JPH0276315A - Input tuning circuit - Google Patents

Abstract

PURPOSE:To decrease a deviation in the band width even in the reception at a broad band, to prevent disturbance and to improve the loss characteristic by forming a 1st inductive impedance with series connection comprising one or two inductors or over and a varactor diode. CONSTITUTION:The inductive impedance whose inductance at a high frequency is smaller than the inductance at a low frequency is formed by series connection comprising stepup coils 12, 13 determinant of an input impedance and a varactor diode 8. As a result, the input impedance at a low frequency is decreased to widen the band width. Moreover, it is possible to increase the input impedance at a high frequency to widen the band width. Moreover, the tuning circuit and the output load are connected via the varactor diode 8 to lower the output impedance at a low frequency and to increase it at a high frequency. As a result, the band width deviation of the tuning circuit is reduced.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a variable capacitance tuning circuit used in a television set, etc. that receives broadband signals.In particular, the present invention relates to a variable capacitance tuning circuit used in a television set that receives broadband signals. Concerning small input tuning circuits.

[Conventional technology]

Conventional tuning circuits that receive wide band signals, such as CATV in the United States, have two variable capacitance diodes, one for tuning and one for coupling, in one tuning circuit, as described in Japanese Patent Application Laid-Open No. 57-2117. was used to enable wideband reception.

[Problem to be solved by the invention]

The conventional technique described above has a problem of large bandwidth deviation when a variable capacitance diode with a wide variation range is used to receive a wideband signal. In other words, the bandwidth is narrow at low frequencies, and the bandwidth is wide at high frequencies. Therefore, if the bandwidth is secured at low frequencies, the bandwidth at high frequencies becomes too wide, resulting in problems such as cross-modulation. If the interference characteristics of the machine are poor, or conversely, the bandwidth is secured at high frequencies, the bandwidth at low frequencies is too narrow, resulting in increased loss in the tuning circuit.

An object of the present invention is to provide a receiver with small bandwidth deviation even in wideband reception, and therefore with good interference characteristics and loss characteristics.

[Means to solve the problem]

The above object is achieved by providing a circuit configuration in which the input/output load impedance is low at low frequencies and high at high frequencies.

[Effect]

The series connection of a step-up coil and a variable capacitance diode, which determines the human power impedance, forms an inductive impedance in which the inductance at high frequencies is smaller than the inductance at low frequencies. the result,
Compared to the case where the input impedance is converted using only a step-up coil, it is possible to lower the input impedance at low frequencies to widen the bandwidth, and increase the input impedance at high frequencies to narrow the bandwidth. Become. Furthermore, by connecting the tuning circuit and the output load via a variable capacity violet diode, the output impedance can be made low at low frequencies and high at high frequencies. As a result, it is possible to make the characteristic more uniform, whereas the conventional band width was narrow at low frequencies and wide at high frequencies.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1st
The figure is a VHF input tuning circuit diagram of a wideband reception television channel that can also receive CATV in the United States, etc. 1 is an input terminal, 2 is a high frequency amplification section, 3 to 5 are bias supply terminals, and 6 to 8 are variable capacitors. 9 is a switching diode, 11 to 13 are coils, 14 to 18 are bypass capacitors, and 19 to 24 are resistors. Switching the band by making the switching diode 9 conductive or non-conductive, 54
~470MH2O frequency band to low band (54~15
6MH2) Tohypan)” (156-470MHz)
It is divided into

During low band reception, a voltage is applied to the terminal 3 to make the switching diode 9 non-conductive. The impedance at the input terminal is made high by the inductive impedance consisting of the coil 12, 15 and the variable capacitance diode 8, and the inductive impedance consisting of the coil 10, the coil 11, and the variable capacitance diode 6), and the high frequency amplification section 2 and consistency is obtained. Then, the tuning point of the circuit is determined by 7°8 to the variable capacitance diode and the coil 10, 11, 12, 13, υ, and the tuning point is changed by applying a tuning voltage to terminal 5 and changing the capacitance value of the variable capacitance diode. . Also·
- When receiving an E-band, a voltage is applied to the terminal 4 to make the switching diode 9 conductive. In this case, the impedance at the input end is increased by the inductive impedance made up of the coil 13 and the variable capacitance diode 8, and the inductive impedance made up of the coil 11 and the variable capacitance diode 6, thereby achieving matching with the high frequency amplification section 2. . The tuning point is determined by the variable capacitance diode 6.48 and the coil 11.13. Here, the operation of the first embodiment shown in FIG. 1 will be explained in detail in comparison with the conventional example shown in FIG. The conventional VHF input tuning circuit of FIG. 2 differs from the embodiment of FIG. 1 in that the variable tone diode 8 of FIG.
9 with different inductance values of 3 and 25, respectively.
It is 26. FIG. 3(a) shows an equivalent circuit of the embodiment during low-band reception.

In (α'), the equivalent route of the conventional example is (b), (b')
This is shown below. 26 is the input end resistance R1, 27 is the input equivalent resistance of the high frequency amplification section 2, the equivalent resistance at the low band low end frequency f is R2, and the equivalent resistance at the high end frequency f2 is R3. . In addition, 28 is the inductive equivalent impedance due to the series connection of the coils 12 and 13 and the variable capacitance diode, and 6C129 is the inductive equivalent impedance due to the series connection of the coils 10 and 11 and the variable capacitance diode 6. with the equivalent impedance of f.

Let R5 be R5, and R6 be f. The capacitance values of the variable capacitance diodes at f, , and f are respectively set as CI and C2, and the series connection of the coils 25 and 26 is set as R9.

(α), (the circuit is further (α'), (b')
However, the value at f of the impedance 31 at the input terminal in the example is changed to R4, f,
R5, and the input end impedance of the conventional example is 3.
If the value at f of 6 is R6, and the value at f is R7, then R
4, R5, R6, and R7 are as follows.

R4#R1(1+,L Near Rs = R1(1+H)"
respectively, B1. B2, Conventional example /, , f,
If the 5(tB bandwidths are respectively B5 and B4, then

In the present invention, by using the variable capacitance diode 8, it is possible to set fiL5>L9 and I,4 (L9. In this case, R4<R6, R5>R7, so Bl>15.B2<B4.In other words, the bandwidth of the embodiment can be made wider at lower frequencies and narrower at higher frequencies compared to the conventional example, and the bandwidth deviation can be improved. The characteristic of the bandwidth of the conventional circuit is shown as tI1.
As shown by the broken line in Figure 6, in the circuit according to the embodiment of the present invention, the bandwidth deviation is smaller than in the conventional circuit, and by narrowing the bandwidth at high frequencies, the interference characteristics of the circuit can be improved. In addition, at low frequencies, the bandwidth is widened and the loss of the tuning circuit is reduced, making the noise finger 11! Characteristics can also be improved. Furthermore, since the variable capacitance diode 8 is newly provided, tuning over a wider frequency range than before is possible. Note that by replacing capacitor 18 in the *tS example of FIG. 1 with a bypass capacitor and using a capacitor with an appropriate capacitance value, it is possible to obtain a bandwidth deviation of v14 gM.

FIG. 5 shows a second embodiment. In FIG. 5, components that perform the same functions as in FIG. 1 are given the same reference numerals, and the difference from FIG. be.

Here again, by setting the capacitor t57 to an appropriate capacity value, it is possible to obtain a desired bandwidth difference. In addition, although FIG. 6 shows an actual example of @3, compared to the first * embodiment, the variable capacitance diode 6 is eliminated, and the variable capacitor 160 has a variable Although the tuning circuit configuration includes a capacitive diode 38, the input impedance changes in the same manner as in the first embodiment, so it goes without saying that the bandwidth deviation can be made smaller than in the conventional case.

So far, we have described the case of switching between two bands using a switching diode, but the same applies to the case of a single band without using a switching diode, or the case of switching to three bands using two switching diodes. Therefore, if the input impedance at high frequencies can be made higher than the input impedance at low frequencies, it is possible to reduce the band deviation.

FIG. 7 shows a fourth embodiment. In the practical example shown in FIG. 7, a variable capacitance diode 40 and a resistor 41 are newly provided compared to the conventional example shown in FIG. In this case, the purpose is achieved by changing the output impedance of the tuned circuit.In this case, the capacitance value of the variable capacitance diode is large at low frequencies and small at high frequencies, so the output impedance of the tuned circuit is low. It is low at low frequencies and high at high frequencies.

As a result, the bandwidth can be made wider at lower frequencies and narrower at higher frequencies than in the past, and the bandwidth deviation can also be reduced in this embodiment.

〔Effect of the invention〕

According to the present invention, since the input impedance can be made lower at low frequencies and higher at high frequencies than in the past, it is possible to reduce the bandwidth deviation of the tuning circuit.

[Brief explanation of the drawing]

tsllIIJ is an input tuning circuit diagram showing the first practical example of the present invention, FIG. 2 is a conventional input tuning circuit diagram, FIG. 3 is a schematic equivalent diagram explaining the effects of the embodiment, and FIG. Characteristic diagrams showing the effects, Figures 5, 6, and 7 are shown in Figure 2. Third.
FIG. 7 is an input tuning circuit diagram of a fourth embodiment. 6, 7.8.38.40...Variable capacitance t diode, 1
0 to 13, 25.26... Coil, 2... High frequency amplification section. Figure 1? 2 High frequency amplification section 6.78 Capacity Tide 10ν/3 Coil 2nd figure 'f (door"IN!) Figure 5 Figure 6

Claims (1)

[Claims] 1. A first variable capacitance circuit including one or more variable capacitance diodes, whose signal source input terminal is grounded by a first inductive impedance, and whose signal source input terminal is grounded by a second inductive impedance. In an input tuning circuit in which the first variable capacitance circuit is connected to a first high frequency amplification circuit made of an active element such as an FET, the first inductive impedance is one or more inductors. An input tuning circuit comprising a series connection of a variable capacitance diode and a variable capacitance diode.