JP3212711B2 - Input tuning circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an input tuning circuit of an electronic tuning tuner used for a high-frequency circuit device such as a television receiver and a video tape recorder.

[0002]

2. Description of the Related Art An input tuning circuit as shown in FIG. 3 is used in a general electronic tuning tuner. In FIG. 3, C1
And C2 are DC component blocking capacitors. L1 and L3 are tuning coils for low band reception. L2 and L4 are tuning coils for high band reception. D1 and D
2 is a band switching switching diode, R1 and R
2 is a switching bias resistor, R3 is a tuning resistor for applying a tuning voltage, C3 is a capacitor for tracking correction and constitutes a trap circuit by parallel resonance with a tuning coil L4 for high band reception, C4 is a tuning capacitor, and TR1 is a tuning capacitor. Transistor for RF amplification, C
5 is a coupling capacitor between the tuning circuit 1 and the RF amplification transistor TR1, and D3 is a tuning variable capacitance diode. The operation of the input tuning circuit configured as described above is well known, and therefore will be omitted, and the tuning frequency will be briefly described. The input tuning circuit 1 has a combined inductance L composed of either the low-band receiving tuning coils L1 and L3 or the high-band receiving tuning coils L2 and L4.
It is configured as a resonance circuit including 0 and the variable capacitance c of the variable capacitance diode D3 by the variable applied tuning voltage VT. In this case, the relationship between the tuning frequency f, the inductance L0, and the variable capacitance c is represented by f = 1 / √ (a · L0 · c). Here, a is a constant. From the equation, when the variable capacitance c is the minimum value cmin, the tuning frequency f is the maximum value fm.
ax, and when the variable capacitance c is at the maximum value cmax, the tuning frequency f is at the minimum value fmin. Let cs be the stray capacitance,
By substituting these into the equation, the following relationship is obtained: (fmax / fmin) ² = (cmax + cs) / (cmin + cs). By the way, the variable capacitance diode D3
Is small, the variable range of the resonance frequency f (fmin to fm) is obtained from the equation.
Since ax) also becomes smaller, the reception band is divided into high and low.

Further, recently, with the spread of CATV, it has become necessary to expand the receiving range of a tuner.
Variable-capacitance diodes with large characteristics (in to cmax) have come to be used in tuning circuits. Furthermore, the variable range of the resonance frequency f of the tuning circuit (fmin to fmax)
In order to greatly increase the load, it is necessary to greatly improve the degree of load in a circuit other than the tuning circuit. However, if the reception frequency increases with the expansion of the reception range, there arises a problem that the influence of the input capacitance of the RF amplification transistor TR1 cannot be ignored.

In order to reduce the influence of the input capacitance of the RF amplifying transistor TR1 on the tuning circuit when the reception frequency is high, generally, a circuit configuration in which a variable capacitance diode D4 is arranged as shown in FIG. The coupling capacitance between the tuning circuit and the RF amplifying transistor TR1 is reduced.

In FIG. 4, the same components as those in FIG. 3 are denoted by the same reference numerals. C6 is a DC component blocking capacitor. The variable capacitance diodes D3 and D4 have the same characteristic value. The variable capacitance diode D4 functions as a coupling correction for suppressing a gain deviation in a band by changing a coupling capacitance with the RF amplification transistor TR1. Further, in this case, as for the combined capacitance c of the variable capacitance diodes D3 and D4, the ratio of (cmax / cmin) increases, and (fmax / fmin) ² increases according to the equation. In other words, the resonance frequency f Variable range (fmin to f
Since max) can be made large, the variable capacitance diode D4 also functions as a tuning correction capacitance. FIG.
In FIG. 4 and FIG. 4, a trap circuit including a capacitor C3 and a tuning coil L4 for high band reception is provided to reduce image disturbance.

[0006]

As described above, the trap circuit constituted by the capacitor C3 and the tuning coil L4 for high band reception is provided to reduce image disturbance at the time of reception of each channel. However, since the resonance frequency of the trap circuit is fixed, the reception signal is cut off when receiving a channel having a reception band frequency that matches the resonance frequency of the trap circuit. In this case, the trap circuit cannot be provided. There is a problem that a channel that cannot reduce image disturbance remains.

In order to improve such a point, the present invention provides an input tuning circuit which reduces image interference over the entire band by changing the resonance frequency of a trap circuit which reduces image interference in conjunction with a tuning voltage. I do.

[0008]

According to the present invention, a high frequency amplifying transistor is provided in an input tuning circuit provided with an image trap circuit in a signal path for removing an image signal of another channel which affects the reception of a specific channel.
Parallel to the capacitor for coupling with the
Synchronized with coil for image trap and capacitor for image trap
A variable capacitance diode whose capacitance changes with voltage
To connect the image trap circuit
It is characterized by having been formed.

[0009]

According to such a configuration, for example, for an image signal of a channel that interferes with a specific channel, the frequency of the trap circuit is selected to a frequency that does not affect the specific channel. At the time of receiving a channel, both channels can be received without any trouble by shifting from the reception frequency of the channel.

[0010]

FIG. 1 shows an embodiment of the present invention. In the figure, one end of a DC component blocking capacitor C1 is connected to an input terminal IN, and the other end of the DC component blocking capacitor C1 is connected to one end of a low band receiving tuning coil L1 and one end of a low band receiving tuning coil L3. (Connection point A). The other end of the low-band reception tuning coil L1, one end of the high-band reception tuning coil L2, and the anode of the switching diode D1 are connected (connection point B). The other end of the high-band receiving tuning coil L2, a terminal for applying the high-band operating voltage BH, and one end of the DC component blocking capacitor C2 are connected (connection point C), and the other end of the DC component blocking capacitor C2 is connected. Ground.

The other end of the low-band reception tuning coil L3, one end of the high-band reception tuning coil L4 and the anode of the band switching diode D2 are connected (connection point D). The cathode of the band switching diode D2, the cathode of the band switching diode D1 and the switching bias resistors R1,
R2 is connected at one end (connection point E), and the other end of the switching bias resistor R1 is connected to the low band operating voltage BL.
Is connected, and the other end of the switching bias resistor R2 is grounded.

The other end of the tuning coil L4 for high band reception, one end of the tuning capacitor C4 and one end of the coupling capacitor C5 are connected (connection point F). The other end of the coupling capacitor C5, one end of the DC component blocking capacitor C6, and the RF amplification transistor TR1 are connected (connection point G).

The other end of the tuning capacitor C4, one end of the image trapping coil L5, one end of the image trapping capacitor C7, one end of the tuning voltage applying bias resistor R3, and the cathode of the coupling correction variable capacitance diode D4. The variable capacitance diode D3 is connected to the cathode of the variable capacitance diode D3 (connection points H, I, J), the other end of the tuning voltage application bias resistor R3 is connected to the terminal for applying the tuning voltage VT, and the tuning variable capacitance diode D3 is connected. The anode of is grounded. The coupling correction variable capacitance diode D4 suppresses the gain deviation in the band by changing the coupling capacitance with the RF amplification transistor TR1 by the tuning voltage.

The other end of the DC component blocking capacitor C6, the other end of the image trapping coil L5, the other end of the image trapping capacitor C7, the anode of the coupling correction variable capacitance diode D4, and one end of the bias resistor R4. (Connection points K, L, M), and the other end of the bias resistor R4 is grounded. As described above, a resonance circuit X including the image trap coil L5, the tuning capacitor C4, the coupling capacitor C5, the DC component blocking capacitor C6, the image trap capacitor C7, and the tuning correction diode D4 is configured.

For example, when high band reception is selected by applying a high band operating voltage BH, the resonance circuit X constitutes a parallel resonance circuit as shown in FIG. And D4 have the function of a variable capacitor whose capacity can be changed by the tuning voltage VT, and are represented by the symbol of the variable capacitor. As described above, since the resonance circuit X includes the variable capacitance diode D4, the resonance frequency of the resonance circuit X can be arbitrarily changed by changing the tuning voltage VT to be applied. Therefore, the resonance circuit X
Can be matched with the image frequency, and in this case, the resonance circuit X functions as an image trap. (The resonance circuit X is hereinafter referred to as “image trap X”)

Next, an image trapping condenser C
The advantage of No. 7 will be described. When setting the resonance frequency of the image trap X, the input tuning circuit and the coupling capacitor C5 of the RF amplification transistor TR1 greatly affect the resonance frequency variable range of the image trap X.
There is a restriction on the variable range of the resonance frequency of the image trap X. If the image trap capacitor C7 is connected, the image trap X by the coupling capacitor C5 can be used.
Has little effect on the resonance frequency variable range, and the resonance frequency of the image trap X can be set arbitrarily.

[0017]

As described above, according to the input tuning circuit of the present invention, since the image trap circuit is configured so as to include the variable capacitance diode for tuning correction, the tuning voltage to be applied is changed. The resonance frequency of the trap circuit that reduces image disturbance becomes variable. For example, for an image signal of a channel that interferes with a specific channel, the frequency of the trap circuit is selected to a frequency that does not affect the specific channel. By displacing them, both channels can be received without any trouble. As a result, it is possible to reduce the image disturbance over the entire band while keeping all the channels in the band receivable. further,
As the reception frequency increases with the expansion of the reception range, RF
The influence of the input capacitance of the amplifying transistor becomes large, so to avoid this, the variable capacitance diode for coupling capacitance correction which is conventionally provided between the input tuning circuit and the subsequent RF amplifying transistor is used. In order to fulfill the function, a large reverse applied voltage is required, but the variable capacitance diode for correcting the coupling capacitance is also used as the variable capacitance diode for tuning correction, and the reverse applied voltage for correcting the coupling capacitance is corrected by tuning correction It can be used as a working voltage.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram embodying the present invention.

FIG. 2 is an equivalent circuit diagram of a circuit configuration embodying the present invention.

FIG. 3 is a conventional circuit configuration diagram.

FIG. 4 is another conventional circuit configuration diagram.

[Explanation of symbols]

 C1, C2, C6 DC component blocking capacitor C3, C7 Image trapping capacitor C4 Tuning capacitor C5 Coupling capacitor R1, R2 Band switching bias resistor R3 Tuning voltage application bias resistor R4 Bias resistor L1, L3 Low band tuning coil L2, L4 High band tuning coil D1, D2 Band switching diode D3 Tuning variable capacitance diode D4 Tuning correction variable capacitance diode TR1 RF amplification transistor X Image trap (resonance circuit) BH High band operating voltage BL Low band operating voltage VT Tuning voltage A, B, C, ..., M Connection point

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-52323 (JP, A) JP-A-2-250422 (JP, A) JP-A-6-97779 (JP, A) JP-A-2- 241230 (JP, A) Japanese Utility Model Application No. 61-128,843 (JP, U) Japanese Utility Model Application No. 2-41519 (JP, U) Japanese Utility Model Application No. 61-184318 (JP, U) (58) Fields surveyed (Int. ⁷ , DB name) H03J 5/24 H04B 1/18

Claims (2)

(57) [Claims] 1. An input tuning circuit provided with an image trap circuit in a signal path for removing an image signal of another channel which affects the reception of a specific channel, and a capacitor for coupling with a high frequency amplification transistor.
In parallel with the image trap coil and image
The capacitance value varies depending on the
Before connecting a parallel circuit consisting of
An input tuning circuit characterized by forming an image trap circuit. 2. The input tuning circuit according to claim 1, wherein said variable capacitance diode also has a function of correcting a coupling capacitance between an input tuning circuit and a high-frequency amplifying transistor at a subsequent stage by a tuning voltage. .