JP2559706Y2 - Broadband oscillation circuit - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wideband oscillation circuit suitable for use in a television or a video tape recorder (VTR).

[0002]

2. Description of the Related Art FIG. 5 shows a conventionally known broadband oscillation circuit with a collector grounded clap type AFT (automatic fine tuning) circuit. The oscillation frequency of the broadband oscillation circuit is mainly determined by a resonance circuit composed of a half-wavelength inductive line 20, which is a kind of inductive element, a tuning variable capacitance diode 10, and a tuning capacitance 6, and a terminal. The oscillation frequency is selected from 12 by the tuning voltage TU applied to the tuning variable capacitance diode 10 in a reverse bias state. On the other hand, the AFT circuit
An FT correction capacitor 7 and an AFT variable capacitor diode 8 connected in series are connected in parallel to the tuning capacitor 6 and A
AFT control voltage CV applied to FT voltage application terminal 11
As a result, the capacitance of the AFT variable capacitance diode 8 changes. The change in capacitance changes the resonance capacitance of the entire wide-band oscillation circuit, and finely controls the oscillation frequency. This is mainly for correcting fluctuations in the oscillation frequency due to changes in the ambient temperature, fluctuations in the power supply voltage, and the like.

[0003]

By the way, the AFT circuit in the above-mentioned broadband oscillation circuit has an AFT control width Δf.
(Oscillation frequency correction range) differs depending on the oscillation frequency of the oscillation circuit, and its frequency characteristic is obtained as follows. First, the resonance capacitance viewed from the inductive line 20 is as shown in FIG. Here, it is assumed that the value of the AFT variable capacitance diode 8 is 7 pF at the time of 0 control and is reduced to 5 pF at the time of maximum control. In addition, tuning variable capacitance diode 1
0 indicates that the capacity when oscillating on the LOW channel (510 MHz) is VD1L, and the HIGH channel (890 MHz)
The capacitance at the time of oscillation in z) is VD _1H . Further, each constant is set as follows.

Tuning capacitance 6: capacitance C6; 10 pF AFT correction capacitance 7: capacitance C7; 2 pF AFT variable capacitance diode 8: capacitance VD ₂ ; 7 pF AFT variable capacitance diode 8: capacitance VD ₂ '; 5 pF tuning variable capacitance diode 10: Capacitance VD _1L ; 17 pF Tuning variable capacitance diode 10: Capacitance VD _1H ; 3 pF Under such conditions, the combined capacitance C _TL (at 0 control) and C _TL ′ (at maximum control) during oscillation in the LOW channel are , _{respectively, C TL = 6.880pF, C TL} '=
6.834 pF. Further, the AFT control width Δf _L is obtained according to the following equation, and becomes +1.71 MHz.

[0005]

[Formula 1] Similarly, the combined capacitance C _TH (at the time of 0 control) and C _TH '(at the time of maximum control) during oscillation in the HIGH channel
Are C _TH = 2.382 pF and C _TH ′ = 2.3, respectively.
It becomes 76 pF. Therefore, the AFT control width Δf _H is +
1.12 MHz. Next, in the circuit shown in FIG. 6, when exactly the same calculation is performed when the capacitance C7 of the AFT correction capacitance 7 is changed to 3 pF, Δf _L becomes +2.
81 MHz and Δf _H are +1.67 MHz. FIG. 7 is a frequency characteristic diagram of the AFT control width Δf showing the above result. The above calculation result indicates that the capacitance of the AFT variable capacitance diode 8 is equal to the capacitance V according to the AFT control voltage CV.
This is an example in the case where the capacitance is reduced from D ₂ (7 pF) to the capacitance VD ₂ ′ (5 pF). For example, when the capacitance is increased from 7 pF to 9 pF, the same result can be obtained only by changing the sign to minus. As described above, in the conventional oscillation circuit, there is a problem that the AFT control width Δf has a deviation such that the AFT control width Δf is small when the oscillation frequency is high and is large when the oscillation frequency is low.

FIG. 8 is a circuit diagram showing a configuration of a UHF band broadband oscillation circuit obtained by modifying the circuit of FIG. 5 in order to correct the deviation of the AFT control width Δf. In this figure, elements having the same functions as those in FIG. 5 are denoted by the same reference numerals, and description thereof is omitted. In this broadband oscillation circuit, the capacitance 1 is sufficiently smaller than the capacitance 7 so that the inductive line 20 and the AFT variable capacitance diode 8 are connected in parallel.
3 (for example, 0.5 pF) is inserted between the cathode of the tuning variable capacitance diode 10 and the cathode of the AFT variable capacitance diode 8. The AFT characteristic of this broadband oscillation circuit, when calculated in the same manner as the above-described calculation of the AFT control width Δf, is as shown by a broken line in FIG. Is improved, and an AFT characteristic having a constant frequency characteristic is obtained.

However, if an AFT circuit is added to the resonance circuit, an unnecessary resonance circuit is likely to be formed when mounting on a printed circuit board due to the inductance of the pattern and the stray capacitance between the patterns depending on the grounding position.
As a result, the AFT characteristics (frequency characteristics) undulate. In particular, as shown in FIG. 8, when the number of elements is large, the inductance and the stray of the pattern tend to be large on the layout, and as described above, even if the deviation between the HIGH channel and the LOW channel is improved,
A point where the characteristic changes sharply on the way is likely to occur. FIG.
Is an example of the AFT characteristic in which such undulation has occurred.
FIG. 11 shows unnecessary resonance circuits I, II, I formed by the inductance and stray capacitance of the pattern when the broadband oscillation circuit shown in FIG. 8 is mounted on a printed circuit board.
FIG. 2 is a circuit diagram illustrating an example of II (solid line). In this figure, reference numerals 17 and 18 indicated by broken lines indicate pattern inductance, and reference numeral 19 indicates stray capacitance.

As described above, in the conventional wideband oscillation circuit shown in FIG. 5, the AFT control width Δf is small when the oscillation frequency is high, and large when the oscillation frequency is low.
There is a problem that a deviation occurs depending on the oscillation frequency.
Further, in the conventional broadband oscillation circuit shown in FIG. 8, a point where the AFT characteristic changes abruptly in the middle is likely to occur, which causes a problem that an unnecessary resonance circuit is formed.

The present invention has been made in view of the above-mentioned circumstances, and does not form an unnecessary resonance circuit, is simple in circuit design, and can easily obtain an AFT characteristic having a flat frequency characteristic. It is intended to provide a circuit.

[0010]

In order to solve the above-mentioned problems, according to the invention of claim 1, one end of an inductive element and one end of a first variable capacitance diode for selecting an oscillation frequency are provided. Are connected at a first connection point, one end of a correction capacitor is connected to the other end of the first variable capacitance diode, and a second variable capacitance diode for fine tuning of the oscillation frequency is connected to the other end of the inductive element. One end is connected, the other end of the second variable capacitance diode and the other end of the correction capacitor are connected at a second connection point,
A resonance circuit in which the first connection point and the second connection point are connected by a small-capacitance capacitor; a first feedback capacitor interposed between each base and the emitter; And a pair of transistors connected by two feedback capacitors, wherein the resonance circuit is connected between the bases of the pair of transistors.

According to a second aspect of the present invention, one end of the first variable capacitance diode for selecting an oscillation frequency and one end of a small capacitance capacitor are connected to one end of the inductive element. Is connected to one end of an oscillation frequency fine tuning second variable capacitance diode and one end of a tuning capacitor, and the other end of the tuning capacitor and the other end of the first variable capacitance diode are connected to each other. 1, the other end of the second variable capacitance diode and the other end of the small capacitance capacitor are connected at a second connection point, and the first connection point and the second connection point And a resonance circuit connected by a correction capacitor,
A first feedback capacitor is interposed between each base and the emitter, and a pair of transistors whose emitters are connected by a second feedback capacitor are provided between the bases of the pair of transistors. The resonance circuit is connected.

[0012]

According to the first aspect of the present invention, the tuning voltage is the first voltage.
Is supplied to the first variable capacitance diode connected in series to the inductive element at the connection point. The oscillation frequency is mainly determined by the inductive element, the first variable capacitance diode, and the like. A predetermined control voltage is supplied to a second connection point to which the correction capacitor and the second variable capacitance diode are connected, and the control voltage changes the capacitance of the second variable capacitance diode.
As a result, the capacitance of the entire resonance circuit changes, and fine control of the oscillation frequency is performed. Further, the pair of transistors for the oscillator has a balanced circuit configuration floating at a high frequency when viewed from the ground point, and it is not necessary to provide a ground point in the circuit. Therefore, no inductance is generated by the pattern with the ground circuit interposed.

According to the invention, the tuning voltage is supplied to the first connection point between the tuning capacitor and the first variable capacitance diode connected in series. The oscillation frequency is mainly determined by the inductive element, the first variable capacitance diode, and the tuning capacitor. Also, the second
A predetermined control voltage is supplied to a second connection point where the variable capacitance diode and the small capacitance capacitor are connected.
The control voltage changes the capacitance of the second variable capacitance diode. As a result, the capacitance of the entire resonance circuit changes, and fine control of the oscillation frequency is performed. Further, the pair of transistors for the oscillator has a balanced circuit configuration floating at a high frequency when viewed from the ground point, and it is not necessary to provide a ground point in the circuit. Therefore, no inductance is generated by the pattern with the ground circuit interposed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a configuration of an embodiment of the present invention. In this figure, the elements having the same functions as those of the related art shown in FIG. By the way, in order to improve the undulation of the AFT characteristic, there is a solution to include a damping element such as a core and a resistor in the unnecessary resonance circuit. However, although this method can solve the swell, it is not an essential solution since an unnecessary resonance circuit remains. In addition, a complicated unnecessary resonance circuit may be formed depending on the arrangement state of components.

Therefore, the present embodiment is characterized in that the broadband oscillation circuit has a balanced circuit configuration as shown in FIG. In the illustrated resonance circuit, the tuning voltage TU is supplied from the terminal 12 via the resistor 14 to the tuning variable capacitance diode 1.
0 is supplied to one end. The other end of the variable capacitance diode 10 has a 波長 wavelength, which is a kind of inductive element.
An inductive line 9 is connected in series. In order to correct the AFT control amount, the inductive line 9 and the variable capacitance diode 10 have a correction capacitor 7 and an AF
The variable capacitance diode 8 for T is connected in parallel. A capacitor 13 is connected between a connection point P1 between the inductive line 9 and the variable capacitance diode 10 and a connection point P2 between the correction capacitance 7 and the variable capacitance diode 8. Further, the AFT control voltage CV is supplied to the connection point P2 via the resistor 15. One end of the inductive line 9 is grounded by a ground resistor 16 having a resistance value substantially equal to that of the resistor R1.

The oscillator transistors 4 and 4 are constituted by ICs (integrated circuits), and feedback capacitors 3, 2 and 3 connected in series are connected between the respective bases. At the connection point of 3 and 2,
The emitters of the respective transistors 4, 4 are connected. Further, clap capacitors 5 and 5 are interposed in a signal path connecting the resonance circuit and the bases of the transistors 4 and 4, respectively. The resonance circuit shown in FIG. 1 is in a state of floating at a high frequency when viewed from the ground point. That is, in terms of high frequency, it is not necessary to provide a ground point in the circuit. Therefore, there is no inductance due to the pattern interposed with the ground circuit as shown in FIG. In addition, a stray capacity 19 shown in FIG.
9, no loop circuit is formed, so that no unnecessary resonance circuit is formed and the circuit is not affected.

FIG. 2 is an equivalent circuit of the resonance capacitance in this embodiment. Here, each constant at the time of 0 control is set as follows. Capacitance 13: Capacitance C13; 0.25 pF AFT correction capacitance 7: Capacitance C7; 2 pF The other constants are the same as in FIG. In FIG. 2, the combined capacitances C _TL (at the time of 0 control) and C _TL ′ (at the time of maximum control) at the time of oscillation in the LOW channel are C _TL = 7.062 pF and C _TL ′ = 6.9994 pF, respectively.
Becomes Further, the AFT control width Δf _L is obtained according to the above-described formula 1, and is +2.29 MHz. Similarly, H
The combined capacitance C _TH (at the time of 0 control) and C _TH ′ (at the time of maximum control) during oscillation in the IGH channel are respectively C _TH =
2.583 pF and C _TH '= 2.569 pF. Therefore, the AFT control width Δf _H is +2.42 MHz.

Next, in FIG.
When the same calculation is performed for the case of changing to F, AF
The T control width Δf _L is +2.82 MHz, and the AFT control width Δf _H is +3.96 MHz. The result is illustrated in the characteristic diagram shown in FIG. Here, the solid line shown is the AFT control width Δf when the capacitance C13 is 0.25 pF, and the broken line is the AFT control width Δf when the capacitance C13 is changed to 0.5 pF.

As is apparent from the drawing, the selection of the correction capacitors 7 and 13 makes it possible to obtain a smooth and desired AFT.
The frequency characteristics of the control width can be obtained. Further, as described above, first, the control width of the LOW channel is set by the capacitance C7 of the correction capacitance 7, and then the control width of the HIGH channel is set by the capacitance C3, thereby intentionally increasing the control width of the HIGH channel. You can also. As described above, in the balanced wide-band oscillation circuit shown in FIG. 1, the frequency deviation of the AFT characteristic is improved, and it is not necessary to pay attention to avoid an unnecessary resonance circuit. An AFT characteristic having a simple frequency characteristic can be easily obtained.

FIG. 4 shows another embodiment of the present invention, in which the oscillator is constituted by an inductive line 9 of 1/4 wavelength, and
It is a circuit diagram to which a T circuit was added. In the figure, the tuning volume
The quantity 6 and the tuning variable capacitance diode 10 are connected in series at a connection point P3, and a tuning voltage TU supplied from the terminal 12 is supplied to the connection point P3. Further, the AFT variable capacitance diode 8 and the small capacitance 13 are connected to a connection point P4.
And the AFT voltage application terminal 1 is connected to this connection point P4.
The AFT control voltage CV is applied from 1. Also in this broadband oscillation circuit, similarly to the circuit shown in FIG. 1, the deviation of the AFT characteristic is improved, and it is easy to design without worrying about the generation of an unnecessary resonance circuit, and it has a flat frequency characteristic without undulation. AFT characteristics can be easily obtained.

In each of the embodiments, the resonance circuit is described as using a quarter-wave inductive line as an inductive element. In the present invention, the resonance circuit uses a coil as an inductive element. There may be.

[0022]

As described above, according to the first aspect of the present invention, one end of the inductive element and one end of the first variable capacitance diode for selecting the oscillation frequency are connected at the first connection point. One end of a correction capacitor is connected to the other end of the first variable capacitance diode, one end of a second variable capacitance diode for oscillation frequency fine tuning is connected to the other end of the inductive element, The other end of the variable capacitance diode and the other end of the correction capacitor are connected at a second connection point, and the first connection point and the second connection point are connected by a small capacitance capacitor. A first feedback capacitor interposed between each base and the emitter, and a pair of transistors connected to each other by a second feedback capacitor. Because of connecting the resonant circuit between each other based register is not unnecessary resonance circuit is formed, it is easy to design, is the advantage that it is possible to easily obtain a flat AFT characteristic of the frequency characteristic is obtained.

According to the invention, one end of the first variable capacitance diode for selecting the oscillation frequency and one end of the small capacitance capacitor are connected to one end of the inductive element, and one end of the inductive element is connected to the other end of the inductive element. One end of a second variable capacitance diode for fine tuning of the oscillation frequency and one end of a tuning capacitor are connected to the other end, and the other end of the tuning capacitor and the other end of the first variable capacitance diode are connected to the first. The other end of the second variable capacitance diode and the other end of the small capacitance capacitor are connected at a second connection point, and the first connection point and the second connection point And a resonance circuit connected by a correction capacitor, a first feedback capacitor is interposed between each base and the emitter, and each emitter is connected by a second feedback capacitor. A pair of transistors, and the resonance circuit is connected between the bases of the transistors. Therefore, an unnecessary resonance circuit is not formed, the design is easy, and the AFT characteristic having a flat frequency characteristic is easily obtained. The advantage is that it can be done.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of a resonance circuit in the broadband oscillation circuit shown in FIG.

FIG. 3 is a frequency characteristic diagram showing AFT characteristics of the broadband oscillation circuit shown in FIG.

FIG. 4 is a circuit diagram showing a configuration of another embodiment of the present invention.

FIG. 5 is a circuit diagram showing the configuration of a conventional broadband oscillation circuit with a collector-grounded clap type AFT (automatic frequency tuning) circuit.

FIG. 6 is an equivalent circuit diagram of a resonance circuit in the conventional broadband oscillation circuit shown in FIG.

7 is a frequency characteristic diagram of an AFT control width Δf (oscillation frequency correction range) of the equivalent circuit shown in FIG.

8 is a circuit diagram showing a configuration of a conventional oscillation circuit in which a circuit is modified to correct a deviation of Δf in the broadband oscillation circuit shown in FIG.

FIG. 9 is an AFT of the broadband oscillation circuit shown in FIGS. 5 and 8;
FIG. 4 is a frequency characteristic diagram showing an example of a characteristic.

FIG. 10 is a frequency characteristic diagram showing occurrence of a point where a sharp change occurs in the AFT characteristic of the broadband oscillation circuit shown in FIG. 8;

FIG. 11 is a circuit diagram showing examples I, II, and III of an unnecessary resonance circuit formed when mounted on a printed circuit board.

[Explanation of symbols]

2 Feedback capacitance (second feedback capacitor) 3 Feedback capacitance (first feedback capacitor) 4 Transistor 6 Tuning capacitance (tuning capacitor) 7 Correction capacitance (correction capacitor) 8 AFT variable capacitance diode (second variable) 9 Capacitive diode 9 Inductive line ( Inductive element) 10 Variable capacitance diode for tuning (First variable capacitance diode) 13 Capacitance (Small capacitance capacitor) P1, P3 Connection point (First connection point) P2, P4 Connection point ( Second connection point)

Claims (4)

(57) [Scope of request for utility model registration] 1. One end of an inductive element and one end of a first variable capacitance diode for selecting an oscillation frequency are connected at a first connection point, and a correction capacitor is connected to the other end of the first variable capacitance diode. One end and tuning capacitor
One end of the one end and is connected, a second variable capacitance diode for the other end to the oscillation frequency fine tuning of the inductive element
And the other end of the tuning capacitor are connected, and the second
The other end of the variable capacitance diode is connected to the other end of the correction capacitor at a second connection point, and the first connection point and the second connection point are connected by a small capacitance capacitor. And a pair of transistors each having a first feedback capacitor interposed between each base and emitter and having their emitters connected by a second feedback capacitor. The resonance circuit between
3. A wide-band oscillation circuit according to claim 1, wherein one end and the other end of said tuning capacitor are connected. 2. One end of an inductive element is connected to one end of a first variable capacitance diode for selecting an oscillation frequency and one end of a small capacitance capacitor, and the other end of the inductive element is connected to a second variable for tuning. One end of a capacitance diode is connected to one end of a tuning capacitor, the other end of the tuning capacitor is connected to the other end of the first variable capacitance diode at a first connection point, and the second variable capacitance is connected. A resonance circuit in which the other end of the diode and the other end of the small-capacitance capacitor are connected at a second connection point, and the first connection point and the second connection point are connected by a correction capacitor; A first feedback capacitor is interposed between the base and the emitter, and a pair of transistors whose emitters are connected by a second feedback capacitor are provided. The resonant circuit between the base of the transistor
3. The broadband oscillation circuit according to claim 1, wherein one end and the other end of said inductive element are connected. 3. The broadband oscillation circuit according to claim 1, wherein said inductive element is a quarter-wave resonance line. 4. The broadband oscillation circuit according to claim 2, wherein said inductive element is a quarter-wave resonance line.