JPS5992608A - Power amplifier circuit - Google Patents

Abstract

PURPOSE:To eliminate the need for a transformer for composition by providing the 3rd winding to the output transformer of each power amplifier which combines outputs of plural power amplifiers and connecting all serial circuits of winding and resistances in parallel. CONSTITUTION:Bridge-connected amplifiers A1, A2, A3, A4, and A5 input the same excitation input IN-2 and send outputs to transformers T. Output windings of the transformers T are connected in series and their outputs are combined together and sent to an output terminal OUT. Resistances R for absorption are connected to the 3rd windings (n), which are connected in parallel; when the value of the absorbing resistance R is (RL/5).(n3/n2)<2>, the current flowing through the 1st winding n1 is proportional to only an input voltage e1, so isolation is attained. Therefore, the transformer for composition is unnecessary, so the size and weight are reduced and the number of amplifiers are selected optionally.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power amplifier circuit that can easily synthesize a large number of power amplifiers.

Fig. 1 is a block diagram of a power amplifier circuit formed by combining conventional bridge-connected power amplifiers. In the figure, INLj is a power supply terminal, lN-2 is an excitation input terminal, OUT is an output terminal, and T
- is a high-frequency transformer, and A and -%-A4 are bridge-connected power amplifiers (hereinafter simply referred to as amplifiers). Further, the amplifiers A1 to A4 are each composed of the same circuit. For example, in the amplifier A1, e is an excitation input terminal, and B is an excitation input terminal.
is the power terminal, T.

is an excitation transformer, Ql-Ql is a MOS FET, C
, are decoupling capacitors, C2 is a coupling capacitor, and (+) and (-) are output terminals from which outputs having an opposite phase relationship are obtained.

Here, in the amplifier A1, when an input is given to the excitation input terminal e, the excitation transformer To causes the MOS
An excitation voltage is applied between the dirt sources of the FETs Qt to Q4. As a result, the illustrated excitation transformer To
Ql , Ql and Q according to the polarity signal of the winding of
2, Q3 is turned on alternately.

Switching off works. As a result, the output terminal (+
) and (-), a waveform appears in which the amplitude is the power supply voltage of the power supply terminal B and the polarity is switched at the frequency of the excitation input from the excitation input terminal e. In other words, an output converted to alternating current (high frequency) is obtained.

Next, since the obtained output is not of a ground type, it is isolated in terms of direct current by a correspondingly arranged high frequency transformer Tl, and is also subjected to balanced-unbalanced conversion. At this time, impedance transformation is also performed if necessary, and amplifiers A2 to
It goes without saying that each of A4 performs the same operation as described above.

As described above, the output from the amplifier AI%A4 is obtained as a ground signal through the corresponding high frequency transformer 'rl-'r4, and then the respective signals, in this case, the outputs of the four systems are combined. It is. That is, each output is T
12+Rt2 and T's< l R34 and T 123
41 R1234 is synthesized by a hybrid synthesis circuit, and the output is obtained from the output terminal OUT. In addition, in the above description, T111 + T
34 r T 1234 is a high frequency transformer for hybrid synthesis, and R12*R34* R1234 is a resistor for unbalance absorption.

However, in the circuit configuration as described so far, (1) In addition to the output transformer (high frequency transformer TI-T4) for converting bridge output to unbalanced output, a hybrid transformer for synthesis (high frequency transformer T12 +
T 34 + and Tl234) are required, which complicates the circuit configuration and increases the occupied area (volume).

(2) The number of amplifiers A- is 2" (n = 1, 2,
Except for the combination of 3, -), the power is no longer the same during combination, so the conditions for this increase and the combination becomes difficult.

(3) Design with a constant compatible load impedance, and as the number of combinations (number of amplifiers A-) increases, the impedance ratio required for the corresponding high-frequency transformer T- increases, making it unsuitable for multiple combinations. It is.

Furthermore, in the example shown in Figure 1, the high frequency transformers used are T, -T4 and T12 + T34 and T1234.
There were many problems, such as the need for three types (which increases as the number of amplifier outputs to be synthesized increases).

The present invention has been made in view of these points, and
3 for output voltage for bridge output-unbalanced output conversion
A composite circuit is constructed by applying windings. That is, in a power amplifier circuit that operates by combining the outputs of multiple amplifiers, a three-winding output transformer is arranged for each amplifier, and the first winding of the three windings is are connected to the outputs of their corresponding amplifiers, the second windings are all connected in series to serve as the output terminals of the power amplifier circuit, and the third windings are each connected with an absorption resistor in series. , are connected in parallel, and this configuration is intended to eliminate the problems of the prior art described above. Hereinafter, the present invention will be explained using figures.

FIG. 2 is a block diagram showing an embodiment of the power amplification circuit according to the present invention. In the figure, A1 to A5 are bridge-connected amplifiers similar to those of the conventional one; There are five, which is a difficult number. T is a high-frequency output transformer consisting of three windings, and the rest is the same as that in FIG. Further, the output transformer T having three windings is arranged corresponding to the amplifiers A1 to A5 (5), and the first winding nl
are connected to the output terminals of amplifiers A and -A5 which provide high frequency outputs. In addition, the second winding n2 has all its windings connected in series to reach the output terminal OUT, and the third winding n3 has its winding starts all connected in common, and the winding ends are each terminated with an absorption resistor R, in other words. Then, the third windings n3 each have an absorbing resistor R inserted in series and are connected in parallel.

Here, if the output transformer T is an ideal transformer, the value of the absorption resistance R is equivalent to simply connecting the outputs of the amplifiers A1 to A5 in series, and the value of the absorption resistance R is equivalent to simply connecting the outputs of the amplifiers A1 to A5 in series. If it is zero, the third winding n3 is the amplifier AI%A
Amplifier A1 acts to equalize the output voltages of A1 and A1.
It is clear that this is equivalent to connecting the outputs of ~A5 in parallel.

Next, we will use Figure 3 to show that when the value of the absorption resistance R is selected and set in advance, the loads of each amplifier A and %A5 have isolation characteristics from each other, and the operation is equivalent to hybrid synthesis. Explain (6).

FIG. 3 is an explanatory diagram illustrating the principle of the synthesis operation of the present invention. In the figure, T is a three-winding output transformer similar to the output transformer shown in FIG. Discussed as. In addition, the input voltage el, e2゜e3 + e4 #es is supplied to the first winding nl of each transformer, and the second winding n2 is all connected in series to the load resistor RL, and the second winding n2 is connected in series to the load resistor RL. The windings n3 of No. 3 are all connected in parallel after an absorption resistor R is inserted in series with each winding.

Note that although the common connection point of the absorption resistors R is grounded in the figure, it is not particularly necessary to ground it, and it may be used depending on the usage condition at that time.

Here, the load resistance R in the circuit connected as above
The voltage eo of L is = (et+ez+es+84+es) ”(
1) It becomes 1. Also, the voltage ex at the common connection point of the second winding n2 is \, which is the average voltage of the N third windings, in this case five. Also, as a relational expression for the current in one winding of a transformer, the load current (or the current in the second winding) is expressed as i0
sIf the current in the first winding is 'Ltt and the current in the third winding is i31, to n2 = Zll nl Zll n3
''(3) holds.Furthermore, the third winding current i3
1 can be found as follows, and the load current i6 can be found as follows.

Next, in each equation (1) to (5) obtained above, (3)
Substitute equations (4) and (5) into equations, and then (1),
Substituting equation (4) and substituting equation (2), ...(6) To find the first winding current i+x,...
...(7) becomes. Here, if the following conditions are satisfied, the term (eI+...10 s) will be eliminated, and the first winding current i11 will be proportional only to the input voltage e. That is, it is understood that the circuit operates as a synthesis circuit with isolation between each input in the case of .

Note that in the above formula (9), N is the number of amplifiers to be combined, which is 2.
3.4..., which in this case is '5''.

(9) As can be understood from the above explanation, according to the present invention, (1) a new Since a transformer for hybrid synthesis is not required, the space is small and the circuit is simple, which is effective in terms of size and weight reduction, economy, and reliability.

(2) The number (N) of amplifiers to be combined is not particularly limited compared to the conventional one; for example, as shown in FIG.

It is easy to realize five combinations as explained in FIG. 3, and it is possible to perform an optimal design using the minimum necessary number of combinations.

(3) Regarding synthesis characteristics, isolation between each input is guaranteed, and since no frequency-dependent circuit elements are used, wideband characteristics comparable to that of a wideband transformer can be obtained, and the number of amplifiers to be synthesized has increased. However, since the second windings of the corresponding output transformers are connected in series, the applicable load impedance does not decrease and can be realized with a transformer with an appropriate turns ratio.

(10) (4) As shown in equation (9), the resistance value of the absorbing resistor R can be selected by the third winding, and it is only necessary to prepare a composite number of the same rating, so the component elements can be standardized. can be achieved.

(5) Since one terminal of the absorption resistor can be grounded, a general dummy load for termination can be used, and unbalance can be easily detected.

Excellent effects such as these can be obtained.

FIG. 4 is a circuit diagram showing another embodiment of the power amplifier circuit according to the present invention, which is different from the combination of five amplifiers described above, and is a case of combining the outputs of any number of two or more amplifiers. The absorption resistance value R in the case of N number of elements can be obtained by the same calculation as in the first embodiment described above.

In addition, in the circuit shown in Figure 4, the degree of balance is improved in order to improve the balanced-unbalanced conversion characteristics of the bridge output or to reduce the effect of stray capacitance between windings when the outputs of output transformers T are connected in series. Although a conventional transformer TB is used, this does not impair the effects of the present invention as described above. Furthermore, the power supply terminal and excitation terminal of each amplifier A, -A5 are connected to lN11゜lN-12+ ''' IN-I n and l
The configuration is such that power is supplied from an independent power supply or modulator (not shown) such as N-21+ lN-22"' lN-2n, and excitation is provided by an independent excitation circuit (not shown), but even in this case, the first It operates in the same manner as in the embodiment and does not cause any problems.Amplifiers A, -
Similarly to the first embodiment, A5 is a bridge-connected amplifier, but its amplifying element only needs to have a predetermined function, and is not limited to the circuit configuration shown in FIG.

Regarding the value of the absorption resistance R mentioned above, it is not necessarily necessary to use a value equal to the calculated value, but it is possible to intentionally vary it from the calculated value within the allowable range and use it with a composite characteristic similar to series connection or parallel connection. It is also possible to do so, and there is no need to specifically explain it.

As described above in detail, according to the present invention, any number of bridge-connected amplifiers can be easily synthesized, so there is no need to use elements with high element loss (for example, 100 watt class) to obtain large power. It can be used in high-output radio broadcasting equipment using certain solid-state power amplifier circuits, and the excellent effects described above can be expected.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a power amplifying circuit by combining conventional bridge-connected power amplifiers, FIG. 2 is a block diagram showing an embodiment of the power amplifying circuit according to the present invention, and FIG. 3 is a combining operation of the present invention. FIG. 4 is a block diagram showing another embodiment of the power amplifier circuit according to the present invention. ■N1+lN-11+lN-12+ ”・lN-In is the power supply terminal, lN-2゜lN-21, lN-22, -I
N-2n is the excitation input terminal, OUT is the output terminal, A, #A
, T is an amplifier, T is a high frequency output transformer, R is an absorption resistor, and TB is a transformer for improving balance. (13) Procedural amendment (voluntary) 58.37 Director General of the Japan Patent Office (Monday/Monday) 1. Indication of the case 1982 Patent Application No. 201890 2. Name of the invention Power amplifier circuit 3. Person making the amendment

Claims (1)

[Scope of Claims] A power amplifier circuit that operates by combining the outputs of a plurality of power amplifiers, comprising: a bridge-connected power amplifier that obtains outputs in an opposite phase relationship between corresponding terminals; and a power amplifier of the bridge connection. A three-winding output transformer is arranged corresponding to the amplifier, and the first winding of the three-winding output transformer is connected to the output of the corresponding bridge-connected amplifier, and the second winding is connected to the output of the corresponding bridge-connected amplifier. A power amplifier circuit characterized in that all of the windings are connected in series to form an output terminal, and the third winding is configured by inserting an absorption resistor in series with each winding and connecting all of them in parallel.