JPS59152714A - Variable dual tuning circuit - Google Patents

Abstract

PURPOSE:To suppress the change in a band width at a broad band width over a wide variable frequency range by a coupling both single tuning circuits with a capacitor having a minute capacitance further in a variable dual tuning circuit of the M coupling system. CONSTITUTION:Both single tuning circuits are coupled by the capacitor C6 having a minute capacitor further in a variable dual tuning circuit of M coupling system. In using this tuning circuit for an inter-stage dual tuning circuit of a tuner for a TV receiver, the circuit is designed to be tuned to frequencies 93.5MHz-219.5MHz, and the frequency is converted into an intermediate frequency by a mixer 4 and a local oscillating circuit 3 tracked with the inter-stage dual tuning circuit 2. The C6 is selected to be 0.5PF, but this value depends on the varied frequency and in the variable tuning circuit of 120-300MHz, the C6 is selected to be 0.2-0.3PF. The band width ratio of the ch1-ch12 at an intermediate frequency output is 2.08 times (11.0MHz/5.3MHz) and compressed by nearly 30% more than a conventional method.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable double tuning circuit using variable tuning elements.

Variable double tuning circuits are widely used in TV receivers and FM receiver tuner circuits, etc., and in recent years, most of them have been computerized, and variable capacitance has been used as a variable capacitive element. diode is used.

This double-tuned circuit is a combination of two single-tuned circuits, and there are three ways to combine them, as shown in FIG. 1 (ta+) to (C). FIG. 1 (al is called a C-coupling, where one tuning circuit consists of a variable capacitance content c1 and a fill L1, and the other C4> tuning circuit consists of a variable capacitor C2 and a coil L2. Content C
It is a combination of 3. However, in this C coupling method, the degree of coupling changes depending on changes in the frequency characteristics of the coupled content C3.
Used for rIJ variable modulation tuning circuit with small J ratio. Content c4. C5 is for compression to the input/output circuit side.

Figure 1 (BL shows a dual-use tuning circuit coupled with a coil L3), and Figure 1 (C1 shows an M-coupling method in which both coils L1 and L2 are coupled together (the equivalent circuit is the same for the dual-force type). This is a rare item, and can be used in a variable double-tuned circuit with a relatively large 1+J ratio (also, since the change in coupling degree is small,
TV receivers use VHF high band (ch4
~12) is the M bonding force equation, and the low band (chi~3)
It is common to use the L bonding force equation.

However, as tuners, including those used in CATV in the United States, have become increasingly wide-band, the frequency variable ratio has changed from the conventional 1.3 to 1.
5 to 2.0 to 2.5, and in these high variable ratio variable double-tuned circuits, the state area width between channels (-3clB frequency range, hereafter the same ) is large, and the bandwidth of the high hand and low hand changes by a factor of 2.5~:(,0).

This means that the difference in selectivity between channels increases, causing a deterioration of the interference rejection ability in the high hand.

However, it has sufficient performance for limited applications where the input level is specified, such as CATV.
It is currently being used.

However, in order to eliminate this problem for other applications, some manufacturers have adopted a method of increasing the number of hunts and keeping the variable ratio per band low, but this naturally increases costs significantly. This is causing a problem.

The present invention has been developed to solve this problem, and its purpose is to provide a variable double-tuned circuit that suppresses the difference in bandwidth of each band at a high variable ratio as described above. .

The embodiments of the present invention will be described above. FIG. 2 shows an embodiment of the variable double-tuned II old Raku.
j, the tuning circuit is further C-coupled with a capacitor C6 of minute capacitance (fi).

Figure 3 is this time! [Receiving TV using Raku] This is an experimental circuit that imitates the interstage double-tuned circuit of Iku's Tuli, and in the range of 1 to 25 ■ tuning electric power applied to terminal l, 93
．． 5MIIz (Japan cbl) ~219.5MI
Set a1 to synchronize with Iz (Japan c l+ 12)
The frequency is converted into an intermediate frequency by a mixer 4 using a double tuning circuit 2 and a local oscillation circuit 3 which performs tracking.

5 is a quotient frequency amplifier circuit, and 6 is a 75Ω terminator.

Capacitor C1 shown in FIG. 2 is composed of a variable capacitance diode and a semi-fixed capacitor C7, and capacitor C2 is composed of a variable capacitance diode D2 and a semi-fixed capacitor C8. Capacitor C9 and CIO is for DC cut.

The microcapacitance capacitor C6 for C coupling is 0,511
F, and this value varies depending on the mouth J variable frequency, and is 12
0.2-0.3 for variable tuning circuit from 0 to 300 MIIz
Becomes PF.

In addition, resistance R1 is 75Ω, resistance R2 is IKΩ, resistance 1
? 3 and R4 are 100Ω, capacitor C4 is 1811,
Condenser C5 is 3PF, capacitors C7 and 08 are ~2r'F, capacitors C9 and CIO are 1000P.
F, condenser CI soil is 1.5 PF.

The variable ratio of the μJ variable tuning circuit 1 becomes slightly narrower due to the addition of the C-coupling capacitor C6, but the parallel capacitor C7
, C8 by 0.2 to 0.31]F compared to the conventional one, it is possible to obtain a variable ratio equivalent to that of the conventional one, and there is no problem.

The experimental results are shown in FIGS. 4 to 9.

In FIGS. 4 to 9, (al is the intermediate frequency output when the conventional 1+J modulation modulation tuning is used, and (bl is the intermediate frequency output when the variable double tuning circuit of this embodiment is used.

In the figure, FV is a video carrier wave (58,75Mllz)
, FC is the color subcarrier (55, 17 old 1z), I's
For example, the audio carrier IJL (54, 25M1lz).

The bandwidth comparison results are as follows.

As mentioned above, the conventional circuit has a power of 2.95 times (16,2/5
．． 5) In the implementation circuit of the present invention, the bandwidth ratio was reduced to 2.
．． It is compressed by about 30% to 08 times (11,0/5.3).This is taken as a characteristic difference due to the difference in selectivity, and the attenuation of FV of the upper and lower adjacent channels when 10 channels are received. Now that we have compared the degrees, let's move on to the next step.

As shown above, there is a difference of 5 to 6 tlB, and this difference is used as a difference in cross-modulation characteristics for a TV receiver tuner.
It appears as it is. In addition, % IF rejection,
This embodiment also has a positive effect on image rejection.

Note that the above is an M-coupled variable double-tuned δ) C-coupled to the old jJ path with a minute capacitance, but it is isometrically the same as an L-coupled iJ variable tuning circuit and an M-coupled variable double-tuned circuit. Therefore, the same effect can be obtained by C-coupling this linearly coupled variable double-tuned circuit with a minute capacitance.

As described above, the present invention is characterized in that changes in bandwidth can be suppressed extremely effectively in a wide variable frequency range.

[Brief explanation of drawings]

FIG. 1 (ai to (bl) is a circuit diagram showing each coupling method of the double-tuned circuit, FIG. 2 is a circuit diagram showing each coupling method of the double-tuned circuit, and FIG.
3 is an experimental circuit diagram of the circuit of the embodiment shown in FIG. 2, FIG. 4 is an intermediate frequency characteristic diagram of the first channel, and FIG. 5 is a circuit diagram of the circuit.
The figure shows the intermediate frequency characteristic diagram of the 3rd channel, Figure 6 shows the intermediate frequency characteristic diagram of the F channel, Figure 7 shows the intermediate frequency characteristic diagram of the 4th channel, and Figure 8 shows the intermediate frequency characteristic diagram of the 9th channel. frequency 1
Fig. 9 is an intermediate frequency characteristic diagram of the 12th channel, and in Figs.
bl has the characteristics >j< in accordance with the embodiment of the present invention. C6...Minute capacitance converter for C coupling. Patent applicant: Zefu Laru Co., Ltd. Patent attorney
Nagao Tomei (0) j Lead Wave Kan (MHz) Figure 9 (ch12) (b) No customer] Hoboba E1t (MHz) Ni E bow: 1.3-1 Itotome Mo1 Mi jn
２I) 'i￥! ,i” (:
) 5 Koishi) (j) 1981 7 1] Director General of the Japan Patent Office Wakasugi, Kazuo 1, Indication of the case 1988 Patent Application No. 26017 2, Name of the invention Variable double tuning circuit 3, Amendment Relationship with the case involving a person who does 7, l1li
Positive object Specification 1-Brief explanation of drawings-18,
Contents of correction

Claims (1)

[Claims] (1) In a double-tuned circuit using a variable capacitance element, L
J-modulation/de-tuning characterized in that two single tuning circuits which are M-coupled are C-coupled by a minute capacitance to suppress changes in the bandwidth within the I:Ir variable frequency range. circuit.