JPS6214726Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates primarily to improvements in power amplifiers used for audio, and particularly to power amplifiers with improved fidelity and efficiency.

Conventional power amplifiers generally have a class A amplifier or a class B amplifier. By the way, class A amplifiers have good fidelity but have the drawback of large power loss, and class B amplifiers have good efficiency but have the drawback of generating crossover distortion, switching distortion, etc. Therefore, the applicant of this invention has proposed the first method to solve all of the above-mentioned drawbacks.
The power amplifier shown in the figure was provided (Patent Application No. 53-3902).
issue). As shown in the figure, this power amplifier includes an input stage amplifier circuit 1, an output stage amplifier circuit 2 driven by the output of the input stage amplifier circuit 1, and supplies power to the output stage amplifier circuit 2. It is composed of a floating power supply 3 and a bootstrap amplifier 6 that drives the common emitters of transistors 4 and 5 of the output stage amplifier circuit 2, and the midpoint of the floating power supply 3 is connected to the output terminal 7.
Further, an output signal obtained at the output terminal 7 is fed back to the input stage amplifier circuit 1 via a resistor 8. In this circuit, the bootstrap amplifier 6 is composed of an input stage amplifier circuit and an output stage amplifier circuit, and outputs an output that amplifies the input signal of the input stage amplifier circuit 1 and changes in the same way as the output voltage of the output terminal 7. Vb is applied to the common emitters of transistors 4 and 5, so that the output voltage Vcc of floating power supply 3 is always applied between the emitters and collectors of transistors 4 and 5. . As a result, the output voltage of floating power supply 3
If Vcc is set to the minimum voltage (usually 2 to 5 V) that makes transistors 4 and 5 active, even if transistors 4 and 5 are operated in class A mode, the power loss due to these transistors 4 and 5 will be reduced. can be kept to a minimum. Furthermore, the efficiency of this power amplifier is mainly determined by the efficiency of the bootstrap amplifier 6, but in the case of this power amplifier, the distortion contained in the output of the bootstrap amplifier 6 has almost no effect on the output signal. Therefore, the bootstrap amplifier 6 can be configured as a class B or class D amplifier, thereby making it possible to increase the efficiency. That is, this power amplifier improves both efficiency and fidelity by combining an output stage amplifier circuit 2 operating in class A and a bootstrap amplifier 6 operating in class B or D.

However, this power amplifier still has the drawback that the circuit is complicated and the cost increases, and a solution to this drawback has been desired.

This invention was made based on these circumstances, and its purpose is to provide a power amplifier with a simple configuration that is excellent in both efficiency and fidelity.In order to achieve this purpose, In this invention, in place of the bootstrap amplifier 6 in the power amplifier shown in FIG. It is designed to drive.

Hereinafter, embodiments of this invention will be described with reference to the drawings.

FIG. 2 is a circuit diagram showing the basic configuration of the power amplifier according to this invention.
0 is connected to the inverting input terminal of the input stage amplifier circuit 11 (operational amplifier), the non-inverting input terminal of the input stage amplifier circuit 11 is grounded via the resistor 12, and the output terminal of the input stage amplifier circuit 11 is connected to the DC power supply. It is connected to the bases of transistors 15 and 16 (amplification elements) via transistors 13 and 14, respectively. In this case, DC power supply 1
Reference numerals 3 and 14 are for supplying bias to the transistors 15 and 16, and biases are set by these DC power supplies 13 and 14 so that the transistors 15 and 16 operate in class A mode. Further, the DC power supplies 13 and 14 and the transistors 15 and 16 constitute a complementary push-pull amplifier circuit 17. The collector of the transistor 15 is connected to the positive voltage terminal of a DC power supply 18a (voltage Vc) constituting the floating power supply 18, and the collector of the transistor 16 is connected to the negative voltage terminal of the DC power supply 18b (voltage Vc), which constitutes the floating power supply 18. power supply 18
The midpoint N of is connected to the output terminal 19. The output terminal 19 is connected to the input terminal of an amplifier 20 whose gain is "1" or less, the output terminal of this amplifier 20 is connected to the common emitter of the transistors 15 and 16, and the positive power supply terminal 20a of the amplifier 20 is connected to the DC power supply 21.
The negative power supply terminal 20b of the amplifier 20 is connected to the positive voltage terminal of the amplifier 20.
are connected to the negative voltage terminals of the DC power supply 22, respectively. Note that the amplifier 20 is a non-inverting amplifier. Negative voltage terminal of the DC power supply 21 and DC power supply 22
Both positive voltage terminals are grounded, a load resistor 23 is inserted between the output terminal 19 and the ground, and a feedback resistor 24 is inserted between the output terminal 19 and the non-inverting input terminal of the input stage amplifier circuit 11. It is interposed.

In the power amplifier configured in this way, if the gain of the amplifier 20 is set to 1, for example, the common emitter potential of the transistors 15 and 16 will be exactly the same as the output voltage Vo obtained at the output terminal 19, and as a result, , the emitter-collector voltage of transistors 15 and 16 is always DC power supply 18.
It becomes equal to each output voltage Vc of a and 18b. Therefore, each output voltage of DC power supplies 18a and 18b
By setting Vc to the minimum voltage that will keep transistors 15 and 16 active (typically 2 to 5 volts), the power dissipation of transistors 15 and 16 will be minimized even if they are operated in class A. It becomes possible to press the Note that if the gain of the amplifier 20 is set to "1" or more, oscillation occurs, and if it is set to be "1" or less, the power consumption of the transistors 15 and 16 increases accordingly.

Further, the emitters of the transistors 15 and 16 are fixed to the output potential of the amplifier 20, and the transistors 15 and 16 operate with their emitters grounded. Therefore, transistor 1
5 and 16 have gains, thereby making it possible to reduce the gain of the input stage amplifier circuit 11, which is the previous stage circuit.

On the other hand, power to the load 23 is supplied from DC power supplies 21 and 22 via an amplifier 20 and transistors 15 and 16. Therefore, by configuring the amplifier 20 as a class B or class D power amplifier, it is possible to make the efficiency of this power amplifier substantially the same as that of a conventional class B or class D amplifier. In addition, in this power amplifier, the transistors 15 and 16, the DC power supplies 18a and 18b, and the amplifier 20 enter a negative feedback loop configured with a resistor 24, so that the distortion component generated in the amplifier 20 is caused by the negative feedback effect. The effect on the output voltage Vo is reduced, and as a result, the distortion factor of the output voltage Vo is lower than that of the transistor 1 operating in class A.
This is an extremely small value determined by the distortion components of 5 and 16. In this case, since the transistors 15 and 16 have a gain as described above, there is an advantage that the amount of feedback is large. Furthermore, in this power amplifier, the input of the amplifier 20 is connected to the output terminal 1.
9, so this amplifier 20
The configuration can be simplified (see FIG. 3).

Next, a specific example of this invention will be described. FIG. 3 is a circuit diagram showing the configuration of a power amplifier which is a specific embodiment of this invention, and in this figure, parts corresponding to the circuit parts shown in FIG. 2 are given the same reference numerals.

In FIG. 3, the input stage amplifier circuit 11 includes a differential amplifier circuit 32 having transistors 30 and 31 and a differential amplifier circuit 35 having transistors 33 and 34.
It is a complementary differential amplifier circuit consisting of
7 and 38 bases. Then, the output of the predrive circuit 36 is transmitted to the transistors 15 and 16 of the complementary push-pull amplifier circuit 17.
supplied to each base. Note that the reference numeral 39 is a bias circuit for the transistors 15 and 16, and this bias circuit 39
6 is designed to perform class A operation.

On the other hand, the amplifier 20 is an emitter-follower amplifier having a gain of approximately "1" and transistors 40 and 41. Bias setting diodes 42 and 43 are inserted between the bases of the transistors 40 and 41.
43 provides class B operation.
The connection point of the diodes 42 and 43 is connected to the output terminal 19, and the common emitter of the transistors 40 and 41 (point P in the figure) is connected to the transistor 1.
5 and 16 are connected to a common emitter (point Q in the figure).

In the power amplifier configured as described above, when a positive input signal is applied to the input terminal 10, for example, the collector potentials of the transistors 31 and 34 both shift to the positive direction, and the operating state of the transistor 37 shifts to the cut-off direction. The operating states of the transistors 38 each transition to the conductive direction. As a result,
The operating state of the transistor 15 shifts to the cut-off direction, and the operating state of the transistor 16 shifts to the conducting direction, thereby generating a positive output voltage at the output terminal 19. When a positive output voltage is generated at the output terminal 19, the operating state of the transistor 40 immediately changes to the conducting direction (the transistor 41 is in the cut-off state), and as a result, current flows from the positive voltage terminal of the DC power supply 21 to the next path. Power is supplied to the load resistor 23. That is, a current flows in the following path: positive voltage terminal of DC power supply 21 → transistor 40 → point P → point Q → transistor 16 → DC power supply 18b → output terminal 19 → load resistor 23 → ground. Note that in this case, the transistor 15 operates in class A operation, and its operating current is supplied from the floating power supply 18.

On the other hand, when a negative input signal is applied to the input terminal 10, each part of the circuit shown in FIG. . That is, the positive voltage terminal of the DC power supply 22 → the load resistor 23 → the DC power supply 18a → the transistor 15 → the Q point → the P point → the transistor 41 →
Current is supplied through a negative voltage terminal of the DC power supply 22 .

It goes without saying that this power amplifier also provides the same effect as described in FIG. 2. Furthermore, as is clear from the figure, the configuration of the amplifier 20 is much simpler than the conventional one.

As explained above, this invention includes an input stage amplifier circuit that amplifies an input signal, a complementary push-pull amplifier circuit driven by the output of the input stage amplifier circuit, and a complementary push-pull amplifier circuit that is driven by the output of the input stage amplifier circuit. It has a floating power supply that supplies power to the circuit, an output terminal connected to the midpoint of this floating power supply, and an amplifier with a gain of "1" or less that uses the signal obtained at this output terminal as an input signal, The output of the amplifier with a gain of "1" or less drives a common electrode of an amplifying element constituting the complementary amplifier circuit, and the signal obtained at the output terminal is fed back to the input stage amplifier circuit. As a result, the floating power supply and its drive circuit are included in the feedback loop, which reduces fluctuations in the floating power supply system and distortion components of the amplifier, resulting in excellent efficiency and fidelity. A power amplifier can be obtained with a simple configuration. Furthermore, since the complementary pump-pull amplifier circuit can be configured to have a gain, the amount of feedback can be increased, and the gain of the input stage amplifier can be reduced. can.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of a conventional power amplifier, FIG. 2 is a circuit diagram showing the basic configuration of this invention, and FIG. 3 is a circuit diagram showing a specific embodiment of this invention. 11... Input stage amplifier circuit, 15... Amplifying element (transistor), 16... Amplifying element (transistor), 17... Complementary push-pull amplifier circuit, 18... Floating power supply, 19...
Output terminal, 20...amplifier.

Claims (1)

[Scope of utility model registration request] An input stage amplifier circuit that amplifies an input signal, a complementary push-pull amplifier circuit driven by the output of the input stage amplifier circuit, a floating power supply that supplies power to the complementary push-pull amplifier circuit, and It has an output terminal connected to the midpoint of the floating power supply, and an amplifier with a gain of "1" or less that uses the signal obtained at this output terminal as an input signal, and uses the output of the amplifier with a gain of "1" or less as an input signal. A power amplifier characterized in that the common electrode of the amplification elements constituting the complementary amplifier circuit is driven, and the signal obtained at the output terminal is fed back to the input stage amplifier circuit.