JPS6113641B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultra-high frequency band electronic tuning circuit particularly suitable for a UHF band electronic tuning tuner. More specifically, the present invention relates to a planar circuit configuration of an electronically tuned tuner.

Conventional electronically tuned tuners with high-frequency amplification stages are
As shown in FIG. 1, it is composed of four resonant circuit sections. Fig. 1 is a basic configuration diagram of a case with high frequency amplification. Each resonant circuit section is composed of a coaxial line, a capacitor is connected to one end or both ends of each, and a shielding plate 10 is installed between each stage. are provided and are coupled by providing a coupling hole.

In FIG. 1, an input signal from an input terminal 21 is first coupled to a resonant circuit 12 through a coupling loop 11.

The signal then passes through a high-frequency amplification stage 24 with bipolar transistors or field effect transistors, passes through a double-tuned circuit with resonant circuits 13 and 14, and enters a mixing section 20. On the other hand, the resonant circuit 15 is the resonant part of the local oscillator section 25, and its output enters the mixing section 20 in the same way as above, where the high frequency input side and the local oscillator side are mixed by the mixing diode, and the intermediate frequency is sent to the output terminal. Take it out from 22. The varactor diodes 16, 17, 18, and 19 have their capacitances changed by applying a DC voltage from an externally applied voltage terminal 23. The tuning frequency of each resonant circuit can then be changed.

However, with the above configuration, electromagnetic field leakage is large, significantly degrading the performance of the circuit.

In view of the above-mentioned drawbacks, the present invention provides an electronic tuning circuit in which electromagnetic field leakage is small and variations due to assembly are small.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a plan view illustrating the principle of the electronic tuning circuit of the present invention. FIG. 2A shows a circular loop type circuit, and FIG. 2B shows a rectangular loop type circuit.Although their shapes are different, they are based on exactly the same principle.

The resonant line sections 28 and 29 are ring-shaped as shown in FIG. 2, and a varactor diode 30 and a capacitor 31 are mounted at both ends thereof. The capacitor 31 also serves to block direct current from the direct current voltage terminal 32 applied to the varactor. The choke coil 33 is a return path for DC voltage.

FIG. 2C shows an equivalent circuit of FIGS. 2A and 2B, and the resonance condition is obtained by the following formula.

(1/ω _r ) ² = C _V C _S / C _V + C _S (Z ₀ tan
β _T /ω _r +L _S ) [However, ω _r : Resonant angular frequency C _S : Capacitance value of capacitor 31 C _V : Capacitance value of varactor diode 30 Z ₀ : Characteristic impedance of resonant line sections 28 and 29 β : Resonant line Phase constant _T of the sections 28 and 29: Total length of the resonant line sections 28 and 29 L _S : Series inductance value of C _V and C _S ] According to the configuration shown in Fig. 2 above, (i) RF in the tuned circuit No grounding, low loss,
Furthermore, since it can be patterned, there is little variation due to assembly.

(ii) Since the circuit is a closed loop, there is little leakage of electromagnetic fields.

It has the following effects.

Specifically, a silicon varactor diode is used as the varactor diode 30, and Z ₀ = 65Ω in the above formula, _T
= 40 mm, C _S = 15 pF, and when variable tuning is designed in the 450 to 800 MHz band, the relationship between the tuning voltage and the resonant frequency is as shown in FIG. 2D.

Furthermore, FIG. 2E shows the frequency characteristics of the no-load Q (Q ₀ ) of the resonator. The no-load Q is approximately determined by the series resistance R _S of the varactor diode 30;
When a low-loss fixed capacitor is used instead of the diode 30, the no-load Q is about 250, and there is little change within this band. Note that epoxy glass was used as the printed circuit board, and the resonator was patterned and measured.

Figure 2F shows the measured values of the 3 dB bandwidth and insertion loss. Compared to the BPF of a normal shortened λg/2 resonator (suspended structure using an epoxy glass substrate), the insertion loss is almost the same in the high frequency range and about 1.5 dB in the low frequency range according to the configuration shown in Figure 2B. Improvement was seen.

Next, one embodiment of the present invention will be described.

In order to further improve the Q value of the circuit shown in Figure 2 and to reduce the cost by reducing the number of manufacturing steps, the second
The capacitor 31 shown in the figure has an integrated structure, and is integrated with the resonant line sections 28 and 29 to form a planar circuit.

FIG. 3 shows a specific example of the resonant line. 3A, B, and C are patterns formed on a dielectric substrate, and FIG. 3D is a sectional view taken along line A-A'. 3A, B, and C are all the same in principle, and make resonant lines 28 and 29, and a capacitor 34 forms a capacitance with a dielectric substrate 35 sandwiched therebetween. In the case of the rectangular loop type resonant circuit shown in FIG. 3B, the resonant lines 28 and 29
Since the outer shell is straight, it has the advantage that it can be easily connected to an external line. Further, when a large capacity is required, a structure as shown in FIG. 3C is suitable. That is, the third
In Figure D, the resonant line 28 is connected to the other resonant line 29.
The dielectric substrate 35 is connected to the opposite side of the substrate 35 by penetrating the dielectric substrate 35 in the middle so as to be in contact with the dielectric substrate 35.
A capacitor 34 is constituted by the upper and lower lines 28 and 29 sandwiching the upper and lower lines 28 and 29. The shaded areas in FIGS. 3A, B, and C are the integrated capacitor parts.

The variable capacitance diode 30 connects the resonant lines 28 and 2
Connect between 9 and 9. In addition, in the case of a large capacitance, another embodiment is to extend this capacitor portion to the entire area of the resonant line.

FIG. 4 shows an example of a configuration based on this idea. As is clear from the figure, in this embodiment, the resonant line 28 on the front side
A capacitor is constructed between the entire region of the wafer and the resonant line 29 on the back side, and a variable capacitance diode 30 is fixed between the capacitor and the resonant line 29 on the back side. In order to prevent the resonant lines 28 and 29 from being short-circuited to each other at this attachment part, a part of the resonant line 29 is taken out to the front side and a variable capacitance diode 30 is fixed thereto.

In either method, in order to improve the performance of the resonant lines formed on the front and back surfaces of the dielectric substrate 35 at ultra-high frequencies, especially in the UHF band, the patterned substrate is held in a suspended structure within a metal casing to form an electronic tuning circuit. Form. In FIG. 5, a dielectric substrate 35 is fixed in a metal casing 51 with a support 52. As shown in FIG.
Since the dielectric substrate 35 is floating in the air within the container, an integrated capacitor can be easily formed by forming the resonant lines 28 and 29 on the upper and lower sides.

In the above embodiment, fine adjustment of the variable tuning frequency is possible by trimming the area between the dielectric substrates between the upper and lower resonant lines.
Furthermore, in order to form a capacitor and obtain a desired capacitance, the dielectric substrate must have a certain thickness and size. The thinner the thickness, the easier it is to obtain a capacitance value, so the cost can be reduced from a material standpoint, and the dielectric material used has a smaller dielectric loss (tan δ), which is better in terms of circuit characteristics.

As an example, the resonant line shown in FIG. 3C is held in a suspended structure and the dielectric substrate 35 is
A 0.4 mm Teflon glass resin substrate is used, the capacitor area is 15 mm ² (approximately 11 pF), the capacitance change of the variable capacitance diode 30 is in the range of 1:7.6, and the height inside the metal case is kept at 15 mm. As a result, we were able to cover the tuning frequency range from 470MHz to 920MHz.

FIG. 6 shows a configuration example of a planar electronic tuner using the resonant circuit shown in FIG. 3C, and only the principle high-frequency circuit portion is shown. Further, the high frequency amplification section is omitted because it is sufficient to add a resonant circuit as in FIG. 1. This will be explained below using figures.
A high frequency input signal in the UHF band enters from the input terminal 61 and passes through the coupling loop 62 to the double tuning circuit 63,
64 and enters the mixing circuit 73. On the other hand, the local oscillator section 67 enters the mixing circuit 73 through the tuned resonance section 66, is mixed with the input signal by the mixing diode 65, and an intermediate frequency signal is taken out from the terminal 70.
A DC voltage is applied to the variable capacitance diode 68 from the terminal 71, and the chiyoke coil 69 serves as its return path. A planar resonant line including a ground conductor 72 is formed on the substrate, and as shown in the cross-sectional view B, a substrate 75 on which the resonant line is formed is held in a metal casing 74.

The dielectric substrate 74 is provided at an asymmetrical position upwardly and downwardly on the casing 75 which serves as an outer grounding and shielding plate. By making it asymmetrical in this way, the spread of the electromagnetic field can be reduced, and there is no need to use a conventional interstage shielding plate.

As described above, the present invention includes a ring-shaped resonator in which substantially U-shaped or semicircular first and second conductors are opposed to each other and provided on one principal surface of a dielectric substrate; 1. A capacitance section between the first and second conductors provided at one end where the second conductor faces each other, and a variable capacitance diode provided at the other end, the capacitance section comprising: One end of a first conductor provided on one main surface of the dielectric substrate is provided by penetrating the dielectric substrate and extending to the other main surface of the dielectric substrate, and one end of the second conductor is provided so as to penetrate the dielectric substrate and extend to the other main surface of the dielectric substrate. By configuring them to face each other via the dielectric substrate, (i) there is no RF grounding in the tuning circuit, resulting in low loss;
Furthermore, since it can be patterned, there is little variation due to assembly.

(ii) Since the circuit is a closed loop, there is little leakage of electromagnetic fields.

(iii) A suspended structure can reduce the dielectric loss of the substrate and at the same time can be expected to improve the temperature characteristics. On the other hand, a low-cost substrate (for example, epoxy glass, etc.) can be used as a substrate because it does not cause any problem even if the dielectric loss is a little bad.

It has the following effects and has great industrial value.

[Brief explanation of drawings]

Fig. 1 is a basic configuration diagram of a conventional electronic tuning tuner, Fig. 2 A and B are plan views explaining the principle of the electronic tuning circuit of the present invention, and Fig. 2 C is an equivalent circuit diagram of Fig. 2 A and B. , Figure 2D is a characteristic diagram showing the relationship between the tuning voltage and resonant frequency of the electronic tuning circuit, Figure 2E is a characteristic diagram of the no-load Q frequency of the electronic tuning circuit,
FIG. Figure D is a cross-sectional view of the same, Figure 4A is a plan view of another embodiment, Figure B is a cross-sectional view of the same, Figure 5 is a cross-sectional view showing an example of the configuration of the electronic tuning circuit, and Figure 6A is a plan view of another embodiment. A plan view of the tuning circuit, and B is a sectional view thereof. 28, 29... Resonance line section, 30... Variable capacitance diode, 32... DC voltage terminal, 33... Chiyoke coil, 34... Capacitor, 35... Dielectric substrate, 51... Metal casing.

Claims (1)

[Claims] 1. A ring-shaped resonant line formed by substantially U-shaped or semicircular first and second conductors facing each other is provided on one main surface of the dielectric substrate, and the first and second A capacitance section between the first and second conductors is provided at one end where the conductors face each other, and a variable capacitance diode is provided at the other end, and the capacitance section is located on one main surface of the dielectric substrate. One end of the first conductor provided extends through the dielectric substrate to the other main surface of the dielectric substrate, and is opposed to one end of the second conductor via the dielectric substrate. An electronic tuning circuit configured to