JPS6033007B2 - oscillation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oscillation circuit used in a tuner of a television receiver or the like.

In recent years, tuners for television receivers, etc.
Broadcast receiver functions in the UHF band are now indispensable.

Therefore, the oscillation circuit used in such a tuner must be configured to have sufficient characteristics in the UHF band, but in the UHF band, stray inductance and stray has a large effect on the capacitance characteristics, and therefore, in most cases, is the most practical configuration to obtain the desired characteristics.
It adopted a structure in which circuit components were arranged spatially and wired three-dimensionally (hereinafter referred to as a three-dimensional structure).

However, such a three-dimensional structure has poor workability and is problematic in terms of cost, so a planar structure using a printed circuit board has been desired.

However, with a planar structure, the arrangement of circuit components is limited to a plane, so the area occupied is larger than that of a three-dimensional structure, and there are also restrictions on printed pattern formation on the board, resulting in long wiring sections. At the same time, the wiring patterns become unnecessarily close to each other, so stray inductance and stray capacitance increase more than in the case of a three-dimensional structure, which greatly affects the characteristics of the oscillation circuit, making it impossible to obtain the required characteristics. Ta.

In particular, the effect of increasing stray inductance is that the ground terminal of each component cannot be kept at a sufficiently low potential with respect to the common potential point.For example, in an oscillation circuit, the ground terminal of the oscillation transistor and the common potential point (hereinafter referred to as ground), if a stray inductance of more than a certain value exists, normal oscillation operation will not occur.

This will be explained with respect to the circuit shown in FIG.

In the figure, 1 is an oscillation transistor, 2 is a feedback capacitor, 3 is a bias resistor, and 4 is an inductance that is inevitably formed due to the circuit configuration, and is named base lead inductance.

5 is a bypass capacitor, 6 is a coupling capacitor, 7
, 8, 11 are bias resistors, 9 is a choke coil, 1
0 is the damping resistor, 12 is the tuning capacitor, 1
3 is a tuning coil, 14 is a variable capacitance diode for tuning,
15 is a power supply terminal, 16 is a tuning voltage terminal, and 17 is a resonant circuit that determines the oscillation frequency of the oscillation circuit.

This oscillation circuit is composed of a base-grounded transistor 1, which oscillates due to the feedback effect generated from the collector to the emitter by a capacitor 2, and performs oscillation at a frequency determined by a resonance circuit 17.

It is of the so-called electronic tuning type, in which the capacitance of the variable capacitance diode 14 is changed by the tuning voltage supplied from the terminal 16 to tune to the frequency required for the UHF band tuner. Now, in such an oscillation circuit, if this is made into a planar structure using a printed circuit board, for example, the base lead inductance 4 increases, and if the inductance value exceeds a certain limit, the oscillation operation will be affected. .

Note that this base lead inductance 4 actually includes the inductance due to the electrode lead wire of the transistor, the lead wire of the capacitor 5, and the wiring from the grounding point of the resonant circuit 17 to the lead wire of the transistor. Here, in order to simplify the explanation, it is expressed as one inductance 4.

Among the effects of this increase in base lead inductance 4, what is particularly problematic is the hysteresis phenomenon when the oscillation frequency is changed.

In other words, as shown in Figure 2, if the horizontal axis represents the tuning voltage supplied to the terminal 16, and the resulting change in the oscillation frequency is shown on the vertical axis, part of the change is shown as the curve in the figure. When a hysteresis phenomenon occurs in and the tuning voltage is changed,
In a certain tuning voltage range, the oscillation frequency changes dramatically and suddenly shifts from a low frequency to a high frequency or vice versa, making it impossible to achieve sufficient tuning.

This phenomenon occurs when the base lead inductance 4 is
・It does not occur when the value is suppressed to a small value.

However, when using a planar structure as described above,
The base lead inductance is 4 if it is a three-dimensional structure.
Since it is not possible to make the size small, hysteresis inevitably occurs, making it impossible to obtain a product that can withstand practical use. Conventionally, in order to eliminate this drawback and obtain an oscillation circuit with a planar structure, there has been a method of providing a small capacitance capacitor between the emitter of the transistor 1 and ground, for example.

However, when a capacitor is inserted between the emitter and ground in this way, problems such as oscillation stopping at the high frequency part of the oscillation frequency or a decrease in the oscillation output occur, and the local oscillation for the tuner's mixing circuit is caused. This had the disadvantage that the signal bell decreased, deteriorating the noise figure and power gain of the tuner as a whole, and the hawk modulation characteristics also deteriorated, making it susceptible to interference signals.

SUMMARY OF THE INVENTION An object of the present invention is to provide an oscillation circuit with excellent productivity, which eliminates the drawbacks of the prior art described above and whose characteristics do not deteriorate even in a planar structure.

In order to achieve this object, the present invention is characterized in that a series resonant circuit is provided between the emitter of the oscillation transistor and ground. Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 3 shows an oscillation circuit according to an embodiment of the present invention, in which parts equivalent or identical to those of the circuit in FIG. 1 are given the same numbers, and detailed explanation thereof is omitted. The difference between this embodiment and the circuit shown in FIG. 1 is that the oscillation transistor 1
A series resonant circuit consisting of a coil 20 and a capacitor 21 is provided between the emitter and ground.

Next, its operation will be explained.

As already explained, when the inductance value of the base lead inductance 4 increases due to, for example, the oscillation circuit having a planar structure, a hysteresis phenomenon occurs in the oscillation operation.

Therefore, if a capacitor of small capacity is provided between the emitter of the transistor 1 and the ground, the hysteresis phenomenon can be suppressed, but the oscillation output will be significantly reduced and it will not be practical.
This state will be described with reference to FIG.

The characteristic curve in Fig. 4 has the inductance value Le of the coil 20 as Fujiki, and the oscillation output as the vertical axis.
Each curve uses the value of the capacitance Ce of the capacitor 21 as a parameter, and in each curve, an x mark indicates a portion where a hysteresis phenomenon occurs, and a 0 mark indicates a portion where the hysteresis phenomenon is suppressed.

In this FIG. 4, the capacitance of the capacitor 21 Ce=2p
As is clear from the curve of F, if the capacitor 21 is made of Fox F, the hysteresis phenomenon will not occur even if the inductance Le of the coil 20 is 0, but the oscillation output will drop so much that it cannot be put to practical use. This state of Le=0 and Ce=pF corresponds to the case where only a capacitor is used in the prior art. Next, if Ce = 1.5 pF, the drop in oscillation output will be considerably reduced, and the hysteresis phenomenon can be suppressed by rubbing the inductance Le of the coil 20 from 1 to 1 or HI, but it is still insufficient. It cannot be said that oscillation output is obtained. However, capacitor 21
If the capacitance Ce is set to lpF and the inductance Le of the coil 20 is set to 10 to 16 nH, a considerable oscillation output can be obtained and the hysteresis phenomenon can be suppressed, so that it can be made sufficiently practical.

Then, the capacitance Ce of the capacitor 21 is set to 0.5 pF,
By keeping the inductance Le of the coil 20 at 14 to 1 H, a sufficiently large oscillation output can be obtained without hysteresis.

Therefore, even if the inductance of the base lead inductance 4 becomes considerably large, an oscillation circuit with sufficient characteristics can be obtained, and the oscillation circuit can have a planar structure with excellent workability. Note that the △ mark indicates the initial state where Ce, Lc=0.

At this time, unless the values of the coil 20 and capacitor 21 are selected within a range such that the resonant frequency of the series resonant circuit formed by the coil 20 and capacitor 21 is considerably higher than the oscillation frequency of the oscillation circuit, oscillation will occur. Although the feedback phase in the circuit changes and oscillation becomes impossible, as is clear from FIG. Dripping is extremely easy.

In the embodiment shown in FIG. 3 above, the series resonant circuit consisting of the coil 20 and the capacitor 21 is connected to the transistor 1.
However, the connection point on the ground side of this series resonant circuit is not limited to the ground, but the connection point from the base of transistor 1 to the ground, that is, the base lead inductance in Figure 3. 4 and capacitor 5
Similar effects can be obtained by connecting to any part of the series circuit.

For example, one terminal of a series resonant circuit consisting of a capacitor 21 and a coil 20 is connected to the emitter of transistor 1, and the other terminal is connected to the base of transistor 1, or to the midpoint of the wiring forming base lead inductance 4. Even when connected, almost the same effect can be obtained.

FIG. 5 shows an embodiment in which the present invention is applied to a planar structure, that is, a printed circuit board.

In this embodiment, the coil 20 and capacitor 21 of the embodiment shown in FIG. 3 are formed by a substrate pattern, and a series resonant circuit consisting of these is provided between the emitter and base of the transistor 1. In Figure 5, the same as Figure 3,
Or the same parts are given the same numbers, and 22
Reference numeral 23 indicates a wiring portion of the substrate pattern for supplying a bias voltage to the base terminal B of the oscillation transistor, and 23 indicates a wiring portion of the substrate pattern for connecting the connection pattern land of the bypass capacitor 5 and the base terminal B. This is a part that is required depending on conditions such as the above conditions and maintaining the distance between circuit elements at a predetermined dimension. In other words, it is a portion that does not exist when the three-dimensional structure is investigated, and thus mainly forms the base lead inductance 4 shown in FIG. 3. 24 is a pattern land portion 26 for connecting the pattern wiring portion 22 and the emitter terminal E.
25 is a pattern portion forming a ground (common ground point).

In this embodiment, a series resonant circuit provided between the emitter E and the base B of the transistor 1 is formed by a pattern wiring portion 22 and a stray capacitance 24.

As a result, as in the embodiment shown in FIG. 3, the hysteresis phenomenon can be completely suppressed without reducing the oscillation output, and the oscillation circuit can have excellent workability due to its planar structure.

As is clear from Fig. 4, the values of the inductance of the coil and the capacitance of the capacitor constituting the series resonant circuit can be sufficiently obtained from the wiring part of the normal board pattern. According to this method, an oscillation circuit with excellent characteristics in which hysteresis is suppressed can be obtained without adding any special circuit elements, and the substrate pattern for supplying DC bias to transistor 1 is shared. Therefore, the board pattern does not become particularly complicated.

Of course, in the embodiment shown in FIG. 5 as well, the resonant frequency of the series resonant circuit formed between the base and emitter of transistor 1 must be kept higher than the oscillation frequency, and this is practically possible. is as already explained.

Further, in the above embodiments, the oscillation transistor is used as a base-grounded circuit, but the present invention is not limited to this, and it goes without saying that the same effect can be obtained even if the oscillation transistor is configured as a collector-grounded circuit. Nor.

Furthermore, as is clear from the above, the present invention is particularly effective when the oscillation circuit has a planar structure, but even when a three-dimensional structure is adopted, the base lead inductance becomes large due to the structure. It is equally effective in some cases.

As explained above, according to the present invention, even when it is impossible to obtain sufficient characteristics in the UHF band due to large stray inductance due to the configuration of the oscillation circuit, the oscillation circuit can be easily configured and have excellent characteristics. can be obtained.

As a result, the oscillation circuit in the UHF band has a planar structure with good workability, and a UHF tuner with excellent characteristics can be obtained at low cost.

[Brief explanation of the drawings] Figure 1 is a wiring diagram showing an example of a secondary oscillation circuit used in a UHF tuner, etc. Figure 2 is its characteristic curve diagram, Figure 3
5 is a wiring diagram of an oscillation circuit according to an embodiment of the present invention, FIG. 4 is a characteristic curve diagram thereof, and FIG. 5 is a pattern wiring diagram of an oscillation circuit according to another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Oscillation transistor, 4... Base lead inductance, 17... Resonance circuit, 20... Emitter coil, 21... Emitter capacitor, 22, 23, 2
5, 26... Wiring part based on board pattern. O short Z diagram

Claims (1)

[Scope of Claims] 1. In an oscillation circuit in which a floating inductance exists between a ground electrode terminal of an oscillation transistor and a low potential terminal of a resonant circuit for determining an oscillation frequency, the emitter terminal of the transistor and the floating inductance An oscillation circuit characterized in that a series resonant circuit having a resonant frequency higher than the oscillation frequency is provided between one end of the circuit or a dividing point thereof. 2. The oscillation circuit according to claim 1, wherein at least one of an inductance element and a capacitance element constituting the series oscillation circuit is formed by a substrate pattern. 3. The oscillation circuit according to item 2, wherein the substrate pattern forming the inductance element also serves as at least a part of the substrate pattern for supplying DC bias to the oscillation transistor.