JPH07105667B2 - Power amplifier - Google Patents

Description

TECHNICAL FIELD The present invention relates to a push-pull type power amplifier having an output transformer with a center tap.

2. Description of the Related Art Generally, this type of power amplifier is provided with various types of negative feedback in order to improve the characteristics of the output stage. 2 and 3
The figure shows the configuration of a conventional power amplifier.

In FIG. 2, 1 is an output transformer, 2 and 3 are output transistors, 4 and 5 are drive transistors connected to the output transistors 2 and 3 by Darlington connection, 6 and 7 are emitter resistors of the output transistors 2 and 3, and 8 Reference numerals 9 and 9 are emitter resistors of the transistors 4 and 5, 10 is a stabilizing power supply circuit block, resistor 12 and the input transformer 13 form a bias circuit, and 11 is a circuit block for bias stabilization.
Next, the operation of this conventional example will be described. In FIG. 2, the input phase-divided by the input transformer 13 is input to the output stage biased to the B class and performs power amplification as an emitter follower circuit. Therefore, also in this conventional example, the performance of the output stage is improved due to the negative return loop called the emitter follower.

In FIG. 3, 31 is an output transformer, 32 and 33 are output transistors, 34 and 35 are drive transistors connected to the output transistors 32 and 33 by Darlington connection, 36 and 37 are emitter resistors of the output transistors 32 and 33, 38 and 39 are emitter resistors of the transistors 34 and 35, 40 is a stabilized power supply circuit block, 41 and 42 and 43 and 44 are bias circuits,
41 and 43 are circuit blocks for bias stabilization, 45
And 46 are coupling capacitors, 47 and 48 and 52 and 53 are differential amplification transistors, 51 and 56 are emitter resistors, 49, 50, 54,
55 is a collector resistance and 57 is a negative feedback resistance. Next, the operation of this conventional example will be described. In FIG. 3, the input phase division is performed by a two-stage differential amplifier circuit composed of transistors 47, 48 and 52, 53, and input to the output stage biased to the B class via coupling capacitors 45, 46. Perform power amplification. Negative feedback is output winding 31 for feedback winding 31
A is provided, and the performance of the output stage is improved by feeding back to the differential amplifier circuit including the transistors 52 and 53 in the preceding stage via the negative feedback resistor 27.

Problems to be Solved by the Invention However, the above conventional example has the following problems. That is, since the input transformer is used in the conventional example of FIG. 2, an abnormality due to electromagnetic coupling with the power transformer or the output transformer or another negative feedback is required for the amplification stage up to the input transformer. There was a problem. Further, in the conventional example of FIG. 3, since negative feedback is applied from the output transformer, there is a problem that the performance of the output transformer including the feedback winding is easily affected by the entire power amplifier.

The present invention solves such a conventional problem, and an object of the present invention is to provide an excellent power amplifier which can solve the problems related to ground by forming a balance circuit as a whole.

Means for Solving the Problems In order to achieve the above-mentioned object, the present invention has an output transformer having a set-up on the primary side and an output driven by push-pull with a collector connected to both load terminals of the primary side of the output transformer. A first amplifying means having a transistor; and a second amplifying means comprising an output terminal composed of a pair of operational amplifiers and connected to the output transistor respectively, and an input terminal connecting positive and negative phase inputs to each other through a resistor. Each of the input terminals of the second amplifying means is connected to both load terminals on the primary side of the output transformer to form a feedback circuit.

Operation According to the present invention, therefore, balanced negative feedback can be performed, all stages can be directly connected circuits, electromagnetic influence on the input can be eliminated, stable negative feedback with good characteristics, etc. can be performed.
Further, it has an effect that the influence on the input from the ground circuit can be eliminated.

Embodiment FIG. 1 shows the structure of an embodiment of the present invention. In FIG. 1, 1 is an output transformer, 2 and 3 are output transistors, 4 and 5 are drive transistors connected to the output transistors 2 and 3 in Darlington connection, 6 and 7 are emitter resistors of the output transistors 2 and 3, and 8 , 9 are emitter resistors of the transistors 4 and 5, 10 is a stabilized power supply circuit block, and 11 and 13 are circuit blocks for bias stabilization which constitute a bias circuit together with the resistors 12 and 13. 15 and 16 are resistors for supplying bias to the operational amplifiers 17 and 18, 19 and 20 are feedback resistors of the operational amplifiers 17 and 18, and 21 to 24 are operational amplifiers 17 and 18
, And 25 and 26 are negative feedback resistors from the output stage.

Next, the operation of the above embodiment will be described. In the above embodiment, the input section connects two operational amplifiers 17 and 18 in parallel with the input opposite phase for phase division of the input signal. The operational amplifiers 17 and 18 are bias circuits 11 and 12, and
The output stage is biased to be class B by 13 and 14. And output transformer 1 with center tap
Utilizing the fact that the output of opposite phase is output to both side terminals t ₁ and t ₂ of this terminal.
Return to 18). By doing so, the negative feedback can be applied with the bias of the B class, with all stages directly connected and in a balanced form.

As described above, according to the above-described embodiment, since the feedback is directly connected without the feedback winding of the output transformer, the frequency characteristic,
There are merits that feedback can be performed with stable phase characteristics and the output transformer is structurally simple. Moreover, since the input transformer is not used, it is not affected by various electromagnetic inductions, and the distortion and frequency characteristics, which are limited by the performance of the input transformer, are improved, and it is possible to reduce the size in terms of component mounting.

As is apparent from the above embodiment, the present invention eliminates the input winding and the return winding of the output transformer of the push-pull type power amplifier using the output transformer with the center tap, and directly connects and balances the power. The amplifier circuit is configured, and has the effect of stabilizing the circuit, improving performance, and simplifying the circuit.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a power amplifier in one embodiment of the present invention, and FIGS. 2 and 3 are circuit diagrams of a conventional power amplifier. 1 ... Output transformer, 2 ... Output transistor, 3 ...
Output transistor, 4 ...... Drive transistor, 5
...... Drive transistor, 17,18 …… Op Amp.

Claims (1)

[Claims] 1. An output transformer having a center tap on the primary side, a first amplifying means having a collector connected to both load terminals of the primary side of the output transformer and having push-pull driven output transistors, and a pair of operational amplifiers. And an output terminal connected to the output transistor and positive,
A second amplifying means including an input terminal connecting the negative-phase inputs to each other via a resistor, each input terminal of the second amplifying means being connected to both load terminals on the primary side of the output transformer, respectively. A power amplifier comprising a circuit.