JPS631104A - Local oscillator - Google Patents

Abstract

PURPOSE:To extend the variable range of the oscillation frequency by impressing a voltage, which is changed reversely to the DC voltage, which is impressed to a varactor diode of a resonance circuit, based on a transistor (TR). CONSTITUTION:The output from a subtractor 22 is given to the base of a TR 21 for the purpose of changing the base potential of the TR 21 reversely to the change of a tuning voltage BT, and the base bias of the TR 21 is reduced and a voltage VCB between the collector and the base is raised when the tuning voltage BT rises. An input capacity Cob is reduced in this manner to raise a maximum oscillation frequency. If the tuning voltage BT is reduced, the base bias of the TR 21 is raised and the voltage VCB between the collector and the base is reduced to increase the input capacity Cob, thereby reducing a minimum oscillation frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a television tuner 31 (a wideband local oscillation device used for F downconversion, etc.).

2. Description of the Related Art Recently, television tuners, SHF down converters, etc. require oscillation at high frequencies, and variable oscillation circuits using distributed constant circuits are often used.

Line impedance Zin in a distributed constant circuit has characteristic impedance Z. , the terminal impedance of the line is ZR9, and the line length is l, however, β=2π/λ (
λ: Wavelength) River...(2), and in the first equation, z
When R-0, 2 engineering n: ko2゜tanββ
...(3), and this is Z. The normalized characteristics range from 0 to λ/4 as shown in Figure 4.
It becomes inductive between λ/4 and λ/2, and capacitive between λ/4 and λ/2. A resonant circuit can be constructed by utilizing the area between O and λ/4 of this line and providing a capacitance thereto.

Conventionally, a reflection type oscillator is constructed by connecting this resonant circuit to an amplifier.

FIG. 5 shows an example, in which 50 is a resonator section, 51
is an amplifier. 52 is a resonant line, and 53°54.55 is a coupling capacitance. The resonant circuit is composed of the resonant line 52, the capacitance CvD of the variable capacitance diode 56, and the total capacitance of the stray capacitance Cf of the circuit.

If this total capacitance is 00, then at the resonance point, 1/ω
. C0: Zot＆npl −・−・・−
There is the relationship (4), and the circuit in Figure 5 has ω. oscillates.

The maximum oscillation frequency with such a configuration is the total capacitance C8
and the line length β of the resonant line 62. Line length l
is derived from the above fourth equation, where λ=C9 for λ of β=2π/λ
Substituting /fo Cv-3×108 [m) yields.

Minimum capacitance value C of currently available variable capacitance diode 66
Since vnmin is about 0.7 (1) F), considering the stray capacitance 67 o, s (pF), the total capacitance c
o is 0.7+o, ts = 1.2 (pF). Set the maximum oscillation frequency to 1760 (MHz) and Zo to [
Ω], then β=0.027 [m].

If the substrate is glass epoxy or alumina, multiply by the wavelength shortening rate. For glass epoxy, /=0.027 , o○9 [m].

Therefore, when a local oscillator is configured using this line length, the frequency f. The total capacitance C8 required to vary is calculated from the fourth equation as follows. fof:soo (MHz') to 1900
(MHz), the total capacitance C8 required to change up to 0.7 (1 MHz) is the value shown on the vest.
)F) ~s (pF) When using a variable capacitance diode, the total capacitance is 1.2 with the addition of a stray capacitance of 0.5 pF (1) The variable width of F, l ~e, ts (pF:) has a frequency f. is 900 (MHz) to 1750 (MHz) j f change - j Ruko,! : Indicates.

Note that the calculation results in the table above are the characteristic impedance Z of the resonant line 62. = 60 [Ω], the required maximum oscillation frequency f 0
．． 7 (pF), and the line length required to obtain f at a value of 1-27 [Moe].

In a television tuner circuit, the first video intermediate frequency must be set at 900 to cover the entire world frequency range.
When set to the MHz band, the range is approximately 900MHz to 1900MHz.
An oscillation range of MHz is required. However, this range of variation cannot be achieved within the range of the total capacitance from 1.2 [pF) to e,s (pF).

Therefore, conventionally, as shown in FIG. 5, the resonant line 62 of the resonator section 50 is divided into β1 and β2, and a switch diode 68 is interposed between the dividing point and the ground. The length of the resonant line 52 is switched and used by applying a voltage through the resistor 59 (or a choke coil) and turning the switch diode 58 on and off.

However, since the switch diode 68 has a capacitance C1 (1 [pF] to 2 [pF] in the case of a plastic package) consisting of a reverse bias capacitance and a package stray capacitance, the capacitance Of , the resonant line 52 is always in an alternating current state with a length l, and even when the switch diode 58 is non-conducting, it cannot obtain the length (β, +12), and is variable in high frequency bands. It was difficult to expand the scope.

Therefore, a local oscillator has been proposed that can oscillate over a wide range by switching the switch diode between conduction and non-conduction even in high frequency bands. This local oscillator includes a tuning diode whose capacity can be varied by a first external DC potential;
A resonant line and a switch diode whose conduction and non-conduction are switched by a second external DC potential are connected in series in an AC manner, and this is interposed between the pace or collector of the amplification transistor and ground, and the switch diode is connected to the switch diode. When the resonant line is not conductive, one end of the resonant line is grounded in an alternating current manner via a capacitor in parallel with the switch diode.

An example of this will be explained below using FIG. 6. Resonator part 6Q
and the amplification/width section 61 are connected through a coupling capacitor 62, and a tuning voltage B, which is a first external DC potential, is applied to one end of the coupling capacitor 62 on the side of the base vibration body section via a high resistance 63. There is. A variable capacitance diode 66, a resonant line 66, and a switch diode 67 are connected in series in AC terms between the connection point of high resistance 63 and coupling capacitance 62 (base of amplification transistor 64 in AC terms) and ground. It has been intervened.

Specifically, the cathode of a variable capacitance diode 67 is connected to the connection point between the high resistance 63 and the coupling capacitance 62, one end of the resonant line 66 is connected to the anode of the variable capacitance diode 67, and the other end of the resonant line 66 is connected to the high resistance 68 and is connected to the anode of the switch diode 6T via a coupling capacitor 69, and the cathode of the switch diode 67 is grounded. Further, a switch voltage Bs, which is a second external DC potential, is appropriately applied to the connection point between the switch diode 67 and the coupling capacitor 69 via a high resistance 70.

In the resonator section 60, when the switch diode 67 is made conductive by the switch voltage Bs, the resonance line 66 is directly grounded via the coupling capacitor 69, and the influence of the capacitor 71 connected in parallel with the switch diode 67 is almost negligible. Does not occur. Therefore, the resonant capacitance is the sum of the tuning capacitance CVD of the variable capacitance diode 65, the coupling capacitance 62.69, and the stray capacitance CJ including the amplifier section 61, but the coupling capacitance 62°69 is equal to the tuning capacitance Cv. Since a large value is used, the actual total capacity C8 becomes CO-''Cv9Cf (8).

By the way, when the switch diode 67 becomes non-conductive,
The switch diode is grounded via Cfo of capacitor 1. Here, the capacitance Cf is extremely small compared to the coupling capacitance 62.69, so this capacitance cannot be ignored in series connection, and the total capacitance C0 is: C= +01 CvIllCf.

becomes.

From the comparison between the eighth equation and the ninth equation, it can be seen that when the switch diode 67 is non-conducting, the resonant capacitance is smaller and the oscillation frequency is higher than when the switch diode 67 is conducting.

(fo= 1(pF), C1= o, es(pF)
, Cvo = o, 7 (pF: 1 to 6 (pF)), the variable range of the total capacitance C0 in the above equation 8 is 1, 2
(pF) ~ s, 5 (pF), and the frequency change range shown in the above clothing is from 900 (MHz) to 1750 (M
H2:] can be obtained. In the case of the above formula 9, the change in total capacitance C0 is 0.91 (pF) to 1.3 ts
(pF], and the range of Y in the table (7) is 1700 [MH
2,] to 1900 (MHz) can be obtained.

That is, by configuring as shown in FIG. 6 and appropriately switching the switch voltage Bs, the variable range can be expanded to the range Z in the table above, from 900 (MHz) to 1900 (MHz).

Note that in the resonator section 6o, a variable capacitance diode 65
Since the switching diode 67 needs to be turned on and off by the reverse bias voltage of the tuning voltage B, and the switch voltage Bs, the resonant line 66 is connected to both diodes 65.
It is important that diodes 67 are inserted in series, and the orientation of diodes 65 and 67 does not particularly matter. Further, as the capacitor 6 connected in parallel with the switch diode 6, only the capacitance of the switch diode during reverse bias may be used, or another capacitor may be set. resonator section 60 on the base of
are connected, and the collector of the transistor e4 is grounded through a capacitor 72. A bias is applied to the collector through a resistor 73, and the collector is connected to the base through a resistor 74 to receive a base potential. The base bias need not be of the self-feedback type. A coil 75 connected to the emitter of the transistor 640 is a choke coil for extracting power. resistance 76
is an emitter resistor for extracting the oscillation output through the coupling capacitor 77. Note that there are various methods for extracting the excavated output, including a method in which the capacitance is set to 10 pF and the output is extracted from the collector, and a method in which the excavation output is extracted by inductive coupling with the resonant line 66 or capacitive coupling.

Problems to be Solved by the Invention However, in order to absorb variations in the variable capacitance diode 66, the resonant line 66, etc., the maximum oscillation frequency and minimum oscillation frequency portions are further expanded by 100100 () or more to widen the variable range. On the other hand, the configuration shown in FIG. 6 has the disadvantage that it is difficult to further enlarge it.

In view of the above problems, the present invention provides a local oscillation device that can further expand the variable range of the oscillation frequency by increasing the maximum oscillation frequency and lowering the minimum oscillation frequency.

Means for Solving the Problems In order to solve the above problems, the local oscillator of the present invention applies a tuning voltage B to the base of the transistor in the amplifier section.
By applying a DC potential that changes inversely to the increase or decrease in T, a high potential is applied to the base of the transistor when the tuning voltage B is low, and a low potential is applied to the base of the transistor when the tuning voltage BT is high. By applying a potential,
V of the transistor. This makes it possible to expand the variable range of the oscillation frequency by utilizing the lI-ob characteristic.

Effects According to the above means, the maximum oscillation frequency can be made higher and the minimum oscillation frequency can be made lower than in the configuration according to the prior art, and the oscillation frequency can be expanded.

Embodiment Hereinafter, one embodiment of a local oscillation device according to the present invention will be described based on the drawings.

FIG. 1 is a circuit diagram of a local oscillation device according to an embodiment of the present invention, in which 10 is a resonator section and 11 is an amplification section. A high resistance 1 is connected to the coupling capacitance 12 with the amplifier section 11 in the resonator section 1Q.
A tuning voltage BT, which is a first external DC potential, is applied through 3. A cathode of a variable capacitance diode 14 is connected to the connection point between the coupling capacitance 12 and the high resistance 13, and a resonant line 15 is connected to the anode of the variable capacitance diode 14.
The other end of 5 is grounded through a high resistance 16 and connected to a switch diode 18 through a coupling capacitance 17. A connection point between the coupling capacitor 17 and the switch diode 18 is grounded by a stray capacitor or a specific capacitor 19, and a switch voltage BS, which is a second external DC potential, is applied across the high resistor 20. Furthermore, the output from the subtracter 22 is given as a pace potential to the connection point between the coupling capacitor 12 and the transistor 21 in the amplifier section 11.

The output of the subtracter 22 is the tuning voltage B? which is the first external DC potential. The difference between the tuning voltage B and the reference voltage vr is appropriately level-softened and level-suppressed, and is a DC voltage that has a characteristic that is inversely proportional to the increase or decrease in the tuning voltage B.

The collector of the transistor 21 of the amplifier 11 is grounded via a capacitor 23 and biased via a resistor 24 . A choke coil 25 is connected to the emitter of the transistor 21 and grounded via an emitter resistor 26. The capacitor 27 is for taking out the oscillation output and is connected to the emitter of the transistor 21, but various methods can be considered for taking out the oscillation output.

In the above oscillation circuit, the resonant capacitance includes the capacitance CvD of the variable capacitance diode 14, the parallel capacitance Cvs of the switch diode 18 and the capacitor 19, the input capacitance C0b1 of the transistor 21, and the stray capacitance added in parallel to each of these. It is the series summation of the additions.

If the switch diode 18 is conductive due to the switch voltage Bs, the capacitance at both ends of the switch diode 18 is 0, but if it is not conductive, it has a capacitance Cvs. Therefore, the resonant capacitance is larger when the switch diode 18 is conducting than when it is not conducting, and the same resonant line 1
5, the oscillation frequency changes as shown in FIG.

The base potential of the transistor 21 is the tuning voltage B.

If it is a constant value regardless of , the result will be as shown by the solid line in FIG. 2, and if variations in parts are taken into consideration, it is necessary to expand the variable range of the oscillation frequency as shown in the broken line in FIG. 2.

Therefore, in order to obtain a desired frequency range, in this embodiment, the output from the subtracter 22 is given to the pace in order to cause the base potential of the transistor 21 to change inversely to the increase/decrease of the tuning voltage BA. Tuning voltage B? When VcB becomes high, the pace bias of the transistor 21 is lowered, and the collector and pace voltage vcB is increased. Thus, as shown in Figure 3, by reducing the input capacitance Cob, υ,
Maximum oscillation frequency can be increased. Conversely, tuning voltage B.

If V becomes low, the pace bias of transistor 21 is increased, and the collector and pace voltage V. By lowering B, the input capacitance Co
By increasing b, the minimum oscillation frequency can be lowered.

Effects of the Invention As described above, according to the present invention, the variable capacitance diode i'? :, by applying a voltage that changes inversely to the applied DC voltage to the transistor pace, vam -Co
Since the variation range of the resonant capacitance is substantially expanded using the b characteristic, the variation range of the oscillation frequency can be expanded with a simple configuration.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a local excavation device according to an embodiment of the present invention, and FIG. 2 is an oscillation frequency and tuning voltage B. Figure 3 shows the characteristics of the relationship between vCB and C of the transistor.
0b, FIG. 4 is an impedance characteristic diagram of a single-sided terminated λ7/4 line, and FIGS. 5 and 6 are circuit diagrams of conventional local oscillator devices, respectively. 10...Common camera unit, 11...Amplification unit, 14
...Paris cap (tuning) diode, 16.
... Resonance line, 18 ... Switch diode, 21 ... Amplification transistor, 22 ...
...Subtractor. Name of agent: Patent attorney Toshio Nakao and 1 other person10
--- PC4a big/none): Zut ---519
'? ;4---Basso, 7°Tykeed IJ-Ichien 擾ゑ 1 give f8--Suinonakui λ-゜゛Br--7 possible words C Vr--1 standard +8

Claims (1)

[Claims] A series circuit in which a tuning diode whose capacity is controlled by a first external DC voltage, a resonant line, and a switch diode whose conduction and non-conduction are switched by a second external DC voltage are connected in series, and this series circuit. is connected in series to the base or collector of the amplifying transistor, and a DC voltage corresponding to a change in inverse proportion to the increase/decrease of the first external DC voltage is applied to the base of the amplifying transistor to vary the oscillation frequency within a variable range. A local oscillation device characterized by comprising: control means for enlarging the oscillator.