JPS6258166B2 - - Google Patents

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 _-1 is a power supply terminal, IN _-2 is an excitation input terminal, OUT is an output terminal, a T-high frequency transformer, and A ₁ to _{A 4} are bridge-connected power amplifiers (hereinafter simply referred to as amplifiers). The amplifiers A ₁ to _{A 4} are each composed of the same circuit. For example, in the amplifier A ₁ , e is an excitation input terminal, B is a power supply terminal, T ₀ is an excitation transformer, and Q ₁ to Q ₄ are MOS FETs. , _C1 is a decoupling capacitor, _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, an excitation voltage is applied between the gates and sources of the MOS FETs _Q1 to _Q4 by the excitation transformer _T0 . As a result, Q ₁ , Q ₄ and Q ₂ , Q ₃ are alternately switched on and off according to the polarity signal of the winding of the illustrated excitation transformer T ₀ . As a result, a waveform appears between the output terminals (+) and (-) whose amplitude is the power supply voltage of the power supply terminal B and whose polarity is switched at the frequency of the excitation input from the excitation input terminal e. That is, an output converted to alternating current (high frequency) is obtained. Next, since the obtained output is not of the ground type, it is isolated in terms of direct current by a correspondingly arranged high frequency transformer T ₁ and is converted from balanced to unbalanced. It goes without saying that at this time, impedance transformation is performed if necessary, and each of the amplifiers A ₂ to _{A 4} operates in the same manner as described above.

As described above, the outputs from amplifiers A ₁ to _{A 4} are:
The signals are obtained as ground signals through corresponding high frequency transformers _T1 to _T4 , and then the respective signals, in this case, the outputs of the four systems are combined. That is, each output is T ₁₂ , R ₁₂ and T ₃₄ , R ₃₄ and
It is synthesized by a hybrid synthesis circuit composed of T ₁₂₃₄ and R ₁₂₃₄ , and the output terminal is output as an output.
It is obtained from OUT. In the above description, T ₁₂ , T ₃₄ , and T ₁₂₃₄ are high-frequency transformers for hybrid synthesis, and R ₁₂ , R ₃₄ , and R ₁₂₃₄ are resistors for unbalance absorption.

However, in the circuit configuration described so far, (1) In addition to the output transformers (high-frequency transformers T ₁ to _{T 4} ) for converting bridge output to unbalanced output, a hybrid transformer for synthesis (high-frequency transformer
T ₁₂ , T ₃₄ , and T ₁₂₃₄ ) are required, which complicates the circuit configuration and increases the occupied area (volume).

(2) The number of amplifiers A is 2 ⁿ (n=1, 2, 3,
(...) will not have the same power when they are combined, so the conditions for that will increase and the combination will not be easy.

(3) If the compatible load impedance is designed to be constant, as the number of combinations (number of amplifiers A-) increases, the impedance ratio required of the corresponding high-frequency transformer T- increases, making it unsuitable for multiple combinations.

Furthermore, in the example shown in Figure 1, three types of high-frequency transformers are required: T ₁ to T ₄ , T ₁₂ , T ₃₄ , and T ₁₂₃₄ (this increases as the number of amplifier outputs to be combined increases). There was a problem.

The present invention has been made in view of these points, and consists of applying three windings to an output transformer for converting a bridge output to an unbalanced output, thereby constructing a synthesis circuit. That is, in a power amplifier circuit that is made up of a plurality of amplifiers and operates by combining their outputs, a three-winding output transformer is arranged for each amplifier, and the first winding of the three windings is The outputs of the corresponding amplifiers are connected, all of the second windings are connected in series to serve as the output terminals of the power amplifier circuit, and the third windings are each connected in series with absorption resistors and connected in parallel. It is configured by connecting
With this configuration, it is possible 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 amplifier circuit according to the present invention. In the figure, A ₁ to _{A 5} are bridge-connected amplifiers similar to the conventional ones; There are five, which is a difficult number to synthesize. T is a high-frequency output transformer consisting of three windings, and the rest is the same as that shown in FIG. Furthermore, the output transformer T of the third winding is arranged corresponding to the amplifiers _A1 to _A5 , and the output transformer T of the third winding is
n ₁ is connected to the output terminals of amplifiers A ₁ to _{A 5} from which high frequency output can be obtained. In addition, all of the second winding n ₂ are connected in series to reach the output terminal OUT, and the third winding n ₃ has all its winding starts connected in common, and each winding end is terminated with an absorption resistor R. In other words, each of the third windings _n3 is connected in parallel with an absorbing resistor R inserted in series.

Here, if the output transformer T is an ideal transformer, when the value of the absorption resistance R is ∞, it is equivalent to simply connecting the outputs of amplifiers A ₁ to _{A 5} in series, and the value of the absorption resistance R If is zero, the third winding _n3 acts to equalize the output voltages of amplifiers _A1 to _A5 , so it is clear that this is equivalent to connecting the outputs of amplifiers _A1 to _A5 in parallel. It is.

Next, Figure 3 shows that when the value of the absorption resistor R is selected and set in advance, the loads of each amplifier _A1 to _A5 have isolation characteristics from each other, and the operation is equivalent to hybrid synthesis. Explain using.

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. discuss. In addition, input voltages _{e 1 ,} e ₂ , e ₃ ,
e ₄ and e ₅ are supplied, the second winding n ₂ is all connected in series and connected to the load resistor R _L , and the third winding
For _n3 , absorbing resistors R are inserted in series with each winding, and all are connected in parallel. In addition, in the figure, absorption resistance R
Although the common connection point is grounded, there is no particular need to ground it, and it may be used depending on the usage condition at the time.

Here, the voltage e ₀ of the load resistor R _L in the circuit connected as above is e ₀ =n ₂ /n ₁ e ₁ +n ₂ /n ₁ e ₂ +n ₂ /n ₁ e ₃ +n
₂ /n ₁ e ₄ +n ₂ /n ₁ e ₅ =n ₂ /n ₁ (e ₁ +e ₂ +e ₃ +e ₄ +e ₅ )...(1). Also, the voltage ex at the common connection point of the second winding n ₂
teeth, , which means N third windings, in this case 5
is the average voltage of Also, as a relational expression for the current in one winding of a transformer, the load current (or current in the second winding) is i ₀ , the current in the first winding is i ₁₁ , and the current in the third winding is i 0 .
If the current in the winding is i ₃₁ , then i ₀ n ₂ = i ₁₁ n ₁ − i ₃₁ n ₃ …(3) holds true. Furthermore, the third winding current i ₃₁ is determined by i ₃₁ =1/R・(n ₃ /n ₁ e ₁ −ex) (4), and the load current i ₀ is determined by i ₀ = e ₀ / It can be found by R _L (5).

Next, in each equation (1) to (5) obtained above, equation (3) is
Substituting equations (4) and (5), further substituting equations (1) and (4), and substituting equation (2), we get 1/R _L・n ₂ /n ₁・(e ₁ +…+e ₅ )・n ₂ =i ₁₁・n ₁ −1/R・{n ₃ /n ₁・e ₁ −n ₃ /5n ₁ (e ₁ +…
+e ₅ )}・n ₃ ...(6) From this, the first winding current i ₁₁ is calculated as follows: i ₁₁ = (n ₂ /n ₁ ) ²・1/R _L (e ₁ +...+e ₅ )+(
n ₃ /n ₁ ) ²・1/Re ₁ −(n ₃ /n ₁ ) ²・1/5R・(e ₁ +…
+e ₅ )…(7). Here, (n ₂ /n ₁ ) ²・1/R _L = (n ₃ /n ₁ ) ²・1
/5R (8) When the condition (8) is satisfied, the term (e ₁ +...+e ₅ ) is eliminated, and the first winding current i ₁₁ is proportional only to the input voltage e ₁ . That is, it is understood that when R=R _L /N·(n ₃ /n ₂ ) ² (9), the circuit operates as a combining circuit with isolation between each input.

In the above equation (9), N is the number of amplifiers to be combined, which is 2, 3, 4, etc., and is "5" in this case.

As can be understood from the above explanation, according to the present invention, (1) new hybrid synthesis can be achieved by simply adding a third winding to each output transformer that is always connected to the output side of a bridge-connected amplifier; Since no transformer is required, the space is small and the circuit is simple, which is effective in reducing size and weight, economy, and reliability.

(2) The number of amplifiers to be synthesized (N) is not particularly limited compared to conventional ones;
It is easy to realize five combinations as explained in FIGS.

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

(4) As shown in equation (9), the resistance value of the absorption resistor R can be selected by the third winding, and since it is sufficient to prepare a composite number of resistors with the same rating, standardization of the constituent elements 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 expected.

FIG. 4 is a circuit diagram showing another embodiment of the power amplifier circuit according to the present invention, which differs from the combination of the five amplifiers described above and shows the case of combining the outputs of an arbitrary number of two or more amplifiers. The absorption resistance value R in the case of N number of filters is calculated as R=R _L /N·(n ₃ /n ₂ ) ² by the same calculation as in the first embodiment described above.

In addition, in the circuit shown in Fig. 4, in order to improve the balanced-unbalanced conversion characteristics of the bridge output or to reduce the adverse effects of stray capacitance between the windings when the outputs of the output transformer T are connected in series, Although the transformer T _B 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 ₁ to _{A 5} are connected to IN− ₁₁ ,
IN− ₁₂ , …IN− _1o and IN− ₂₁ , IN− ₂₂ …IN− _2o
Although the configuration is such that power is supplied from an independent power source or modulator (not shown) and excited by an independent excitation circuit (not shown), the operation is the same as that of the first embodiment in this case as well. No problems will occur. The amplifiers A ₁ to _{A 5} are also bridge-connected amplifiers as in the first embodiment, but the amplifying elements only need to have a predetermined function and are limited to the circuit configuration shown in FIG. 1. It's not a thing.

Regarding the value of absorption resistance R mentioned above,
It is not necessary to use a value that is equal to the calculated value, but it is also possible to intentionally vary the calculated value within an allowable range and use it with composite characteristics similar to series or parallel connection, and this is not a matter that requires special explanation. be.

As described above in detail, according to the present invention, an arbitrary number of bridge-connected amplifiers can be easily synthesized, so that large power It can be used in high-output radio broadcasting equipment using solid-state power amplifier circuits that need to obtain high power, and the excellent effects described above can be expected.

[Brief explanation of the drawing]

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. IN- ₁ , IN- ₁₁ , IN- ₁₂ ,...IN- _1o are power supply terminals, IN- ₂ , IN- ₂₁ , IN- ₂₂ ,...IN- _2o are excitation input terminals, OUT is output terminal, _A1 to A ₅ is the amplifier, T
is a high frequency output transformer, R is an absorption resistor, and T _B is a balance improvement transformer.

Claims (1)

[Scope of Claims] 1. 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 having an opposite phase relationship between respective terminals; A three-winding output transformer is arranged corresponding to the power 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 constructed by inserting an absorption resistor in series with each winding and connecting all of them in parallel.