JPH061879B2 - Matching circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is used in, for example, a transmitter for medium-wave or short-wave radio broadcasting, and the output power is compared centering on a carrier frequency. Connected between a balanced output power amplification circuit that amplifies the transmission signal by a full bridge circuit and a load circuit such as an unbalanced input transmission antenna to distribute the balanced output to an unbalanced output. The present invention relates to a matching circuit for performing balanced / unbalanced conversion and impedance conversion between a balanced input / output circuit and an unbalanced input / output circuit, such as performing matching between the two.

(Prior Art) Conventionally, a high-frequency power amplifier such as a transmitter for radio broadcasting needs a large output power, and thus D is generally used.
The class bridge method is adopted. In this case, most of the amplifier elements are configured by using semiconductor elements such as FETs (field-effect transistors). At present, in consideration of the limit of allowable power of the elements, the limitation of withstand voltage, etc., a balanced output type amplifier is used. The composition is taken. In this case, for example, a load circuit such as a transmitting antenna is usually an unbalanced circuit, and therefore, in order to give the balanced output of the class D bridge power amplification circuit to the load circuit with an unbalanced input, a load circuit is provided between the power amplification circuit and the load circuit. A matching circuit is provided.

The following conditions are given to this matching circuit.

(1) When one of the electrodes of the power supply is grounded, the output is balanced with respect to ground, but the load circuit is often unbalanced with respect to ground, and the balanced output is unbalanced. Must be converted to output.

(2) In order to operate the amplifier element in class D operation, either the voltage waveform or the current waveform at the output point of the element must be a sine wave. Therefore, for example, when the current is selected to be a sine wave, the load circuit can be regarded as a resistor at the fundamental wave of the output frequency as seen from the element, and the impedance becomes higher as the output frequency becomes higher. Or it must have the function of a low-pass filter.

(3) In general, it is often difficult to design the input impedance of the load circuit and the optimum load impedance of the amplifier circuit so that they match each other. Therefore, a transformer for impedance conversion must be provided.

From the above conditions, the matching circuit used in the conventional high frequency power amplifier is configured as shown in FIG. That is,
This matching circuit 12 transforms the balanced output of the class D bridge circuit 11 composed of amplifier elements Q1 to Q4 by FETs into a transformer 12
Converts to unbalanced output by 1 and performs impedance conversion at the same time. The unbalanced output is input to the LC bandpass filter 122 to remove unnecessary DC components or low frequency components, and only the fundamental frequency component is extracted, and then supplied to the unbalanced input load circuit 13. It was done. In this matching circuit 12, the amplifying elements Q1, Q2, Q
If the currents flowing in 3 and Q4 are sine waves, transformer 12
The current flowing on the primary side of 1 also becomes a sine wave, and the voltage becomes a square wave.

However, in the conventional matching circuit as described above, although the power to be supplied to the load circuit is only the fundamental wave component, the characteristic required for the transformer 121 is that the fundamental wave passes with a small loss. It's not enough to let them do it. Further, in order to perform class D operation, it is necessary to pass a considerably high frequency wave with a small loss, and a transformer with a wide band and low loss is required. This becomes difficult to realize as the carrier frequency increases. Furthermore, the transformer usually has a small number of turns when increasing the pass frequency, but since the turns ratio must be determined with a small number of turns, the impedance conversion ratio becomes discrete,
It becomes difficult to obtain the required conversion ratio.

(Problems to be Solved by the Invention) As described above, the conventional matching circuit has problems that the loss of the transformer increases and the degree of freedom of impedance conversion decreases as the frequency increases.

Therefore, the present invention has been made to solve the above problems, and even if the operating frequency becomes high, it is possible to freely set the impedance conversion ratio with low loss without requiring a transformer that is difficult to realize. It is an object to provide a matching circuit that can be performed.

[Configuration of the Invention] (Means for Solving the Problems) In order to achieve the above object, a matching circuit according to the present invention is connected between a balanced output circuit having a balanced output and an unbalanced load circuit, In the case of performing matching between the balanced output circuit and the unbalanced load circuit, a first transformer having at least first and second windings electromagnetically coupled to each other,
Each one end of the second winding is connected to each output end of the balanced output circuit, and the other end of the first winding is connected to the input end of the unbalanced load circuit. By connecting the other end to the reference potential point, the transformer is used as a transmission type transformer, and the transmission type transformer performs the conversion from balanced to unbalanced. Then, at least one of the balanced output circuit and the balanced / unbalanced conversion means or between the balanced / unbalanced conversion means and the unbalanced load circuit has a low impedance with respect to the transmission frequency and other frequencies. A transmission signal is converted into an impedance through an impedance conversion circuit having a high impedance. Further, a capacitor is interposed in the balanced transmission line of the balanced / unbalanced conversion means and the impedance conversion means to block a direct current component, and the transformer is configured not to have an impedance conversion function.

(Operation) Since the matching circuit configured as described above uses the ordinary transformer as the transmission type transformer, the heat generation amount is small and the power loss is extremely small as compared with the case of the normal use mode.
Moreover, since the impedance conversion is performed independently of the transformer, the conversion ratio can be freely adjusted.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

FIG. 1 shows the configuration when the present invention is applied to the conventional high frequency power amplifier shown in FIG. In the figure, the same parts as those in FIG. 6 are designated by the same reference numerals, and only different parts will be described here.

That is, reference numeral 14 in FIG. 1 is a matching circuit according to the present invention. This matching circuit 14 is a class D bridge power amplifier circuit.
After each impedance output of each of the 11 balanced outputs is converted by an impedance conversion circuit 141 including coils L1 and L2 and a capacitor C1, each conversion output is converted into a normal transformer 14 via coupling capacitors C2 and C3.
Input to the first and second winding input terminals of two electromagnetically coupled to each other. Then, one of the winding output terminals is grounded and the other winding output terminal is connected to the load circuit 13 to form a transmission type transformer.
It is designed to perform unbalance conversion.

The impedance conversion circuit 141 is developed in a balanced system so as to be equivalent to the known LC type impedance conversion circuit shown in FIG. 2, and is designed so as to convert to an impedance required in an unbalanced system, and then the capacitance of the capacitor C1. Is made equal to the capacitor C0 of the equivalent circuit, and the inductance of the coils L1 and L2 is set to 1/2 of the inductance of the coil L0 of the equivalent circuit.

As the coupling capacitors C2 and C3, those having sufficiently small impedance at the output frequency are used. The transmission transformer 142 provides the necessary blocking impedance to allow conversion from balanced to unbalanced at the output frequency.

In the above configuration, when a square wave voltage is applied to the input side of the output matching circuit 14 now, the current flowing through the impedance conversion circuit 141 becomes a sine wave of only the fundamental wave, and both ends of the capacitor C1 are balanced with respect to the ground. , A voltage corresponding to the impedance conversion ratio is generated. Capacitor C1 is V _DD
This is for shutting off the DC voltage supplied from the power source, and can be ignored at high frequencies if the capacity is sufficiently large. Therefore, both the voltage and the current applied to the transmission type transformer 142 are substantially only the fundamental wave. Therefore, the transmission type transformer 142 can convert a balanced output into an unbalanced output with almost no heat generation, that is, without causing power loss.

Here, it is ideal that the transmission type transformer 142 has an electric length of ¼ wavelength at the used frequency, but in practice, the blocking impedance for the used frequency of the transmission type transformer 142 is the load circuit 13. If the input impedance is about 10 times or more, it can be sufficiently used. The transmission type transformer 142
If it is not possible to increase the blocking impedance of, use a three-winding type 143 as shown in FIG. 3 for the transmission type transformer, and use a third winding electromagnetically coupled with the first and second windings. 1,
The mismatch can be reduced by connecting the one end of the first winding and the ground so that the direction of the electric current is opposite to that of the second winding.

Therefore, the matching circuit with the above configuration does not require a transformer that is difficult to realize even if the frequency to be transmitted becomes high,
The power loss can be sufficiently reduced as compared with the conventional circuit. Further, the impedance conversion ratio can be freely set by arbitrarily setting or changing each constituent element of the impedance conversion circuit.

In the above embodiment, the balanced output of the power amplifier circuit is converted into the unbalanced output after the impedance conversion is performed first. However, as shown in FIG. The impedance conversion may be performed by the impedance conversion circuit 143 after the unbalanced conversion is performed. In this case, the impedance conversion circuit 143
Can be configured by the coil L1 and the capacitor C1, and the number of elements can be reduced.

Further, as shown in FIG. 5, when the multistage bandpass filter including the coils L3 to L6 and the capacitors C4 to C8 is used as the impedance conversion circuit 144, the capacitors C5 and C6 interposed in series in the balanced transmission line are the first. If used as the coupling capacitors C2 and C3 in the figure, the constituent elements can be shared.

In the above circuit, if the impedance conversion means and the balanced / unbalanced conversion means are each formed by forming at least a part of the circuit constituent elements on the strip line based on the distributed constant, it can be made extremely smaller than the conventional circuit. it can. Moreover, this matching circuit has reversibility. For this reason,
For example, unbalanced 50 [Ω] feeder and balanced 300 [Ω]
It can also be used for matching with a folded dipole antenna. Furthermore, although the above description has been given of the case where the transmission type transformer is configured by an ordinary transformer, when designing the transmission type transformer from the beginning, only the frequency components necessary for transmitting the same electric power are allowed to pass. Therefore, it is possible to make the size extremely smaller than that of the conventional transformer.

EFFECTS OF THE INVENTION As described above, according to the present invention, it is possible to provide a matching circuit with low loss and free setting of impedance conversion ratio without requiring a transformer that is difficult to realize even if the frequency used increases. Can be provided.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a matching circuit according to the present invention, FIG. 2 is an equivalent circuit diagram for explaining the basic configuration of an LC type impedance conversion circuit of the embodiment, and FIG. A circuit diagram showing another configuration of the transmission type transformer of the example, FIGS. 4 and 5 are circuit diagrams showing another embodiment of the matching circuit according to the present invention, and FIG. 6 is a configuration of a conventional matching circuit. It is a circuit diagram showing. 11 ... Class D bridge power amplifier circuit, 12, 14 ... Matching circuit, 121
… Transformers, 122… LC bandpass filters, 141, 144…
LC type impedance conversion circuit, 142, 143 ... Transmission type transformer, 13 ... Load circuit.

Front page continuation (72) Inventor Shigeo Mori 2-2-1 Jinnan, Shibuya-ku, Tokyo Inside the Japan Broadcasting Corporation Broadcasting Center (72) Haruhiko Yura 1 Komukai Toshiba-cho, Kawasaki-shi, Kanagawa Prefecture Ceremony company Toshiba Komukai factory (72) Inventor Tsutomu Sato 1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Stock company Toshiba Komukai factory

Claims (5)

[Claims] 1. A matching circuit, which is connected between a balanced output circuit having a balanced output and an unbalanced load circuit and performs matching between the balanced output circuit and the unbalanced load circuit, at least electromagnetically coupled to each other. A transformer having first and second windings, one end of each of the first and second windings is connected to each output end of the balanced output circuit, and the other end of the first winding is connected. Balanced / unbalanced conversion means, which is connected to the input terminal of the unbalanced load circuit and connects the other end of the second winding to a reference potential point to convert from balanced to unbalanced, and the balanced output・
It is interposed between the unbalanced conversion means or at least one of the balanced / unbalanced conversion means and the unbalanced load circuit, and has a low impedance with respect to the transmission frequency and a high impedance with respect to other frequencies. An impedance conversion means; and a DC component blocking means for blocking a DC component by interposing a capacitor in a balanced transmission path of the balanced / unbalanced conversion means and the impedance conversion means,
A matching circuit characterized in that the transformer is not provided with an impedance conversion function. 2. The impedance conversion means is configured by interposing an LC type impedance conversion circuit including an inductor and a capacitor in a signal input / output transmission line. Matching circuit. 3. The impedance conversion means has a high-pass filter formed by interposing a capacitor in the input / output transmission line, and is used as this high-pass filter. Matching circuit. 4. A transformer used in the balance / unbalance conversion means comprises a third winding electromagnetically coupled to the first and second windings, and the third winding is connected to the first and second windings. The first winding is connected between one end of the first winding and the reference potential point so that the current direction is opposite to that of the second winding. Matching circuit described. 5. The impedance conversion means and the balanced / unbalanced conversion means each form at least part of a circuit constituent element on a strip line based on a distributed constant. The matching circuit according to any one of items 1 to 4.