JPS643081B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to an oscillation circuit that can be used in a down converter circuit for a television tuner circuit SHF as a broadband local oscillation circuit in a system using a heterodyne system. .

Conventional configuration and its problems Line impedance Zin in distributed constant circuit
If the characteristic impedance Zo, the terminal impedance Z _R of the line, and the line length are l, then Zin=ZoZ _R +jZo·tanβl/Zo+jZ _R ·tanβl (1). However, β=2π/λ (λ: wavelength) ...(2) When Z _R = 0 in equation (1), Zin=jZotanβl ...(3) The characteristic normalized by Zo is As shown in Figure 1, it changes as inductive between 0 and λ/4, capacitive between λ/4 and λ/2, and so on.

Utilizing the range between 0 and λ/4 of this line, Quantities can be connected to form a resonant circuit.

Conventionally, there is a reflection type oscillator constructed by connecting this resonant circuit to an amplifier. As shown in Figure 2, this consists of a tuning diode (hereinafter referred to as varactor diode) _D1 whose capacity can be varied by a first external DC voltage, and a second external DC voltage connected to the other end of this tuning diode. _This is an oscillation circuit in which a resonant capacitor is formed by the combined capacitance of a switch diode D ₂ that can be switched between conduction and non-conduction depending on a voltage, and a capacitor Cf _D connected in parallel to this switch diode D 2. In the figure, block A is a resonant section, and block B is an amplification section. Moreover, L ₁ indicates a resonant line. C ₁ and C ₂ are large capacitors for coupling.

The resonance is caused by the capacitance C _D1 of the line L ₁ and the varactor diode D ₁ , the stray capacitance Cf of the circuit, the capacitance C _D2 of the switching diode D ₂ , and the switching diode
It consists of a circuit consisting of a composite capacitor of capacitance Cf _D connected in parallel with D ₂ . If this combined capacitance is Co, then at the resonance point there is the following relationship: 1/ωoCo=Zotanβl (4), and the circuit shown in Figure 2 oscillates at this ωo.

The resonant block A is connected to the amplifier block B through a coupling capacitance _C1 , and the tuning voltage BT is applied through a high resistance _R1 .
has been added. The cathode of a varactor diode D ₁ is connected to the intersection of the coupling capacitance C ₁ and the high resistance R ₁ , the resonant line L ₁ is connected to the anode of the varactor diode D ₁ , and a part of the resonant line L ₁ Grounded through high resistance _R2 . Resonant line L ₁ passes through coupling capacitance C ₂ to switching diode D ₂
connected to. The intersection of the coupling capacitance C ₂ and the switching diode D ₂ is equivalent to the stray capacitance connected in parallel to the switching diode D ₂ or a sufficiently small capacitor approximately equal to this stray capacitance, and the reverse bias that occurs when non-conducting. capacity
Grounded by Cf _D. Further, a switch voltage B _S is applied to the intersection of the coupling capacitance C ₂ and the switching diode D ₂ through a high resistance R ₃ .

In this resonant part A, a switching diode
When D ₂ conducts, the resonant circuit has a coupling capacitance C ₂
The capacitance Cf _D has almost no effect. Therefore, the resonant capacitance is the sum of the tuning capacitance C _D1 of the varactor diode D ₁ , the coupling capacitances C ₁ and C ₂ , and the stray capacitance Cf including the amplifier block B, but the coupling capacitances C ₁ and C ₂ are the tuning capacitance. Since a large value is used for C _D1 , the effective combined capacitance Co becomes Co≈C _D1 + Cf (5).

By the way, when the switching diode _D2 becomes non-conductive, the switching diode _D2 has a capacitance.
It is grounded through Cf _D , but the capacitance Cf _D is the coupling capacitance
Since it is extremely small compared to C ₁ and C ₂ , it cannot be ignored, and Co≒1/1/C _D1 +1/Cf _D +Cf (6) ≒Cf _D・C _D1 /Cf _D +C _D1 +Cf.

Here, if Cf _D = 1PF, Cf = 0.5PF C _D1 = 0.7PF to 6PF, the variable range of the composite capacitance Co in equation (5) is 1.2PF to 6.5PF.
So, if the resonant line _L1 has an impedance of 50Ω and a line length of 14.2mm, the frequency variable range is 900MHz ~
It becomes 1750MHz.

In the case of equation (6), the change in composite capacitance Co is 0.91PF~
It becomes 1.35PF and can obtain a frequency variable range of 1700MHz to 1900MHz.

Therefore, by making the switching diode _D2 conductive and non-conductive using the switch voltage B _S shown in Fig. 2, a frequency variable range from 900MHz to 1900MHz is attempted to be obtained _. There is the inconvenience that an applied positive/negative switching voltage is required.

OBJECTS OF THE INVENTION The present invention eliminates the drawbacks of the prior art and provides an oscillation circuit that can be used with a single power supply and can be switched in conjunction with a tuning voltage.

Structure of the Invention In the present invention, a tuning diode whose capacitance can be varied by a first external DC potential, a resonant line, and a switching diode whose anode is applied with a second external DC voltage serving as a reference voltage are connected in series. and connect it to the base or collector of the transistor that constitutes the amplifier circuit, and connect a capacitor in parallel to this switching diode,
By applying the first external DC voltage applied to the above tuning diode to the cathode of the switching diode, and grounding one end of the series circuit consisting of the tuning diode, the resonant line, and the switching diode in an alternating current manner, the switching diode The switching is performed in conjunction with the first external DC voltage applied to the tuning diode, and the two power supplies, positive and negative, which required switching, can be performed with a single power supply.

DESCRIPTION OF EMBODIMENTS An oscillation circuit according to an embodiment of the present invention will be described below with reference to FIGS. 2 and 3.

FIG. 3 shows the configuration of the oscillation circuit. In FIG. 3, block C is a resonant section and block D is an amplification section. The resonant block C is connected to the amplifier block D through a coupling capacitance _C1 , which has a high resistance.
The tuning voltage which is the first external DC potential through _R1
BT has been added. The cathode of the tuning diode D ₁ is connected to the intersection of the coupling capacitance C ₁ and the high resistance R ₁ , the resonant line L ₁ is connected to the anode, and a part of the resonant line L ₁ is grounded through the high resistance R ₂ .
Resonant line L ₁ is connected to the anode of switching diode D ₂ through coupling capacitance C ₂ . One end of a specific capacitor Cf _D is connected to the intersection of the coupling capacitor C ₂ and the switching diode D ₂ , and the other end of Cf _D is connected to the cathode of the other end of the switching diode D ₂ . Further, a second external DC voltage B _S serving as a reference voltage is applied to the intersection of the coupling capacitance C ₂ and the switching diode D ₂ through a high resistance R ₃ . The other end (cathode) of the switching diode _D2 is grounded through a coupling capacitor _C8 . Further, a tuning voltage B T or a voltage V _B obtained by dividing the tuning voltage B _T by the high resistance R _{7 and the resistance R 8 is} applied to the intersection of the switching diode D ₂ and the coupling capacitance C ₈ through the high resistance R ₇ . In this resonant part C, as the reference voltage B _S
Apply a voltage of value V _S.

When a voltage with a value of V ₁ < (V _S ) < V ₂ is applied to BT as a tuning voltage, the switching diode D ₂ becomes conductive in the range of V ₁ ≦V _B < _VS , and the resonator has a coupling capacitance C ₂ , C ₈ , and the capacitance Cf _D
has almost no effect. Therefore, the resonant capacitance is the tuning capacitance C _D1 of the tuning diode D ₁ and the coupling capacitance C ₁ , C ₂ , C ₈
and the stray capacitance Cf including the amplifier block D, but the coupling capacitances C ₁ , C ₂ , C ₈ are the tuning capacitance C _D1
Since a large value is used for , the effective combined combined capacitance Co becomes Co≈C _D1 +Cf.

By the way, when the tuning voltage B _T changes, its divided voltage
When V _B falls within the range of V _S <V _B ≦V ₂ , the switching diode D ₂ becomes non-conductive, and the capacitance Cf _D is extremely small compared to the coupling capacitances C ₁ , C ₂ , and C ₈ and cannot be ignored. The composite capacitance Co is Co≒1/1/C _D1 +1/Cf _D +Cf ≒Cf _D ·C _D1 /Cf _D +C _D1 +Cf.

By employing this configuration in this way, the reference voltage B _S can be used with a single power supply and can be switched in conjunction with the tuning voltage B _T.

In the resonant block C, the tuning diode D ₁ has a reverse bias voltage of the tuning voltage B _T , and the switching diode D ₂ has a bias reference voltage B _S
What is important is that the tuning voltage B _T is also applied, and the orientation of the diodes D ₁ and D ₂ does not particularly matter.

Block D represents the amplification section as described above, and the resonant section is connected from block C to the base of transistor _Q1 , and the collector of transistor _Q1 is grounded through the large capacitance _C6 . A bias is applied to the collector of the transistor Q ₁ through a resistor R ₅ and is fed back to the base through a resistor R ₄ to provide a base voltage. Note that the base bias does not need to be of the self-feedback type. transistor
The capacitor C ₅ between the emitter collector of Q ₁ is used to ground the shortest path between the emitter and the ground in an alternating current manner, and the capacitor C ₅ improves the stability of broadband oscillation. Further, C ₃ and C ₄ are bypass capacitors, respectively, and L ₂ is a chiyoke coil to extract high power. R ₆ is the emitter resistance and the capacitance
The oscillation output is taken out through _C7 , and the current is approximately
Approximately 10dBm of power can be extracted at 38mA. There are various ways to take out the oscillation output; it is also possible to take out the oscillation output from the collector by setting the capacitance of _C6 to about 10PF, or to take it out by inductance or capacitance coupling to the resonant line. .

Considering the power consumption, it is best to take it out from the emitter. There are many ways to extract the output or set the resonant line, but in the present invention, a variable voltage is applied to the switching diode in the resonator section, and the tuning voltage turns the switching diode into conduction and non-conduction. The important points are that the conduction is controlled automatically and that a single power supply can be used for switching. In the illustrated example, the resonator section is connected to the base of the transistor _Q1 , but this transistor may be configured as a base-grounded type or emitter-grounded type and the resonator section connected to its collector. The action and effect can be obtained.

In this example, a capacitor with a specific capacitance C _fD is connected in parallel to a switching diode, but if the above-mentioned sufficiently small capacitance can be obtained by the stray capacitance and reverse bias capacitance of the switching diode, is the above capacitor
The same effect can be achieved by omitting C _fD .

Effects of the Invention As described above, according to the present invention, the frequency of the oscillation circuit can be automatically switched using a single power supply, and a circuit with a simple configuration can be realized.

[Brief explanation of drawings]

Fig. 1 is a characteristic diagram showing the impedance of a one-side terminated λ/4 line, Fig. 2 is a circuit diagram of a conventional oscillation circuit, Fig. 3 is a circuit diagram of an oscillation circuit according to an embodiment of the present invention, and Fig. 4 is a characteristic diagram showing the relationship between reverse bias voltage and reverse bias capacitance of a switching diode. C... Resonant section, D... Amplifier, L ₁ ... Resonant line, D ₁ ... Varactor (tuning) diode, D ₂
...Switching diode, _Q1 ...Transistor, B _T ...First external DC voltage, B _S ...Reference voltage.

Claims (1)

[Claims] 1 A switching diode with a reverse bias capacitance that occurs when non-conducting with a stray capacitance or a small capacitor connected in parallel, and a tuning diode whose capacitance can be varied by a resonant line and a first external DC voltage are connected in AC series. One end of this series circuit is electrically coupled to the base or collector of the amplification transistor, and the other end is connected to the AC ground, and a resistor or chiyoke coil is connected to the anode of the switching diode. A second reference voltage within the variation range of the first external DC voltage is applied, a first external DC voltage is applied to the cathode side of the switching diode through a resistor or a chiyoke coil, and the first external DC voltage is By changing the
An oscillation circuit characterized in that the above-mentioned switching diode is automatically made conductive or non-conductive.