -' -. ,. . ,. , -. . ,, F, ^ .-. F, .. . conductor state, the connection point between the tuning coil 55 for high band reception and the tuning coil 56 for lower band reception as well as the connection point between the tuning coil 72 for high band reception and the coil tuning 73 for lower band reception are connected to ground. As a result, the varactor diode 54 and the tuning coil 55 for high band reception in the first tuning circuit 51 form a parallel circuit. Similarly, the varactor diode 71 and the tuning coil 72 for high band reception in the second Tuning circuit 52 also form a parallel circuit. The high frequency equivalent circuit that results in this state is a multiple tuning circuit shown in Fig. 6 characterized in that direct current blocking capacitors and resistors are ignored. The desired tuning frequency can be obtained by adjusting the ratings applied to the varactor diodes 54 and 71. In order to change the multi-tuning circuit of a tuner shown in FIG. 5 to a state of reception of lower-band television signals having each, for example, a frequency in the range of 90 MHz to 108 MHz, a generally 5V voltage is applied to terminal 67 for lower band reception and no voltage is applied to terminal 65 for high band reception. With a voltage of 5V applied to terminal 67 for lower band reception, a voltage is applied to the switching diodes 62 and 80 in a backward direction, putting both switching diodes 62 and 80 in a non-conductive state. As a result, the varactor diode 54, the tuning coil 55 for high band reception, the tuning coil 56 for lower band reception and the coupling coils 58 in the first tuning circuit 51 form a parallel tuning circuit, which In the following, it will be called a main tuning circuit. Similarly, the tuning coil 72 for high band reception, the tuning coil 73 for lower band reception, the coil 58 and the varactor diode 71 in the second tuning circuit 52 also form a parallel tuning circuit. A desired tuning frequency can be obtained by adjusting the voltages applied to the varactor diodes 54 and 71. It should be mentioned that, with the multiple tuning circuit switched to a state of reception of lower band television signals, a voltage is applied to the diodes switches 62 and 80 in the backward direction. In general, when a voltage is applied to a diode in a backward direction, a capacitance of approximately 0.2 pF is typically generated between the terminals. If the capacitance generated between the terminals of the switch diode 62 by the voltage applied in the backward direction and the capacitance generated between the terminals of the switch diode 80 by the voltage applied in the backward direction are equivalent to the capacitance of a capacitor 83, a circuit High frequency equivalent of multiple tuning circuit, put in this state, is a multiple tuning circuit shown in Fig. 7 characterized in that direct current blocking capacitors and resistors are ignored.

As shown in Figure 7, due to the existence of a capacitor 83, the varactor diode 54, the tuning coil 55 for high band reception and the capacitor 83 in the first tuning circuit 51 as well as the varactor diode 71, the tuning coil 72 for high-band reception and the capacitor 83 in the second tuning circuit 52 form a new tuning circuit 84, hereinafter called a parasitic tuning circuit apart from the main tuning circuit. The tuning frequency of the parasitic tuning circuit 84 is a different frequency from the first tuning circuit 51 and the second tuning circuit 52. Assume, for example, that the desired tuning frequency of the main tuning circuit is 127 MHz. in this case, the tuning frequency of parasitic tuning circuit 84 appears in a UHF band on the scale of 600 to 700 MHz. In this way, the multiple tuning circuit in the lower band reception state shows a selection characteristic of frequency as shown by a solid line in figure 4. As shown in the figure, the characteristic also has a cusp representing a tuning sequence produced by the parasitic tuning circuit 84 as shown in an EJ portion in the figure next to a cusp that represents a tuning frequency produced by the synth circuit main display as shown in a portion A in the figure. A signal having a frequency in the tuning frequency tuning circuit scale 84 is supplied to a mixer 78, which is connected to the output terminal of this multiple tuning circuit. The mixer 78 mixes the input signal generated by the parasitic tuning circuit 84 with an oscillation signal to generate a signal with an intermediate frequency in the range of 54 MHz to 60 MHz. The mixing process also produces a by-product signal with a frequency equal to the difference between the frequency of the signal at the tuning frequency by the parasitic tuning circuit 84 and N times the frequency of the oscillating signal or equal to the sum of the frequency of the signal at the tuning frequency by the parasitic tuning circuit 84 and N times the frequency of the oscillation signal. This by-product signal acts as an interruption to the intermediate frequency signal. For example, when the desired tuning frequency of the main tuning circuit is 127 MHz, the tuning frequency of the oscillation signal is 182 MHz, which is greater than the desired tuning frequency of the main tuning circuit by 57 MHz. The mixer 78 emits a signal with an intermediate frequency of 57 MHz, which is equal to the difference between the tuning frequency of 609 MHz of the input signal generated by the parasitic tuning circuit 84 and a frequency of 552 MHz, which is equal to N times the frequency of 184 MHz of the oscillation signal where N = 3.

BRIEF DESCRIPTION OF THE INVENTION Thus, the purpose of the present invention is to attack the problems described above to provide a tuning multiple circuit of a tuner showing an optimum frequency selection characteristic obtained as a result of the elimination of an effect of a new tuning circuit parasitic formed by a static capacitance created by a non-conducting state of a switch diode in the lower band receiving state of the multiple tuning circuit. In order to solve the problems described above, the present invention provides a multiple tuning circuit of a tuner, the circuit comprising a primary tuning circuit and a secondary tuning circuit characterized in that: the secondary tuning circuit includes: a first Varactor diode; a series circuit of a first coil for receiving high band and a second coil for receiving lower band, with the series circuit connected in parallel to the first varactor diode; a switch diode connected between ground and a connection point between the first coil and the second coil; a second varactor diode with one of its ends connected to a connection point between the first coil and the first varactor diode; and a capacitor connected between the other end of the second varactor diode and a connection point between the first coil and the second coil, in parallel to a circuit of the second varactor diode and the first coil, the other end of the second varactor diode is used as an output terminal of the multiple tuning circuit; in the first coil, the second varactor diode and the capacitor form a eliminator circuit. In a multiple tuning circuit of a tuner, the capacitance of the capacitor is adjusted to a value approximately equal to the capacitance between terminals of the switching diode in a non-conductive state.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing a multiple tuning circuit of a tuner provided by the present invention; Figure 2 is a diagram showing an equivalent circuit of the multiple tuning circuit of a tuner provided by the present invention in a high band reception state; Figure 3 is a diagram showing an equivalent circuit of the multiple tuning circle of a tuner provided by the present invention in a lower band receiving state; Fig. 4 is a diagram showing the frequency selection feature of a multiple tuning circuit of the conventional tuner and the multiple tuning circuit of a tuner provided by the present invention in a lower band receiving state; Figure 5 is a diagram showing the multiple tuning circuit of the conventional tuner; Figure 6 is a diagram showing an equivalent circuit of the multiple tuning circuit of the conventional tuner in a high band reception state; and Figure 7 is a diagram showing an equivalent circuit of the multiple tuning circuit of the conventional tuner in a lower band reception state.

DETAILED DESCRIPTION OF THE PREFERRED MODALITY A preferred embodiment implementing a multi-tuning circuit of a tuner provided by the present invention is described with reference to FIGS. 1 to 4. FIG. 1 is a diagram showing a multiple tuning circuit of a tuner provided by the tuner. present invention. As shown in the figure, the tuning circuit comprises a primary tuning circuit 11 and a secondary tuning circuit 12. The first tuning circuit 11 includes a series circuit of a direct current blocking capacitor 13 and a varactor diode. 14. The first tuning circuit 11 also includes another series circuit of a tuning coil 15 for high band reception, a tuning coil 16 for lower band reception, a resistor 17, a coupling coil 18 and a capacitor of Direct current blocking 19, which are connected to each other in the order shown in the figure. The series circuit and the other series circuit form a parallel circuit. The anode and the cathode of the varactor diode 14 are connected to ground and to the direct current blocking capacitor 13 respectively. The other terminal of the direct current blocking capacitor 19 is also connected to ground. The connection point between the direct current blocking capacitor 13 and the tuning coil 15 serves as an input terminal of the multiple tuning circuit. This input terminal is connected to a high frequency amplifier 20 in the next stage. A series circuit comprising a direct current blocking capacitor 21, a switching diode 22 and a direct current blocking capacitor 23, is connected between the connection point between the tuning coil 15 for high-band reception and the coil of tuning 16 for receiving lower band and ground. In this series circuit, the anode and the cathode of the switch diode 2 ?. they are connected to the direct current blocking capacitor 21 and the direct current blocking capacitor 23 respectively. This connection point between the direct current blocking capacitor 21 and the switching diode 22 is connected to a switching terminal 25 for high-band reception by means of a power-supply resistor 24.

The connection point between the switching diode 22 and the direct current blocking capacitor 23 is connected to a switching terminal 27 for receiving lower band by means of a power supply resistor 26. In addition, the connection point between the switching diode 22 and the direct current blocking capacitor 23 is connected to ground by means of a bias resistor 28. The connection point between the varactor diode 14 and the direct current blocking capacitor 13 is connected to a tuning voltage terminal 30 by means of a power-supply resistor 29. The second tuning circuit 12 includes a parallel circuit comprising a first varactor diode 31 and a series circuit. The series circuit comprises a first tuning coil 32 for high band reception, a direct current blocking capacitor 33, a second tuning coil 34 for receiving lower band, a resistor 35, a direct current blocking capacitor 36, the coupling coil 18 and the direct current blocking capacitor 19, that connect to each other in the order shown in the figure. The anode and cathode of the varactor diode 31 are connected to ground and to the tuning coil 32 for high band reception respectively. The connection point between the varactor diode 31 and the tuning coil 32 for high band reception is connected to a series circuit of a second varactor diode 37 and a direct current blocking capacitor 38. The anode and the cathode of the diode varactor 37 are connected to the direct current blocking capacitor 38 and to the tuning coil 32 for high-band reception respectively. The other end of the direct current blocking capacitor 38 is connected to an output terminal of the multiple tuning circuit. The output terminal is connected to a mixer 39 in the next stage. In the mixer 39, an oscillation signal generated by an oscillator not shown in the figure is mixed with a signal output by the multiple tuning circuit to produce an intermediate frequency signal. A capacitor 40 connects a connection point between the direct current blocking capacitor 33 and the tuning coil 34 for high-band reception to a connection point between the varactor diode 37 and the direct current blocking capacitor 38. A diode switch 41 is used to connect a connection point between the direct current blocking capacitor 33 and the tuning coil 34 for high band reception to a connection point between the switching diode 22 and the blocking capacitor d) direct current 23 The anode of the switch diode 41 is connected to the connection point between the direct current blocking capacitor 33 and the tuning coil 34 for high band reception. On the other hand, the cathode of the switch diode 41 is connected to the connection point between the switch diode 22 and the direct current blocking capacitor 23.

It should be noted that the capacitance of the capacitor 40 is adjusted to a value approximately equal to the capacitance between terminals of the switch diode 41 in a non-conductive state. The anode of the switch diode 41 is connected to a switching terminal 25 for high band reception by means of a power-supply resistor 42. On the other hand, the cathode of the switching diode 41 is connected to a switching terminal 27 for band reception The connection point between the tuning coil 32 for high-band reception and the varactor diode 31 is connected to the tuning voltage terminal 30 by means of a power-supply resistor. power 43. In the configuration described above, when a voltage is applied to terminal 25 for high band reception, the switching diodes 22 and 41 are each placed in the conductive state. When a voltage is applied to the terminal 27 for reception of the lower band, on the other hand, the switching diodes 22 and 41 are each placed in a non-conductive state. In this way, the multiple tuning circuit can be changed from a high band reception state to a lower band reception state or vice versa. It is worth mentioning that, in order to change the multiple tuning circuit of a tuner shown in Fig. 1 to a state ? t. *, # & * »*** ¿-. 4 i,,,: .-. . i, »> . *,, > tofc ^ of reception of high-band television signals each having, for example, a sequence on the scale of 170 MHz to 222 MHz, a voltage of typically 5 V is applied to terminal 25 for high-band reception and is not applies voltage to terminal 27 for lower band reception. With a voltage of 5 V applied to terminal 25 for high band reception, a voltage is applied to the switching diodes 22 and 41 in the forward direction by putting both switching diodes 22 and 41 in the conducting state. In this conductive state, the connection point between the tuning coil 15 for high-band reception and the tuning coil 16 for receiving the lower band and the connection point between the direct-current blocking capacitor 33 and the tuning coil 34 for high band reception are connected to ground. As a result, the varactor diode 14 and the tuning coil 15 for high band reception in the first tuning circuit 11 form a parallel circuit. Similarly, the varactor diode 31 and the tuning coil 32 for high band reception in the second tuning circuit 12 also form a parallel circuit. A high frequency equivalent circuit resulting in this state is a multiple tuning circuit shown in Fig. 2 characterized in that direct current blocking capacitors and resistors are ignored. By adjusting the voltages applied to the varactor diodes 14 and 31, a desired tuning frequency can be obtained. In addition, the varactor diode 37 and the capacitor 40 form a scavenger circuit.

In order to change the multiple tuning circuit of a tuner shown in Fig. 1 to a state of reception of lower band television signals each having, for example, a frequency in the range of 90 MHz to 180 MHz, it applies a voltage of typically 5 V to terminal 27 for lower band reception and no voltage is applied to terminal 25 for high band reception. With a voltage of 5 V applied to the terminal 27 for lower band reception, a voltage is applied to the switch diode 22 and the switch diode 41 in a backward direction, putting both the switch diode 22 and the switch diode 41 in a non-switched state. driver. As a result, the varactor diode 14, the tuning coil 15 for high band reception, the tuning coil 16 for lower band reception and the coil 18 in the first tuning circuit 11 form a parallel tuning circuit, which will be called in the following main tuning circuit. Similarly, the tuning coil 32 for high-band reception, the tuning coil 35 for high-band reception, the coil 18 and the varactor diode 31 in the second tuning circuit 12 also form a parallel tuning circuit. By adjusting the voltages applied to the varactor diodes 14 and 31, a desired tuning frequency can be obtained. It should be mentioned that, with the multiple tuning circuit switched to a lower band television signal reception state, a voltage is applied to the switch diode 22 and the switch diode 41 in the backward direction. In general, when voltage is applied to a diode in the backward direction, a capacitance of approximately 0.2 pF is generated between the terminals. If the capacitance generated between the terminals of the switch diode 22 by the voltage applied in the backward direction and the capacitance generated between the terminals of the switch diode 41 by the applied voltage in the backward direction are equivalent to the capacitance of the capacitor 44, an equivalent circuit High frequency of the multiple tuning circuit set in this state is a multiple tuning circuit shown in Figure 3 characterized in that direct current blocking capacitors and resistors are ignored. As shown in Figure 3, due to the existence of a capacitor 44, the varactor diode 14, the tuning coil 15 for high band reception and the capacitor 44 in the first tuning circuit 11 as well as the varactor diode 31, the tuning coil 32 for high-band reception and the capacitor 44 in the second tuning circuit 12 form a new tuning circuit 45, hereinafter called a parasitic tuning circuit apart from the main tuning circuit. The tuning frequency of the parasitic tuning circuit 45 is a different frequency to the first tuning circuit 11 and to the second tuning circuit 12. When the desired tuning frequency of the main tuning circuit is 127 MHz for example, the tuning frequency of the parasitic tuning circuit 45 appears in a UHF band on the scale of 600 to 700 MHz.

However, by providing the capacitor 40, the tuning coil 32 for high-band reception, the varactor diode 37 and the capacitor 40 in the secondary tuning circuit 12 form a new tuning circuit 46, hereinafter referred to as the elimination circuit apart from the main tuning circuit 5. The capacitances of the capacitor 40 and the varactor diode 31 are set equal to those of the capacitor 44 and the varactor diode 37 respectively. In addition, by sharing the tuning coil 32 for high band reception, the eliminator circuit 46 and the parasitic tuning circuit 45 have tuning frequencies equal to each other.

In this way, the multiple tuning circuit in the lower band reception state shows a frequency selection characteristic as shown by the dotted line in FIG. 4. As shown in the figure, with the main tuning circuit having a tuning frequency of 127 MHz, the cusp on the frequency scale of 600 to 700 MHz generated by the parasitic tuning circuit in the conventional configuration almost disappears. As a result, the mixer 39 does not generate an interruption signal. It should be noted that, in the multi-tuning circuit in high-band reception state, a knock-out effect caused by the varactor diode 37 and the capacitor 40 shown in FIG. 2 raises the Q of the secondary tuning circuit 12, making the frequency selection characteristic curve more acute. As a result, the mixed modulation feature also improves. and ^^^^^ E * ^ & & 3 As described above, in accordance with the present invention, in a lower band receiving state, when again providing a capacitor, a tuning coil for high band reception , a varactor diode and the capacitor form a eliminating circuit. It is thus possible to eliminate a cusp of frequency characteristic caused by a parasitic tuning circuit again formed by a capacitance between the terminals of a switch diode in a non-conductive state. As a result, the interruption to the signal with an immediate frequency can be eliminated. Furthermore, in accordance with the present invention, in a state of lower-band reception, the newly provided capacitor and the varactor diode result in a eliminating effect, which raises the Q of the secondary tuning circuit, making the frequency selection feature. As a result, the mixed modulation feature also improves. Further, in accordance with the present invention, by adjusting the capacitance of the newly provided to a value approximately equal to the capacitance between terminals of a switch diode in a non-conducting state, the tuning frequency of the eliminating circuit can be made equal to that of the parasitic tuning circuit.

Claims (2)

NOVELTY OF THE INVENTION CLAIMS

1. - A multiple tuning circuit of a tuner, comprising the circuit, a primary tuning circuit and a secondary tuning circuit characterized in that: the secondary tuning circuit includes: a first varactor diode; a series circuit of a first coil for reception of high band and a second coil for reception of lower band, with the series circuit connected in parallel to the first varactor diode; a switch diode connected between ground and a connection point between the first coil and the second coil; a second varactor diode with one of its ends connected to a connection point between the first coil and the first varactor diode; and a capacitor connected between the other end of the second varactor diode and a connection point between the first coil and the second coil in parallel to a circuit of the second varactor diode and the first coil, the other end of the second varactor diode is used as a output terminal of the multiple tuning circuit; and the first coil, the second varactor diode and the capacitor form a eliminator circuit.

2. A multiple tuning circuit of a tuner according to claim 1, further characterized in that the capacitance of the capacitor is adjusted to a value approximately equal to the capacitance between the terminals of the interrupting diode in a non-conductive state.