JP2002290211A - Band switching dual tuning circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably couple a primary tuning circuit with a secondary tuning circuit with less dispersion when the tuning circuit is tuned to a high frequency band and a low frequency band through band switching. SOLUTION: The band switching dual tuning circuit is configured with high band coils 2c, 11c and low band coils 2d, 11d that are connected in series with each other and respectively provided with a primary tuning circuit 2 and a secondary tuning circuit 11 and with a coupling coil 4 that mutually couples the primary tuning circuit 2 and the secondary tuning circuit 11. The band switching dual tuning circuit is also configured such that both terminals of the low band coils 2d, 11d are switched in a short-circuited state or in an open state and the coupling coil 4 electromagnetically couples the primary tuning circuit 2 and the secondary tuning circuit 11 in the short-circuited state and in the open state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a band switching type double tuning circuit used in a television tuner or the like, wherein a tuning frequency is switched between a high frequency side and a low frequency side of a reception frequency band.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional band-switching type double tuning circuit provided between a high frequency amplifier circuit and a mixing circuit of a television tuner, for example. One varactor diode 52
The anode of a is coupled, the cathode is grounded at a high frequency, and this cathode is connected to the tuning voltage terminal Tu. A tuning voltage for changing the capacitance value of the first varactor diode 52a is applied to the tuning terminal Tu. One end of a high-band coil 52b is connected to the anode of the first varactor diode 52a, and one end of a low-band coil 52c is connected to the other end. Then, the other end of the low-band coil 52c is grounded via the coupling coil 53.

A first switch diode 54 is provided between the connection point between the high-band coil 52b and the low-band coil 52c and the ground, the anode of which is coupled to the above-mentioned connection point at high frequency, and the cathode thereof is at high frequency. Grounded. The anode is connected to the switching voltage terminal Hb,
The cathode is connected to the switching voltage terminal Lb.

On the other hand, the anode of the second varactor diode 56a in the secondary tuning circuit 56 is coupled to the output terminal 55, the cathode is grounded at a high frequency, and the cathode is connected to the tuning voltage terminal Tu. The high band coil 5 is connected to the anode of the second varactor diode 56a.
6b is connected to one end, and the other end is connected to one end of a low-band coil 56c. Then, the other end of the low-band coil 56c is grounded via the coupling coil 53.

A second switch diode 57 is provided between the connection point between the high-band coil 56b and the low-band coil 56c and the ground, the anode of which is connected to the connection point at high frequency, and the cathode of which is at high frequency. Grounded. The anode is connected to the switching voltage terminal Hb,
The cathode is connected to the switching voltage terminal Lb.

In the above configuration, the double tuning circuit is
To tune to the high band, a high-level switching voltage is applied to the switching voltage terminal Hb. Then, the switch diodes 54 and 57 are turned on, and the connection point between the high-band coil 52b and the low-band coil 52c in the primary tuning circuit 52 and the connection point between the high-band coil 56b and the low-band coil 56c in the secondary tuning circuit 56 have a high frequency. Grounded. As a result, the low-band coils 52c and 56c and the coupling coil 53
The primary tuning circuit 52 is constituted by a first varactor diode 52a and a high band coil 52b, and the secondary tuning circuit 56 is constituted by a second varactor diode 56a and a high band coil 56b. The coupling between the tuning circuits 52 and 56 is obtained by adjusting the physical distance between the high band coils 52b and 56b.

On the other hand, when tuning to the high band of the VHF band, a high-level switching voltage is applied to the switching voltage terminal Lb. Then, the switch diodes 54 and 57 are turned off, and the high-band coil 5
A low-band coil 52c is added in series to 2b, and a low-band coil 56c is added in series to the high-band coil 56b in the secondary tuning circuit 56. The coupling between the primary tuning circuit 52 and the secondary tuning circuit 56 is appropriately set by the coupling coil 53 connected to each of the low band coils 52c and 56c.

[0008]

SUMMARY OF THE INVENTION However, VHF
When tuned to the high band of the band, the high-band coils to be coupled to each other are hardly coupled to each other due to the small inductance value, and the coupling of the high-band coils due to the variation in the physical positional relationship and the variation in the shape and dimensions of each high-band coil. The strength also varied, and it was difficult to obtain accurate double tuning characteristics. In particular, on the low frequency side of the same tuning frequency band, the coupling becomes weak, and the tuning characteristics (response) become steep, so that a desired bandwidth cannot be sufficiently obtained and the image is susceptible to image disturbance.

In view of the above, it is an object of the present invention to stably couple a primary tuning circuit and a secondary tuning circuit when tuning to a high frequency band and a low frequency band by band switching with little variation. .

[0010]

Means for Solving the Problems To solve the above problems,
A high-band coil and a low-band coil provided in the primary tuning circuit and the secondary tuning circuit, respectively; and a coupling coil that couples the primary tuning circuit and the secondary tuning circuit to each other. Then, both ends of each of the low-band coils are configured to be switched to a short-circuited state or a non-short-circuited state, and in both the short-circuited state and the non-short-circuited state, the primary tuning circuit and the secondary tuning circuit are formed by the coupling coil. Were electromagnetically coupled to each other.

Also, one end of each of the low-band coils is grounded via the coupling coil, and the other end is connected to each of the high-band coils, and a first switch diode is connected in parallel to one of the low-band coils. The second switch diode was connected in parallel to the other low-band coil, and both the first and second switch diodes were turned on or off.

Further, one end of each of the low-band coils is grounded via the coupling coil, and the other end is connected to each of the high-band coils. One switch diode is connected, a second switch diode is connected between a connection point between the low band coil and the coupling coil and one end of the first switch diode, and the first and second switch diodes are connected. Were turned on or off together.

Further, the anode of the second switch diode is connected to the cathode of the first switch diode.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIG. A television signal output from a high-frequency amplifier circuit (not shown) is input to the input terminal 1. An anode of a first varactor diode 2a in the primary tuning circuit 2 is coupled to the input terminal 1 via a coupling capacitor 3, a cathode of which is grounded at high frequency by a DC cut capacitor 2b, and a cathode of which is connected to the first varactor diode 2b. 2a is connected to a tuning voltage terminal Tu to which a tuning voltage for changing the capacitance value of 2a is applied. The DC cut capacitor 2b exhibits a low impedance in high frequency, and the same applies to a DC cut capacitor described below. One end of a high-band coil 2c is connected to the anode of the first varactor diode 2a, and one end of a low-band coil 2d is connected to the other end. Then, the other end of the low band coil 2 d is grounded via the coupling coil 4.

An anode of a first switch diode 6 is connected to a connection point between the high band coil 2c and the low band coil 2d via a DC cut capacitor 5, and the cathode thereof is connected to the low band coil 2d and the coupling coil by a DC cut capacitor 7. 4 is connected to the connection point. The anode is connected to the switching voltage terminal Hb, the cathode is grounded via the bias resistor 8 and the feed resistor 9
Is connected to the switching voltage terminal Lb.

On the other hand, an anode of a second varactor diode 11a in the secondary tuning circuit 11 is connected to an output terminal 10 connected to a mixing circuit (not shown) by a coupling capacitor 12, and its cathode is connected to a high frequency by a DC cut capacitor 11b. The cathode is connected to a tuning voltage terminal Tu. One end of a high band coil 11c is connected to the anode of the second varactor diode 11a, and the low band coil 11d is connected to the other end.
Are connected at one end. And the low band coil 11d
Is grounded via the coupling coil 4.

An anode of a second switch diode 14 is connected to a connection point between the high band coil 11c and the low band coil 11d via a DC cut capacitor 13, and a cathode thereof is connected to a cathode of the first switch diode 6. You. The anode is a switching voltage terminal Hb
Connected to.

In the above configuration, the double tuning circuit is
When tuning to the high band, the switching voltage terminal Hb
Is applied with a high-level switching voltage. Then, the first and second switch diodes 6 and 14 are turned on, and both ends of the low-band coil 2d in the primary tuning circuit 2 and both ends of the low-band coil 11d in the secondary tuning circuit 11 are short-circuited. As a result, the other ends of the high band coils 2c and 11c are grounded via the coupling coil 4 in terms of high frequency. The coupling coil 4 electromagnetically couples the primary tuning circuit 2 and the secondary tuning circuit 11 to form a double tuning circuit.
Is determined by the constant setting.

On the other hand, when tuning to the low band of the VHF band, a high-level switching voltage is applied to the switching voltage terminal Lb. Then, the first and second switch diodes 6, 14 are turned off, and the low-band coil 2d is added in series to the high-band coil 2c in the primary tuning circuit 2,
In the secondary tuning circuit 11, a low band coil 11d is added in series to the high band coil 11c. The coupling between the primary tuning circuit 2 and the secondary tuning circuit 11 is appropriately obtained by the coupling coil 4 connected to each of the low-band coils 2d and 11d.

Although not shown, the cathodes of the first and second switch diodes 6 and 14 are connected directly to the connection points between the other ends of the low-band coils 2d and 11d and the coupling coil 4 to cut the direct current. The capacitor 7, the bias resistor 8, the power supply resistor 9, and the switching voltage terminal Lb can be eliminated.

As described above, in the present invention, when tuning to the high frequency band, each low band coil 2
Since both ends of d and 11d are short-circuited and the primary tuning circuit 2 and the secondary tuning circuit 11 are coupled by the coupling coil 4, the coupling is insufficient even when switching to tune to a high frequency band. In addition, variations in coupling due to variations in shape of the high-band coils 2b and 11b are eliminated.

FIG. 2 shows a configuration of another embodiment, in which each varactor diode 2a, 11a and each high-band coil 2e, 11e in the primary and secondary tuning circuits 2, 11 are provided.
The interconnection between the low-band coils 2d and 11d and the coupling coil 4 is the same as the configuration shown in FIG. 1, but the connection between the first and second switch diodes 6 and 14 is different.

That is, the first switch diode 6 is connected to the connection point between the high band coil 2c and the low band coil 2d in the primary tuning circuit 2 and the high band in the secondary tuning circuit 11 by the DC cut capacitors 21 and 22 connected to both ends thereof. Coil 11c and low band coil 11
It is connected between the connection points with d. Then, the anode of the first switch diode 6 is connected to the switching voltage terminal Hb. Further, the anode of the second switch diode 14 is connected to the cathode of the first switch diode 6, and the cathode is connected to the connection point between the two low-band coils 2 d and 11 d and the coupling coil 4.

In the configuration of FIG. 2, the switching voltage terminal Hb
When a high-level switching voltage is applied to both the first and second switching diodes 6 and 14, both ends of the two low-band coils 2 d and 11 d are short-circuited.
If no switching voltage is applied, the switch diodes 6 and 14 remain off, so that the low-band coil 2
d and 11d are not short-circuited. Therefore, switching is performed so as to tune to the high band and the low band as in the configuration of FIG. Since a common current flows through the two switch diodes 6 and 14, the current consumption is reduced by half with respect to the configuration of FIG.

[0025]

As described above, both ends of each low-band coil of the primary and secondary tuning circuits are configured to be switched to a short-circuit state or a non-short-circuit state, and the coupling coil is switched in both the short-circuit state and the non-short-circuit state. Because the primary tuning circuit and the secondary tuning circuit are electromagnetically coupled to each other, there is no shortage of coupling even when switching to tune to a high frequency band, and the shape of each high-band coil Variations in coupling due to dimensional variations and the like are eliminated.

Also, one end of each low-band coil is grounded via a coupling coil, each other end is connected to a respective high-band coil, and one low-band coil is connected in parallel with a first switch diode. A second switch diode was connected in parallel to the other low-band coil, and both the first and second switch diodes were turned on or off, so each low-band coil was switched only when tuned to a higher frequency band. The coil can be excluded from each tuning circuit.

Also, one end of each low band coil is grounded via a coupling coil, the other end is connected to each high band coil, and a first switch is provided between each connection point between the low band coil and the high band coil. Connect a diode,
The second switch diode was connected between the connection point between the low-band coil and the coupling coil and one end of the first switch diode, and both the first and second switch diodes were turned on or off. Only when switching to tune to the frequency band, each low-band coil can be excluded from each tuning circuit.

Further, since the anode of the second switch diode is connected to the cathode of the first switch diode, a common current flows through the two switch diodes, so that the current consumption is reduced by half.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a band switching type double tuning circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of another embodiment of the band switching type double tuning circuit of the present invention.

FIG. 3 is a circuit diagram showing a configuration of a conventional band switching type double tuning circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input terminal 2 Primary tuning circuit 2a First varactor diode 2b DC cut capacitor 2c High band coil 2d Low band coil 3 Coupling capacitor 4 Coupling coil 5 DC cut capacitor 6 First switch diode 7 DC cut capacitor 8 Bias resistor 9 Feeding resistance Reference Signs List 10 output terminal 11 secondary tuning circuit 11a second varactor diode 11b DC cut capacitor 11c high band coil 11d low band coil 12 coupling capacitor 13 DC cut capacitor 14 second switch diode 21, 22 DC cut capacitor

Claims (4)

[Claims] 1. A high-band coil and a low-band coil respectively connected in series and provided in a primary tuning circuit and a secondary tuning circuit, respectively, and the primary tuning circuit and the secondary tuning circuit are coupled to each other. Having a coupling coil, both ends of each of the low-band coils are configured to be switched to a short-circuited state or a non-short-circuited state, and in both the short-circuited state and the non-short-circuited state, the primary tuning circuit and the A band switching type double tuning circuit characterized in that a secondary tuning circuit is electromagnetically coupled to each other. 2. One end of each low-band coil is grounded via the coupling coil, and the other end is connected to each high-band coil. A first switch diode is connected in parallel to one of the low-band coils. The band switching according to claim 1, wherein a second switch diode is connected in parallel to the other low band coil, and both the first and second switch diodes are turned on or off. Type double tuning circuit. 3. One end of each of the low-band coils is grounded via the coupling coil, and the other end is connected to each of the high-band coils. A third terminal is connected between each connection point between the low-band coil and the high-band coil. One switch diode is connected, a second switch diode is connected between a connection point between the low band coil and the coupling coil and one end of the first switch diode, and the first and second switch diodes are connected. 2. The band-switchable double-tuned circuit according to claim 1, wherein both are turned on or off. 4. The band switching double-tuned circuit according to claim 3, wherein an anode of said second switch diode is connected to a cathode of said first switch diode.