JP2930806B2 - Tuner circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tuner circuit used in a high-frequency circuit device such as a television receiver or a video tape recorder, and more particularly to an input circuit for switching a receiving band using a switching diode. And a tuner circuit.

[0002]

2. Description of the Related Art A conventional tuner circuit will be described with reference to FIGS. In the case of a normal VHF tuner, the frequency range cannot be covered only by the capacitance change of the variable capacitance diode VD1, so that a high-band coil and a low-band coil are provided on each of the hot side and the ground side, and a switching diode D2 for band switching is provided.
D3 is provided and the inductance is varied by ON / OFF to cope with this. Here, L3 is a hot side low band coil, L4 is a hot side high band coil, while L1 is a low band coil and L2 is a high band coil on the earth side.

When a low band is selected, when a positive voltage is applied to the low band power supply terminal BL, a voltage divided by the bias resistors R1 and R2 is applied to the cathodes of the switching diodes D1 and D2, and both switching diodes become non-conductive. As shown in FIG. 6A, both the hot side and the ground side have a high band coil and a low band coil connected in series. However, since the high-band coil is much smaller than the low-band coil, the tuning circuit uses the hot-side low-band coil L3 as shown in FIG.
And a low-band coil L1 on the ground side, a capacitance VC of the variable capacitance diode VD1 and an additional capacitance C constituted by an input capacitance of the transistor Q1 and the like.

When the high band is selected, the switching diode D is opened by opening the low band power terminal BL and applying a positive voltage to the high band power terminal BH.
2, a forward voltage is applied to D3, and it becomes conductive. Therefore, as shown in FIG. 6C, on the hot side, the low-band coil L3 is canceled by the coupling capacitor C5 and the switching diode D3, and the series resistance RD3 of the switching diode D3 and the high-band coil L4 are connected in series. Becomes Similarly, on the ground side, the series resistance RD2 of the diode D2 and the high-band coil L2 are connected in series.

Therefore, when the high band is selected, FIG.
As shown in the figure, the coil is composed of a hot-side high-band coil L4 and a resistor Rc connected in series thereto, a ground-side high-band coil L2 and a capacitor VC and an additional capacitor C formed by a variable-capacitance diode VD1 and an Rb connected in series thereto. A single tuning circuit is obtained.

An FET is connected to the transistor Q1 of the high frequency amplification stage.
In a tuner circuit using (field-effect transistors) and selecting a signal by switching between high band and low band, the gain in the low band is larger than the gain in the high band due to the characteristics of the FET. .
In order to eliminate the gain difference, a damping resistor R3 is connected between a connection point between the hot side low band coil L3 and the high band coil L4 and a connection point between the ground side low band coil L1 and the high band coil L2. Only when the low band is selected, the tuning circuit is damped to reduce the gain.

[0007]

However, the tuner circuit constructed as described above has an extremely large number of components and connection points, and has a high mounting density when all components are mounted on a board having a fixed area. There is a problem that the mounting work is difficult, the yield is low, and the product cost is considerably increased due to the parts cost and the working cost. When the high band is selected, the series resistance of the switching diodes D2 and D3 is connected in series to both the hot side and the ground side of the tuning coil, so that the tuning circuit is damped, the gain is reduced, and the NF (noise figure) is reduced. There was a problem that worsened.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and reduces the number of components to improve the yield of the soldering operation. An object of the present invention is to provide a tuner circuit in which NF is reduced and NF is improved.

[0009]

[Means for Solving the Problems] In order to solve the above-mentioned problems
According to a first aspect of the present invention, in a tuner circuit having an input circuit for switching a reception band using a switching diode, a low-band coil and a high-band coil on the hot side of the input circuit are directly connected to each other, A coupling capacitor is connected between one end of the band switching bias resistor and directly connected to the hot side low band coil.
The band switching bar and the ground-side low-band coil of
A first band switching diode is connected between one end of the bias resistor and a low band on the ground side.
High band coil on the earth side directly connected to the coil
Between the connection point and one end of the band switching bias resistor.
Connected to a second switching diode,
The other end of the band switching bias resistor is grounded at high frequency.
The bias resistor is used as a damping resistor when receiving low band.
It is configured to work .

According to a second aspect of the present invention, there is provided a tuner circuit having an input circuit for switching a receiving band using a switching diode, wherein a low band coil and a high band coil on the hot side of the input circuit are directly connected. ,
Connect a coupling capacitor between the connection point and one end of the band switching bias resistor, and a ground-side low band
High band coil on the earth side directly connected to the coil
Connect a switching diode for band switching to the connection point of
And the other end of the band switching bias resistor has a high frequency.
The structure is grounded in waves .

[0011]

According to such a configuration, in either of the first and second inventions, when the low band is selected, the bias resistor connected to the band switching terminal connects the hot side low band coil and the high band coil through the coupling capacitor. Connected to the connection point to dampen the tuning circuit.

When the high band is selected, the switching diode is turned on so that the low band coil is canceled. At this time, in the first invention, only the high-band coil is provided on the hot side, and the high-band coil and the switching diode connected in series to the high-band coil are provided on the ground side. Both the hot side and the ground side are composed of only high band coils.

According to the first aspect of the present invention, since the input tuning circuit damps only the ground side coil by the switching diode, deterioration of NF (noise figure) can be prevented. In the second aspect of the present invention, since there is no damping by the switching diode on both the hot side and the ground side, NF is further improved.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a circuit diagram of a tuner circuit according to one embodiment of the first invention. Low band coil L3,
The input terminal of L1 and the anode of the switching diode D1 are connected via a coupling capacitor C1 to a filter circuit (not shown) connected to the preceding stage of this circuit.

The low-band coils L3 and L1 and the high-band coils L4 and L2 are connected in series on both the hot side and the ground side, and the high-band coil L2 on the ground side.
Is connected to the high band power supply terminal BH and the bypass capacitor C7. The output terminal of the hot side high band coil L4 is connected to the variable capacitance diode VD1 and the tracking correction capacitor C6 via the coupling capacitor C2, and further connected to the gate 1 of the high frequency amplification FET Q1 via the coupling capacitor C3. You.

A coupling capacitor C4 is connected to a connection point between the low-band coil L3 and the high-band coil L4 on the hot side, and the other end of the coupling capacitor C4 has cathodes of switching diodes D1 and D2 and a bias resistor R2.
1, connected to R2. The bias resistor R1 is grounded, the bias resistor R2 is connected to the low-band power supply terminal BL and the bypass capacitor C8, and the anode of the switching diode D2 is connected to the connection point between the low-band coil L1 and the high-band coil L2 on the ground side. Have been.

Next, in the tuner circuit having the above configuration,
The state when each band is selected will be described. (A) When low band is selected When a positive voltage is applied to the low band power supply terminal BL, the bias resistances R1, R2 are applied to the switching diodes D1, D2.
The voltage divided by 2 is applied, and both switching diodes D1 and D2 are turned off. Thus, the input tuning circuit becomes as shown in FIG. here,
CD1 and CD2 are the capacitances of the diodes D1 and D2.
Since L2 is sufficiently smaller than L1, this input tuning circuit constitutes a single tuning circuit damped by the combined resistance R 'of the bias resistors R1 and R2, as shown in FIG. 2B.

(B) When high band is selected By opening the low band power terminal BL and applying a positive voltage to the high band power terminal BH, a forward voltage is applied to the switching diodes D1 and D2, and both switching diodes D1 , D2 conduct. As a result, the low-band coil L3 on the hot side is canceled by the series resistance RD1 of the switching diode D1 and the coupling capacitor C4, and the two switching diodes D3 on the low-band coil L3 on the ground side.
1 and D2 are canceled by the series resistance components RD1 and RD2. Therefore, when the high band is selected, as shown in FIG. 2C, the series resistance R of the earth side high band coil L2 and the switching diode D2 connected in series thereto.
A single tuned circuit composed of the capacitance VC and the additional capacitance C by D2, the hot side high band coil L4 and the variable capacitance diode VD1. Therefore, this single tuning circuit is damped only by the series resistance of the switching diode on the ground side. That is, since the damping is not performed on the hot side, it is possible to prevent deterioration of NF (noise figure).

FIG. 3 shows another embodiment of the first invention.
In the same figure, the input terminals of the low-band coils L3 and L1 and the cathode of the switching diode D1 are connected to a coupling capacitor C1.
The anodes of D1 and D2 are connected to each other and connected to a coupling capacitor C4 and a high-band bias resistor R2.
The high-band bias resistor R2 is a bypass capacitor C
8 is connected to a high-band power supply terminal BH grounded. The other end of the coupling capacitor C4 is connected to a connection point between the hot-side low-band coil L3 and the high-band coil L4, and a cathode of the switching diode D2 is connected to a ground-side connection point between the low-band coil L1 and the high-band coil L2. Connected to the high-band coil L2
Is connected to the low-band power supply terminal BL, the bypass capacitor C7, and the bias resistor R1. The operation in each band is the same as in the case of FIG. 1, and FIG.
Shows an equivalent circuit in the high band.

Next, a second embodiment of the present invention will be described. FIG. 7 is a circuit diagram of a tuner circuit according to one embodiment of the present invention. The input terminals of the low-band coils L3 and L1 are connected via a coupling capacitor C1 to a filter circuit (not shown) connected to the preceding stage of this circuit. On both the hot side and the ground side, the low band coils L3, L1 and the high band coils L4, L2 are connected in series, and the ground side terminal of the ground side high band coil L2 is a high band power terminal BH and a bypass capacitor C7.
Connected to. The output side terminal of the hot side high band coil L4 is connected to the variable capacitance diode VD1 and the tracking correction capacitor C6 via the coupling capacitor C2 and further to the high frequency amplification F via the coupling capacitor C3.
Connected to the gate of ETQ1.

A coupling capacitor C4 is connected to the connection point between the low-band coil L3 and the high-band coil L4 on the hot side. The other end of the coupling capacitor C4 has a cathode of a switching diode D1 and bias resistors R1 and R2.
Connected to. The bias resistor R1 is grounded, the bias resistor R2 is connected to the low-band power supply terminal BL and the bypass capacitor C8, and the anode of the switching diode D1 is connected to the connection point between the low-band coil L1 and the high-band coil L2 on the ground side. Have been.

Next, a state when each band is selected in the tuner circuit having the above configuration will be described. (A) When low band is selected When a positive voltage is applied to the low band power supply terminal BL, a voltage divided by the bias resistors R1 and R2 is applied to the switching diode D1, and the switching diode D1 becomes non-conductive. As a result, the input synchronization circuit becomes as shown in FIG.
It becomes as shown in. Here, since L2 is sufficiently smaller than L1, this input tuning circuit constitutes a single tuning circuit damped by the combined resistance R 'of the bias resistances R1 and R2 as shown in FIG. 8B.

(B) When high band is selected By opening the low-band power supply voltage terminal BL and applying a positive voltage to the high-band power supply terminal BH, a forward voltage is applied to the switching diode D1 and the switching diode D1 becomes conductive. I do. As a result, the low-band coil L3 on the hot side and the low-band coil L1 on the ground side are connected in parallel by the coupling capacitor C4 and cancelled. Therefore, when the high band is selected, as shown in FIG. 8 (c), the combined inductance becomes L 'outside the tuning circuit, and the tuning circuit has the capacity VC of the ground side high band coil L2, the hot side high band coil L4, and the variable resistance diode VD1. Is formed as a single tuning circuit.

FIG. 9 shows another embodiment of the second invention.
In FIG. 9, the input terminals of the low-band coils L3 and L1 are connected to a coupling capacitor C1. On both the hot side and the ground side, the low band coils L3 and L1 and the high band coils L4 and L2 are connected in series, and the low band terminal BL, the bypass capacitor C7 and the bias are connected to the ground side terminal of the high band coil L2 on the ground side. The resistor R1 is connected. Hot side low band coil L
A coupling capacitor C4 is connected to the connection point of the high band coil L4 and the other end of the coupling capacitor C4. The other end of the coupling capacitor is connected to the anode of the switching diode D1 and the bias resistor R2. The bias resistor R2 is connected to the high-band power supply terminal BH and the bypass capacitor C8, and the cathode of the switching diode D1 is connected to the connection point between the low-band coil L1 and the high-band coil L2 on the earth side. The operation in each band is the same as that in the case of FIG. 7, and FIGS. 10A and 10B show the equivalent circuits when the low band is selected, and FIG. 10C shows the equivalent circuit when the high band is selected.

[0025]

As described above, according to the first and second embodiments of the present invention, when the low band is selected, the bias resistor connected to the band switching terminal is connected to the hot low band coil and the high band through the coupling capacitor. Since it is connected to the connection point of the use coil and serves as a damping resistance of the tuning circuit, it is not necessary to separately provide a damping resistance as in the related art, and the number of components and the number of connection points can be reduced. Therefore, the mounting area of the components on the board having a fixed area can be reduced to facilitate the soldering operation and improve the yield, and the cost of the product can be reduced by reducing the component cost and the operation cost. Also,
In the first invention, when the high band is selected, the series resistance of the switching diode is connected in series only to the ground side coil, so that the damping of the tuning circuit is extremely reduced as compared with the conventional example. Therefore, it is possible to prevent a decrease in gain, that is, a deterioration in NF (noise figure). In the second aspect, when the high band is selected, the series connection with the series resistance of the switching diode is eliminated on both the hot-side ground side and the NF can be further improved as compared with the first aspect.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a tuner circuit embodying the first invention.

FIG. 2 is an equivalent circuit diagram when the low band and the high band are selected.

FIG. 3 is a circuit diagram of another embodiment of the first invention.

FIG. 4 is an equivalent circuit diagram when the low band and the high band are selected.

FIG. 5 is a circuit diagram of a conventional example.

FIG. 6 is an equivalent circuit diagram when the low band and the high band are selected.

FIG. 7 is a circuit diagram of a tuner circuit embodying the second invention.

FIG. 8 is an equivalent circuit diagram when the low band and the high band are selected.

FIG. 9 is a circuit diagram of another embodiment of the second invention.

FIG. 10 is an equivalent circuit diagram when the low band and the high band are selected.

[Explanation of symbols]

C1 to C5 Coupling capacitor C6 Tuning correction capacitor C7 to C9 Bypass capacitor L1 Earth side low band coil L2 Earth side high band coil L3 Hot side low band coil L4 Hot side high band coil D1 to D3 Switching diode VD1 Variable capacitance diode Q1 High-frequency amplification FET R1, R2 Band switching bias resistor R3 Low band damping resistor R4 Tuning voltage application resistor R5 to R7 FET bias resistor R 'Combined resistor (by bias resistors R1, R2) L' Combined inductance (low band coil L1, L
3)

Continuation of the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) H04B 15/00-15/02 H03J 5/24 H04B 1/18

Claims (2)

(57) [Claims] In a tuner circuit having an input circuit for switching a reception band using a switching diode, a low-band coil and a high-band coil on the hot side of the input circuit are directly connected to each other, and the connection point and band switching are performed.
Connect a coupling capacitor between one end of the bias resistor for
And an earth-side low-band coil directly connected to the hot-side low- band coil and the band switching via.
A first band-switching switching diode is connected between one end of the resistor and a low-band coil on the ground side.
Of the high-band coil on the earth side directly connected to the
Between the connecting point and one end of the band switching bias resistor.
2 switching diodes, and
The other end of the bias resistor for switching
Ass resistance acts as a damping resistor during low band reception
Tuner circuit, characterized in that the memorial. 2. A tuner circuit having an input circuit for switching a receiving band using a switching diode, wherein a low-band coil and a high-band coil on the hot side of the input circuit are directly connected to each other, and the connection point and band switching are performed.
Connected to one end of the bias resistor and connected directly to the low-band coil on the ground side.
Switch to the connection point of the high band coil on the ground side
Connecting a switching diode for
A tuner circuit characterized in that the other end of the switching bias resistor is grounded at a high frequency .