JPS5915057Y2 - Transmission line type balanced unbalanced conversion transformer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a transmission line type balanced/unbalanced conversion transformer used, for example, in push-pull type power amplifiers in the VHF band and UHF band.

This type of conventional transformer uses one coaxial line 11 as shown in FIG. 12 and the other ends of the off-center conductor 11 are connected to a pair of balanced terminals 15 and 16, respectively.

The coaxial line 11 has an impedance connected to the unbalanced terminal 14, for example, the same impedance as the impedance of the signal source or load, and the length is generally around 1/4 wavelength λ of the signal source frequency. It is determined.

When the transformer as described above is used as a distributor, a signal is applied to the unbalanced terminal 14, and a signal is applied to the balanced terminal 15.
A signal is distributed to 16 and appears, and this distributed signal is 1
It has a phase difference of 80°.

When the transformer is used as a combiner, the signals applied to the balanced terminals 15 and 16 appear combined at the unbalanced terminal 14.

Next, FIG. 2 shows an example of a push-pull type power amplifier for the VHF band and UHF band in which the above transformer is used.

11 and 11' are transformers, respectively, and semi-flexible coaxial cables are used.

The signal applied to the unbalanced terminal 14 of the transformer 11 is unbalanced-balanced converted by the transformer 11 and output to the balanced output terminal 1.
5.16 and appears with a phase difference of 180°.

These signals are applied to the base of transistor 25.26 via an impedance matching circuit consisting of capacitors 21, 22.23 and coil 24.36.

Therefore, transistors 25 and 26 alternately amplify every half period of the signal, and these amplified outputs are sent to coils 27 and 2.
balanced terminals 15', 16 of the transformer 11' through an output matching circuit consisting of 8 and capacitors 29, 30, 31.
', where it is subjected to balanced-to-unbalanced conversion and taken out as an amplifier output to an unbalanced terminal 14'.

Note that 32° 33, 34, 35 in the figure is a choke coil that blocks the signal.

In an amplifier as described above, transistors 25,26
In order for these to ideally perform push-pull operation, the circuits connected to them need to be completely symmetrical.

However, the transformer 11 and transistors 25 and 26 on the input side
Looking at the connection relationship with the transistor 25, the coil 24
, the outer conductor 12 of the transformer 11 via the capacitor 21
On the other hand, the transistor 26 is connected to the center conductor 13 of the transformer 11 via a coil 36 and a capacitor 22.

Therefore, the electrical resistance due to the difference in the cross-sectional area of each conductor 12, 13 and the difference in high frequency loss due to the skin effect, etc., cause an unbalance in the excitation power of the transistors 25 and 26.

Further, the external conductor 26 of the transformer 11 tends to form a low impedance between it and the ground, and therefore the transistor 2
This will cause an imbalance in the excitation power of 5.26.

The unbalance for each output as well as the unbalance for each of these transistors 25 and 26 is
．． 26 and the center conductor 13 and outer conductor 12 of the output side transformer 11', the ideal push-pull operation is inhibited.

Furthermore, when the above-mentioned transformer 11' is used on the output side of a high-power power amplifier, heat generation due to loss can no longer be ignored, and the heat dissipation conditions are poor, especially in the center conductor 13, so the power used is reduced. restrictions were sometimes added.

The present invention was developed in view of the above circumstances, and involves connecting one center conductor and the other outer conductor to each other at one end of two coaxial lines, grounding one connection point, and connecting the other. connecting one center conductor and the other outer conductor to each other at each other end of the coaxial line, and connecting each connection point to two corresponding balanced terminals. This provides a transmission line-shaped balanced-unbalanced conversion transformer that can equalize the characteristics of two balanced terminals when looking at the coaxial line side and does not cause unbalanced connections to circuits using the transformer.

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

In Figure 3, 41 and 42 are coaxial lines, respectively.
They have approximately the same length and the same impedance.

One end of each of the coaxial lines 41, 42 is connected to the central conductor 13 and the outer conductor 12, one of which is grounded and the other connected to the unbalanced terminal 14.

Further, the other ends of the coaxial lines 41, 42 are connected to one center conductor 13 and the other outer conductor 12, and each of these connecting portions is grounded to a corresponding balanced terminal 15, 16.

The characteristic impedance of each of the coaxial lines 41 and 42 is twice the impedance connected to the unbalanced terminal 14, for example, the impedance of the signal source or load, and each length is generally around λ/4 of the signal source frequency. It is determined that it will become.

Therefore, the impedance of the above transformer is the coaxial line 4
It can be considered as a parallel connection of 1.42 characteristic impedances and is equal to the signal source (or load) impedance.

The transformer with the above configuration exhibits almost the same effect as the conventional transformer described above with reference to FIG. 1, but the difference from the transformer in FIG. This means that the characteristics are the same.

That is, each balanced terminal 15.16 is connected to a coaxial line 41.4, respectively.
This is because they are connected to one center conductor 13 and the other outer conductor 12 of 2, and are symmetrically connected to each other.

Therefore, when connecting the lance to a circuit in which the above transformer is used, this circuit is connected to the balanced terminal 1 of the transformer.
Compared to 5.16, there is an advantage that no unbalance occurs due to the characteristics.

In addition, in the transformer with the above configuration, the coaxial lines 41 and 42 are connected in parallel, so the conductor resistance is reduced and the heat generation is balanced.
Since heat dissipation conditions are improved, even higher power can be used.

Therefore, if the above transformer is used in place of the conventional transformer in the push-pull type amplifier shown in Fig. 2, the circuit can be connected without disturbing the balance of the excitation power of the transistors 25 and 26. The advantage is that high power can be used because of good operation and good heat dissipation conditions.

This circuit side is shown in FIG. 4, and the same parts in FIG. 4 as in FIG. 2 are given the same reference numerals.

Note that if the transformer shown in FIG. 3 is used and the circuit is connected as shown in FIG. 5, a 180° distributor can be constructed.

That is, an unbalanced component absorbing circuit 51 is inserted between the balanced terminals 15 and 16, and is further grounded via an unbalanced component absorbing resistor 52.

Further, in the above embodiment, the characteristic impedance of each coaxial line 41, 42 is twice the impedance of the signal source or load connected to the unbalanced terminal 14, but for example, the impedance on the unbalanced terminal 14 side is 50 g. ,
The impedance between the balanced terminals 15 and 16 is 1,25J7
If the coaxial line length is λ/4, the impedance becomes B11=25g, which can be realized using a coaxial line with a characteristic impedance of 50g.

A transformer with a special impedance, e.g. 17Ω
It goes without saying that in order to realize a transformer, coaxial lines having characteristic impedances of 50Ω and 25Ω may be connected in parallel as shown in FIG.

As mentioned above, the present invention combines two coaxial lines with arbitrary characteristic impedances as needed, so that the output characteristics of the two balanced terminals are perfectly balanced, and the line loss is low and the heat dissipation effect is improved. It is possible to provide a balanced/unbalanced conversion transformer with a good transmission line shape.

[Brief explanation of the drawing]

Fig. 1 is a configuration explanatory diagram showing a conventional transmission line type balanced/unbalanced conversion transformer, Fig. 2 is a circuit diagram showing an example of use of the transformer shown in Fig. 1, and Fig. 3 is a transmission line type balanced/unbalanced conversion transformer according to the present invention. FIGS. 4 and 5 are circuit diagrams showing an example of the use of the transformer shown in FIG. 3, respectively. 12...Outer conductor, 13...Center conductor, 14...Unbalanced terminal, 15.16...
・Balanced terminal, 41.42... Coaxial line.

Claims (1)

[Scope of utility model registration request] Two coaxial lines of approximately equal length are used, and one end of each is connected to one center conductor and the other outer conductor, one of these connections is grounded, and the other is connected to an unbalanced terminal. The other end portions of the coaxial line are connected to one center conductor and the other outer conductor, and these connection portions are connected to two balanced terminals in correspondence with each other. Transmission trace shaped balanced unbalanced conversion transformer.